Arnaud Tognetti
email: arnaud.tognetti@gmail.com

Guila Ganem

Michel Raymond

Charlotte Faurie

Female mound-building mice prefer males that invest more in building behavior, even when this behavior is not observed

Keywords: cues, parental investment, preference, personality, sexual selection, cooperation

Significance statement

In the mound-building mouse, individuals gather to build a common mound within which juveniles will spend the winter months. As some males invest more in building than others, we questioned whether females would prefer males that invest more in building behaviors, even though females could not observe males' building behaviors before mate choice. We assessed male investment in building and conducted choice tests. Females were more attracted to males that invested more in building, even when building was not observed. Hence, building investment seems detectable by phenotypic cues that differ from building behavior per se. Further, the males' investment in building was negatively correlated with their direct offspring care assessed during retrieval trials. Our findings indicate that two alternative paternal care strategies may exist in this species, and that mate choice might influence the evolution of their remarkable collective building.

Introduction

Behavioral traits often form a suite of correlated traits, so-called behavioral syndromes (Sih et al. 2004a, b;[START_REF] Réale | Personality and the emergence of the pace-of-life syndrome concept at the population level[END_REF]. For example, aggressiveness is associated positively with exploratory behavior and boldness in a number of species (Sih et al. 2004a, b;[START_REF] Groothuis | Avian personalities: characterization and epigenesis[END_REF][START_REF] Boon | Personality, habitat use, and their consequences for survival in North American red squirrels Tamiasciurus hudsonicus[END_REF][START_REF] Réale | Male personality, life-history strategies and reproductive success in a promiscuous mammal[END_REF], and negatively associated with parental care [START_REF] Mutzel | Parental provisioning behaviour plays a key role in linking personality with reproductive success[END_REF]). These behavioral correlations could result from natural and sexual selection that favor particular trait combinations (Sih et al. 2004a;[START_REF] Réale | Personality and the emergence of the pace-of-life syndrome concept at the population level[END_REF][START_REF] Schuett | Sexual selection and animal personality[END_REF][START_REF] Schuett | Do female zebra finches, Taeniopygia guttata, choose their mates based on their 'personality'?[END_REF][START_REF] Pruitt | Reproductive consequences of male body mass and aggressiveness depend on females' behavioral types[END_REF][START_REF] Kortet | Females prefer bold males; an analysis of boldness, mate choice, and bacterial resistance in the field cricket Gryllus integer[END_REF]. Because of such associations, mate choice could indirectly select for a behavioral trait that is not a mate choice criterion, or even for signals or cues of behaviors that mates did not observe. For example, by preferring exploratory males, zebra finch females (Taeniopygia guttata) simultaneously select for more aggressive males due to an association between these traits [START_REF] Schuett | Do female zebra finches, Taeniopygia guttata, choose their mates based on their 'personality'?[END_REF]). Here we address whether individuals' investment in a common good could be indirectly selected for by an association of such behaviors with other sexually selected traits or cues. Such an association would indicate a potential role of mate preference, and possibly sexual selection, in the evolution of collective behavior and cooperation [START_REF] Putland | Has sexual selection been overlooked in the study of avian helping behaviour?[END_REF][START_REF] Tognetti | Sexual selection of human cooperative behaviour: an experimental study in rural Senegal[END_REF][START_REF] Van Vugt | Men behaving nicely: Public goods as peacock tails[END_REF][START_REF] Arnocky | Altruism predicts mating success in humans[END_REF]).

Our study model, Mus spicilegus, is a socially monogamous mouse, endemic to southeastern Europe, which possesses a mound-building behavior that is unique among mice [START_REF] Tong | Mus spicilegus[END_REF]. After a period of reproduction from spring to late summer, during which each adult breeding pair produces 4 to 5 litters in individual burrows of simple design [START_REF] Sokolov | Mus spicilegus[END_REF], several individuals gather in late summer to collectively build a common structure in which juveniles born in late summer and early autumn will overwinter in a nest chamber located under the mound [START_REF] Muntyanu | Ecological features of an overwintering population of the Hillock mouse (Mus hortulanus Nordm) in the South-West of the USSR[END_REF][START_REF] Garza | Social structure of the mound-building mouse Mus spicilegus revealed by genetic analysis with microsatellites[END_REF][START_REF] Poteaux | Socio-genetic structure of moundbuilding mice, Mus spicilegus, in autumn and early spring[END_REF][START_REF] Canady | First knowledge of winter ecology of the mound-building mouse (Mus spicilegus Petenyi, 1882) from Slovakia[END_REF][START_REF] Tong | Causes and Consequences of Cooperative Construction in the Mice Mus spicilegus and Peromyscus polionotus[END_REF]. Several studies indicate that juveniles in a given mound may originate from several breeding pairs (up to 4) where the females are genetically related but the males are unrelated [START_REF] Garza | Social structure of the mound-building mouse Mus spicilegus revealed by genetic analysis with microsatellites[END_REF][START_REF] Poteaux | Socio-genetic structure of moundbuilding mice, Mus spicilegus, in autumn and early spring[END_REF]). In early spring, these mice leave their mounds, disperse (alone or in small kin groups) and form breeding pairs [START_REF] Muntyanu | Ecological features of an overwintering population of the Hillock mouse (Mus hortulanus Nordm) in the South-West of the USSR[END_REF][START_REF] Sokolov | Mus spicilegus[END_REF][START_REF] Simeonovska-Nikolova | Seasonal changes of some population characteristics of Mus spicilegus Petenyi in North Bulgaria[END_REF][START_REF] Poteaux | Socio-genetic structure of moundbuilding mice, Mus spicilegus, in autumn and early spring[END_REF]). In the northern part of the species' range, construction of mounds takes 14-21 days and occurs from mid-August to mid-November [START_REF] Muntyanu | Ecological features of an overwintering population of the Hillock mouse (Mus hortulanus Nordm) in the South-West of the USSR[END_REF][START_REF] Sokolov | Mus spicilegus[END_REF][START_REF] Canady | First knowledge of winter ecology of the mound-building mouse (Mus spicilegus Petenyi, 1882) from Slovakia[END_REF]). The mounds are built by the accumulation of plant materials covered with earth and are up to four meters in diameter and typically 0.5 meters high when freshly built [START_REF] Muntyanu | Ecological features of an overwintering population of the Hillock mouse (Mus hortulanus Nordm) in the South-West of the USSR[END_REF][START_REF] Sokolov | Mus spicilegus[END_REF], which supports the view that they are built collectively (a single mouse cannot build such a large structure alone [START_REF] Szenczi | Social behavior, cooperation and ecological constraints on two closely related mice species[END_REF]).

The precise age structure of mound builders has yet to be established in natural conditions [START_REF] Hölzl | Why do the mounds of Mus spicilegus vary so much in size and composition?[END_REF][START_REF] Tong | Causes and Consequences of Cooperative Construction in the Mice Mus spicilegus and Peromyscus polionotus[END_REF][START_REF] Tong | Mus spicilegus[END_REF]. Indeed, direct observations of mound building in nature are scarce. Furthermore, trapping success can be relatively low during mound building. For example, observations done during the mound-building period in semi-natural conditions suggest that, even when they were known to be present, the adults were particularly difficult to trap [START_REF] Orsini | Facteurs régissant la répartition des souris en Europe : intérêt du modèle souris pour une approche des processus évolutifs[END_REF]. Moreover, indirect evidence through trapping around the mounds revealed that adults could represent 40% to 60% of the population of mice captured from late August to late October [START_REF] Simeonovska-Nikolova | Spatial organization of the mound-building mouse Mus spicilegus in the region of northern Bulgaria[END_REF][START_REF] Canady | First knowledge of winter ecology of the mound-building mouse (Mus spicilegus Petenyi, 1882) from Slovakia[END_REF][START_REF] Simeonovska-Nikolova | Neighbour relationships and spacing behaviour of mound-building mouse, Mus spicilegus in summer[END_REF][START_REF] Tong | Causes and Consequences of Cooperative Construction in the Mice Mus spicilegus and Peromyscus polionotus[END_REF] indicating that, although often not detected, adults could be present during the mound construction and that juveniles could also contribute to building [START_REF] Sokolov | Mus spicilegus[END_REF][START_REF] Canady | First knowledge of winter ecology of the mound-building mouse (Mus spicilegus Petenyi, 1882) from Slovakia[END_REF]. From November, although some adults are still found around the mounds [START_REF] Canady | First knowledge of winter ecology of the mound-building mouse (Mus spicilegus Petenyi, 1882) from Slovakia[END_REF][START_REF] Tong | Causes and Consequences of Cooperative Construction in the Mice Mus spicilegus and Peromyscus polionotus[END_REF], the population of juveniles increases substantially [START_REF] Garza | Social structure of the mound-building mouse Mus spicilegus revealed by genetic analysis with microsatellites[END_REF][START_REF] Milishnikov | Genotypic variability in populations of moundbuilder mice Mus spicilegus Pet., 1882, at different life-cycle stages[END_REF][START_REF] Canady | First knowledge of winter ecology of the mound-building mouse (Mus spicilegus Petenyi, 1882) from Slovakia[END_REF][START_REF] Tong | Causes and Consequences of Cooperative Construction in the Mice Mus spicilegus and Peromyscus polionotus[END_REF], which could reflect further gathering of mice and/or events of reproduction during the building season.

Altogether, based on the available literature, it seems that the age structure of mound builders may vary, and that one or several breeding pairs and their juveniles of 3-4 weeks old, or only the juveniles, may contribute to build the mound. Hence, selection may drive mound building behavior directly and/or indirectly by increasing survival of juveniles. Here we address whether males that invest more in mound building are preferred by females.

The propensity to build a mound is genetically heritable [START_REF] Orsini | Facteurs régissant la répartition des souris en Europe : intérêt du modèle souris pour une approche des processus évolutifs[END_REF], and investment in mound building in captivity varies between individuals (Simeonovska-Nikolova and Mehmed 2009; [START_REF] Serra | Behavioral differentiation during collective building in wild mice Mus spicilegus[END_REF][START_REF] Hurtado | Specialization in building tasks in the mound-building mouse, Mus spicilegus[END_REF]. Moreover, mound size is highly variable in natural conditions [START_REF] Hölzl | Why do the mounds of Mus spicilegus vary so much in size and composition?[END_REF]) and is positively correlated with insulation against water and temperature fluctuations [START_REF] Hölzl | Insulation capacity of litter mounds built by Mus spicilegus: physical and thermal characteristics of building material and the role of mound size[END_REF][START_REF] Szenczi | Morphology and function of communal mounds of overwintering mound-building mice (Mus spicilegus)[END_REF][START_REF] Szenczi | The contribution of the vegetable material layer to the insulation capacities and water proofing of artificial Mus spicilegus mounds[END_REF]. Since small energy savings influence animal survival even in temperate climate [START_REF] Vogt | Influence of ambient temperature, nest availability, huddling, and daily torpor on energy expenditure in the white-footed mouse Peromyscus leucopus[END_REF][START_REF] Geiser | Metabolic rate and body temperature reduction during hibernation and daily torpor[END_REF]), mound size is thus expected to influence the probability of offspring survival during the European continental winter [START_REF] Hölzl | Insulation capacity of litter mounds built by Mus spicilegus: physical and thermal characteristics of building material and the role of mound size[END_REF][START_REF] Szenczi | Morphology and function of communal mounds of overwintering mound-building mice (Mus spicilegus)[END_REF][START_REF] Szenczi | The contribution of the vegetable material layer to the insulation capacities and water proofing of artificial Mus spicilegus mounds[END_REF]. Hence, it is likely that females would benefit from choosing hardworking builders as such partners would invest more in mound building and/or transmit their building ability to their offspring and therefore improve the probability of offspring survival during winter.

However, female mate choice takes place before mound building (for adult builders) or after the wintering period (for juvenile builders) and, thus, before the potential display of male building behavior [START_REF] Muntyanu | Ecological features of an overwintering population of the Hillock mouse (Mus hortulanus Nordm) in the South-West of the USSR[END_REF][START_REF] Sokolov | Mus spicilegus[END_REF]. Hence, the ability of females to detect male building behavior through other signals/cues should be positively selected for. Alternatively, females could indirectly select for male building behavior through their preferences for other traits associated with males' investment in building. Furthermore, investment in mound building might be seen as a form of parental care. Behavioral experiments in Mus spicilegus revealed that males invest in offspring attendance, and that highly attendant fathers increase not only their own reproductive success but also that of their mate [START_REF] Patris | A comparative study of parental care between two rodent species: implications for the mating system of the mound-building mouse Mus spicilegus[END_REF][START_REF] Feron | Paternal care in the mound-building mouse reduces inter-litter intervals[END_REF]. Parental investment was shown to be advertised by phenotypic traits in several species [START_REF] Hill | Plumage coloration is a sexually selected indicator of male quality[END_REF][START_REF] Östlund | Female fifteen-spined sticklebacks prefer better fathers[END_REF][START_REF] Préault | Male bill colour and age are associated with parental abilities and breeding performance in blackbirds[END_REF][START_REF] Hill | Bird Coloration. Vol. II. Function and Evolution[END_REF][START_REF] Gleason | Testosterone response to courtship predicts future paternal behavior in the California mouse, Peromyscus californicus[END_REF][START_REF] Bartsch | Multiple song features are related to paternal effort in common nightingales[END_REF] and could thus allow females to select good fathers. Hence, a secondary aim of this study was to test whether males that invest highly in mound building also attend more to their offspring, or if these two forms of investment are uncoupled.

We designed our experiment to test whether females preferred males that varied in their contribution in mound building when this behavior was observed versus unobserved, and whether male investment in mound building was positively associated with direct paternal care. We assessed male spontaneous building behavior exhibited during mound construction in captivity by wild mice captured in agricultural fields in Bulgaria while juveniles. Then, we used two-way choice tests to assess females' attraction to males that invest more in mound building versus males that invest less.

Finally, we evaluated post-mating paternal care exhibited by males with different investment in building behavior using pup retrieval experiments: we recorded the number of pups each male retrieved back to the nest after they were removed from it, and the latency to engage in the retrieving behavior. We predicted that females would be more attracted to males that invest more versus less in mound building even when the former did not observe them build. We also predicted that males that invest more in building would invest more in direct paternal care.

METHODS

Capture of wild mice

Mound-building mice were captured in northern Bulgaria in September 2011 and were then kept in the animal facilities of the University of Montpellier in France. We caught the mice in an agricultural area, at least 2 km away from the village of Rakita (GPS coordinates: 43°16'13.171"N 24°16'16.447"E), using Sherman live-traps. At this time of year, the mice had already built their mounds. Live-traps were set around each mound. We weighed and measured all the mice from the nose to the base of their tail upon capture. A total of 30 males and 28 females, all subadults, captured from 14 mounds were used in this study. Same-mound mice, irrespective of their sex, were kept in the same laboratory cages from their capture until the start of the experiments two months later.

Male investment in mound building

We measured the contribution of each male to mound and nest building in large terraria two months after capture. This experiment lasted 8 weeks. Earlier studies have shown that even laboratory-born mice of this species would engage in mound building when building material is made available, suggesting that mound building is a spontaneous behavior [START_REF] Orsini | Facteurs régissant la répartition des souris en Europe : intérêt du modèle souris pour une approche des processus évolutifs[END_REF][START_REF] Hurtado | Specialization in building tasks in the mound-building mouse, Mus spicilegus[END_REF]. Ten groups of three males and two females were constituted. Sex composition was based on the sex-ratio observed in the wild during the mound building period [START_REF] Simeonovska-Nikolova | Seasonal changes of some population characteristics of Mus spicilegus Petenyi in North Bulgaria[END_REF][START_REF] Simeonovska-Nikolova | Behavior of mound-building mouse, Mus spicilegus, during autumn-winter period in captivity[END_REF]. We placed each group in a large terrarium (1 x 1 x 0.8 m) containing approximately 0.2 m 3 of earth and stones. The room was maintained at 21/23°C under a 12:12 light/dark cycle (corresponding roughly to the photoperiod observed in the field in September/October) with lights on at 9.00 pm. Water was available ad libitum, and food was provided on a weekly basis, although daily visits were made to check the well-being of the mice. At the beginning of each observation session, straw and seeds were provided as building materials in addition to the earth and stones already present in the terrariums. Both males and females participated in building. However, we only recorded male behaviors. For each male, five categories of behavior were recorded: the number of times it dug, carried straw, carried seeds, carried stones, and entered the nest (Fig. S1). The latter was recorded because the mice were observed entering the nest to build it and shape it from inside. A single investigator (AT) observed each group during 5 sessions of 1 hour each, approx. one week apart. Males were ear tagged (7.8 x 2.8 mm, Fine Science Tools GmbH) for identification. For each terrarium, the number of metallic earrings (1 or 2) and the side of the tag (right ear, left ear, or both) allowed individual mice to be recognized without having to handle them.

We could constitute only five groups of same-mound individuals (three males and two females). The other five groups included three same-mound males to limit aggression [START_REF] Sokolov | Mus spicilegus[END_REF]) and two same-mound females from a mound different to that of the males. Unfortunately, for four out of these five groups, we observed high female mortality (n=8) during the first night in the enclosure, most likely due to males' aggressiveness. Following this observation, we immediately removed the two remaining females from the fifth terrarium and placed them in a separate cage.

We averaged the data collected during the five observation sessions for each male and for each of the five behavioral items recorded during building (transport of straw, seeds, and stone, digging and entering the nest). As highlighted in Fig. S1, mice build a nest as well as a structure closely resembling a mound that had all the characteristics described in the field: i.e. seed storage covered with earth and plants materials. However, although seed transport and storage did take place (Fig. S1), because 22 out of 30 mice were not observed transporting seeds, we removed this variable from the analysis. A principal component analysis (PCA) was applied to the four remaining behavioral items with the aim of extracting a single factor reflecting male building investment (function prcomp in R).

At the end of this experiment, all individuals were transferred to laboratory cages, and females and males of a given group were kept in separate cages to prevent reproduction. They were maintained in laboratory conditions under a 13.5:10.5 h light/dark cycle (light at 6.30 pm), corresponding to the photoperiod during the breeding season (early spring). Food and water were available ad libitum, and cotton was provided as nesting material. They were kept in these conditions until the beginning of the next experiment.

Female attraction

We measured female attraction to males in a Y maze following the procedure described in [START_REF] Smadja | Subspecies recognition in the house mouse: a study of two populations from the border of a hybrid zone[END_REF] six months after their capture. The stimuli were composed of 5 pairs of males. Males of each pair shared the same terrarium during the mound-building experiment and belonged to one of the five terraria in which females were present. In each of these terraria, we selected among the three males the male that invested the most and the male that invested the least in order to present to the females a choice between contrasting levels of building behavior. To that aim, we used the PCA factor reflecting the most male investment in building (see Results).

Each female was tested once. We tested female attraction to males that invested the most versus the least in building when building was observed (females that shared an enclosure with 3 males during mound building were presented with a choice between the male that invested in building the most or the least in the triad) (n=10 females), and when building was unobserved (females that did not share an enclosure with males were given the choice between a pair of males composed of the males that invested the most and the least from a triad randomly chosen) (n=10 females).

A single investigator (AT) conducted all the tests. All mice were more than 6 months old and sexually mature. To maximize the expression of sexual attraction, females were tested while sexually receptive (i.e., estrus or proestrus/estrus, assessed with vaginal smears).

The Y maze was transparent (plexiglas and plastic ware) and composed of a main branch (5 cm diameter, 35 cm long) connected to two secondary branches (5 cm diameter, 25 cm long). Boxes (35 x 23 x 13 cm) with transparent perforated doors were connected at the end of each branch (for an illustration of the apparatus see: [START_REF] Smadja | Subspecies recognition in the house mouse: a study of two populations from the border of a hybrid zone[END_REF]. One week before the experiment, each female was allowed to explore the empty Y maze for 15 minutes in order to become habituated.

At the start of each test, a female was placed in a box connected to the main branch of the apparatus. The two stimuli were randomly assigned to one or the other peripheral boxes (the identities of the stimuli was not known by the observer). We then opened the door of the female's box and started to record its behavior when the female crossed the box door. In all tests, the females entered both secondary branches of the Y maze. During the 10-minute observation, we recorded the time spent by females: i) in each secondary branch (including when females were in contact with the perforated door but when the male was not behind the door), and ii) interacting with the male, or sniffing or licking the transparent perforated door when the male was just behind the door. This is a classical method to measure female preference (e.g. [START_REF] Smadja | Asymmetrical reproductive character displacement in the house mouse[END_REF][START_REF] Latour | Sexual selection against natural hybrids may contribute to reinforcement in a house mouse hybrid zone[END_REF]) that was shown to constitute a good proxy of female propensity to engage in mating with the preferred male [START_REF] Patris | Female sexual preferences differ in Mus spicilegus and Mus musculus domesticus: the role of familiarization and sexual experience[END_REF][START_REF] Smadja | Subspecies recognition in the house mouse: a study of two populations from the border of a hybrid zone[END_REF]. We implemented General Linear Mixed Models to test whether male attraction was influenced by their investment in building. For this purpose, we used GLMMs with a quasi-binomial error structure (glmmPQL function of the MASS package in R) in which we included the identity of each pair of males as a random effect. In the first model, the response variable was the proportion of time spent by the female in the left versus right side of the maze. In a second model, it was the proportion of time the female was in close contact with the male of the left versus right side of the maze. In both models, we included two explanatory variables: (i) a binary variable concerning male investment in building (1 if the male on the left was the one that invested the most in building behaviors, 0 if it was the male that invested the least) and (ii) a binary variable reflecting the treatment (1 if the female observed male building behaviors, 0 if not). We also tested the interaction between these two variables to test whether observing male building influenced female preferences. When the interaction was not significant, we removed it from the model.

At the end of the experiment, all individuals were returned to their home cage and maintained under laboratory conditions until the next experiment.

Direct paternal care

We used a pup retrieval procedure, a test used commonly to measure parental care in rodents [START_REF] Dudley | Paternal behavior in the california mouse, Peromyscus californicus[END_REF][START_REF] Cohen-Salmon | Differences in patterns of pup care in mice V-Pup ultrasonic emissions and pup care behavior[END_REF], including Mus spicilegus [START_REF] Patris | A comparative study of parental care between two rodent species: implications for the mating system of the mound-building mouse Mus spicilegus[END_REF]. We first randomly paired females (n=20) and 'unfamiliar' males (i.e., captured in different mounds in the field). During the first week, the two members of the pair were maintained in the same cage but separated with a wire net so that they could first become familiar with each other. We maintained them in laboratory conditions under a 13.5:10.5 light/dark cycle (light at 6.30 pm), corresponding to the photoperiod of the breeding season in the field. Food and water were available ad libitum, and cotton was provided as nesting material. Ten of the 20 pairs successfully bred (a low breeding rate is often observed for wild-born mice kept under laboratory conditions, GG pers. obs.) and could hence participate in this experiment that began 18 months after capture. Litter size varied from 5 to 12 pups.

On the day of birth, we placed the mice in a large terrarium (70 x 30 x 30 cm). The terrarium contained clean sawdust, food and water. One corner also contained cotton and cardboard rolls as nestbuilding material.

All males were tested twice: approximately four days (mean ± SD: 3.7 ± 0.8 days) and six days (6.3 ± 0.9 days) after the birth of their first litter. During these two sessions, we first removed the breeding pair from the terrarium. We then removed three of the pups from the nest and placed them at the opposite end of the terrarium. We isolated these three pups from their littermates and the nest by placing a transparent plastic separation in the middle of the terrarium. The male was then put back in the side of the terrarium containing the nest. After 30 seconds, we removed the plastic separation and we measured (i) male latency before the start of retrieval of the isolated pups, and (ii) the number of pups retrieved to the nest during the next fifteen minutes. Both of these measures were averaged over the two test sessions, and we used Spearman correlation tests (two-tailed tests, function cor.test in R) to assess their potential association with the male building score measured during the mound-building experiment (first experiment above). For males that did not retrieve any pups, the male latency to retrieve was set at 15 minutes (i.e., the duration of the experiment). Because the Spearman correlation test relies on ranks, this choice did not influence the results.

Because this species is nocturnal and particularly active during the first few dark hours (Simeonovska-Nikolova and Mehmed 2009), all observations (mound building, female preferences, and paternal investment) were conducted one to two hours after the beginning of the dark period under dim red light. To minimize observer bias, we used blind methods when behavioral data were recorded (preferences tests and retrieval experiments). We recorded all observations using the Observer software Version 5 (Noldus Information Technology). All statistical analyses were performed using the R software, version 3.4.2 (R Core Team 2017).

RESULTS

Male investment in building

In total, during the 50 hours of observation, each male transported 0 to 70 pieces of straw (mean ± SD:

18.1 ± 19.4), and 1 to 99 (20.9 ± 23.9) stones (approximately 1 cm 3 in size). The frequency of digging varied between 0 and 35 times (10.1 ± 8.9), and they entered their nest 2 to 35 times (12.6 ± 9.9). We used a PCA to extract a single factor reflecting male global investment in mound building and avoiding giving too much weight to a specific behavior. The first two axes of the PCA, including the four building items, captured 80% (45% and 34% respectively) of the total variation. The first axis was positively correlated with the number of times a male entered the nest (r = 0.42), negatively correlated with stones transport (r = -0.66) and digging frequency (r = -0.62), and not correlated with straw transport (r = 0.06). We hence considered that this axis could represent a measure of specialization in building tasks [START_REF] Serra | Behavioral differentiation during collective building in wild mice Mus spicilegus[END_REF][START_REF] Hurtado | Specialization in building tasks in the mound-building mouse, Mus spicilegus[END_REF]) rather than a measure of global investment. The second axis was positively correlated with all four variables: frequency of digging (r = 0.28), number of stones (r = 0.17) and straw transported (r = 0.76), and number of entrances into the nest (r = 0.57), and we considered that it could reflect male global investment in building and hence a pertinent measure allowing to identify males that invested the most and the least in building behaviors.

Investment in building was not related to male weight (10.26±0.87 grams) or size (7.14±0.34 cm) at capture (Spearman correlation test: weight: ρ = 0.11, p = 0.58, size: ρ = 0.01, p = 0.95) nor to their weight (11.64±1.6 grams) at the end of the building experiment (ρ = 0.13, p = 0.53). Moreover, we did not detect any difference in individual building when comparing males belonging to mixed groups (containing females) to males belonging to all-male groups (Wilcoxon rank sum test: W = 86, p = 0.43).

Female attraction

We found no effect of the interaction between male investment in building and treatment in any model, suggesting that observing male building behaviors did not influence female attraction (glmmPQL with time spent by females (n=20) in the branches as response variable: t=1.00, P=0.92; glmmPQL with time spent by females (n=15) in close proximity to the males as response variable: t=-1.03, P=0.34).

Male investment in building did not influence the proportion of time females (n=20) spent exploring the two branches (52% of time was spent on the side of the male that invested the most versus the least; glmmPQL: t=1.30, P=0.21; Table S1; Fig. 1). However, it did significantly influence the proportion of time females (n=15) spent in proximity to the males (75% of time was spent close to the male that invested the most versus the least; glmmPQL: t=3.69, P=0.006; Table S2; Fig. 1): females spent more time in close proximity to the male that invested the most in building behaviors compared to the time spent with the male that invested the least (median [1 st quartile; 3 rd quartile] of the difference of time spent with the male that invested the most versus the least in building behaviors=8. 4 [4.6; 11.7] s).

Investment in mound building & direct paternal care

The males (n = 10) retrieved 0 to 3 pups at each session (median [1 st quartile; 3 rd quartile]: 1.5 [0; 3] for the first session; 2.5 [0.25; 3] for the second session). For each male, the number of pups retrieved during the first versus the second session was not significantly different (paired Wilcoxon rank test: 0 [-0.75; 0] pups, V = 5.5, p = 0.68). For sessions in which at least one pup was retrieved (n=12), the latency to retrieve the first pup was between 23 and 810 seconds (171 [36; 325] s).

Direct paternal care was negatively associated with male investment in building: across the 20 sessions, the males that invested more in building retrieved fewer pups back to the nest (Spearman correlation test: n=10 males, ρ = -0.67, p = 0.04; Fig. 2a) and presented a higher latency to retrieve the first pup (n=10 males, ρ = 0.71, p = 0.02; Fig. 2b).

Discussion:

Mate choice and sexual selection could favor the evolution of traits that are not directly selected for [START_REF] Schuett | Sexual selection and animal personality[END_REF][START_REF] Schuett | Do female zebra finches, Taeniopygia guttata, choose their mates based on their 'personality'?[END_REF]. Here we addressed whether mound building, a spontaneous behavior observed both in wild-and laboratory-born individuals of Mus spicilegus, could be favored during female mate choice even though females were not able to observe the building activity of males.

Indeed, the presence of adults and juveniles around mounds during the building period suggests that the two cohorts (adults and juveniles when 3-4 weeks old) could be involved in building [START_REF] Simeonovska-Nikolova | Spatial organization of the mound-building mouse Mus spicilegus in the region of northern Bulgaria[END_REF], 2012;[START_REF] Canady | First knowledge of winter ecology of the mound-building mouse (Mus spicilegus Petenyi, 1882) from Slovakia[END_REF][START_REF] Tong | Causes and Consequences of Cooperative Construction in the Mice Mus spicilegus and Peromyscus polionotus[END_REF], further indicating that mate choice would take place before mound building (for the adults) or after (for the juveniles) and involve unfamiliar partners [START_REF] Garza | Social structure of the mound-building mouse Mus spicilegus revealed by genetic analysis with microsatellites[END_REF]. Aiming to get insight into the mechanisms favoring building behavior, we asked whether female mate choice could favor males that invest more versus less in mound building behaviors and whether males that invest more are also more involved in direct parental care using pup-retrieval experiments.

Our findings indicate that females were more attracted to males that invested more in building behaviors over males that invested less, even when building behaviors were not observed. This suggests that female attraction to males could be influenced by cues that are different from building behaviors per se, or by attraction to traits associated with male investment in building. We also show that direct parental care is negatively correlated with male investment in mound building, suggesting a trade-off between these two behaviors.

Our findings raise the question of which signals or cues females are responding to when they show an attraction to males that invest more in mound building. In our experiment, females were more attracted to males that invested more versus less in building, even without having observed them build.

Hence, phenotypic cues advertising male investment in building may exist in this species. Such cues could be based on acoustic, olfactory, or visual traits, since all of them are involved in mice communication (e.g.: [START_REF] Hurst | Scent wars: the chemobiology of competitive signalling in mice[END_REF][START_REF] Musolf | Ultrasonic courtship vocalizations in wild house mice, Mus musculus musculus[END_REF]) and were available to females in our test apparatus. Their detection by females could influence their sexual preferences, as some sexual pheromones do in several species, including mice [START_REF] Roberts | Darcin: a male pheromone that stimulates female memory and sexual attraction to an individual male's odour[END_REF][START_REF] Li | Aversion and attraction through olfaction[END_REF]. An alternative explanation could also be that female attraction to males that invest more in building was not directed to building per se but to other traits with which investment in building is associated. We did not observe any link between male size or weight and investment in building, suggesting that male condition is unlikely to be one of these traits. Interestingly, experimental studies in the moundbuilding mouse found that agonistic behaviors between unfamiliar males and females are positively linked with sexual motivation [START_REF] Busquet | What triggers reproductive life? Effects of adolescent cohabitation, social novelty and aggression in a monogamous mouse[END_REF][START_REF] Simeonovska-Nikolova | Sociosexual behavior of female mound-building mice, Mus spicilegus, in a forced-pairing experiment[END_REF].

Because of the expected high cost of mound building and its important role in the success of overwintering, individuals that invest more in mound building are likely to more aggressively protect resources and defend their mound from intruders. We can therefore speculate that male aggressiveness or dominance might be sexually selected traits associated with building, leading to the indirect selection of building behavior through female mate choice. During our preference tests, we did not observe agonistic behaviors between males and females through the perforated doors; furthermore, males that invested more in mound building were not observed to try to attract more female attention than males that invested less. However, chemosensory cues of dominance and aggressiveness are present in the urine and preputial glands of male mice and therefore could have been detected by females during their interactions with the males [START_REF] Harvey | Pattern of volatile compounds in dominant and subordinate male mouse urine[END_REF][START_REF] Hurst | Scent wars: the chemobiology of competitive signalling in mice[END_REF][START_REF] Soini | Comparison of urinary scents of two related mouse species, Mus spicilegus and Mus domesticus[END_REF][START_REF] Mucignat-Caretta | Message in a bottle: major urinary proteins and their multiple roles in mouse intraspecific chemical communication[END_REF]. Follow-up studies should thus investigate which traits are used by female Mus spicilegus during mate choice that are associated with building behavior. Such studies may particularly focus on dominance, aggressiveness and other personality traits.

In Mus spicilegus, the inclination of females to prefer males that invest more in mound building could be an adaptive strategy. Choosing a male that invests highly in building could increase females' fitness in several ways. First, since mound size is positively correlated with water-insulation and soil temperature inside the mound (Hölz et al. 2011;[START_REF] Szenczi | Morphology and function of communal mounds of overwintering mound-building mice (Mus spicilegus)[END_REF][START_REF] Szenczi | The contribution of the vegetable material layer to the insulation capacities and water proofing of artificial Mus spicilegus mounds[END_REF], choosing a male that invests more energy and time in mound building could increase offspring survival during the winter. Second, mound-building behavior seems to be genetically heritable [START_REF] Orsini | Facteurs régissant la répartition des souris en Europe : intérêt du modèle souris pour une approche des processus évolutifs[END_REF]). If the level of investment in building was also heritable, by choosing a male that invests more in building, females could improve the ability of their offspring to build a mound, and hence increase the chance of survival of their own progeny. Third, given the attractiveness of the males that invest more in building behaviors, females could also increase their sons' reproductive success (sexy son hypothesis: [START_REF] Weatherhead | Offspring quality and the polygyny threshold: "the sexy son hypothesis[END_REF].

Interestingly, we found a negative correlation between direct paternal care and building investment. Previous experimental studies involving the mound-building mouse found intense paternal investment, such as covering and warming the pups [START_REF] Patris | A comparative study of parental care between two rodent species: implications for the mating system of the mound-building mouse Mus spicilegus[END_REF], and males that exhibited the highest levels of offspring attendance increased their reproductive success by reducing their mate's inter-litter intervals [START_REF] Feron | Paternal care in the mound-building mouse reduces inter-litter intervals[END_REF]. As both parental investment and building are likely to be energetically costly, the negative association observed between them may indicate the existence of a tradeoff. In addition, since parents are likely to build a mound for their offspring, mound building may be considered a form of parental care (as defined by [START_REF] Royle | The evolution of parental care[END_REF]). In this case, this negative association might suggest the existence of two alternative parental care strategies. Hence, an interpretation of our results could be that different behavioral traits may correspond to different types of fathers with regard to how they take care of offspring. Such alternative strategies in offspring care were previously observed in some cooperative breeding species, such as cichlids, Neolamprologus pulcher, or the noisy miner, Manorina melanocephala, in which different types of helpers seem to exist [START_REF] Arnold | Division of labour within cooperatively breeding groups[END_REF][START_REF] Bergmüller | Adaptive behavioural syndromes due to strategic niche specialization[END_REF], but to our knowledge, they were not extensively studied in relation to parental care.

Cooperative behavior is defined as a behavior that benefits others while reducing the relative fitness of the performer of that behavior and hence could be selected against [START_REF] West | Evolutionary explanations for cooperation[END_REF].

Mound building possesses a priori those characteristics and we propose that it may be considered as a cooperative behavior, favored by female mate choice as observed in humans [START_REF] Farrelly | Altruists attract[END_REF][START_REF] Tognetti | Assortative mating based on cooperativeness and generosity[END_REF][START_REF] Tognetti | Men increase contributions to a public good when under sexual competition[END_REF][START_REF] Arnocky | Altruism predicts mating success in humans[END_REF]) and some cooperatively breeding birds [START_REF] Reyer | Investment and relatedness -a cost/benefit analysis of breeding and helping in the pied kingfisher (Ceryle rudis)[END_REF][START_REF] Jones | Parentage, mate removal experiments, and sex allocation in the cooperatively breeding bell miner, Manorina melanophyrs[END_REF][START_REF] Doutrelant | Helping has signalling characteristics in a cooperatively breeding bird[END_REF].

A limitation of our study concerns the small sample sizes, due to restrictions on field captures, and unexpected mortality events. Nevertheless, male investment in building significantly influenced female attraction and this result is particularly promising for more extensive research.

In conclusion, our results raise questions about the mechanisms involved in the evolution of mound building and provide support to the hypothesis that such behavior could be detectable by phenotypic cues different from building per se. While the mechanisms enabling females to prefer the males that invest the most in building behaviors in this species are still unknown, our results suggest that mate choice might influence the evolution and maintenance of mound building. Last but not least, several authors pointed out the collaborative aspect of mound building, and some evidence indicates that several breeding pairs and their offspring could be involved in building this common good. Future studies should test whether building could be considered a cooperative behavior and whether sexual selection is another pathway by which cooperative building in this species might evolve. Table S2. Influence of male investment in building and treatment on the proportion of time the female spent in contact with the male of the left versus right side of the maze (n= 15). We used a Generalized linear mixed model fitted by penalized quasi-likelihood (glmmPQL, binomial error), with male pair's identity as a random effect. We included two explanatory variables: a binary variable concerning male investment in building (1 if the male on the left was the one that invested the most in building behaviors, 0 if it was the male that invested the least) and a binary variable reflecting the treatment (1 if the female observed male building behaviors, 0 if not). The initial model also considered the interaction between male investment in building and treatment, but it was excluded during model simplification due to its non-significance. At the beginning of the experiment, the soil of each terrarium was uniformly covered with earth and stones. Additional material (straw and seeds) were added weekly at the center of each terrarium.

All mice built a nest made of straw in a corner of the terrarium (A), and constructed a 'mound like' stucture made of stone and straw (B). Under some parts of the 'mound like' structures we observed the presence of seeds indicating seeds transport, gathering and storage (C). Tunnels were also observed (D).

A B D C

Fig. 1

 1 Fig. 1

Fig. 2

 2 Fig. 2

Figure S1 :

 S1 Figure S1: Photographs of mounds built in captivity

Acknowledgments

We are very grateful to D. Simeonovska-Nikolova, B. Nikolovi and C. Albinet for their help for the trapping session in Bulgaria. We also thank Z. Groó, Y. Latour, A. Orth, and M. Perriat-Sanguinet, J. Barthes, J. Bovet, M. Derex, L. Danilo, V. Durand, L. Etienne, A. Nitsch, and A. Ravel, to help provided throughout the experiment and A.J. Carter who proofread the manuscript. We also thank the

reviewers for their helpful comments. We thank the Ministry of Environment and Water of Bulgaria, which permitted us to catch specimen of Mus spicilegus. Supports through the ANR -Labex IAST, the CNRS of France (www.cnrs.fr), the Région Languedoc-Roussillon 'Chercheur(se)s d'Avenir' (no.: DGA3/DESR/2012/Q159) and the Fondation des Treilles (www.les-treilles.com) are gratefully acknowledged. This is contribution ISEM 2018-162.

Data availability

The datasets analysed during the current study are available in the figshare repository, https://doi.org/10.6084/m9.figshare.5562664

Compliance with Ethical Standards

Ethical Approval

Mouse sampling was performed with the authorization of the Bulgarian Ministry of the Environment and Water (permit N°33-00-140). The study complied with all the relevant laws of France and mice handling and behavioral tests were authorised by the French authorities (Direction Départementale de la Protection des Populations de l'Hérault -Ministère de l'Agriculture, permit N°C34-265). This study also followed the ABS/ASAB guidelines for the ethical treatment of animals. We were particularly committed to limiting the number of mice trapped and tested, and mice were provided an enriched environment and diversified food to reduce their stress as much as possible.

Conflict of Interest

The authors declare that they have no conflict of interest.

Supplementary data: Tables S1 &S2.

Table S1. Influence of male investment in building and treatment (observed building by the female versus not) on the proportion of time females spent exploring the left versus right side of the maze (n= 20). We used a Generalized linear mixed model fitted by penalized quasi-likelihood (glmmPQL, binomial error), with male pair's identity as a random effect. We included two explanatory variables: a binary variable concerning male investment in building (1 if the male on the left was the one that invested the most in building behaviors, 0 if it was the male that invested the least) and a binary variable reflecting the treatment (1 if the female observed male building behaviors, 0 if not). The initial model also considered the interaction between male investment in building and treatment, but it was excluded during model simplification due to its non-significance.


Arnaud Tognetti
email: arnaud.tognetti@gmail.com

Noriko Yamagata-Nakashima

Charlotte Faurie

Ryo Oda

Are non-verbal facial cues of altruism cross-culturally readable?

Keywords: Cooperation, Facial expressions, Intercultural cues, Smile, Detection

Although both dynamic (i.e., facial expressions) and static facial traits are used as cues of altruism, only static facial traits have been shown to be cross-culturally readable with respect to altruism detection skills. To investigate whether dynamic facial cues of altruism are also cross-cultural, we asked French subjects to estimate the altruism of Japanese individuals on the basis of silent video clips. These video clips were taken from a previous experiment, which found that Japanese raters were able to accurately estimate the altruism of a videotaped Japanese individual. By using the same design and stimuli in France, we found that French raters were unable to assess the altruism of a Japanese individual. Hence, our results suggest that dynamic facial cues of altruistic intent are culturally specific rather than universally readable.

Highlights

• We examined whether dynamic facial cues of altruism are cross-culturally readable.

• French and Japanese raters observed silent video clips of Japanese individuals.

• The Japanese raters correctly assessed Japanese altruism; the French raters did not.

• Dynamic facial cues of altruism are culturally rather than universally readable.

Introduction

Humans are thought to have evolved unique cognitive mechanisms to maintain large-scale cooperation between unrelated individuals [START_REF] Melis | How is human cooperation different?[END_REF]. One of these mechanisms is the "Darwinian algorithm" for cheater detection [START_REF] Cosmides | The logic of social exchange: Has natural selection shaped how humans reason? Studies with the Wason selection task[END_REF], which refers to the capacity to discriminate between cheaters and cooperators. This mechanism is argued to be one of the most ancient of the evolved mechanisms for interpersonal decision-making [START_REF] Cosmides | Cognitive adaptations for social exchange[END_REF][START_REF] Todorov | Evaluating faces on trustworthiness[END_REF]. The capacity to distinguish altruists from egoists by potential partners enables an individual to assort with other individuals according to their propensity to cooperate (D. S. [START_REF] Wilson | Group selection and assortative interactions[END_REF]. This assortment has been suggested to lead to the evolution of cooperation if the advantages of selfish individuals are outweighed by the benefits of mutual cooperation between altruists.

Discriminating between high and low altruistic individuals and estimating trustworthiness and cooperativeness is a fast, spontaneous and intuitive process [START_REF] Bonnefon | The modular nature of trustworthiness detection[END_REF], 2017;[START_REF] Dzhelyova | Temporal dynamics of trustworthiness perception[END_REF][START_REF] Todorov | Evaluating faces on trustworthiness[END_REF] that could be based on both static and dynamic facial traits (e.g., [START_REF] Bonnefon | Can we detect cooperators by looking at their face?[END_REF][START_REF] Fetchenhauer | Not only states but traits -Humans can identify permanent altruistic dispositions in 20 s[END_REF][START_REF] Oda | Altruism can be assessed correctly based on impression[END_REF][START_REF] Tognetti | Is cooperativeness readable in static facial features? An inter-cultural approach[END_REF]. For example, in trust games, decisions regarding whom to trust are biased by static traits, such as attractiveness (R. K. [START_REF] Wilson | Judging a book by its cover: Beauty and[END_REF], similarity to kin [START_REF] Debruine | Facial resemblance enhances trust[END_REF] and the facial width-to-height ratio [START_REF] Stirrat | Valid facial cues to cooperation and trust: Male facial width and trustworthiness[END_REF], 2012). Dynamic facial cues, such as expressions and movements, have also been implicated in the detection of altruism. Using silent video clips of individuals' faces while they were talking about themselves, several studies found that people can predict the altruistic intent of a target individual [START_REF] Brown | Are there nonverbal cues to commitment? An exploratory study using the zero-acquaintance video presentation paradigm[END_REF][START_REF] Fetchenhauer | Not only states but traits -Humans can identify permanent altruistic dispositions in 20 s[END_REF]Oda, Yamagata, et al., 2009). While static facial cues of altruism have been shown to be interculturally readable [START_REF] Tognetti | Is cooperativeness readable in static facial features? An inter-cultural approach[END_REF], dynamic facial cues of altruism have only been studied intra-culturally. Therefore, investigate whether the detection of altruism based on facial expressions was cross-culturally possible, or not, was thus a crucial next step. To fill this gap, we conducted a study in which we asked French subjects to estimate the altruism of Japanese individuals on the basis of silent video clips during which the Japanese individuals spoke about themselves.

Facial emotional expressivity, particularly related to positive emotions, has been shown to be among the non-verbal traits that serve as cues of altruistic intent in several populations [START_REF] Brown | Are there nonverbal cues to commitment? An exploratory study using the zero-acquaintance video presentation paradigm[END_REF][START_REF] Mehu | Smiles when sharing[END_REF][START_REF] Mehu | Duchenne smiles and the perception of generosity and sociability in faces[END_REF][START_REF] Schug | Emotional expressivity as a signal of cooperation[END_REF]. Genuine (Duchenne) smile, characterized by the activity of the orbicularis oculi (surrounding the eyes) in combination with the zygomatic major (raising the corners of the mouth) muscles, seems particularly important in the detection of altruism. This smile is associated with genuine feelings of positive emotion and is difficult to produce deliberately [START_REF] Ekman | The Duchenne smile: Emotional expression and brain physiology: II[END_REF][START_REF] Ekman | Smiles when lying[END_REF], thereby ensuring its honesty.

In addition, several studies have shown the following: (i) highly altruistic individuals exhibit more genuine smiles than less altruistic individuals [START_REF] Brown | Are there nonverbal cues to commitment? An exploratory study using the zero-acquaintance video presentation paradigm[END_REF][START_REF] Centorrino | Honest signaling in trust interactions: smiles rated as genuine induce trust and signal higher earning opportunities[END_REF]Oda, Yamagata, et al., 2009); and (ii) genuine smiles play a role in the assessment of trustworthiness and altruism [START_REF] Centorrino | Honest signaling in trust interactions: smiles rated as genuine induce trust and signal higher earning opportunities[END_REF]Oda, Yamagata, et al., 2009;[START_REF] Reed | Facial expressions as honest signals of cooperative intent in a one-shot anonymous Prisoner's Dilemma game[END_REF] and (iii) influence individuals' decisions regarding with whom to cooperate [START_REF] Centorrino | Honest signaling in trust interactions: smiles rated as genuine induce trust and signal higher earning opportunities[END_REF][START_REF] Johnston | Why are you smiling at me? Social functions of enjoyment and nonenjoyment smiles[END_REF][START_REF] Oda | Altruists are trusted based on non-verbal cues[END_REF][START_REF] Reed | Facial expressions as honest signals of cooperative intent in a one-shot anonymous Prisoner's Dilemma game[END_REF]. For example, Oda, Yagamata et al. (2009) used the self-report altruism scale [START_REF] Johnson | Cross-cultural assessment of altruism and its correlates[END_REF] to measure the altruism of Japanese students, and they recorded the highest and lowest altruistic individuals with a video camera during a self-presentation. By showing 30-second silent video clips of these self-presentations, they found that Japanese raters accurately estimated the altruism of the videotaped Japanese (Oda, Yamagata, et al., 2009), and that highly altruistic individuals were more trusted than less altruistic individuals in a faith game [START_REF] Oda | Altruists are trusted based on non-verbal cues[END_REF]. They also coded these videos to examine which traits the raters used to assess the target's altruism. The results showed that altruists and non-altruists differed in their number of genuine smiles exhibited in the videos, but not for the other cues recorded such as head nods, time per smile, and smile symmetry (Oda, Yamagata, et al., 2009). Hence, genuine smile seems to be the main dynamic trait advertising altruism in the Japanese culture.

Using a trust game, a study conducted in France found similar results [START_REF] Centorrino | Honest signaling in trust interactions: smiles rated as genuine induce trust and signal higher earning opportunities[END_REF]; the French participants were able to predict their partner's trustworthiness based on the presence of genuine smiles that were exhibited during the silent video clips. Genuine smiles influenced the participant's willingness to send money to the partner. In addition, those partners who were rated as smiling more genuinely returned more money on average to the senders, inducing a higher payoff for both partners.

Overall, these studies conducted in several populations strongly suggest that humans have cognitive architecture for assessing altruism and that dynamic facial traits are common cues of social behaviors that might be shared across cultures. Therefore, in our study we predicted that French raters would be able to correctly assess Japanese' altruism based on dynamic facial traits, such as genuine smiles.

However, although facial expressions have long been considered as universal signals, recent studies challenged this conjecture by showing that internal representations of emotions differed between Easterners and Westerners (Jack, Caldara, & Schyns, 2012;[START_REF] Jack | Facial expressions of emotion are not culturally universal[END_REF][START_REF] Jack | Dynamic cultural representations of facial expressions of emotion are not universal[END_REF]. For example, Easterners show a preference for expressive information in the eye region, whereas westerners predominantly feature the mouth (Jack, Caldara, et al., 2012). This cultural difference in facial expressions is likely to affect the perception of some personality traits, such as trustworthiness and altruism. Indeed, it has been found that Japanese participants perceived faces with greater upper-half (around the eyes) smile intensity as more trustworthy, whereas American participants perceived faces with greater lower-half smile intensity as more trustworthy but they were not influenced by the upper-half smile intensity [START_REF] Ozono | What's in a smile? Cultural differences in the effects of smiling on judgments of trustworthiness[END_REF]. Although genuine smile influence perceived trustworthiness in both cultures, these results suggest that the way smiles are dynamically and physically expressed in the face and interpreted by others differs across cultures. Hence, we also predicted that the French raters would be less accurate than the Japanese raters in their assessments of Japanese' altruism.

To sum up, the aim of the current study was to question the cross-cultural validity regarding altruism detection skills based on dynamic facial cues. To this aim, we asked French subjects to estimate the altruism of Japanese individuals on the basis of silent video clips during which the Japanese individuals spoke about themselves. These video clips were taken from a previous experiment (Oda, Yamagata, et al., 2009), in which the authors found that altruists exhibited more genuine smiles than non-altruists, enabling Japanese raters to accurately estimate a target's altruism (see above). Because genuine smiles seem to be used as cues of altruistic intent in different populations, such as in Japan [START_REF] Oda | Altruists are trusted based on non-verbal cues[END_REF]Oda, Yamagata, et al., 2009), France [START_REF] Centorrino | Honest signaling in trust interactions: smiles rated as genuine induce trust and signal higher earning opportunities[END_REF] or the USA [START_REF] Reed | Facial expressions as honest signals of cooperative intent in a one-shot anonymous Prisoner's Dilemma game[END_REF], and thus could be a universal cue of altruistic intent, we predicted that French raters would estimate the altruism of Japanese individuals correctly. Nevertheless, because cultural difference is likely to affect facial expressions [START_REF] Jack | Facial expressions of emotion are not culturally universal[END_REF] and their perception [START_REF] Ozono | What's in a smile? Cultural differences in the effects of smiling on judgments of trustworthiness[END_REF], we also predicted that the French raters would be less accurate than the Japanese raters in their assessments of altruism.

Methods

Videotaping of Japanese individuals

We used the same video clips of natural conversations that were used by [START_REF] Oda | Altruists are trusted based on non-verbal cues[END_REF] and Oda, Yamagata, et al. (2009) as stimuli. To select the most versus the least altruistic individuals for videotaping, we used the self-report altruism scale employed by [START_REF] Johnson | Cross-cultural assessment of altruism and its correlates[END_REF]. This scale was previously validated by showing significant differences in the number of lottery tickets shared in the dictator game between those who scored in the top 10th percentile and the bottom 10th percentile [START_REF] Brown | Are there nonverbal cues to commitment? An exploratory study using the zero-acquaintance video presentation paradigm[END_REF].

Male Japanese undergraduates (n = 69; mean age: 18.7 years ± 0.9 s.d.) were asked to indicate how often they performed each altruistic act described in the 56 statements of the altruism scale from 1 (never) to 5 (very often). All the participants were volunteers from a class at the Nagoya Institute of Technology, Japan. The participants' scores were then transformed into percentiles. The 90th percentile and above on the scale represented the most altruistic individuals, while the 10th percentile and below represented the least altruistic individuals. Using these criteria, we chose the seven most and seven least altruistic individuals. These 14 people were called and asked to participate in the videotaping. Six among the most and four among the least altruistic individuals agreed to participate. They were brought to the laboratory one at a time. The experimenter, who was unaware of each person's category, sat just beside a video camera in front of the target person who was asked to make a self-presentation discussing his likes and dislikes.

Close shots of the target (above the shoulder) in front of a white screen were videotaped. The videos were transformed into digital files and the first 30 s of each presentation was selected. Then, the video clips were edited into a sequence of the 10 targets' presentations. The sound was deleted to control for the verbal content.

The detection of altruism by French raters

To test whether French raters are able to estimate Japanese altruism, 151 French men and 252 French women (non-French were excluded for the analyses), ranging from 18 to 26 years old (mean age: 19.5 years ± 1.4 s.d) were recruited on a voluntary basis from 11 classes at the University of Montpellier, France. We obtained written informed consent from all of the participants.

The procedure followed that of Oda, Yamagata, et al. (2009). First, the raters were asked to indicate how often they had performed each altruistic act described in the seven statements of the altruism scale (Table 1) that were previously found to have the greatest effect sizes for distinguishing the six most and the four least altruistic individuals (Oda, Yamagata, et al., 2009).

Then, the participants were told that they would be viewing a series of videotaped people making self-presentations. The video clips were always projected on screens of similar sizes that were located in the classrooms. We explained to the perceivers that these people, like themselves, had filled out the seven-item questionnaire. The perceivers were then asked to predict the altruism scores of each target for each of the seven items of the questionnaire. The series of video clips was then presented a second time. All the groups observed the same ten targets, but the order of the presentation was randomized for each group.

Items of the altruism scale

As a part of a group of people, I have done menial jobs that needed doing without being asked even though they were not part of my responsibilities.

I have donated goods or clothes to a charity. I have helped an acquaintance obtain something important that he or she needed (e.g., a job, a place to live).

I have 'picked up the slack' for another worker when he or she couldn't keep up the pace.

I have helped a classmate whom I did not know that well with a homework assignment when my knowledge was greater than his or hers.

I have helped a new fellow-employee at work get settled on the job and learn the tasks involved, even though it was not part of my job.

I have helped someone I didn't know get up when (s)he slipped or tripped and fell down.

Table 1. The seven items of the altruism scale given to the French raters. The French version, which was given to the participants, is available upon request.

Statistical analyses

We implemented linear mixed models (lmer function of the lme4 package in R) to test whether the French raters (non-French raters were excluded) were able to estimate the self-reported altruism score of the Japanese targets. We included both the identities of the Japanese targets and those of the French raters as random-effect variables to prevent potential pseudoreplication problems. The response variable was the predicted altruism scores assessed by the raters (sum of the 7 items of the questionnaire). We included the following three explanatory variables in the models: the actual altruism score of the Japanese target (sum of the 7 items of the questionnaire), and the rater's sex and the raters' altruism score (sum of the 7 items). We also tested the interactions between the actual Japanese targets' altruism scores with both the raters' sex and the raters' altruism scores to examine whether the ability to detect altruistic intent was influenced by a rater's sex and his/her own altruism score. We included all the main effects and interaction terms in the initial model, which was then simplified by sequentially removing all the non-significant interaction terms to achieve the minimal adequate model.

All the statistical analyses were performed using the R software, version 3.1.2 (R Core Team, 2017).

Results

On average, each rater's self-reported altruism score (sum of the 7 items of the questionnaire) was 9.9 for the men and 10.7 for the women. The Japanese targets' altruism scores (sum of the 7 items) assessed by the men and women raters were, on average, 9.8 and 10.3, respectively.

None of the interaction terms tested in the initial linear mixed model were significant (interaction with the raters' sex: χ 2 =0.49, df=1, P=0.48, with the raters' self-reported altruism scores: χ 2 =0.01, df=1, P=0.93), suggesting that the raters' sex and altruism did not influence their ability to assess the altruism of the Japanese targets. The minimal linear mixed model (interaction terms excluded) showed no effect of the actual target altruism (χ 2 =1.34, df=1, P=0.25; Table 2), suggesting that the French raters did not correctly assess the altruism of the Japanese targets. In addition, the raters' sex did not influence the altruism scores given to the Japanese targets (χ 2 =1.89, df=1, P=0.17; Table 2). However, the raters' altruism significantly influenced their perception of the targets' altruism: the more altruistic raters gave higher altruism scores to the targets (χ 2 =57.41, df=1, P<0.0001; For each factor, the estimate, standard error of the mean (SE), degrees of freedom (df), χ 2 statistic and p-value of the likelihood ratio test of the comparison between the full model and the model without the factor, are given. For categorical variables, the estimates are for one category compared to the reference category (underlined term). Both the identities of the Japanese target and the French raters were included as random-effect variables.

Discussion

Although dynamic facial traits, such as a genuine smile, have been repeatedly shown to be a cue of altruistic intent [START_REF] Bonnefon | Can we detect cooperators by looking at their face?[END_REF], only static facial traits have been shown to be interculturally readable with respect to altruism detection skills [START_REF] Tognetti | Is cooperativeness readable in static facial features? An inter-cultural approach[END_REF]. To investigate whether dynamic facial cues of altruism could also be cross-cultural, we showed silent video clips of Japanese individuals to French raters and examined the French raters' altruism detection skills. A previous study using the same video clip stimuli found that Japanese raters were able to correctly assess the altruism of the videotaped Japanese (Oda, Yamagata, et al., 2009). They also found that altruists and non-altruists differed in their number of genuine smiles exhibited in the videos. However, by using the same design and the same stimuli in France, our results showed that the French raters were unable to assess the altruism of the Japanese targets. This result suggests that dynamic facial cues of altruistic intent are intra-culturally rather than universally readable.

The original study, from which we used the video clips, found that the videotaped Japanese likely advertised their altruistic intent through genuine smiles [START_REF] Oda | Altruists are trusted based on non-verbal cues[END_REF]Oda, Yamagata, et al., 2009). During a trust game, the French raters' decisions regarding whom to trust were also influenced by their partners' genuine smiles [START_REF] Centorrino | Honest signaling in trust interactions: smiles rated as genuine induce trust and signal higher earning opportunities[END_REF].

Genuine smile is thus a likely candidate as universal cue of altruism. It is, therefore, surprising that the French raters did not correctly assess the Japanese individuals' altruism based on their genuine smiles in the current study. However, recent evidence has emphasized the complexities of designating smiles as genuine or false [START_REF] Krumhuber | Can Duchenne smiles be feigned? New evidence on felt and false smiles[END_REF]. In addition, the marker of a genuine smile by itself (i.e., activity of the orbicularis oculi muscle) seems not always reliable for inferring whether a smile is spontaneous and genuine [START_REF] Krumhuber | Can Duchenne smiles be feigned? New evidence on felt and false smiles[END_REF][START_REF] Reed | Facial expressions as honest signals of cooperative intent in a one-shot anonymous Prisoner's Dilemma game[END_REF]. The difficulty in distinguishing between smile types (genuine or false), and thus, in detecting altruistic intent, could be reinforced by the potential existence of cultural differences in facial expressions between the French and Japanese.

Facial expressions have long been considered as universal signals to convey emotional states that are recognized across all cultures. The universality hypothesis proposes that six basic internal human emotions (i.e., happiness, surprise, fear, disgust, anger, and sadness) are expressed using the same facial movements across all cultures [START_REF] Ekman | A new pan-cultural facial expression of emotion[END_REF][START_REF] Ekman | Pan-cultural elements in facial displays of emotion[END_REF], supporting the idea of universal recognition. However, several studies challenged this conjecture by showing that internal representations of emotions differed between east Asian (i.e., Chinese) and western Caucasian (i.e., Europeans) individuals (Jack, Caldara, et al., 2012;[START_REF] Jack | Facial expressions of emotion are not culturally universal[END_REF][START_REF] Jack | Dynamic cultural representations of facial expressions of emotion are not universal[END_REF]. For example, there is evidence showing that easterners show a preference for expressive information in the eye region, whereas westerners predominantly feature the eyebrows and mouth (Jack, Caldara, et al., 2012). Similarly, east Asians represent emotional intensity essentially with eyes movements in happiness, fear, disgust, and anger, whereas west

Caucasians represent emotional intensity with other parts of the face [START_REF] Jack | Facial expressions of emotion are not culturally universal[END_REF].

These results suggest that facial expressions of emotions are culturally specific.

This cultural difference in facial expressions is likely to affect the perception of some personality traits, such as trustworthiness and altruism. Indeed, it has been found that Japanese participants perceived faces with greater upper-half (around the eyes) smile intensity as more trustworthy, whereas they perceived faces with greater lower-half (around the mouth) smile intensity as less trustworthy [START_REF] Ozono | What's in a smile? Cultural differences in the effects of smiling on judgments of trustworthiness[END_REF]. In contrast, American participants perceived faces with greater lower-half smile intensity as more trustworthy, but there was no influence of the upper-half smile intensity [START_REF] Ozono | What's in a smile? Cultural differences in the effects of smiling on judgments of trustworthiness[END_REF]. Hence, both subtle culturally specific variations in the expression of genuine smile and the way in which they are culturally perceived might explain the inability of the French raters in detecting altruism from Japanese facial expressions.

Dynamic facial traits were not the only potential cues of altruism available to the French raters on the video clips. Static facial traits were also available to them. Several studies have shown that static facial traits influence the detection of trustworthiness and altruism [START_REF] Bonnefon | The modular nature of trustworthiness detection[END_REF][START_REF] Stirrat | Valid facial cues to cooperation and trust: Male facial width and trustworthiness[END_REF], 2012;[START_REF] Tognetti | Is cooperativeness readable in static facial features? An inter-cultural approach[END_REF]. In addition, one study showed that some of these traits are interculturally readable between France and Senegal [START_REF] Tognetti | Is cooperativeness readable in static facial features? An inter-cultural approach[END_REF].

Although the French raters did not correctly assess Japanese altruism, we cannot rule out the existence of such intercultural cues between France and Japan. Indeed, detection rates based on static facial cues are highly sensitive to noise. For example, the presence of nonfacial traits, such as hair and clothing, impairs cooperation detection based on facial photographs [START_REF] Bonnefon | The modular nature of trustworthiness detection[END_REF], whereas displaying only the inner features of the face (i.e., using facial photographs that are cropped at the ears, eyebrows and chin) improve it [START_REF] Bonnefon | The modular nature of trustworthiness detection[END_REF][START_REF] Bonnefon | Can we detect cooperators by looking at their face?[END_REF]. In the video clips used in the current study, clothing, hairstyle, skin tone and even body movements were available to the raters and could then impede the processing of the French raters. Further studies using facial photographs are necessary to examine whether Japanese static facial cues of altruism are readable by French raters.

This study presents several strengths and limitations. Although it is the first to investigate whether dynamic cues of altruism could be interculturally readable, the investigation is restricted to only two populations and therefore should be extended to other cultures in order to provide broader conclusions. Indeed, the fact that French raters did not correctly assess Japanese altruism does not exclude the possibility that altruistic intent would be readable across cultures that are closer, either geographically or historically. For example, anthropological research has highlighted other cultural differences than facial expressions between Eastern and Western cultures, such as differences in the relative importance of inner versus outward expression of moral beliefs (as described in: [START_REF] Benedict | The chrysanthemum and the sword: Patterns of Japanese culture[END_REF][START_REF] Frost | The Hajnal line and gene-culture coevolution in Northwest Europe[END_REF]). In addition, it would be also interesting to carry out the reverse design with

French videos and Japanese raters to examine to which extent genuine smile and its perception vary across cultures. Indeed, because Caucasian versus Japanese raters perceive smiles with greater intensities in the mouth as more and less trustworthy, respectively [START_REF] Ozono | What's in a smile? Cultural differences in the effects of smiling on judgments of trustworthiness[END_REF], we can expect that high altruist Caucasian individuals would be perceived as low altruists by Japanese raters.

In conclusion, although dynamic facial traits, such as genuine smiles, do advertise altruistic intent in several populations (e.g., France: [START_REF] Centorrino | Honest signaling in trust interactions: smiles rated as genuine induce trust and signal higher earning opportunities[END_REF]Japan: Oda, Yamagata, et al., 2009;USA: Reed et al., 2012) and could thus be universal cues of altruism, the subtle variations in their dynamic and physical expressions in the face, which are strongly influenced by culture [START_REF] Jack | Facial expressions of emotion are not culturally universal[END_REF][START_REF] Ozono | What's in a smile? Cultural differences in the effects of smiling on judgments of trustworthiness[END_REF], seem to impede their interculturally readability.

Table 2 . Linear mixed model of the Japanese targets' altruism score as rated by the French raters.

 2 Table 2).

	Predictor variables	Estimate	SE	χ 2	df	P-value
	(Intercept)	6.28	1.16
	Japanese's altruism scores	0.07	0.06	1.34	1	0.25
	French rater's altruism scores	0.25	0.03	57.41	1	<0.0001
	Rater's sex
	Women/Men	0.28	0.21	1.89	1	0.17

expectations in the trust game. Political Research Quarterly, 59(2), 189-202.

Acknowledgements

Supports through the ANR -Labex IAST, the CNRS of France (www.cnrs.fr) and the Région Languedoc-Roussillon 'Chercheur(se)s d'Avenir' (no.: DGA3/DESR/2012/Q159) are gratefully acknowledged.