PhD Nadine M Hamieh
email: nadine.hamieh@iplesp.upmc.fr

Ph.D Pierre Student

Meneton

Ph.D Emmanuel Wiernik

Ph.D Frederic Limosin

Ph.D Marie Zins

Ph.D Marcel Goldberg

Ph.D Maria Melchior

† , Sc.D Cedric Lemogne

Depression, treatable cardiovascular risk factors and incident cardiac events in the Gazel cohort

Keywords: depression, cardiac events, hypertension, diabetes, dyslipidemia, epidemiology

Background: Depression is an important risk factor of cardiovascular disease (CVD), a leading cause of death worldwide. One of the reasons underlying this association may be that depression modifies the association between treatable cardiovascular risk factors and cardiac events (angina pectoris or myocardial infarction). We tested this hypothesis in a cohort study of middle-aged men and women in France followed for 20 years.

Methods: 10,541 Gazel working men and women free of cardiovascular disease at baseline (1993) were followed-up over 20 years for validated incident cardiac events. Depression was measured at baseline and every three years with the Center for Epidemiological Studies-Depression (CES-D). We used time-dependent Cox regression models to calculate hazard ratios (HR) of cardiac events associated with depression, main treatable cardiovascular risk factors (hypertension, diabetes, and dyslipidemia), and their interactions, adjusting for demographic, lifestyle and clinical characteristics.

Results: Over 20 years of follow-up, 592 incident cases of cardiac events were identified.

Depression was significantly associated with incident cardiac events (HR 1.55, P=0.002), as was hypertension (HR 1.49, P=0.02), diabetes (HR 2.54, P=0.001), and dyslipidemia (HR 1.55, P=0.003). No statistically significant interactions were observed between depression and hypertension, diabetes or dyslipidemia in relation to incident cardiac events (all P ≥0.16).

Conclusions:

The association between depression and cardiac events is unlikely to be explained by a heightened impact of hypertension, diabetes or dyslipidemia.

INTRODUCTION

Cardiovascular diseases (CVD) and depression are respectively leading causes of death [START_REF]Cardiovascular diseases (CVDs)[END_REF] and disability [START_REF][END_REF] worldwide according to World Health Organization. CVD is estimated to contribute to 31% of total mortality, that is approximately 17.7 million deaths in 2015 [START_REF]Cardiovascular diseases (CVDs)[END_REF]: which is an increase by 0.7 million from 2013-2015 [START_REF] Murray | Global, regional, and national age-sex specific all-cause and cause-specific mortality for 240 causes of death, 1990-2013: a systematic analysis for the Global Burden of Disease Study[END_REF]. Currently, depression affects more than 300 million individuals: this number increased by 18% from 2005-2015 [START_REF][END_REF]. In France, CVD is the second leading cause of death with approximately 140,000 deaths per year [4] (27% of all deaths in 2011) [START_REF] Tzoulaki | Worldwide Exposures to Cardiovascular Risk Factors and Associated Health Effects: Current Knowledge and Data Gaps[END_REF], while the prevalence of depression is estimated at 5 to 12% in the general population [START_REF] Chee | The current state of mental health surveillance in France[END_REF].

CVD and depression are highly comorbid, and this association is probably bidirectional. Approximately 30-45% of patients with CVD suffer from elevated levels of depressive symptoms [START_REF] Celano | Depression and cardiac disease: a review[END_REF] and while depression predicts CVD onset (i.e. depressed individuals are 1.5 times higher to develop CVD compared to non-depressed [START_REF] Wulsin | Do depressive symptoms increase the risk for the onset of coronary disease? A systematic quantitative review[END_REF]), the opposite can also be the case. One of the potential explanations is that depression co-occurs with traditional cardiovascular risk factors [START_REF] Gaye | High level of depressive symptoms as a barrier to reach an ideal cardiovascular health. The Paris Prospective Study III[END_REF] such as obesity [START_REF] Phillips | Depressive symptoms, anxiety and well-being among metabolic health obese subtypes[END_REF][START_REF] Lagrotte | The relative association of obstructive sleep apnea, obesity and excessive daytime sleepiness with incident depression: a longitudinal, population-based study[END_REF], hypertension [START_REF] Graham | Comorbidity of depression and anxiety disorders in patients with hypertension[END_REF], diabetes [START_REF] Mommersteeg | The association between diabetes and an episode of depressive symptoms in the 2002 World Health Survey: an analysis of 231,797 individuals from 47 countries[END_REF][START_REF] Ali | The prevalence of co-morbid depression in adults with Type 2 diabetes: a systematic review and meta-analysis[END_REF], hypercholesterolemia [START_REF] Almeida | HDL cholesterol and the risk of depression over 5 years[END_REF] and smoking [START_REF] Dierker | Smoking and depression: an examination of mechanisms of comorbidity[END_REF][START_REF] An | Smoking, heavy drinking, and depression among U.S. middle-aged and older adults[END_REF][START_REF] Yun | Association of smoking status, cumulative smoking, duration of smoking cessation, age of starting smoking, and depression in Korean adults[END_REF]. Several large-scale prospective studies found that major depression, or subthreshold depressive symptoms, are independent risk factors of CVD [START_REF] Celano | Depression and cardiac disease: a review[END_REF][START_REF] Hare | Depression and cardiovascular disease: a clinical review[END_REF][START_REF] Van Der Kooy | Depression and the risk for cardiovascular diseases: systematic review and meta analysis[END_REF][START_REF] Case | Atypical depression and double depression predict new-onset cardiovascular disease in U.S. adults[END_REF][START_REF] Ford | Depression is a risk factor for coronary artery disease in men: the precursors study[END_REF][START_REF] Lichtman | Depression as a risk factor for poor prognosis among patients with acute coronary syndrome: systematic review and recommendations: a scientific statement from the American Heart Association[END_REF]. Additionally, a metaanalysis conducted on prospective cohort studies to assess the association between depression and the incidence of coronary heart disease (CHD) and myocardial infarction in 2014, adjusting for obesity, diabetes, cholesterol, hypertension, alcohol intake, smoking, physical activity, age and gender, found a relative risk (RR) for both CHD and myocardial infarction of 1.30 with a 95% confidence interval (CI) of 1.18-1.40 [START_REF] Gan | Depression and the risk of coronary heart disease: a meta-analysis of prospective cohort studies[END_REF]. Two other meta-analyses showed that depressed individuals who were free of CHD at baseline were 1.5 times more likely to develop CHD as compared with non-depressed individuals, independent of CHD risk factors [START_REF] Celano | Depression and cardiac disease: a review[END_REF][START_REF] Nicholson | Depression as an aetiologic and prognostic factor in coronary heart disease: a meta-analysis of 6362 events among 146 538 participants in 54 observational studies[END_REF]. Thus, depression seems directly related to CVD, however the possibility that it acts as a moderator of other established risk factors has not been fully examined.

One limitation of previous studies is that most assumed that changes in cardiovascular risk factors over time do not vary with depression. In addition, some critical mechanisms potentially linking depression with CVD risk, such as access to treatment and adherence to medication, have rarely been taken into account. Since depression is a well-established risk factor of poor adherence to medication across a large variety of health conditions [START_REF] Eze-Nliam | The association of depression with adherence to antihypertensive medications: a systematic review[END_REF], including treatable cardiovascular risk factors (i.e. hypertension, diabetes, dyslipidemia) [START_REF] Hare | Depression and cardiovascular disease: a clinical review[END_REF][START_REF] Wang | Noncompliance with antihypertensive medications: the impact of depressive symptoms and psychosocial factors[END_REF][START_REF] Stilley | Psychological and cognitive function: predictors of adherence with cholesterol lowering treatment[END_REF][START_REF] Ciechanowski | Depression and diabetes: impact of depressive symptoms on adherence, function, and costs[END_REF], one may hypothesize that depression can heighten the risk of CVD associated with these preventable risk factors. In other words, depression could act as an effect modifier of traditional cardiovascular risk factors. Previous studies found indication of an interaction between depression and hypertension [START_REF] Polanka | Are Cardiovascular Risk Factors Stronger Predictors of Incident Cardiovascular Disease in U.S. Adults With Versus Without a History of Clinical Depression?[END_REF] as well as with diabetes (in women) [START_REF] Rutledge | Relationships between cardiovascular disease risk factors and depressive symptoms as predictors of cardiovascular disease events in women[END_REF], but were not consistent with each other and did not model depression as a time-dependent variable.

Given that cardiovascular risk factors and depressive symptoms can vary over time, it is important to test for interactions between these different sources of risk in a longitudinal framework. The present study took advantage of the repeated assessment of depression and hypertension, diabetes and dyslipidemia in the Gazel cohort for 20 years of follow-up to examine whether depression modifies the prospective association between these treatable risk factors and incident cardiac events. We focused on hypertension, diabetes and dyslipidemia since they are known as cardiovascular risk factors with established pharmacologic treatment and because depression has been associated with poor adherence to these medications, hence we hypothesized that their association with incident cardiac events would increase in the presence of depressive symptoms.

MATERIALS AND METHODS

Study population

The Gazel cohort, a prospective study, was initiated in 1989 among 20,625 employees [START_REF] Tzoulaki | Worldwide Exposures to Cardiovascular Risk Factors and Associated Health Effects: Current Knowledge and Data Gaps[END_REF]614 women and 15,011 men aged 35-50 and 40-50 respectively) of Électricité de France-Gaz de France (EDF-GDF) [START_REF] Goldberg | Cohort Profile Update: The GAZEL Cohort Study[END_REF][START_REF] Meneton | A Global View of the Relationships between the Main Behavioural and Clinical Cardiovascular Risk Factors in the GAZEL Prospective Cohort[END_REF]. These participants represented 46% of the EDF-GDF employees of this age range. Participants were followed-up yearly since 1989 through administrative databases (i.e. human resources databases) and postal self-administrated questionnaires. In the present analyses, we included participants who completed the Center for Epidemiologic Studies Depression Scale (CES-D) in 1993 (n=14,893). These 14,893 participants were significantly older, more likely to be physically inactive, had a higher occupational grade, were less likely to be female and to report diabetes, hypertension and dyslipidemia compared to those who did not complete the CES-D questionnaire. In this population, participants with a cardiac event before 1994 (n=332), and missing data on our variables of interest (hypertension, diabetes, dyslipidemia, occupational grade, parental CHD history, obesity, smoking status and physical inactivity) before 1993 (n=4,020) were excluded. Hence, our final population consisted of 10,541 participants who were followed-up for cardiac events from January 1, 1994-December 31, 2014. These individuals were significantly older, more likely to be non-smokers, non-obese, had a higher occupational grade, were less likely to be female and to report depression and dyslipidemia compared to non-participants with completed CES-D questionnaire (29.2%).

The 'Commission Nationale Informatique et Liberté' and 'Institut National de la Santé et de la Recherche Médicale' ethics committee approved the study [START_REF] Meneton | A Global View of the Relationships between the Main Behavioural and Clinical Cardiovascular Risk Factors in the GAZEL Prospective Cohort[END_REF][START_REF] Chevalier | A registry of ischaemic cardiopathies among active workers at Electricite de France-Gaz de France. Program development and first results[END_REF] and all the participants provide written informed consent.

Assessment of cardiac events

Diagnosis of cardiac events was performed using two different sources over a 20 years follow-up period from January 1, 1994 to December 31, 2014. First, while participants were actively employed, cases of coronary heart disease were identified in the ad-hoc registry set up by the EDF-GDF medical department [START_REF] Chevalier | A registry of ischaemic cardiopathies among active workers at Electricite de France-Gaz de France. Program development and first results[END_REF] and medically validated. Second, after participants retired, diagnoses were based on self-reported cardiac events that were systematically validated. Specifically, all participants were asked to report whether they had been diagnosed or hospitalized due to cardiovascular disease including angina pectoris or myocardial infarction in the 12 months preceding the yearly Gazel questionnaire. If a participant was alive, gave consent, and reported at least 1 cardiac event, he/she was contacted to transmit his/her medical records. All cardiac events were validated by two trained investigators.

Assessment of cardiovascular risk factors of interest

Information on hypertension, diabetes and dyslipidemia was collected annually from 1993-2013 from participants' self-reports on the following 2 questions: "In the list below, indicate the diseases that you have suffered from in the past 12 months?" and "Among the health problems that you have indicated, which ones are new (i.e. they have appeared in the last 12 months)?" These cardiovascular risk factors were considered separately but also in a cumulative manner, combining hypertension, diabetes and dyslipidemia over the entire follow-up and irrespective of the risk factor (0, 1, 2, and 3).

Assessment of depressive symptoms

Information on depression has been assessed every three years since 1993 using the validated French version of the CES-D, a scale composed of 20 items of depressive symptoms [START_REF] Fuhrer | La version française de l'échelle CES-D (Center for Epidemiologic Studies-Depression Scale). Description et traduction de l'échelle d'autoévaluation [The French version of the CES-D (Center for Epidemiologic Studies-Depression Scale)[END_REF].

The CES-D questionnaire has a high internal consistency coefficient of 0.8-0.9 across community samples [START_REF] Radloff | The CES-D Scale: A Self-Report Depression Scale for Research in the General Population[END_REF]. This screening test measures sadness, loss of interest, appetite, sleep, thinking, guilt, fatigue, agitation and suicidal thoughts during the previous week on a scale of 0 (<1 day) to 3 (5 to 7 days). Women who scored ≥23 and men who scored ≥17 were considered to be clinically depressed [START_REF] Fuhrer | La version française de l'échelle CES-D (Center for Epidemiologic Studies-Depression Scale). Description et traduction de l'échelle d'autoévaluation [The French version of the CES-D (Center for Epidemiologic Studies-Depression Scale)[END_REF]. In addition, depression was also assessed using a continuous variable taking the interquartile range (the difference between the 25 th and 75 th percentiles, i.e. 10 points) as a unit to deal with the small sample size of validated cardiac events when stratifying by depression status.

Assessment of covariates

Socio-demographics such as sex, age, occupational grade (low: manual and clerical; medium: technical; high: managerial positions) were collected from the EDF-GDF human resources records at baseline. Parental history of CHD (yes: either mother or father had CHD before the age of 60, no), weight (continuous, kg), height (continuous, meters), current smoking status (yes: current smokers; no: former and non-smokers) and physical inactivity (yes: none; no: occasionally or ≥1 week) were collected annually from participants' self-administered questionnaires since 1993. Obesity was measured by body mass index, BMI (yes: BMI ≥30; no: <30 kg/m 2 ).

Statistical analysis

Each participant contributed person-time from the start date of our study, January 1, 1994 until the diagnosis of a cardiac event, death, the last follow-up questionnaire or December 31, 2014, whichever occurred first. We computed descriptive statistics such as ANOVA, Chisquare and Fisher's exact tests to compare participants' characteristics by incident cardiac events and depression status. Chi-square and Fisher's exact tests were computed for discrete variables whereas ANOVA test was computed for continuous ones.

Cox proportional hazard regressions were used to calculate the hazard ratios (HR) and 95% confidence intervals (CI) of depression and cardiovascular risk factors of interest in relation to incident cardiac events. All models controlled for participants' age (in years) and sex. Multivariable models were additionally adjusted for obesity, smoking status, parental CHD, occupational grade and physical inactivity. Except for gender, age, parental CHD history and occupational grade, all characteristics were studied as time varying covariates using the programming statement method described by Powell and Bagnell [START_REF] Powell | Your "Survival" Guide to Using Time-Dependent Covariates[END_REF]. To further explore whether depression could predict incident cardiac events independently of hypertension, diabetes and dyslipidemia, we conducted analyses in different subpopulations.

Only the cumulative cardiovascular risk factors variable combining hypertension, diabetes and dyslipidemia over the entire follow-up in these subpopulations was not considered as time-dependent. The roughly parallel stratified Kaplan-Meier curves log (-log (survival)) versus log (time) transformation verified the proportionality of hazards.

To test the hypothesis that depression is an effect modifier of hypertension, diabetes and dyslipidemia regarding the risk of incident cardiac events, we tested for statistical interactions between depression and these risk factors, simultaneously including depression, each risk factor and their interaction in the statistical model. Additionally, we tested for the interaction of depression with sex in relation to incident cardiac events.

All p-values were two-sided with an  = 0.05. All statistical analyses were conducted using the SAS statistical software version 9.4 (SAS, Cary, NC) and its derived discovery software JMP version 12.

RESULTS

At baseline, 22.5% of the study population was depressed based on the CES-D score (n=2,368 participants) (Table 1). In a previous study based on the same study population [START_REF] Lemogne | When Blue-Collars Feel Blue: Depression and Low Occupational Grade as Synergistic Predictors of Incident Cardiac Events in Middle-Aged Working Individuals[END_REF], we found that being female (P=0.02), a smoker (P=0.03), a physically inactive person (P<0.0001), and having a lower occupational grade (P<0.0001), dyslipidemia (P=0.004) and hypertension (P=0.0003) were significantly associated with depression.

During the 20 years of follow-up, 592 individuals had a cardiac event (Table 1), yielding an incidence rate of 292 per 100,000 person-years [START_REF] Lemogne | When Blue-Collars Feel Blue: Depression and Low Occupational Grade as Synergistic Predictors of Incident Cardiac Events in Middle-Aged Working Individuals[END_REF]. These cardiac events included 485 CHD-related events (i.e. 160 angina pectoris and 315 myocardial infarction cases) and 117 other cardiac events (e.g. heart failure, cardiac arrhythmia). Overall, compared to participants with no incident cardiac event, those who had an incident cardiac event were more likely to be male, obese, to smoke, have a parental history of CHD and have diabetes or dyslipidemia. Among participants with an incident cardiac event, concurrent depression was not associated with any of the treatable cardiovascular risk factors whereas it was associated with hypertension (P=0.0002) and dyslipidemia (P=0.008) in those without incident cardiac events.

Depression was significantly associated with an incident cardiac event both adjusting for sex and age (HR 1.72, 95% CI 1.37-2.17, P <0.001) and in fully-adjusted models (HR 1.55, 95% CI 1.17-2.05, P=0.002). Adjusting for sex, age and depression, individuals with hypertension, diabetes or dyslipidemia were at a higher risk of developing a cardiac event (Table 2). These associations remained statistically significant in the fully-adjusted model, but their magnitude was reduced. However, we observed no statistically significant interaction between depression and each of hypertension, diabetes and dyslipidemia (all P ≥0.16). When depression was modelled as a continuous variable, the findings were similar (Table 3) but with different magnitudes in terms of HRs and p-values for interaction.

Men were at a higher risk of having a cardiac event compared to women both in minimally-adjusted (HR 1.85, 95% CI 1.35-2.53, P=0.0001) and fully-adjusted models (HR 1.82, 95% CI 1.24-2.68, P=0.002). No statistical interaction between depression and sex was observed: p-values for interaction were 0.79 in minimally-adjusted and 0.70 in fully-adjusted models (data not shown).

To further explore whether depression could predict incident cardiac events independently of hypertension, diabetes and dyslipidemia, despite the lack of significant interaction, we conducted analyses in different subpopulations according to the presence of these risk factors (Table 4). Overall, the fully-adjusted models yielded no compelling evidence that the risk of developing a cardiac event associated with depression increased in the presence of these risk factors. More specifically, the HR for individuals who had none of these risk factors over the entire follow-up was similar to the HR of those who had the three risk factors (1.34 versus 1.37).

DISCUSSION

The aim of this prospective study was to examine whether the association between treatable cardiovascular risk factors, namely hypertension, diabetes and dyslipidemia and incident cardiac events varied according to the presence of depression in a socioeconomically and geographically heterogeneous French population over a period of 20 years. In line with most previous studies [START_REF] Wulsin | Do depressive symptoms increase the risk for the onset of coronary disease? A systematic quantitative review[END_REF][START_REF] Gaye | High level of depressive symptoms as a barrier to reach an ideal cardiovascular health. The Paris Prospective Study III[END_REF][START_REF] Van Der Kooy | Depression and the risk for cardiovascular diseases: systematic review and meta analysis[END_REF][START_REF] Case | Atypical depression and double depression predict new-onset cardiovascular disease in U.S. adults[END_REF][START_REF] Nicholson | Depression as an aetiologic and prognostic factor in coronary heart disease: a meta-analysis of 6362 events among 146 538 participants in 54 observational studies[END_REF][START_REF] Polanka | Are Cardiovascular Risk Factors Stronger Predictors of Incident Cardiovascular Disease in U.S. Adults With Versus Without a History of Clinical Depression?[END_REF][START_REF] Rutledge | Relationships between cardiovascular disease risk factors and depressive symptoms as predictors of cardiovascular disease events in women[END_REF][START_REF] Meneton | A Global View of the Relationships between the Main Behavioural and Clinical Cardiovascular Risk Factors in the GAZEL Prospective Cohort[END_REF][START_REF] Nabi | Does depression predict coronary heart disease and cerebrovascular disease equally well? The Health and Social Support Prospective Cohort Study[END_REF][START_REF] Seldenrijk | Depression, anxiety and 6-year risk of cardiovascular disease[END_REF][START_REF] Almas | Severity of Depression, Anxious Distress and the Risk of Cardiovascular Disease in a Swedish Population-Based Cohort[END_REF][START_REF] Wu | Depression and the Risk of Myocardial Infarction and Coronary Death: A Meta-Analysis of Prospective Cohort Studies[END_REF][START_REF] Whang | Depression and risk of sudden cardiac death and coronary heart disease in women: results from the Nurses' Health Study[END_REF], depression was independently associated with incident cardiac events adjusting for differences in clinical and lifestyle patterns. The present investigation's unique contribution is the study of possible interactions between depression and these risk factors. Contrary to our a priori hypothesis, we found no evidence of modification of the effects of hypertension, diabetes or dyslipidemia by depression.

Interactions between depression and these risk factors were not statistically significant and stratified analyses did not provide compelling indication that depression could predict incident cardiac events to a different extent among individuals with or without these risk factors over the entire follow-up. Thus, it is unlikely that non-adherence to medications related to these risk factors substantially explains the association between depression and incident cardiac events.

Although our results fall within the range of fully-adjusted HRs reported in the literature (i.e. 1.18 to 3.60) when confounders were measured at baseline, they are not consistent with negative studies, including one of our group also based on Gazel study data [START_REF] Lemogne | When Blue-Collars Feel Blue: Depression and Low Occupational Grade as Synergistic Predictors of Incident Cardiac Events in Middle-Aged Working Individuals[END_REF][START_REF] Vogt | Mental health status as a predictor of morbidity and mortality: a 15-year follow-up of members of a health maintenance organization[END_REF]. Interestingly, this discrepancy results from the fact that this previous study did not model depression as a time-dependent variable [START_REF] Meneton | A Global View of the Relationships between the Main Behavioural and Clinical Cardiovascular Risk Factors in the GAZEL Prospective Cohort[END_REF]. Here, modelling depression as well as hypertension, diabetes and dyslipidemia, was critical to test our hypothesis since these risk factors might appear during follow-up and depression level varies over time.

Our study is original in that we systematically searched for interactions between depression and each risk factor of interest regarding the incidence of cardiac events. Although the well-known association between depression and poor adherence to medications led us to hypothesize a significant interaction, this was not observed with hypertension, dyslipidemia or diabetes. Overall, there was no evidence for a consistent increase in the risk of cardiac events when depressed each time a risk factor was added. The lack association among individuals with no dyslipidemia could be explained by a lack of statistical power. Therefore, our results did not provide support for our initial hypothesis.

There are some notable strengths in these analyses. First, it is the first study to explore the interaction of depression with cardiovascular risk factors in relation to incident cardiac events, taking into account variation in these risk factors over the follow-up by using timedependent variables in Cox proportional hazard models. Second, ours is a prospective study with repeated measures with a long follow-up of 20 years with a very low attrition rate [START_REF] Goldberg | Cohort Profile Update: The GAZEL Cohort Study[END_REF][START_REF] Lemogne | When Blue-Collars Feel Blue: Depression and Low Occupational Grade as Synergistic Predictors of Incident Cardiac Events in Middle-Aged Working Individuals[END_REF]. Third, the Gazel cohort is a diverse population in terms of geography and socioeconomic position [START_REF] Goldberg | Cohort Profile Update: The GAZEL Cohort Study[END_REF]. Fourth, the reliance upon a thoroughly validated diagnosis of cardiac events ensures the accuracy and reliability of our findings.

However, some limitations are present. Although this study was prospective, a randomized design was obviously impossible so that its observational nature prevents us from drawing causal inferences regarding the relationship between depression and incident cardiac events. Another limitation is that cardiovascular risk factors were self-reported. It is noteworthy that self-report accuracy may not be influenced by depressive status [START_REF] Jeffery | Does clinical depression affect the accuracy of self-reported height and weight in obese women?[END_REF][START_REF] Barnes | Accuracy of self-reported weight and height and resulting body mass index among obese binge eaters in primary care: relationship with eating disorder and associated psychopathology[END_REF] and that the present associations with cardiac events were consistent with the literature, thus providing evidence of external validity/generalizability. However, we cannot rule out that a non-differential misclassification occurred leading to some underestimation of the impact of these risk factors of on cardiac events.

Although our use of validated cardiac events is a strength, the total number of cases was relatively low they did not include fatal cases and false negatives may have occurred. In addition, the hypothesis of a mediation by lack of medication adherence was not tested directly, hence future studies should be conducted. A related limitation is that, since we focused on cardiovascular risk factors with an established pharmacologic treatment, our analysis did not search for an interaction with overweight or obesity, despite their strong association with depression [START_REF] Milaneschi | Depression and obesity: evidence of shared biological mechanisms[END_REF][START_REF] Marx | Comorbidities in the diseasome are more apparent than real: What Bayesian filtering reveals about the comorbidities of depression[END_REF]. Another limitation is that the CES-D does not measure major depression but rather depressive symptoms. However, it is noteworthy that even subthreshold depressive symptoms have been found to predict onset of cardiac events [START_REF] Meneton | A Global View of the Relationships between the Main Behavioural and Clinical Cardiovascular Risk Factors in the GAZEL Prospective Cohort[END_REF].

CONCLUSIONS

In conclusion, our finding showing that depression is associated with incident cardiac events independently of hypertension, diabetes or dyslipidemia has clinical implications. First, it can serve to convince physicians and public health decision makers that depression is a cardiovascular risk factor on its own. Indeed, the impact of depression may be comparable to that of hypertension and dyslipidemia in relation to incident cardiac events. Second, it suggests that non-behavioral pathways such as inflammation or autonomic dysregulation [START_REF] Tawakol | Relation between resting amygdalar activity and cardiovascular events: a longitudinal and cohort study[END_REF] should be further explored. Chi-square (or Fisher's exact test when necessary) and ANOVA tests were computed for discrete and continuous variables respectively.

Table 1 .

 1 Baseline characteristics of 10,541 participants in Gazel cohort by depression and incident cardiac events

			Cardiac events*			Absence of cardiac events
					Absence of				Absence of
		Overall	Total	Depression †	depression P	Total	Depression †	depression	P
		(n=10,541) (n=592)	(n=130)	(n=462)		(n=9,949) (n=2,238)	(n=7,711)
	Mean (SD) CES-D
			12.1 (8.1)				12.6 (8.9)
	score	12.6 (8.9)		24.3 (6.8)	8.7 (4.3)	N/A		25.6 (7.3)	8.8 (4.9)	N/A
	Mean (SD) age, years	47.8 (3.5)	49.0 (2.9) 48.5 (3.0)	49.1 (2.8)	0.03	47.8 (3.5) 47.8 (3.5)	47.8 (3.5)	0.55
	Gender (male), %	74.5	96.0	93.1	96.8	0.08	76.3	71.5	73.8	0.03
	Occupational grade					<0.0001				<0.0001
	Low, %	11.8	9.8	19.2	7.1		11.9	15.1	10.9
	Medium, %	55.5	49.0	53.9	47.6		55.9	58.1	55.3
	High, %	32.7	41.2	26.9	45.2		32.2	26.8	33.8
	Parental CHD history,
			21.1				11.5
	%	68.8		24.6	20.1	0.27		12.0	11.3	0.36
	Obesity, %	6.0	10.5	11.5	10.2	0.70	5.7	6.4	5.5	0.25

Table 2 .

 2 Depression and cardiovascular risk factors in relation to incident cardiac events in the Gazel cohort, 1994-2014 (hazard ratios (HR),

	95% confidence intervals (CI), p-value for interaction)
		Minimally-adjusted model*			Fully-adjusted model †
		Total
			HR (95% CI)	P	P-interaction	HR (95% CI)	P	P-interaction
		cases
	Depression ∞
	No	462	1.00	Ref	…	1.00	Ref	…
	Yes	130	1.72 (1.37-2.17)	<0.0001		1.55 (1.17-2.05)	0.002
	Hypertension
	No	495	1.00	Ref	0.32	1.00	Ref	0.79
	Yes	97	1.71 (1.37-2.22)	<0.0001		1.49 (1.06-2.10)	0.02
	Diabetes
	No	570	1.00	Ref	0.16	1.00	Ref	0.16
	Yes	22	2.88 (1.87-4.44)	<0.0001		2.54 (1.46-4.42)	0.001
	Dyslipidemia
	No	423	1.00	Ref	0.42	1.00	Ref	0.87

Table 3 .

 3 Risk of incident cardiac events associated with depressive symptoms (CES-D score) and cardiovascular risk factors in the Gazel cohort, 1994-2014 (hazard ratios (HR), 95% confidence intervals (CI), p-value for interaction)

		Minimally-adjusted model*			Fully-adjusted model †
		Total
			HR (95% CI)	P	P-interaction	HR (95% CI)	P	P-interaction
		cases
	CES-D score **	592	1.31 (1.16-1.48)	<0.0001	…	1.29 (1.12-1.49)	0.0003	…
	Hypertension				0.23			0.30
	No	495	1.00	Ref		1.00	Ref
	Yes	97	1.78 (1.36-2.33)	<0.0001		1.49 (1.06-2.09)	0.02
	Diabetes				0.50			0.31
	No	570	1.00	Ref		1.00	Ref
	Yes	22	2.99 (1.92-4.65)	<0.0001		2.54 (1.46-4.43)	0.001
	Dyslipidemia				0.50			0.83
	No	423	1.00	Ref		1.00	Ref
	Yes	169	1.73 (1.36-2.20)	<0.0001		1.53 (1.15-2.05)	0.004
	* Adjusted for sex, age in years and depression

Table 4 .

 4 Risk of incident cardiac events associated with depressive symptoms (CES-D score) in subpopulations according to cardiovascular risk factors of interest in the Gazel cohort, 1994-2014 (hazard ratios (HR), 95% confidence intervals (CI), p-value for interaction) Adjusted for sex, age in years and depression † Adjusted for sex, age in years, depression, hypertension, diabetes, dyslipidemia, occupational grade, parental CHD history, obesity, smoking status and physical inactivity § HR values of incident cardiac events by depressive symptoms were given for one interquartile range of CESD-score as 10 units

	Minimally-adjusted*	Fully-adjusted model †
	Total cases	P	P
	HR (95% CI) §	HR † (95% CI) §

*

ACKNOWLEDGMENTS

Nadine Hamieh is supported by Philippe Jabre Association to conduct this project which is part of her PhD thesis. Cedric Lemogne was supported by a grant from IReSP (LEMOGNE AAP16_PREV-13).The Gazel cohort is supported by 'Agence nationale de la recherche', 'Institut National de la Santé et de la Recherche Médicale', 'Agence française de sécurité sanitaire de l'environnement et du travail' and 'Caisse d'Assurance Maladie des Industries Electriques et Gazières'.

DECLARATION OF INTEREST

Cedric Lemogne declares grants, personal fees and non-financial support from Lundbeck, personal fees from Servier, non-financial support from Otsuka Pharmaceuticals, and personal fees from Janssen-Cilag, outside the submitted work. Frederic Limosin has received speaker and consulting fees from AstraZeneca, Janssen, Lundbeck, Otsuka Pharmaceuticals, Roche and Servier.


Erwan Renaudo

Sandra Devin

Benoît Girard

Raja Chatila

Rachid Alami

Mehdi Khamassi

Aurélie Clodic

Learning to interact with humans using goal-directed and habitual behaviors

In order to improve adaptation capabilities of robots for human-robot interaction, we take inspiration from psychology and neuroscience to propose a hybrid control architecture. This architecture is based on the multiple Experts approach that is mainly used for mammal behavior modelling. We propose to couple a human-aware task planner (HATP) with a model-free reinforcement learning to allow the robot to learn behaviors relevant to solve tasks in interaction, taking advantage from the a-priori knowledge provided to the planner and the cheap decision capability of the reinforcement learning agent. We evaluate this architecture in a HRI task of cleaning a table and show that the combination of Experts (planner and reinforcement learning agent) increases the learning speed of the learning agent.

I. INTRODUCTION

Studies on mammals in psychology and neuroscience have provided strong evidence that two categories of behavior exist and mammals switch between them [START_REF] Dickinson | Actions and habits: The development of behavioral autonomy[END_REF], [START_REF] Balleine | Human and rodent homologies in action control: corticostriatal determinants of goal-directed and habitual action[END_REF]. Goal-directed behaviors -relying on costly but adaptive planned long-term consequences of actions [START_REF] Balleine | Goal-directed instrumental action: contingency and incentive learning and their cortical substrates[END_REF] -and habitual behaviors -reactive behaviors fitted to a stable given context -have been extensively studied [START_REF] Dolan | Goals and habits in the brain[END_REF], modeled as Experts using the theory of Reinforcement Learning [START_REF] Sutton | Introduction to Reinforcement Learning[END_REF]. The computational principles underlying the switch between behaviors is an ongoing research topic [START_REF] Daw | Uncertainty-based competition between prefrontal and dorsolateral striatal systems for behavioral control[END_REF], [START_REF] Keramati | Speed/accuracy tradeoff between the habitual and goal-directed processes[END_REF], [START_REF] Dezfouli | Habits, action sequences and reinforcement learning[END_REF] and some applications of these principles to robotics [START_REF] Caluwaerts | A biologically inspired meta-control navigation system for the psikharpax rat robot[END_REF], [START_REF] Renaudo | Design of a control architecture for habit learning in robots[END_REF] have produced promising results both for modelling the underlying mechanisms and improving robot capabilities.

On the other hand, the emergence of robots as collaborators of human users increases the need for them to be given robust adaptation capabilities. For a more efficient interaction, robots should be able to perform correctly on a collaborative task no matter if the user is known and predictable or new and unreliable. One key point to allow robots to interact with other agents is to integrate them in the planning process. This has been achieved by Human Aware Task Planner (HATP) [START_REF] Lallement | Hatp: An htn planner for robotics[END_REF] that, among others, outputs a plan with both the robot's and the other agent's action flows, some actions being joint and some being independent.

In this paper, we apply behavioral architecture principles in a human-robot interaction task (simulated "table cleaning" task [START_REF] Alami | When the robot considers the human[END_REF]), in order to verify both the generality of the multiple behaviors approach and its efficiency for interaction and adaptability to various human users. We propose an architecture with HATP as goal-directed behavior and a model-free reinforcement learning algorithm (MF) as habitual behavior. Whereas the HATP planner embed knowledge on how to solve the task in interaction, its ability to plan bootstraps learning of the model-free algorithm. When the latter has learnt, the robot can rely on its cheap decision capability to avoid planning but still perform correctly. As a proof of concept, we evaluate the performance of each behavior controlling alone the robot, and a random mixture of HATP and MF propositions. We show that HATP performs better than MF on the task, as it starts with an initial knowledge. The combination of HATP and MF improves the performance of the robot on the task, widening the results from [START_REF] Renaudo | Design of a control architecture for habit learning in robots[END_REF] on a different, more complex task. The MF actually learns faster, taking advantage from HATP knowledge and guidance.

II. CONTROL ARCHITECTURE

A. Experts

We have two systems able to provide the next action to do to the robot:

• Human-Aware Task Planner (HATP) [START_REF] Lallement | Hatp: An htn planner for robotics[END_REF]. This planner allows the robot to take into account a human partner in a cooperative context. As a HTN planner, HATP uses known preconditions and effects of actions in order to find the best plan that reaches the goal. It takes as input a list of all possible actions and their description in terms of preconditions and effects and also a description of the current world state as a set of predicates with a closed world assumption. Then, it looks for the combination of actions that minimizes the solution cost. This cost is computed based on execution time and human-aware costs, e.g the balance of efforts between agents or waiting time of the human partner. This plan is then executed step by step until the goal is reached. It is thus well-suited to be the Goal-Directed Expert in our architecture. • Qlearning algorithm (MF). It is a one layer neural network implementation of a Qlearning algorithm, a model-free reinforcement learning algorithm [START_REF] Sutton | Introduction to Reinforcement Learning[END_REF].

From the activity generated by the current state, each action receives a value depending on the connection weights between input neurons and output (action) neurons. These values are converted into probability of selection using the Boltzmann function. Each action performed is valued by a feedback, strengthening or decreasing the connection between state and action, thus the probability to select each action in a certain state evolves over time, in order to maximize the accumulation of this feedback signal.

Both systems have advantages and drawbacks, but are in fact complementary:

• HATP has a priori knowledge, provided by a human expert, stored in the task domain. It provides a complete plan and it does not require a learning phase. However, it can happen that it is not able to find a plan. Moreover, it becomes slower to provide a solution as soon as the domain gets bigger or the combinatorics increases. • The Qlearning algorithm requires a learning phase that could be long but it is always able to propose an action. Moreover, once the learning phase has been realized, the system proposes the most interesting action known without planning, and thus is very fast. On the other hand, if the task changes, learning has to be done again according to the new conditions, which is even longer than learning from scratch.

Our idea it to find how to combine them to take advantage of both. In this paper, we will explain how we Fig. 1. The control architecture of the robot. The Decision layer is a multiple Experts architecture, arbitrated by the MetaController. In parallel, the Goal-directed Expert, which is long to plan but can take action consequences into account, and the Habitual Expert, which is quick to plan but slow to learn the policy, propose an action. The final decision (chosen action) is sent to the Executive and Functional Layers for execution. use HATP planning system to bootstrap the Qlearning algorithm. This has two goals, the first one is obviously to fasten the learning phase of the algorithm, the second one is to enable the learning algorithm to learn a policy that is quite consistent in order to avoid too many inconsistent behavior of the system when it will be faced to a real human.

B. Architecture

We adapt the model from [START_REF] Renaudo | Design of a control architecture for habit learning in robots[END_REF] to the layered architecture from [START_REF] Alami | An architecture for autonomy[END_REF] except that in the Decision Layer, the Value Iteration Model-based algorithm is replaced by the Human-Aware Task Planner (HATP). Consequently we have two Experts: one called Goal-Directed Expert that is hold by HATP, one called Habitual Expert that is hold by Qlearning. Figure 1 gives an overview of the architecture.

Experts receive the current state estimation of the world (it matches the state description, see section III) from the perception processing, they both receive exactly the same information. They then send their next action proposition to the MetaController. The MetaController arbitrates between the two propositions and send the chosen action to the supervision system to be executed. The Habitual Expert receives back the executed action in order to learn. The system loops at the end of the action execution.

In this setup, we only use a random arbitration between Experts propositions. Few of the criteria proposed Fig. 2. The Robot and the human partner are facing the table. One tape is on human side, two tapes and the trashbin are on robot side. At left, the initial state. At right, the final state.

in [START_REF] Renaudo | Which criteria for autonomously shifting between goal-directed and habitual behaviors in robots?[END_REF] are directly applicables, as they mostly rely on the probability distributions maintained by their Experts for decision. Using HATP implies that the MetaController has no probability information on the action proposed by the goal-directed Expert. Thus, exploration of relevant criteria will be discussed in section V.

III. TASK DESCRIPTION

The task is inspired from [START_REF] Alami | When the robot considers the human[END_REF]. The goal of the task is for the robot to clean the table with the help of a human partner. Cleaning the table is equivalent to "all items are in the thrashbin" (or none are on the tablebut the first expression of the goal is more restrictive on the final state to be in). Some of the objects can be out of its range, so the human partner should help. Figure 2 shows the setup.

The task has been run in simulation for now, but the running algorithms to pilot the robot are the same than the ones running on the real robot.

We construct the state manipulated by the architecture as a vector of the following boolean facts on environment. These facts are computed based on geometry in [START_REF] Sisbot | Situation assessment for human-robot interactive object manipulation[END_REF]. The set of actions that are available for both actors are the following: PickObject, ThrowObject, GiveToHuman = (give(from robot), take(from human)), TakeFromHuman =(give(from human), take(from robot)), Wait, Goto (Object, Trashbin, Human).

The Wait action allows the robot to wait until the human performs an action (or until a time limit is reached). HATP returns this action when, according to its plan, the next robot action cannot be executed without human intervention (e.g. only one tape remains, out of robot range). In simulation, we give to the human a "collaborative behaviour": he performs the actions that HATP planned for him and participates to a handover when the robot needs to. Thanks to this action, the robot will indirectly learn the behaviour of the human partner.

If the behaviour of the human changes (e.g. he becomes less cooperative or has a different way to solve the task), the wait action will not have the same effects and so, the robot will learn to achieve the task in a different way.

IV. RESULTS

We evaluate the performance of the robot using the cumulative reward obtained during the task duration. One reward unit is given to the robot when the table is empty and the robot waits. The setup is then reinitialized and the task can be done again, thus the cumulative reward corresponds to the number of times the task has been solved. We study the performance of each Expert (HATP and MF) controlling the robot alone, and then the combination of them. All experiments last the same fixed time, but the number of decisions taken at the end may vary.

From figure 3, we observe the performance of each Expert alone and the combination by looking the number of rewards during a fixed duration (i.e. the number of times the system is able to solve the task).. We observe a poor performance of the MF alone, which is not able to solve the task more than three times. As the MF has no initial knowledge, it has to discover the right sequence of actions, which is non trivial as the number of states and actions is quite big.

The random combination HATP-MF is performing much better than the MF alone, solving the task 25 times in average. However, HATP alone perform even better, solving the task 34 times in average. Indeed, the task is easy enough to solve for HATP and the time required to find a plan is negligible here. As the simulated human always performs the actions planned by HATP, the plan found by HATP is always optimal and will never change during the task execution. Accordingly, the random combination of HATP and the MF performs worst as it can include actions proposed by the MF that make the plan non optimal.

Figure 4 shows the number of actions proposed to the supervision system during each experiment. We can see that the MF alone suggests twice to three times more actions than HATP or the combination in the same given time. This is mainly due to the way each Expert decides: the MF only needs to compute the values of each action (which is propagating the state activity to action neurons) and to draw an action from the resulting probability distribution. It proposes a lot of infeasible actions and the supervision system will not spend time to execute them as it will stop to the preconditions verifications. HATP checks for action preconditions when planning and so, for each of the action proposed by HATP, the supervisor spend time to execute it (or try to execute it if the action is not really feasible according to the geometry). The number of actions suggested by the combination of Experts is closer to the one with HATP alone while remaining lightly higher. It can be explained by the fact that a part of the actions proposed by the combination comes from HATP and, for the ones coming from the MF, HATP helps it to learn faster a solution, causing it to propose less infeasible actions.

Finally, we analyse the effect of combination on learning of MF in Figure 5. Learning is evaluated by weights amplitude, namely the sum of weights absolute value over actions. The MF starts with weights initialized to zero, each learning step increases or decreases the value of some of the weights, until convergence. The figure shows that learning occurs much earlier for the combination of Experts than when the MF is alone. The combination has a bootstrapping effect and the knowledge about the task from HATP is transfered to the MF. This shows that a human-provided a priori knowledge can be used to guide exploration and learn quicker. Even if not tested in this experiment, this means that a change in task condition for which HATP can find a new plan can be learnt quickly by the MF, so the robot will be able to adapt to the new conditions without taking too much time.

V. DISCUSSION

We proposed the Decision Layer of a robotic control architecture combining two Experts: a human-aware planner (HATP) and a model-free reinforcement learning agent (MF). We evaluated each Expert on a simulated "table cleaning" task in interaction with a human. We showed that combining the Experts' action proposition significantly increases the performances and the learning speed compared to the MF alone. In term of pure performance, the combination performs worst than HATP alone in this task. However, we strongly believe that having a combination of Experts compared to HATP alone will be beneficial even if the performance decreases. Indeed, the addition of the learning agent will allow the system to find a solution in some specific cases where the planner can be blocked (e.g. HATP does not take into account the geometry and can find plan feasible at a symbolic level but not in reality). Moreover, the learning agent will allow the robot to adapt its behaviour if the human does not act as expected by HATP. In future work we will test the system with a more complex task that will challenge more HATP and with different behaviours for the human.

Here, we used a random criterion as a proof of concept: it is a starting point to validate our principle on a much more realistic task than in [START_REF] Renaudo | Design of a control architecture for habit learning in robots[END_REF]. However, in order for a human being to trust the robot enough to collaborate on a task, the behavior can not be random when the MF is still learning. Thus the need for a relevant criterion implies that the latter is able to take into account the state of learning of the MF and gives it control only when learning has converged into a stable policy. Give to the MetaController an information on the variation of MF weights can allow for a more clever arbitration.

In our architecture, we start with a difference between the initial knowledge provided to each Expert. We could provide an equivalent knowledge to the MF, which would be able to find a good behavior since the beginning. However, we choose not to do it because this knowledge, as is the knowledge given to HATP, would be human-provided, and thus will not be necessarily well-adapted to the robot. For example, the knowledge in HATP may consider that the task can be solved by taking the tape out of robot's range from the human partner giving it. It makes the assumption that any human partner will actively participate in solving the task. But the one that provided this knowledge neglects that the partner may not understand what is expected from her or may be afraid of the robot. Providing the same -potentially wrong -knowledge to the MF will prevent it to try unexpected behavior, explore the task space and eventually find a better-suited solution for a real world problem.

HATP is indeed limited to the knowledge the human gave to it. If it happens that a case has been forget by its designer, HATP is blocked. The use of simulation could help us to find these kind of limitations and the use of the learning algorithm could help to find a suited solution that then could be added to HATP domain. HATP is able to devise a plan not only for the robot but also for the human it interacts with. It is well suited for interaction because it can take into account general knowledge about how the task should unfold from a human perspective (and predictability is something you are looking at when you interact with somebody). However, if we think about interaction, we have also to think about adjustment given the human the robot interacts with. Flexibility of learning could help in that direction. It could help, for example, to tune costs used by HATP to compute its plan so it is better suited for interaction with a given person.

In order to validate more generally this approach, the experiment will be done on a real robot and with real human partners interacting, as our architecture is easily transferable from simulation to real world. This will provide some behavioral variability from non-simulated human partners. We will also be able to study different ways to give reward to the robot: it is given from the simulation in this work, but it could be extracted from analysing the reaction from robot's partner and increase robot's autonomy.

•

  Object isReachableBy Robot (including Trashbin) • Object isReachableBy Human (including Trashbin) • Object isIn Trashbin • Human isReachableBy Robot • Robot hasInHand Object • Human hasInHand Object These facts are computed from the point of view of the robot.

Fig. 3 .

 3 Fig. 3. Mean cumulative reward on 10 simulations where the robot repeatedly fulfils the task. Errorbars represent the standard deviation from the mean every 100 decisions.

Fig. 4 .Fig. 5 .

 45 Fig. 4. Number of action per experiment. Dashed line is the mean number of action depending on the control method (MF only, HATP only or combination).

ACKNOWLEDGEMENTS

This work has been funded by a DGA (French National Defence Agency) scholarship (ER), by the Project HABOT from Ville de Paris and by French Agence Nationale de la Recherche ROBOERGOSUM project under reference ANR-12-CORD-0030.


Samira Fediras

Rachid Rouag
email: rachid_rouag@yahoo.fr

Nadia Ziane

Anthony Olivier

Arnaud Béchet

Slim Benyacoub

POPULATION STRUCTURE AND MORPHOMETRICS OF THE EUROPEAN POND TURTLE (Emys orbicularis (LINNAEUS, 1758)) AT LAKE TONGA, ALGERIA

A total of 100 specimens of Emys orbicularis were collected and marked at Lake Tonga (northeastern of Algeria) during 3 consecutive years (2013, 2014, 2015). Most of the turtles inhabit a canal where they remain throughout the whole activity season (March to October) and where they overwinter as well. Carapace Length (CL) and body weight (BW) were measured for each individual of E. orbicularis. The size of the turtles of our population was more similar to those of northern European populations than to the Mediterranean populations; females were significantly larger than the Spanish and Italian populations. The population size was calculated as 108.50 and the density as 8.63 turtles/ha. From 6.52 to 12.77% of the population were juveniles. The adult sex ratio was slightly in favor of males (males:females = 1.12, P < 0.005).

INTRODUCTION

The European Pond Turtle, Emys orbicularis (Linnaeus, 1758) is one of the most widely distributed water turtle species ranging from Northwestern Africa in the west to the former Aral sea in the east, and from the Latvia in the north to the Turkish-Syrian border in the south [START_REF] Fritz | Emys orbicularis (Linnaeus, 1758) -Europäische Sumpfschildkrote[END_REF][START_REF] Fritz | Die Europaische Sumpfschildkrote[END_REF]. Populations of the European pond turtle are considered endangered in several parts of their range [START_REF] Servan | Réflexions sur la gestion des reptiles et des tortues en particulier en France: 1-La protection des espèces[END_REF][START_REF] Fritz | Distribution, variety of forms and conservation of the European Pond Turtle[END_REF]. The populations of the species are threatened by destruction and disappearance of their habitats, pesticide use, habitat loss and alteration, and agriculture [START_REF] Fritz | Emys orbicularis (Linnaeus, 1758) -Europäische Sumpfschildkrote[END_REF][START_REF] Fritz | Die Europaische Sumpfschildkrote[END_REF]. The population ecology of European populations of E. orbicularis has been studied by many authors during the last two decades [START_REF] Fritz | Die Europaische Sumpfschildkrote[END_REF]. However, very little information is available on Maghreb populations [START_REF] Fahd | Zur Verbreitung und zum Bedrohungsstatus der Europäischen Sumpfschildkröte (Emys orbicularis) in Marokko[END_REF][START_REF] Donaire | Nuevas localidades para Emys orbicularis occidentalis Fritz, 1993 (Testudines: Emydidae) en El Rif (Noroeste de Marruecos)[END_REF]. Phylogenetic studies have suggested that the eastern Algerian and Tunisian pond turtles represent an undescribed distinct subspecies [START_REF] Fritz | Checklist of chelonians of the world[END_REF][START_REF] Stuckas | Where are you from stranger? The enigmatic biogeography of North African pond turtles ( Emys orbicularis)[END_REF]. However, their population structure and morphometrics remains unknown [START_REF] Fritz | Zur innerartlichen VariabilitaÈt von Emys orbicularis (Linnaeus, 1758). Zwei neue Unterarten von der Iberischen Halbinsel und aus Nordafrika, Emys orbicularis fritzjuergebnosti subsp. nov. und E. o. occidentalis subsp. nov. (Reptilia, Testudines: Emydidae)[END_REF]. In this paper, we study the population structure (age structure, population size, density and sex ratio) and morphological parameters (size structure and weight) of an Algerian population of E. orbicularis. The study took place at Lake Tonga, in the National Park of El Kala, Algeria, in a region where E. orbicularis has never been studied before even if it may represent an important geographical refuge for the north-African subspecies of this chelonian. We compare our results to other populations in the Mediterranean and in Europe.

MATERIAL AND METHODS

Study area. This study was carried out in the National Park of El Kala, in north-eastern Algeria. The study area is a part of the north-eastern Algerian Tell (De [START_REF] Belair | Structure, fonctionnement et perspectives de gestion de quatre complexes lacustres et marécageux (Est algérien)[END_REF]. The climate is Mediterranean [START_REF] Seltzer | Le climat de l'Algérie. Trav. bits Météo. Et Phys. Du globe[END_REF][START_REF] Toubal | Phytoécologie, biogéographie et dynamique des principaux groupements végétaux du massif de l'Edough (Algérie Nord orientale)[END_REF] with moderate rainfall concentrated during winter months. Total annual rainfall was about 630 mm, and the mean monthly rainfall was about 52 mm. The study was carried from March to August in 3 consecutive years (2013 -2015) in the "Canal Messida" situated in the north of Lake Tonga (36°53N 8°31' E). The lake is about 2500 ha with a shallow water body covered by extensive vegetation beds of emergent and floating-leafed plants. It represents one of the most important freshwater areas of northeastern Algeria 1). The main plant species are common reed (Phragmites australis Cav.) and lesser reed mace (Typha angustifolia L.) with some admixture of common bulrush (Scirpus lacustris L.), branched burred (Sparganium erectum L.), and yellow iris (Iris pseudoacorus L.). The submerged and surface-floating vegetation of this lake is dominated by white water-lily (Nymphea alba L.), pondweeds (Potamogeton lucens L.), and water-milfoil (Myriophyllum verticillatum L.) [START_REF] Bakaria | Long-term changes in the size, structure and location of whiskered tern Chlidonias hybrida (P.) nests in deteriorating environmental conditions of a north African lake[END_REF]. The Mediterranean pond turtle (Mauremys leprosa) is another freshwater turtle which is also present in the study site.

a b  1  ,  1  (Fig.
Fieldwork. Only caught by hand method was used in this work because of the lack of traps especially fyke nets, ideal to catch turtles. The turtles were caught in an area of 5 ha of the entire canal. The coastal strip is inspected, and when a turtle is observed in the shallow area, we usually use a net to catch it. Four surveys sessions by one people were carried out. The session consist of the prospection of the canal from 10:00 to 16:00 h. Five in 2013 (from 21 March to 15 August), 6 in 2014 (from 27 March to 18 August), and three in 2015 (from 12 March to 24 August). An interval of at least two week separated the surveys to facilitate the redistribution of the individuals [START_REF] Gibbons | Sex ratios and their significance among turtle populations[END_REF]. From 2013 to 2015, a total of 100 European Pond Turtles were marked by notching its marginal scutes [START_REF] Cagle | A system for marking turtles for future identification[END_REF]. Measures have been taken when turtles are marked, particularly the disinfection of the lime, as well as scutes before and after the notching. On every specimen caught, seven morphometrical variables were measured (Fig. 3) before the release of the individual on the site of capture. Carapace length was measured by a digital caliper (precision ±0.1 mm) with thesame measurement criteria as in [START_REF] Stubbs | The ecology of the Mediterranean tortoise (Testudo hermanni ): a declining population[END_REF]. Body mass of the turtles was measured using a digital balance (precision ±1 g). Sex was determined by secondary sexual characters (e.g., plastral concavity and tail length) [START_REF] Servan | Détermination du sexe ratio adulte de la tortue E. orbicularis dans des populations provenant de 7 étangs de Brenne (Indre, France)[END_REF]. Turtles of less than 12 cm were considered too small to be sex reliably and were classified as juveniles.

Statistical analyses. Population size was estimated using capture-mark-recapture procedures. This method consists in the capture of a certain number of individuals within a natural population, their marking and releasing to the capture point, during a "first capture survey." Then, after a period with no surveys, a "second recapture survey" is done. Population size (N) was determined by Lincoln-Petersen-Bailey formula (1951) for small sample sizes (m 20): where M is the sample of individuals that were captured, marked and measured during the first survey period, n is the number of individuals captured during the second survey period, and m is the number of individuals, captured during the second survey period, that were already marked. Population density (d ) was estimated as d = N/a with N the mean population size and a the sampled area (5 ha).

Age was estimated by counting the number of growth annuli on the shell [START_REF] Castanet | Les méthodes d'estimation de l'âge chez les chéloniens[END_REF][START_REF] Germano | Age determination in turtles: evidence of annual deposition of scute rings[END_REF].

The exact age was difficult to determine on large old turtles by counting annular rings; therefore those turtles were classified as adults on class age superior to 10 years. We used the carapace length to estimate the growth rates, and placed this measure against the age of the various individuals [START_REF] Barbault | Structure et dynamique d'un peuplement de lézards: Les Scincidés de la savane de Lamto[END_REF]. The instantaneous growth rate (IGR) was expressed in mm per time unity (j ) according to the following formula:

CL2 and CL1 are respectively the carapace lengths of the animal at the time t2 and t1.

The growth rate estimates were generated from the turtle's individuals which were first captured in 2013 and then recaptured in 2014 and 2015. We also omitted turtles for which the time between capture and recapture was less than 1 year, in order to ensure that the growth inter-vals cover at least an entire growing season. All statistical analyses were done by the Excel software and Minitab ® 15.1.30.0.

Data collected was used for the estimation of statistical description range (average, standard deviation, range), while the univaried statistics (t-test) was used to analyze the differences between genders.

RESULTS

Population size.

During the period of the study from 2013 to 2015, a total of 100 individuals was captured. The number of individuals captured did not differ from one year to another, being 47 turtles in 2013 and 2014; and 46 individuals in 2015 (Table 1). The mean size of the population for the tree years is 46.66 individuals. Adults dominate the population with 87.23% (2013) to 95.74% (2014) of individuals caught for 4.26% (2014) to 12.77% (2013) of juveniles.

Density. The population density was estimated as 8.63 turtles/ha. Sex ratio. The sex ratio was in favor of males 1.14:1 in 2014 and in favor of females 0.78:1 and 0.79:1 in 2013 and 2015, respectively. When the whole study period was considered, the sex ratio was found as 1.12:1 (÷ 2 = 25.06, P < 0.0001) and it was male-biased. Age structure. Adults dominate the population of E. orbicularis in the study area (89%) for the three years (Fig. 5), while juveniles are represented by a few individuals (11%). Mean age of captured terrapins was 8.32 ± 2.73 years (N = 100). Ages classes between 5 -6 and 9 -10 years were represented by the same rate (21.0%). The individuals with age from 7 to 8 accounted for 27% of the population. with a net increase of size and body weight in females (Fig. 7). The analysis of the growth curve (Fig. 8) for the population revealed that it is more important in females than in males. The growth is quick during the early years and tended to decreases by the 12t h year of life. More precisely, the growth of the males tended to slowdown and to eventually stop by age 10 -11 years old. For female, the growth continues beyond 12 year-old. The instantaneous growth rate of five turtles (2 males, 2 females, and 1 juvenile) that were recaptured in multiple years during the study period (Table 4) indicated that the mean IGR for the males (24.392 × × 10 -3 mm/day) corresponded to an average growth rate of 8.90 mm/year. For females, the mean IGR was 26.218 × 10 -3 mm/day, i.e., a growth rate of 9.57 mm/year. For the juvenile, the IGR is (49.632 × × 10 -3 mm/day) corresponded to a growth rate of 18.12 mm/year. As expected, the growth of juveniles is two times faster than that of males and females. These values confirm the growth curve that is quick in early years. These values also indicate that the growth of females is greater than that of males.

Tableau 2Population Sizes and Sex Ratio of Emys orbicularis on the Study Area

DISCUSSION

Density. the density of our population (8.63 turtles/ha) is close to the one found in the Po Delta Region (northern Italy) with 6.13 individuals/ha [START_REF] Mazzotti | Population structure of Emys orbicularis in the Bardello (Po Delta, Northern Italy)[END_REF]. Important densities were reported for Turkey where 81 turtles/ha were found at Lake Yayla (Ayaz et al., 2007) and up to 225 turtles/ha at Cukurkoy (Western Anatolian) [START_REF] Auer | Population structure of syntopic Emys orbicularis and Mauremys rivulata in western Turkey[END_REF]. In other regions, there were much higher densities, such as in La Selva County (north-eastern Spain) where estimated density is 1030.60 individuals/ha [START_REF] Ramos | Morphometry and biological cycle of a European pond turtle (Emys orbicularis) population from north-eastern Spain[END_REF]. It should be noted that the lack of traps especially fyke nets, ideal for catching turtles is the main cause of the low number turtles captured. Fyke nets are adapted to a site with deep water, more efficient in terms of catch because of larger. The catch by hand is very difficult and time-consuming [START_REF] Woodbury | Uses of marking animals in ecology studies: marking amphibians and reptiles[END_REF]. We estimate that only 10% of the observed turtles were caught during the capture-recapture sessions. However, it is necessary to combine these two methods (hand caught and trapping), since none, used alone, gives a complete description of the structure of the population [START_REF] Servan | Utilisation d'un nouveau piège pour l'étude des populations de cistudes d'Europe Emys orbicularis (Reptilia, Testudines)[END_REF][START_REF] Ream | The influence of sampling methods on the estimation of the population structure in Painted turtles[END_REF]. They are biased by the behavior of different age groups [START_REF] Ream | The influence of sampling methods on the estimation of the population structure in Painted turtles[END_REF]. Body size. Sexual dimorphism is related to differences in history strategies of both sexes [START_REF] Olivier | Ecologie, traits d'histoire de vie et conservation d'une population de Cistude d'Europe Emys orbicularis en Camargue, Laboratoire de Biogéographie et Ecologie des Vertébrés[END_REF]. When smaller males could be advantaged in their mobility and/or search for sexual partners; females tend to a larger size which can be correlated with the clutch size [START_REF] Olivier | Ecologie, traits d'histoire de vie et conservation d'une population de Cistude d'Europe Emys orbicularis en Camargue, Laboratoire de Biogéographie et Ecologie des Vertébrés[END_REF]. We found that females were larger than males in size as in most Emys orbicularis subspecies [START_REF] Zuffi | Body size and clutch size in the European Pond Turtle (Emys orbicularis) from central Italy[END_REF][START_REF] Fritz | Emys orbicularis (Linnaeus, 1758) -Europäische Sumpfschildkrote[END_REF][START_REF] Fritz | Die Europaische Sumpfschildkrote[END_REF][START_REF] Ayres | Sexual dimorphism and morphological differentiation in European pond turtle (Emys orbicularis) populations from northwestern Spain[END_REF]. Also in Algerian, pond turtle population, females (151.00 mm of length and 548.40 g of weight) are larger than males (129.43 mm of length and 321.21 g of weight). The plastron width is significantly higher in females than in males, and especially the posterior part of the plastron ( p < 0.0001, t-test). Considering that there is a positive correlation between the numbers of laid eggs and female size [START_REF] Mitrus | Reproduction of Emys orbicularis (L.) in Central Poland[END_REF][START_REF] Zuffi | Body size and clutch size in the European Pond Turtle (Emys orbicularis) from central Italy[END_REF], as in most Emys orbicularis subspecies [START_REF] Zuffi | Body size and clutch size in the European Pond Turtle (Emys orbicularis) from central Italy[END_REF][START_REF] Fritz | Emys orbicularis (Linnaeus, 1758) -Europäische Sumpfschildkrote[END_REF][START_REF] Fritz | Die Europaische Sumpfschildkrote[END_REF]. The body sizes vary depending on latitude and environmental factors [START_REF] Fritz | Emys orbicularis (Linnaeus, 1758) -Europäische Sumpfschildkrote[END_REF][START_REF] Fritz | Die Europaische Sumpfschildkrote[END_REF] with the populations in the southern area tending to be smaller [START_REF] Fritz | Introduction to zoogeography and subspecific differentiation in Emys orbicularis (Linnaeus, 1758)[END_REF][START_REF] Keller | Aspects of the population structure of Emys orbicularis hispanica from southwestern Spain[END_REF]. Similar observations with respect to latitude were made also in Chrysemys picta [START_REF] Moll | Latitudinal and intersubspecific variation in reproduction of the Painted Turtle Chrysemys picta[END_REF][START_REF] Iverson | Reproductive ecology of the Painted Turtle (Chrysemys picta) in the Nebraska Sandhills and across its range[END_REF].

Quite surprisingly, the size of the individuals of our population was more similar to the size of northern European populations than to the size of the Mediterranean turtles. Females were significantly larger than the Spanish and Italian populations and smaller than the French, German and Polish populations (Table 5). A possible explanation come from Phylogenetic studies which suggested that the eastern Algerian pond turtles represent an undescribed distinct subspecies [START_REF] Fritz | Checklist of chelonians of the world[END_REF][START_REF] Stuckas | Where are you from stranger? The enigmatic biogeography of North African pond turtles ( Emys orbicularis)[END_REF]. The environmental effect (phenotypic) also seems to play, but within the limits imposed by the genotypic effect (phylogenetic constraints) [START_REF] Lombardini | La cistude dans la réserve de l'étang de Biguglia bilan des recherches 2001 -2003[END_REF].

Sex ratio. In an animal species, the sex ratio is a very important ecological factor, which influences the dynamics ofpopulations [START_REF] Girondot | Effects of sexual differences of age at maturity and survival on population sex ratio[END_REF]. According to [START_REF] Fisher | The genetical theory of natural selection[END_REF], the optimum primary sex ratio should be 1:1, but several studies have shown the existence of unbalanced sex ratios [START_REF] Gibbons | Sex ratios and their significance among turtle populations[END_REF]. In the Emydidae family, this ratio varies. Such variations are due to sampling errors [START_REF] Bury | Population ecology of freshwater turtles[END_REF], mortality rate [START_REF] Girondot | Effects of sexual differences of age at maturity and survival on population sex ratio[END_REF], or different behavior between sexes [START_REF] Kofron | Observations on Aquatic Turtles in a Northeastern Missouri Marsh[END_REF][START_REF] Dodd | Population structure and biomass of Sternotherus odoratus (Testudines: Kinosternidae) in a northern Alabama lake[END_REF] influencing capture. [START_REF] Valdeôn | Datos preliminares de dos poblaciones de galâpago europeo (Emys orbicularis) en el sur de Navarra[END_REF] in Navarra obtained preliminary data with a sex ratio 1:1. Ayllon et al. (2010) in Cuenca (Spain), find a sex ratio biased towards males (3.6:1) and it is the case for other Iberian populations [START_REF] Keller | Ecología de poblaciones de Mauremys lep-rosa y Emys orbicularis en El Parque Nacional de Doñana[END_REF]Cordero-Rivera and Ayres-Fernandez, 2004;[START_REF] Segurado | La cistude d'Europe dans la Péninsule ibérique[END_REF][START_REF] Ayres | Sexual dimorphism and morphological differentiation in European pond turtle (Emys orbicularis) populations from northwestern Spain[END_REF]. This is the case of our population during 3 years, when the total number of males was higher than females and the sex ratio was biased for males (1.12:1). Inversely, very variable sex ratio values have been measured in Italian samples of Emys orbicularis, between 1:1 and 1:2.4 [START_REF] Mazzotti | Population structure of Emys orbicularis in the Bardello (Po Delta, Northern Italy)[END_REF][START_REF] Zuffi | Sexual dimorphism in Italian populations of the European pond terrapin, Emys orbicularis[END_REF][START_REF] Mazzotti | La popolazione della testuggine palustre (Emys orbicularis) del Bosco della Mesola[END_REF].

Age structure. The maximum age was 16 years for a male caught in 2014 and 14 years in two females caught in 2015. [START_REF] Auer | Population structure of syntopic Emys orbicularis and Mauremys rivulata in western Turkey[END_REF] reported maximum age almost identical to the one found in our study (i.e., 16 years). In Doñana, data estimated at 28 to 29 the maximum age for males and females respectively [START_REF] Keller | Aspects of the population structure of Emys orbicularis hispanica from southwestern Spain[END_REF]. The age structure of the population is quite common in chelonians, with a majority of adults and a small percentage of juveniles. However, we did not capture hatchlings in the site. This may be explained by the threatened factor, where juveniles stay more hidden in the vegetation and do not show up very often. This is the case for the population of Camargue Gardoise [START_REF] Lyet | La Cistude d'Europe (Emys orbicularis) en Camargue gardoise -Statut des populations et propositions de mesures de protection[END_REF] and the Ebro Delta in Spain [START_REF] Bertolero | Suivi de la population de cistude Emys orbicularis dans le delta de l'Ebre (NE Espagne)[END_REF]. This mainly reflects different behavior between adults and juveniles (Ayres and Cordero, 2007). It is possible that the aquatic habitats where used differently by adults and juveniles [START_REF] Olivier | Ecologie, traits d'histoire de vie et conservation d'une population de Cistude d'Europe Emys orbicularis en Camargue, Laboratoire de Biogéographie et Ecologie des Vertébrés[END_REF]. Finally, it is possible that bias is due to the capture method since hatchlings are smaller and therefore difficult to detect and our sampling was carried by hand. Predation pressure can also be a cause of low numbers of hatchlings, extremely vulnerable because of their soft shells. In our population juveniles are few the three years, especially with the class size between 60 -120 mm. This rate is higher in other populations such as Doñana, Spain (20%) [START_REF] Keller | Ecología de poblaciones de Mauremys lep-rosa y Emys orbicularis en El Parque Nacional de Doñana[END_REF] and Brenne, France (30%) [START_REF] Servan | Détermination du sexe ratio adulte de la tortue E. orbicularis dans des populations provenant de 7 étangs de Brenne (Indre, France)[END_REF]. [START_REF] Braitmayer | Die Europaische Sumpfschildkrote (Emys orbicularis) Menorcas[END_REF] found 12% juveniles in Menorca. This percent can be very low in some population as in . Çukurköy (western Turkey) where the rate is only 1.9%. The major difference between males and females is the size over 160 mm which is more represented in females with an average percent of 38% and with only 5.56% in males.

Growth rates. The only juvenile recaptured has a much higher growth than adults with 19.8% of growth rate. The growth trajectories are characterized by a faster growing period at the youth age and a slow growth trajectory probably after reaching the sexual maturity. The growth is much pronounced in female than male, which can explain the difference in body size between the two sexes.

The first results obtained from this work will constitute a basis for more studies on the reproduction strategy, the behavior and the use of the space in order to obtain details of the movements and to verify the zones actually used by the individuals and to highlight the corridors used. This species is not yet protected in Algeria despite its presence in a National Park and on a site Ramasar, it is often a victim of the operations of clearing the channel which can put the population at risk. Laying sites are also frequently devastated by clearing operations at the lake dykes. The disturbance is also a threat since the site is a touristic area and very frequented especially during the summer. It is, therefore, essential to involve the public, in particular, the users of the wetland (fishermen, farmers, etc.) and tourists in a process of preserving a species that is still vulnerable by the fragility of these habitats. It seems necessary that the various actors involved in wetland conservation, including Chadli Bendjedid University, the management of El Kala National Park, the services of Forests, Hydraulic Services and the services of Agriculture Collaborate to establish long-term conservation strategies for this species.

Figure 1

 1 Figure 1 Location of Lac Tonga with major vegetation types and study area.

Figure 2

 2 Figure 2 General view of the Tonga Lake; b, view of the Messida canal. Photo by S. Fediras.

Figure 3

 3 Figure 3 Morphometrical variables of Emys orbicularis (for abbreviations see Table 3). Photo by S. Fediras

Figure 6

 6 Figure 6 Size structure of the population of Emys orbicularis during three years (N = 100).

FigureFigure 4

 4 Figure 5 ree years (N = 100). Age structure of the population of Emys orbicularis during th

  Figure 7Linear regression of body weight (BW) on carapace length (CL) for Emys orbicularis captured during 3 years (N = 100).

Figure 8

 8 Figure 8 Growth of carapace length of Emys orbicularis.

Acknowledgments. We thank Ayres C.for his valuable corrections and suggestions and anonymous reviewer for helpful comments. We are grateful to Dr. P. Grillas, Program Director in the research center for the conservation of Mediterranean wetlands (Tour du Valat) for receiving us in the research station and for the use of their facilities during our stay. Permits to capture and analyze the turtles used in this study were released by the Director of the National Park of El Kala.