Social Mating System Research Articles

Genetic evidence for variability in the social mating system of the Midday Gerbil (Meriones meridianus)

Abstract Social mating systems (e.g., monogamy, polygamy, or polyandry) are relatively stable behavioral strategies developed by environmental in animals, but the genetic imprint of a particular mating system is often incongruent with the social mating system due to extrapair matings. However, the genetics of mating systems remain little understood in rodents. In this study, we investigated the genetic signature of the mating system of 141 (63 females, 78 males) field-captured midday gerbils (Meriones meridianus)—a rodent species commonly found in the Minqin Desert in China—through microsatellite site analyses of genetic structure and relatedness. Seven pairs of highly polymorphic microsatellite loci were selected and were highly polymorphic, with the combined exclusion probability greater than 0.99. The parent pair paternity test by Cervus 3.0 software show that 11 mother–offspring and nine father–offspring relationships were identified in 2018, involving 26 individuals from 10 families. Similarly, 19 mother–offspring and 19 father–offspring relationships were identified in 2019, involving 48 individuals from 18 families. All three types of genetic mating structure were identified—monogamy (19 families), polyandry (4 families), and polygyny (5 families), providing evidence that the genetics underlying mating systems in this species are variable, can be incongruent with behavioral evidence for social mating systems, and could vary based on environmental cues, including degree of perceived or actual predation.

Divorce rate in monogamous birds increases with male promiscuity and migration distance.

Socially monogamous birds may break up their partnership by a so-called 'divorce' behaviour. Divorce rates vary immensely across avian taxa that have a predominantly monogamous social mating system. Although various factors associated with divorce have been tested, broad-scale drivers of divorce rate remain contentious. Moreover, the influence of sexual roles in divorce still needs further investigation because of the conflicting interests of males and females over mating and fertilization. Here, we applied phylogenetic comparative methods to analyse one of the largest datasets ever compiled that included divorce rates from published studies of 186 avian species from 25 orders and 61 families. We tested correlations between divorce rate and a group of factors: 'promiscuity' of both sexes (propensity to polygamy), migration distance and adult mortality. Our results showed that only male promiscuity, but not female promiscuity, had a positive relationship with divorce rate. Furthermore, migration distance was positively correlated with divorce rate, whereas adult mortality rate showed no direct relationship with divorce rate. These findings indicated that divorce might not be a simple adaptive (by sexual selection) or non-adaptive strategy (by accidental loss of a partner) in birds but it could be a mixed response to sexual conflict and stress from the ambient environment.

Multiple paternity is related to adult sex ratio and sex determination system in reptiles.

The adult sex ratio (ASR, the proportion of males in the adult population) is an emerging predictor of reproductive behaviour, and recent studies in birds and humans suggest it is a major driver of social mating systems and parental care. ASR may also influence genetic mating systems. For instance male-skewed ASRs are expected to increase the frequency of multiple paternity (defined here as a clutch or litter sired by two or more males) due to higher rates of coercive copulations by males, and/or due to females exploiting the opportunity of copulation with multiple males to increase genetic diversity of their offspring. Here, we evaluate this hypothesis in reptiles that often exhibit high frequency of multiple paternity although its ecological and life-history predictors have remained controversial. Using a comprehensive dataset of 81 species representing all four non-avian reptile orders, we show that increased frequency of multiple paternity is predicted by more male-skewed ASR, and this relationship is robust to simultaneous effects of several life-history predictors. Additionally, we show that the frequency of multiple paternity varies with the sex determination system: species with female heterogamety (ZZ/ZW sex chromosomes) exhibit higher levels of multiple paternity than species with male heterogamety (XY/XX) or temperature-dependent sex determination. Thus, our across-species comparative study provides the first evidence that genetic mating system depends on ASR in reptiles. We call for further investigations to uncover the complex evolutionary associations between mating systems, sex determination systems and ASR.

Social network differences and phenotypic divergence between stickleback ecotypes

Abstract Elucidating the mechanisms underlying differentiation between populations is essential to our understanding of ecological and evolutionary processes. While social network analysis has yielded numerous insights in behavioral ecology in recent years, it has rarely been applied to questions about population differentiation. Here, we use social network analysis to assess the potential role of social behavior in the recent divergence between two three-spined stickleback ecotypes, “whites” and “commons”. These ecotypes differ significantly in their social behavior and mating systems as adults, but it is unknown when or how differences in social behavior develop. We found that as juveniles, the white ecotype was bolder and more active than the common ecotype. Furthermore, while there was no evidence for assortative shoaling preferences, the two ecotypes differed in social network structure. Specifically, groups of the white ecotype had a lower clustering coefficient than groups of the common ecotype, suggesting that groups of the white ecotype were characterized by the formation of smaller subgroups, or “cliques”. Interestingly, ecotypic differences in the clustering coefficient were not apparent in mixed groups composed of whites and commons. The formation of cliques could contribute to population divergence by restricting the social environment that individuals experience, potentially influencing future mating opportunities and preferences. These findings highlight the insights that social network analysis can offer into our understanding of population divergence and reproductive isolation.

Density‐dependent changes of mating system and family structure in Brandt's voles (Lasiopodomys brandtii)

AbstractA mating system is an important life history for animals dealing with changing environments. Population density affects the plasticity of a mating system and subsequently the family structure of animals, but its impacts on mating systems and social structures are rarely investigated by using molecular markers in field conditions. In this study, using microsatellite genetic markers, we examined the changes in the social and genetic mating system and family structure of Brandt's voles in the grassland of Inner Mongolia, China, under low‐, medium‐, and high‐density enclosures (each enclosure 0.48‐ha with 4 replicates.) We found, with the increase in population density of the founder voles introduced into the enclosure in early spring, both sexes increased their number of genetic mating partners, while males increased their social partners, resulting in a more promiscuous mating system. The number of genetic fathers and mothers per family, the number of social offspring per founder male or female, and the proportion of extra‐group offspring increased with increased density, indicating that the response of the family structure to density change, which is consistent with the change in mating system observed in our study. Both male and female voles had multiple mates, but males had a larger number of social and genetic mates, the number of social and genetic offspring, and the number of social and genetic families. Our study highlights the significance of density‐dependent plasticity of a mating system and family structure in affecting the population change of small mammals.

Automated radio tracking provides evidence for social pair bonds in an obligate brood parasite

Social monogamy predominates in avian mating systems, but this strategy seems unlikely among brood parasites, where the emancipation from parental care should lead to an increase in numbers of mates for both sexes. Despite this, there is great diversity in mating systems in brood parasitic birds. The Screaming CowbirdMolothrus rufoaxillarisis a brood parasite that specializes almost exclusively on one host, the Greyish BaywingAgelaioides badius. Field observations and a radio telemetry study have indicated that male–female pairs spend a great deal of time together through the day, suggesting that they may be socially monogamous. We tested the hypothesis of social monogamy by radio‐tracking male and female Screaming Cowbirds using an array of automated radiotracking receivers to collect data on spatial behaviour and social mating system. Monogamous pair bonds were recorded through social network analysis. These bonds endured throughout the entire breeding season, with males and females remaining associated throughout the day. In accordance with the hypothesis, paired Screaming Cowbirds spent significantly more time in proximity to their mates than to other conspecifics of the opposite sex, and had similar home‐ranges. Social monogamy in the Screaming Cowbird differed markedly from the social polygyny/promiscuity exhibited by the sympatric congener Shiny CowbirdMolothrus bonariensis, a generalist brood parasite.

Breeding site fidelity is lower in polygamous shorebirds and male-biased in monogamous species.

Sex-bias in breeding dispersal is considered the norm in many taxa, and the magnitude and direction of such sex-bias is expected to correlate with the social mating system. We used local return rates in shorebirds as an index of breeding site fidelity, and hence as an estimate of the propensity for breeding dispersal, and tested whether variation in site fidelity and in sex-bias in site fidelity relates to the mating system. Among 111 populations of 49 species, annual return rates to a breeding site varied between 0% and 100%. After controlling for body size (linked to survival) and other confounding factors, monogamous species showed higher breeding site fidelity compared with polyandrous and polygynous species. Overall, there was a strong male bias in return rates, but the sex-bias in return rate was independent of the mating system and did not covary with the extent of sexual size dimorphism. Our results bolster earlier findings that the sex-biased dispersal is weakly linked to the mating system in birds. Instead, our results show that return rates are strongly correlated with the mating system in shorebirds regardless of sex. This suggests that breeding site fidelity may be linked to mate fidelity, which is only important in the monogamous, biparentally incubating species, or that the same drivers influence both the mating system and site fidelity. The strong connection between site fidelity and the mating system suggests that variation in site fidelity may have played a role in the coevolution of the mating system, parental care, and migration strategies.

Revisiting the components of Macroscelidea social systems: Evidence for variable social organization, including pair‐living, but not for a monogamous mating system

AbstractElephant‐shrews (Macroscelidea) have long been considered the only mammalian order to be completely monogamous, based on observations of their pair‐living social organization. We reviewed primary studies on the four components of social systems (social organization, mating system, social structure, and care system) in elephant‐shrews to evaluate whether they truly are monogamous. To identify gaps in our knowledge of their social system, we reviewed evidence for a pair‐living social organization, mate fidelity (mating system), pair bonds (social structure), and biparental care (care system). Field data were available for eight species and seven were often pair‐living. However, these seven species exhibited intra‐specific variation in social organization; two of these species were also solitary living, two species were also group‐living, and the remaining three species were both solitary and group‐living. The eighth species was exclusively solitary. We reconstructed the ancestral social organization of Macroscelidea using Bayesian phylogenetic mixed‐effects models and found that variable social organization, rather than exclusive pair‐living, was the most likely ancestral state, though there was high uncertainty. No socio‐ecological factors (body size, population density, and habitat) predicted a specific social organization. Observations of mating have been rare, such that no firm statements can be made. However, one unpublished study indicated high levels of extra‐pair paternity. Regarding social structure, there was no evidence of pair‐bonding, but there was evidence of mate guarding. Only maternal care has been observed, with females having very short nursing bouts. Evidence suggests that despite having often a pair‐living form of social organization, Macroscelidea should not be described as a monogamous order, as little or no evidence supports that designation, nor are they exclusively pair‐living (social organization) and we urge further field studies on Macroscelidea social systems.

Social complexity in plateau pikas, Ochotona curzoniae

We investigated factors leading to variation in social complexity or ‘social systems’ among plateau pika family groups within a contiguous local population across 2 years. Plateau pikas are small, diurnal, nonhibernating, sexually monomorphic lagomorphs that occupy family home ranges on open alpine meadows on the Qinghai-Tibetan Plateau. Expression of the social organization, social structure, mating system and parental care system in plateau pikas did not follow expectations from traditional ecological or evolutionary explanations. Variability in plateau pika family group size and the transitions of group size between years allowed us to investigate potential advantages and disadvantages of group living. Evidence that group living served to protect pikas against predation was weak. Although social huddling could have minimized thermoregulatory costs during the extremely cold Tibetan winters, there was no correlation of overwinter survivorship among pika families of different sizes. There was no apparent group-living benefit with regard to foraging, and the occurrence of cohesive social families on the flat, continuous meadow contradicts the hypothesis that sociality is related to patchiness of critical resources. Cost of maintaining burrows appeared unrelated to group size. Most interactions between pikas occurred within family groups and were affiliative (99% of adult interactions; 97% of adult–juvenile interactions), and most interactions between adult males of different family groups were aggressive (96% of interactions). Matings were primarily within families (88% of copulations). Pikas also possess a complex vocal repertoire that enhanced interactions within social families. Demographic constraints associated with variable overwinter survivorship appeared to be the dominant precondition that produced a given family size and mating system type, coupled with selective dispersal by some pikas before the start of the breeding season. Paternal care enhanced juvenile survival, and thus led to an equalization of reproductive success among adults in families with different mating combinations. • Plateau pikas live in families occupying exclusive burrow systems and home ranges. • Pika family group size varied from one to five adults within and between years. • Pikas failed to adhere to conventional explanations for establishment of group size. • Pika families exhibited multiple social mating system types. • Pika families did not adhere to explanations for establishment of mating system types.

Socioecology of the Australian Tree Skink (Egernia striolata)

There is great diversity in social behavior across the animal kingdom. Understanding the factors responsible for this diversity can help inform theory about how sociality evolves and is maintained. The Australian Tree Skink (Egernia striolata) exhibits inter- and intra-population variability in sociality and is therefore a good system for informing models of social evolution. Here, we conducted a multi-year study of a Tree Skink population to describe intra-population variation in the social organization and mating system of this species. Skinks aggregated in small groups of 2–5 individuals, and these aggregations were typically associated with shared shelter sites (crevices and hollows within rocks and trees). Aggregations were typically made up of one or more adult females and, often, one male and/or juvenile(s). Social network and spatial overlap analyses showed that social associations were strongly biased toward kin. Tree skinks also exhibited high site fidelity regardless of age or sex. There were high levels of genetic monogamy observed with most females (87%) and males (68%) only breeding with a single partner. Our results indicate that Tree Skinks reside in small family groups and are monogamous, which corresponds with existing research across populations. Similar to previous work, our study area consisted of discrete habitat patches (i.e., rock outcrops, trees, or both), which likely limits offspring dispersal and promotes social tolerance between parents and their offspring. Our study clearly demonstrates that there is intra-population variability in Tree Skink social behavior, but it also provides evidence that there is a high degree of inter-population consistency in sociality across their geographic range. We also highlight promising possible avenues for future research, specifically discussing the importance of studying the nature and extent of Tree Skink parental care and quantifying the fitness outcomes of kin-based sociality in this species, which are topics that will further our understanding of the mechanisms underlying variation in vertebrate social behavior.

Genetic ancestry predicts male–female affiliation in a natural baboon hybrid zone

Opposite-sex social relationships are important predictors of fitness in many animals, including several group-living mammals. Consequently, understanding sources of variance in the tendency to form opposite-sex relationships is important for understanding social evolution. Genetic contributions are of particular interest due to their importance in long-term evolutionary change, but little is known about genetic effects on male-female relationships in social mammals, especially outside of the mating context. Here, we investigate the effects of genetic ancestry on male-female affiliative behaviour in a hybrid zone between the yellow baboon, Papio cynocephalus, and the anubis baboon, Papio anubis, in a population in which male-female social bonds are known predictors of life span. We place our analysis within the context of other social and demographic predictors of affiliative behaviour in baboons. Genetic ancestry was the most consistent predictor of opposite-sex affiliative behaviour we observed, with the exception of strong effects of dominance rank. Our results show that increased anubis genetic ancestry is associated with a subtle, but significantly higher, probability of opposite-sex affiliative behaviour, in both males and females. Additionally, pairs of anubis-like males and anubis-like females were the most likely to socially affiliate, resulting in moderate assortativity in grooming and proximity behaviour as a function of genetic ancestry. Our findings indicate that opposite-sex affiliative behaviour partially diverged during baboon evolution to differentiate yellow and anubis baboons, despite overall similarities in their social structures and mating systems. Furthermore, they suggest that affiliative behaviour may simultaneously promote and constrain baboon admixture, through additive and assortative effects of ancestry, respectively.

Responses of a pair‐living, sexually monogamous primate to the simulated presence of solitary individuals: A field playback experiment

AbstractLoud calls play an important function in regulating the use of space and structuring social groups and mating systems in a wide range of taxa. In pair‐living territorial animals, where encounters with neighbors and solitary conspecifics are common, these calls are mainly associated with resource defense or mate guarding behaviors. Owl monkeys (Aotus azarae) live in groups of one pair of reproducing adults and 1–4 younger, non‐reproducing individuals. Both sexes disperse when they are around 3 years of age; they become solitary floaters who compete to replace same‐sex adults from other groups. Here, we examined the behavioral responses of Azara's owl monkey pairs toward calls of unpaired and unfamiliar males and females to better understand if the competition between floaters and groups is in relationship to the defense of their territory, their mates, or both. We collected behavioral data from six groups, before, during, and after the playing back of unfamiliar male and female loud calls and of a control stimulus at the center and border of their home ranges. Overall, our results showed that the playback location did not elicit differential responses in the monkeys and that both sexes were more reactive to male than female unfamiliar calls, as evidenced by higher rates of sociosexual and vocal responses, movement toward the playback, and intergroup encounters during and after the experiments. Our study indicates that paired male and female owl monkeys mainly defend their partners toward intruders and emphasizes the need of including the role of sexual competition on both sexes in models about the evolution of pair‐living social organizations and sexual monogamy mating systems.

Sexual, allometric and forest cover effects on giant anteaters' movement ecology.

Knowing the influence of intrinsic and environmental traits on animals’ movement is a central interest of ecology and can aid to enhance management decisions. The giant anteater (Myrmecophaga tridactyla) is a vulnerable mammal that presents low capacity for physiological thermoregulation and uses forests as thermal shelters. Here, we aim to provide reliable estimates of giant anteaters’ movement patterns and home range size, as well as untangle the role of intrinsic and environmental drivers on their movement. We GPS-tracked 19 giant anteaters in Brazilian savannah. We used a continuous-time movement model to estimate their movement patterns (described by home range crossing time, daily distance moved and directionality), and provide an autocorrelated kernel density estimate of home range size. Then, we used mixed structural equations to integratively model the effects of sex, body mass and proportion of forest cover on movement patterns and home range size, considering the complex net of interactions between these variables. Male giant anteaters presented more intensive space use and larger home range than females with similar body mass, as it is expected in polygynous social mating systems. Males and females increased home range size with increasing body mass, but the allometric scaling of intensity of space use was negative for males and positive for females, indicating different strategies in search for resources. With decreasing proportion of forest cover inside their home ranges, and, consequently, decreasing thermal quality of their habitat, giant anteaters increased home range size, possibly to maximize the chances of accessing thermal shelters. As frequency and intensity of extreme weather events and deforestation are increasing, effective management efforts need to consider the role of forests as an important thermal resource driving spatial requirements of this species. We highlight that both intrinsic and environmental drivers of animal movement should be integrated to better guide management strategies.

Social and spatial patterns of two Afromontane crag lizards (Pseudocordylus spp.) in the Maloti‐Drakensberg Mountains, South Africa

AbstractUnderstanding the evolution of vertebrate sociality requires comparative data on social associations across the vertebrate phylogeny. In the case of group‐living lizards (i.e. species that live in stable social aggregations often associated with a shared resource), most work has focused on the Egerniinae in Australia, resulting in a taxonomic and geographic skew to our understanding of reptile sociality. The African cordylid lizards (Cordylidae) are also a promising system to study the evolution of sociality because grouping behaviour varies across the clade. Here, we studied the conspecific grouping behaviour of two crag lizards, Pseudocordylus langi and P. melanotus subviridis that occur at high elevations in the Maloti‐Drakensberg Mountains of South Africa. To better understand their social organisation and mating system, we also present data on their spatial distribution, sexual dimorphism, and bite force. Both Pseudocordylus spp. were sexually dimorphic in morphology (males had larger heads than females of similar body size), colouration (males were more colourful) and female P. langi had a weaker bite force than males. Both P. langi and P. m. subviridis were associated with rocky habitat on the mountainside (e.g. cliffs, rock buttresses, and rock outcrops) and both were spaced apart and rarely in groups (79% of P. langi and 90% of P. m. subviridis were observed alone). Based on our findings, we hypothesise that both Pseudocordylus spp. have a territorial social structure and a polygynous mating system. This novel natural history information about crag lizards supports the assertion that Cordylidae is another model system for examining the evolution of sociality.

Size but not relatedness drives the spatial distribution of males within an urban population of Anolis carolinensis lizards.

The way that individuals are spatially organized in their environment is a fundamental population characteristic affecting social structure, mating system, and reproductive ecology. However, for many small or cryptic species, the factors driving the spatial distribution of individuals within a population are poorly understood and difficult to quantify. We combined microsatellite data, remote sensing, and mark–recapture techniques to test the relative importance of body size and relatedness in determining the spatial distribution of male Anolis carolinensis individuals within a focal population over a five‐year period. We found that males maintain smaller home ranges than females. We found no relationship between male body size and home range size, nor any substantial impact of relatedness on the geographic proximity. Instead, the main driver of male spatial distribution in this population was differences in body size. We also found no evidence for offspring inheritance of their parent's territories. Males were never sampled within their father's territory providing strong support for male‐biased dispersal. This study introduces a novel approach by combining standard mark release capture data with measures of pairwise relatedness, body size, and GPS locations to better understand the factors that drive the spatial distribution of individuals within a population.

The life of Fabian, an Azara’s owl monkey (Aotus azarae) of the Argentinean Chaco

Abstract Species-life history patterns provide insights into the adaptative strategies and importance of social behaviours. The cathemeral activity pattern of Aotus azarae allowed researchers from the Owl Monkey Project of Formosa, Argentina, to witness remarkable life changing events over the complete lifespan of several individuals. Here we summarize the life of Fabian, a male owl monkey we followed from the moment he started searching for a mate until he died. Although still not consistently considered in models of social evolution of mammals, our discovery of a subpopulation of solitary owl monkey floaters forced us to rethink some aspects of their characteristic social organization and mating system. Through the life of Fabian we present some representative examples of the intrasexual competition regulating the social system of the members of this genus during the different stages in the life of individuals, while reporting the first case of extra-pair copulation in wild owl monkeys.

Genetic approach reveals a polygynous-polyandrous mating system and no social organization in a small and isolated population of the screaming hairy armadillo, Chaetophractus vellerosus.

The development of agro-ecosystems in the pastures of the Pampean Region has substantially modified their structure and functioning. Many wild mammal populations in the Argentinean Pampas face habitat loss and/or fragmentation due to human activities, resulting in harmful genetic effects. The screaming hairy armadillo (Chaetophractus vellerosus) is a species considered an indicator of the state of preservation of the environments it inhabits. However, very little information is available about its mating system in the wild. In this sense, an isolated population of the screaming hairy armadillo in the northeast of Buenos Aires Province, which is separated from the main distribution area of the species by about 500 km, requires special attention. Genetic studies that analyzed social behavior and mating systems in Xenarthra are scarce but necessary to establish conservation actions for the isolated screaming hairy armadillo population under study. Thus, we analyzed the existence of a possible social organization in the species, together with its mating system, using a set of previously characterized microsatellites. Our results showed a complex scenario for the dispersal and mating system in this C. vellerosus population. Males disperse and females have a philopatric tendency with some degree of dispersal. This strategy, in combination with a polygynous-polyandrous mating system, could enhance genetic variability in this small and isolated population. In addition, no evidence of social organization was found.

Genetic Structure Associated with the Ecological Traits of Four Species of Phyllostomid Bats Inhabiting Selva El Ocote Biosphere Reserve, Chiapas, México

Phyllostomid bats display a variety of social structures and mating systems; the influence of these features on the distribution of genetic diversity within and between bat populations is currently unknown. Based on the mitochondrial DNA D-loop region, we investigated the relationship between genetic structure and social characteristics in four species of phyllostomid bats (Sturnira hondurensis, Artibeus jamaicensis, Carollia sowelli, and Dermanura tolteca) inhabiting Selva El Ocote Biosphere Reserve (REBISO). According to their ecological characteristics, we expected a relatively high genetic diversity and stable populations, as well as a weak genetic structure in S. hondurensis and C. sowelli, and a moderate one in A. jamaicensis and D. tolteca. The demographic history and mismatch distribution were inferred. Besides, we estimated the time elapsed from demographic change (in number of generations). Finally, we calculated standard genetic diversity indicators and determined the genetic structure, haplotype networks, and conducted spatial autocorrelation analyses. Genetic diversity was higher in S. hondurensis, intermediate in C. sowelli, and low in A. jamaicensis and D. tolteca. The neutrality tests indicated population expansion in A. jamaicensis, C. sowelli, and D. tolteca; S. hondurensis showed differentiation between populations with no apparent demographic changes. The extent of genetic differentiation was high in S. hondurensis, intermediate in C. sowelli, weak in A. jamaicensis, and nil in D. tolteca. The spatial autocorrelation revealed genetic structure at certain geographic distances in A. jamaicensis, C. sowelli, and S. hondurensis, while D. tolteca displayed a low structure at the greatest geographic distances. No clear relationship was evident between ecological attributes and genetic structure in the bat species studied, probably due to the slight differences in the ecological characteristics of these species. Further studies should include ecological factors such as resource availability and habitat selection, as well as nuclear markers, to obtain a biparental genetic estimation. This study highlights the need of conduct further research about the relationship of ecological and genetic traits of tropical bats in high-biodiversity reserves.

Stochasticity in social structure and mating system drive extinction risk

AbstractAs anthropogenic activities continue to threaten species across the globe, many populations have seen dramatic reductions in abundance from historical values. While the underlying causes are varied, such long‐term population declines greatly increase these species’ susceptibility to extinction via stochastic processes. Previous research has established that demographic stochasticity and environmental stochasticity play important roles in extinction risk, but few studies have investigated the role of stochasticity in social dynamics, such as group formation and mating systems. Here, we developed a suite of simulation models incorporating different combinations of stochastic processes, while also varying group size and mating system. Using these models, we evaluated the interacting effects of different mating systems coupled with varied sources of stochasticity on extinction risk. Extinction risk was generally higher for populations with mating systems more dependent on even sex ratios in groups (e.g., monogamy). However, in more flexible mating systems (e.g., polygynandry), stochasticity in the formation of individual groups actually reduced extinction risk in certain scenarios. By identifying the factors most important to the stochastic extinction risk of species with different mating systems and social structures, we provide insight into conservation and management strategies for such species facing population declines.

A framework for conceptualizing dimensions of social organization in mammals.

Mammalian societies represent many different types of social systems. While some aspects of social systems have been extensively studied, there is little consensus on how to conceptualize social organization across species. Here, we present a framework describing eight dimensions of social organization to capture its diversity across mammalian societies. The framework uses simple information that is clearly separated from the three other aspects of social systems: social structure, care system, and mating system. By applying our framework across 208 species of all mammalian taxa, we find a rich multidimensional landscape of social organization. Correlation analysis reveals that the dimensions have relatively high independence, suggesting that social systems are able to evolve different aspects of social behavior without being tied to particular traits. Applying a clustering algorithm allows us to identify the relative importance of key dimensions on patterns of social organization. Finally, mapping mating system onto these clusters shows that social organization represents a distinct aspect of social systems. In the future, this framework will aid reporting on important aspects of natural history in species and facilitate comparative analyses, which ultimately will provide the ability to generate new insights into the primary drivers of social patterns and evolution of sociality.