Litter sex composition influences competitive performance during first reproduction in male mouse lemurs

In litter-bearing mammals, conditions experienced early in life can have long-lasting consequences on adult behavioral and physiological phenotypes, including reproductive fitness and survival. Using data from a large database, we focused our analysis on the consequences of litter composition on the reproductive performance of 131 mouse lemur males during their first breeding season. For male offspring, body mass at birth and at weaning only depended on the litter size (from one to 3), with the lowest values in triplets. Early growth had no relationship with the future reproductive success when males entered their first breeding season. When mouse lemurs were kept in groups with 2 or 3 competitors, males entered sexual competition for priority access to females in estrus, leading to a hierarchy with the dominant male ensuring the successful mating of the females. Genetic paternity tests showed that males born in same-sex litters (M, MM, MMM) were more competitive and fathered more offspring than males born in mixed-sex litters (MF, MMF, MFF), indicating the negative impact of a sister on male reproductive success. However, testosterone levels were unrelated to early growth or litter sex composition but were dependent on social interactions during sexual competition, with higher values in successful males. The effects of litter composition on the mating success of male mouse lemurs might mainly occur through social interactions between male offspring born in same-sex litters. Play fighting between juvenile males could play a major role in their acquisition of the skills required to succeed in sexual competition.

Heritability and genetic correlations of personality, life history and morphology in the grey mouse lemur (Microcebus murinus)

The recent interest in animal personality has sparked a number of studies on the heritability of personality traits. Yet, how the sources variance these traits can be decomposed remains unclear. Moreover, whether genetic correlations with life-history traits, personality traits and other phenotypic traits exist as predicted by the pace-of-life syndrome hypothesis remains poorly understood. Our aim was to compare the heritability of personality, life-history and morphological traits and their potential genetic correlations in a small primate (Microcebus murinus). We performed an animal model analysis on six traits measured in a large sample of captive mouse lemurs (N = 486). We chose two personality traits, two life-history traits and two morphological traits to (i) estimate the genetic and/or environmental contribution to their variance, and (ii) test for genetic correlations between these traits. We found modest narrow-sense heritability for personality traits, morphological traits and life-history traits. Other factors including maternal effects also influence the sources of variation in life-history and morphological traits. We found genetic correlations between emergence latency on the one hand and radius length and growth rate on the other hand. Emergence latency was also genetically correlated with birth weight and was influenced by maternal identity. These results provide insights into the influence of genes and maternal effects on the partitioning of sources of variation in personality, life-history and morphological traits in a captive primate model and suggest that the pace-of-life syndrome may be partly explained by genetic trait covariances.

Heteropaternity of twins in ring-tailed lemurs (Lemur catta)

OBJECTIVES

This project investigated paternity among 14 sets of twins born into a colony of ring-tailed lemurs (Lemur catta) on St. Catherines Island, GA. Female L. catta commonly mate with >1 male, and twins of different sexes confirm that dizygotic twinning can occur in this species. However, no study has previously evaluated twins using genetic data to measure the proportion of mono versus dizygotic twinning in L. catta, and no study has tested for heteropaternity (sirehood by two different males) in this species. We predicted that L. catta would show a predominance of dizygosity and evidence for heteropaternity.

MATERIALS AND METHODS

Paternity was determined for 28 infants (14 sets of twins) via paternity exclusion analyses using 10 polymorphic microsatellite markers, and data were collected on sexual behavior across four mating seasons during the first cycle of mating in each year, which overlapped with the conceptive periods of these infants.

RESULTS

All twins were found to be dizygotic, as evidenced by dissimilar multilocus genotypes between the two infants of each twin pair. Heteropaternity was found in 3 of 14 (21% of) twin pairs, whereas the remaining 11 pairs of twins (79%) shared the same sire. In one case of heteropaternity, one sire was a resident male, and one sire was an extra-group male. An extra-group male also sired one of the same-sire twin pairs. All other sires of twins were group residents.

DISCUSSION

Female multiple mating, which is common to many primates including L. catta, can be viewed as an adaptive reproductive strategy whose function-in addition to fertility assurance or stimulating sperm competition-may be to increase the genetic diversity of a female's offspring, even among infants born in the same birth event. Therefore, during the course of primate evolution, the adaptive benefits of heteropaternity would be expected to have contributed to positive selection for female promiscuity.

Challenges of next-generation sequencing in conservation management: Insights from long-term monitoring of corridor effects on the genetic diversity of mouse lemurs in a fragmented landscape

Long-term genetic monitoring of populations is essential for efforts aimed at preserving genetic diversity of endangered species. Here, we employ a framework of long-term genetic monitoring to evaluate the effects of fragmentation and the effectiveness of the establishment of corridors in restoring population connectivity and genetic diversity of mouse lemurs Microcebus ganzhorni. To this end, we supplement estimates of neutral genetic diversity with the assessment of adaptive genetic variability of the major histocompatibility complex (MHC). In addition, we address the challenges of long-term genetic monitoring of functional diversity by comparing the genotyping performance and estimates of MHC variability generated by single-stranded conformation polymorphism (SSCP)/Sanger sequencing with those obtained by high-throughput sequencing (next-generation sequencing [NGS], Illumina), an issue that is particularly relevant when previous work serves as a baseline for planning management strategies that aim to ensure the viability of a population. We report that SSCP greatly underestimates individual diversity and that discrepancies in estimates of MHC diversity attributable to the comparisons of traditional and NGS genotyping techniques can influence the conclusions drawn from conservation management scenarios. Evidence of migration among fragments in Mandena suggests that mouse lemurs are robust to the process of fragmentation and that the effect of corridors is masked by ongoing gene flow. Nonetheless, results based on a larger number of shared private alleles at neutral loci between fragment pairs found after the establishment of corridors in Mandena suggest that gene flow is augmented as a result of enhanced connectivity. Our data point out that despite low effective population size, M. ganzhorni maintains high individual heterozygosity at neutral loci and at MHC II DRB gene and that selection plays a predominant role in maintaining MHC diversity. These findings highlight the importance of long-term genetic monitoring in order to disentangle between the processes of drift and selection maintaining adaptive genetic diversity in small populations.

Revisiting the Trivers-Willard theory on birth sex ratio bias: Role of paternal condition in a Malagasy primate

Within current theories on potential adaptive manipulation of offspring sex ratio, giving birth to a male or to a female is assumed to depend on the capacity of the mother to invest in offspring to maximize her fitness. The active role of the father in sex ratio bias at birth has been neglected until recently. The human sex ratio at birth is biased towards sons, although in occidental populations, the ratio has decreased regularly for 30 years and could be the consequence of the adverse effects of environmental chemicals on male hormones. In a Malagasy primate, the lesser mouse lemur, the potential effect of paternal testosterone levels on sex ratio bias at birth was tested on 130 litters (278 babies) produced in 52 mixed-sex groups. For each group, social dominance among males was characterized based on aggressive interactions and sexual behaviours. Using a multi correspondence analysis, high testosterone levels in grouped males, particularly those of the dominant male, were significantly correlated with more infants produced in male-biased litters, independent of the female condition. According to these results, predictions for sex ratio bias towards one sex or the other in mouse lemurs were discussed considering the influence of both parents.

High frequency/ultrasonic communication in a critically endangered nocturnal primate, Claire's mouse lemur (Microcebus mamiratra)

The critically endangered Claire's mouse lemur, only found in the evergreen rain forest of the National Park Lokobe (LNP) and a few lowland evergreen rain forest fragments of northern Madagascar, was described recently. The present study provides the first quantified information on vocal acoustics of calls, sound associated behavioral context, acoustic niche, and vocal activity of this species. We recorded vocal and social behavior of six male-female and six male-male dyads in a standardized social-encounter paradigm in June and July 2016 at the LNP, Nosy Bé island. Over six successive nights per dyad, we audio recorded and observed behaviors for 3 hr at the beginning of the activity period. Based on the visual inspection of spectrograms and standardized multiparametric sound analysis, we identified seven different call types. Call types can be discriminated based on a combination of harmonicity, fundamental frequency variation, call duration, and degree of tonality. Acoustic features of tonal call types showed that for communication, mouse lemurs use the cryptic, high frequency/ultrasonic frequency niche. Two call types, the Tsak and the Grunt call, were emitted most frequently. Significant differences in vocal activity of the Tsak call were found between male-female and male-male dyads, linked primarily to agonistic conflicts. Dominant mouse lemurs vocalized more than subdominant ones, suggesting that signaling may present an honest indicator of fitness. A comparison of our findings of the Claire's mouse lemur with published findings of five bioacoustically studied mouse lemur species points to the notion that a complex interplay between ecology, predation pressure, and phylogenetic relatedness may shape the evolution of acoustic divergence between species in this smallest-bodied primate radiation. Thus, comparative bioacoustic studies, using standardized procedures, are promising to unravel the role of vocalization for primate species diversity and evolution and for identifying candidates for vocalization-based non-invasive monitoring for conservation purposes.

Characterisation of urinary WFDC12 in small nocturnal basal primates, mouse lemurs (Microcebus spp.)

Mouse lemurs are basal primates that rely on chemo- and acoustic signalling for social interactions in their dispersed social systems. We examined the urinary protein content of two mouse lemurs species, within and outside the breeding season, to assess candidates used in species discrimination, reproductive or competitive communication. Urine from Microcebus murinus and Microcebus lehilahytsara contain a predominant 10 kDa protein, expressed in both species by some, but not all, males during the breeding season, but at very low levels by females. Mass spectrometry of the intact proteins confirmed the protein mass and revealed a 30 Da mass difference between proteins from the two species. Tandem mass spectrometry after digestion with three proteases and sequencing de novo defined the complete protein sequence and located an Ala/Thr difference between the two species that explained the 30 Da mass difference. The protein (mature form: 87 amino acids) is an atypical member of the whey acidic protein family (WFDC12). Seasonal excretion of this protein, species difference and male-specific expression during the breeding season suggest that it may have a function in intra- and/or intersexual chemical signalling in the context of reproduction, and could be a cue for sexual selection and species recognition.

Modeling the origins of mammalian sociality: moderate evidence for matrilineal signatures in mouse lemur vocalizations

INTRODUCTION

Maternal kin selection is a driving force in the evolution of mammalian social complexity and it requires that kin are distinctive from nonkin. The transition from the ancestral state of asociality to the derived state of complex social groups is thought to have occurred via solitary foraging, in which individuals forage alone, but, unlike the asocial ancestors, maintain dispersed social networks via scent-marks and vocalizations. We hypothesize that matrilineal signatures in vocalizations were an important part of these networks. We used the solitary foraging gray mouse lemur (Microcebus murinus) as a model for ancestral solitary foragers and tested for matrilineal signatures in their calls, thus investigating whether such signatures are already present in solitary foragers and could have facilitated the kin selection thought to have driven the evolution of increased social complexity in mammals. Because agonism can be very costly, selection for matrilineal signatures in agonistic calls should help reduce agonism between unfamiliar matrilineal kin. We conducted this study on a well-studied population of wild mouse lemurs at Ankarafantsika National Park, Madagascar. We determined pairwise relatedness using seven microsatellite loci, matrilineal relatedness by sequencing the mitrochondrial D-loop, and sleeping group associations using radio-telemetry. We recorded agonistic calls during controlled social encounters and conducted a multi-parametric acoustic analysis to determine the spectral and temporal structure of the agonistic calls. We measured 10 calls for each of 16 females from six different matrilineal kin groups.

RESULTS

Calls were assigned to their matriline at a rate significantly higher than chance (pDFA: correct = 47.1%, chance = 26.7%, p = 0.03). There was a statistical trend for a negative correlation between acoustic distance and relatedness (Mantel Test: g = -1.61, Z = 4.61, r = -0.13, p = 0.058).

CONCLUSIONS

Mouse lemur agonistic calls are moderately distinctive by matriline. Because sleeping groups consisted of close maternal kin, both genetics and social learning may have generated these acoustic signatures. As mouse lemurs are models for solitary foragers, we recommend further studies testing whether the lemurs use these calls to recognize kin. This would enable further modeling of how kin recognition in ancestral species could have shaped the evolution of complex sociality.

Paternal kin recognition in the high frequency / ultrasonic range in a solitary foraging mammal

BACKGROUND

Kin selection is a driving force in the evolution of mammalian social complexity. Recognition of paternal kin using vocalizations occurs in taxa with cohesive, complex social groups. This is the first investigation of paternal kin recognition via vocalizations in a small-brained, solitary foraging mammal, the grey mouse lemur (Microcebus murinus), a frequent model for ancestral primates. We analyzed the high frequency/ultrasonic male advertisement (courtship) call and alarm call.

RESULTS

Multi-parametric analyses of the calls' acoustic parameters and discriminant function analyses showed that advertisement calls, but not alarm calls, contain patrilineal signatures. Playback experiments controlling for familiarity showed that females paid more attention to advertisement calls from unrelated males than from their fathers. Reactions to alarm calls from unrelated males and fathers did not differ.

CONCLUSIONS

1) Findings provide the first evidence of paternal kin recognition via vocalizations in a small-brained, solitarily foraging mammal. 2) High predation, small body size, and dispersed social systems may select for acoustic paternal kin recognition in the high frequency/ultrasonic ranges, thus limiting risks of inbreeding and eavesdropping by predators or conspecific competitors. 3) Paternal kin recognition via vocalizations in mammals is not dependent upon a large brain and high social complexity, but may already have been an integral part of the dispersed social networks from which more complex, kin-based sociality emerged.

Acoustic correlates of individuality in the vocal repertoire of a nocturnal primate (Microcebus murinus)

In mammals individual distinctiveness in vocalizations provides the basis for individual recognition and thus plays an important role in social behavior. In this study, first evidence is provided for a nocturnal primate that variation in individual distinctiveness across the vocal repertoire is to some extent determined by the context and the acoustic structure of the call types. Individual distinctiveness was investigated across call types in the gray mouse lemur, a nocturnal primate, living in a dispersed multi-male multi-female social system. To explore to what degree context and acoustic structure predict variations in individual distinctiveness, four major call types were examined (grunts, tsaks, short whistles, and trills). Call types differed in context and acoustic structure and were recorded under controlled experimental conditions. A discriminant function analysis revealed that all call types are individually distinct, but not to the same degree. The findings suggest that variations in individual distinctiveness can to some extent be explained by the context and the acoustic structure of the call types.

Male dominance rank and reproductive success in chimpanzees, Pan troglodytes schweinfurthii

Competition for fertile females determines male reproductive success in many species. The priority of access model predicts that male dominance rank determines access to females, but this model has been difficult to test in wild populations, particularly in promiscuous mating systems. Tests of the model have produced variable results, probably because of the differing socioecological circumstances of individual species and populations. We tested the predictions of the priority of access model in the chimpanzees of Gombe National Park, Tanzania. Chimpanzees are an interesting species in which to test the model because of their fission-fusion grouping patterns, promiscuous mating system and alternative male mating strategies. We determined paternity for 34 offspring over a 22-year period and found that the priority of access model was generally predictive of male reproductive success. However, we found that younger males had higher success per male than older males, and low-ranking males sired more offspring than predicted. Low-ranking males sired offspring with younger, less desirable females and by engaging in consortships more often than high-ranking fathers. Although alpha males never sired offspring with related females, inbreeding avoidance of high-ranking male relatives did not completely explain the success of low-ranking males. While our work confirms that male rank typically predicts male chimpanzee reproductive success, other factors are also important; mate choice and alternative male strategies can give low-ranking males access to females more often than would be predicted by the model. Furthermore, the success of younger males suggests that they are more successful in sperm competition.

Experience-dependent recapture rates and reproductive success in male grey mouse lemurs (Microcebus murinus)

Male mating tactics can vary according to the potential for scramble or contest competition but also as a consequence of individual characteristics, such as body condition and previous experience. The influence of experience, i.e., residency, on male recapture rates and reproductive success was studied in a population of free-living grey mouse lemurs. Long-term capture data from 320 individuals revealed that both sexes had very low recapture probabilities within their first year in the study population, but recapture rates declined less sharply during the following years. Capture results and telemetric analyses on 12 focal males revealed that resident males had larger body mass and larger home ranges than new males. Home range size correlated with the number of accessible females, indicating that resident males had higher probabilities to meet mates than new males. The reproductive success of 132 candidate fathers, representing both resident and new males, was determined by means of molecular genotyping. Paternity determination was successful in 38 cases (success rate: 19%). Sixteen resident males and seventeen new males sired offspring. However, in relation to the number of candidate fathers being present in the mating season, resident males were twice as likely to reproduce successfully as new males. These findings suggest experience-dependent reproductive tactics that most likely correspond to a differential spatial knowledge of resources, mates and potential threats. The results generally agree with the predictions made for a scramble competition regime and demonstrate substantial behavioral plasticity in a nocturnal primate species with a dispersed multi-male/multi-female mating system.

Social lives of adult Mysore slender lorises (Loris lydekkerianus lydekkerianus)

Despite the persistent use of the word "solitary" to describe nocturnal primate social behavior, increasing numbers of studies are revealing sophisticated levels of social interactions among nocturnal primates. This study explores the relationships among 11 adult Mysore slender lorises (Loris lydekkerianus lydekkerianus) studied over 10(1/2) months in Tamil Nadu, India. When all observations regarding dependent offspring are excluded, the animals spent on average 38% of their activity in various forms of neutral, affiliative, and agonistic behaviors. Affiliative behaviors were the most common type of social interaction, and males in general were more social than females. Low values for Cole's index (CI) of association emphasize that females rarely interacted with same-sex conspecifics, but commonly interacted with males. In turn, males also formed strong affiliative relationships with other adult males. This index also indicates that levels of affiliation are strongest among animals that share sleeping sites. The Hinde index (HI) suggests that males control proximity to females more than the reverse. A female's tolerance of multiple males in her home range and at a sleeping site may be related to high spatial variability of food resources. Such resources may constrain females with costly reproductive strategies (up to two sets of twins per annum) to a small home range. With their larger home ranges, males may be able to monopolize females by initiating social interactions, and also provide a benefit to females by contributing to parental care.

First experimental evidence for female mate choice in a nocturnal primate

Female mate choice can be hypothesised in most nocturnal primates, since females show a higher investment in their offspring than males. The aim of this experimental study was to investigate if female grey mouse lemurs perform mate choice and whether age, relatedness (to the male), or male advertisement call activity systematically influence their decisions. A two-way mate choice design was developed in which females could choose between two males. Mate choice was deduced from the time spent in proximity to the males and from mating behaviour. During oestrus 12 of 17 females participated actively in the experiment and all of them showed either a significant spatial (n = 11) or behavioural (n = 1) preference for one male. In four cases copulations were observed. The influence of age on female mate choice was not statistically significant. In the cases with copulations, however, females mostly preferred the older male. This might indicate a preference for older age as an indicator of experience, fitness, and/or status. The influence of relatedness on female mate choice could not be definitely clarified. However, results imply a mechanism of kin recognition on the basis of familiarity. In the majority of choices, females preferred the male with higher trill call activity. Since trill call activity correlates with the relative dominance status of males, these results suggest an importance of the male dominance status for female mate choice in grey mouse lemurs. Altogether our findings indicate that females use a complex of different cues to choose their mates.

Molecular genetic approaches to the study of primate behavior, social organization, and reproduction

In the past several decades, the development of novel molecular techniques and the advent of noninvasive DNA sampling, coupled with the ease and speed with which molecular analyses can now be performed, have made it possible for primatologists to directly examine the fitness effects of individual behavior and to explore how variation in behavior and social systems influences primate population genetic structure. This review describes the theoretical connections between individual behavior and primate social systems on the one hand and population genetic structure on the other, discusses the kinds of molecular markers typically employed in genetic studies of primates, and summarizes what primatologists have learned from molecular studies over the past few decades about dispersal patterns, mating systems, reproductive strategies, and the influence of kinship on social behavior. Several important conclusions can be drawn from this overview. First, genetic data confirm that, in many species, male dominance rank and fitness are positively related, at least over the short term, though this relationship need not simply be a reflection of male-male contest competition over mates. More importantly, genetic research reveals the significance of female choice in determining male reproductive success, and documents the efficacy of alternative mating tactics among males. Second, genetic data suggest that the presumed importance of kinship in structuring primate social relationships needs to be evaluated further, at least for some taxa such as chimpanzees in which demographic factors may be more important than relatedness. I conclude this paper by offering several suggestions of additional ways in which molecular techniques might be employed in behavioral and ecological studies of primates (e.g., for conducting "molecular censuses" of unhabituated populations, for studying disease and host-parasite interactions, or for tracking seed fate in studies of seed dispersal) and by providing a brief introduction to the burgeoning field of nonhuman primate behavioral genetics.

Social organization of the golden brown mouse lemur (Microcebus ravelobensis)

Our study provides the first data on the social organization of the golden brown mouse lemur, a nocturnal primate discovered in northwestern Madagascar in 1994. The study was carried out in two 6-month field periods during the dry season, covering time before and during the mating season. The spatial and temporal distributions of the sexes in the population were investigated by mark/recapture and radiotelemetry. Focal observations and the determination of sleeping associations provided further insights into the sociality of this solitary forager. High intra- and intersexual home-range overlaps occurred throughout the study. In general, individuals of both sexes had spatial access to more than one conspecific of the same and the opposite sex. We found no indication for spatial monopolization of females by certain males. These results suggest a dispersed multimale/multifemale system with a promiscuous mating pattern. Individuals showed temporal stability in their home range locations and interacted regularly with conspecifics. Five sleeping groups were identified during the study period: one female group and four mixed-sex groups. Even though sleeping sites were changed frequently, sleeping-group compositions remained stable over time. Thermoregulatory constraints are the most likely explanation for sleeping-group composition with members of both sexes in this species. Mixed-sex sleeping groups can be described as the basic social unit within this dispersed multimale/multifemale society.