Fossorial adaptations in African mole-rats (Bathyergidae) and the unique appendicular phenotype of naked mole-rats.

Life underground has constrained the evolution of subterranean mammals to maximize digging performance. However, the mechanisms modulating morphological change and development of fossorial adaptations in such taxa are still poorly known. We assessed the morpho-functional diversity and early postnatal development of fossorial adaptations (bone superstructures) in the appendicular system of the African mole-rats (Bathyergidae), a highly specialized subterranean rodent family. Although bathyergids can use claws or incisors for digging, all genera presented highly specialized bone superstructures associated with scratch-digging behavior. Surprisingly, Heterocephalus glaber differed substantially from other bathyergids, and from fossorial mammals by possessing a less specialized humerus, tibia and fibula. Our data suggest strong functional and developmental constraints driving the selection of limb specializations in most bathyergids, but more relaxed pressures acting on the limbs of H. glaber. A combination of historical, developmental and ecological factors in Heterocephalus are hypothesized to have played important roles in shaping its appendicular phenotype.

Paternity Uncertainty and Parent-Offspring Conflict Explain Restrictions on Female Premarital Sex across Societies.

Although norms of premarital sex vary cross-culturally, the sexuality of adolescent girls has been consistently more restricted than that of adolescent boys. Three major theories that attempt to explain restrictions on female premarital sex (FPS) concern male, female, and parental control. These competing theories have not been tested against each other cross-culturally. In this study, we do this using a sample of 128 nonindustrial societies and socioecological predictors capturing extramarital sex, paternal care, female status, sex ratio, parental control over a daughter's mate choice, residence, and marriage transactions, while also controlling for phylogenetic non-independence across societies. We found that multiple parties benefit from restrictions on FPS. Specifically, FPS is more restricted in societies intolerant of extramarital sex and where men transfer property to their children (male control), as well as where marriages are arranged by parents (parental control). Both paternity uncertainty (partitioned among marital fidelity and paternal investment) and parent-offspring conflict (prompting parents to control their daughter's sexuality) were identified as possible mechanisms of FPS restrictions. The evidence for female control is ambiguous, mainly because it can be equally well interpreted as both male control and parental control, and because fathers, rather than mothers, are often the primary decision makers about a daughter's mate choice. Our results also emphasize the importance of social roles, rather than stereotyped sex roles, as a more useful approach to understanding the evolution of FPS restrictions.

Global phylogenetic analysis reveals multiple origins and correlates of genital mutilation/cutting.

Genital mutilation/cutting is costly in terms of health, survival and reproduction, and the long-term maintenance of these practices is an evolutionary conundrum. Previous studies have suggested a mate-guarding function or various signalling functions of genital mutilation/cutting. Here we use phylogenetic comparative methods and two global ethnographic samples to study the origins and socio-ecological correlates of major types of female and male genital mutilation/cutting. Male genital mutilation/cutting probably originated in polygynous societies with separate residence of co-wives, supporting a mate-guarding function. Female genital mutilation/cutting originated subsequently and almost exclusively in societies already practising male genital mutilation/cutting, where it may have become a signal of chastity. Both have originated multiple times, some as early as in the mid-Holocene (5,000-7,000 years ago), considerably predating the earliest archaeological evidence and written records. Genital mutilation/cutting co-evolves with and may help maintain fundamental social structures, hindering efforts to change these cultural practices.

Parental Investment Is Biased toward Children Named for Their Fathers.

Namesaking (naming a child after a parent or other relative) can be viewed as a mechanism to increase perceived parent-child similarity and, consequently, parental investment. Male and, to a lesser extent, firstborn children are more frequently namesakes than female and later-born children, respectively. However, a direct link between namesaking and parental investment has not been examined. In the present study, 632 participants (98 men and 534 women) from Central Europe indicated their first name, sex, birth order, number of siblings, sexual orientation, socioeconomic status, paternal and maternal first names, as well as relationship quality with, and time and financial investment they received from, both parents during childhood. Mixed-effects models revealed associations between namesaking and parental investment. However, the effect of namesaking often appeared significant only in interaction with specific predictors, such as sex and primogeniture. It suggests instead that namesaking has an additive effect-it enhances the effect of biological factors on parental investment. In general, we found evidence for the bias in parental investment linked to name similarity among both parents, and support for the hypothesis that namesaking serves as a mechanism to increase paternity confidence and, thus, paternal investment. The effect of namesaking influences only certain types of parental investment-namely, those at the level of relationship quality. In addition, nonheterosexual orientation was the strongest negative predictor of paternal investment. Our study extends the research on parental investment by showing that cultural mechanisms, such as namesaking, can also exert some influence on parental rearing behavior.

Heat dissipation in subterranean rodents: the role of body region and social organisation.

The relatively warm and very humid environment of burrows presents a challenge for thermoregulation of its mammalian inhabitants. It was found that African mole-rats dissipate body heat mainly through their venter, and social mole-rats dissipate more body heat compared to solitary species at lower temperatures. In addition, the pattern of the ventral surface temperature was suggested to be homogeneous in social mole-rats compared to a heterogeneous pattern in solitary mole-rats. To investigate this for subterranean rodents generally, we measured the surface temperatures of seven species with different degrees of sociality, phylogeny, and climate using infrared thermography. In all species, heat dissipation occurred mainly through the venter and the feet. Whereas the feet dissipated body heat at higher ambient temperatures and conserved it at lower ambient temperatures, the ventral surface temperature was relatively high in all temperatures indicating that heat dissipation to the environment through this body region is regulated mainly by behavioural means. Solitary species dissipated less heat through their dorsum than social species, and a tendency for this pattern was observed for the venter. The pattern of heterogeneity of surface temperature through the venter was not related to sociality of the various species. Our results demonstrate a general pattern of body heat exchange through the three studied body regions in subterranean rodents. Besides, isolated individuals of social species are less able to defend themselves against low ambient temperatures, which may handicap them if staying alone for a longer period, such as during and after dispersal events.

Identifying post-marital residence patterns in prehistory: A phylogenetic comparative analysis of dwelling size.

Post-marital residence patterns are an important aspect of human social organization. However, identifying such patterns in prehistoric societies is challenging since they leave almost no direct traces in archaeological records. Cross-cultural researchers have attempted to identify correlates of post-marital residence through the statistical analysis of ethnographic data. Several studies have demonstrated that, in agricultural societies, large dwellings (over ca. 65 m2) are associated with matrilocality (spouse resides with or near the wife's family), whereas smaller dwellings are associated with patrilocality (spouse resides with or near the husband's family). In the present study, we tested the association between post-marital residence and dwelling size (average house floor area) using phylogenetic comparative methods and a global sample of 86 pre-industrial societies, 22 of which were matrilocal. Our analysis included the presence of agriculture, sedentism, and durability of house construction material as additional explanatory variables. The results confirm a strong association between matrilocality and dwelling size, although very large dwellings (over ca. 200 m2) were found to be associated with all types of post-marital residence. The best model combined dwelling size, post-marital residence pattern, and sedentism, the latter being the single best predictor of house size. The effect of agriculture on dwelling size becomes insignificant once the fixity of settlement is taken into account. Our results indicate that post-marital residence and house size evolve in a correlated fashion, namely that matrilocality is a predictable response to an increase in dwelling size. As such, we suggest that reliable inferences about the social organization of prehistoric societies can be made from archaeological records.

Is the timing of menarche correlated with mortality and fertility rates?

Timing of menarche has largely been studied in the context of a secular trend. However, since mortality and fertility rates are fundamental demographic factors linked to a population's developmental and reproductive characteristics, we expect that the timing of menarche, a precondition to reproduction, is also associated with these vital rates. We conduct an analysis of 89 countries and 21 demographic, socioeconomic, nutritional, and educational variables selected for their known influence on menarche. Model results predict that a country's fertility and adult female mortality rates are significant predictors of mean age at menarche, while other covariates are not. Specifically, menarche is delayed in countries with high mortality and high fertility, which may be proxies for assessing overall environmental quality. We emphasize that, for a comprehensive understanding of the timing of menarche, it is critical to take into account both individual- and population-level influences.

Risk perception of vervet monkeys Chlorocebus pygerythrus to humans in urban and rural environments.

Like other animals, primates respond to predation using behavioural adaptations. Hence, they should optimise their escape strategy under the risk of predation, and flee at a distance, referred to as flight initiation distance (FID), when the fitness-related benefits of staying are balanced against the costs of escape. However, there is an absence of FID studies in primates. In this study, we used vervet monkeys Chlorocebus pygerythrus, a medium-sized African cercopithecoid, as a model species to investigate the influence of environment type (urban and rural), group size (defined as the number of visible neighbours), sex and age on FID when approached by a human. We found significantly shorter FID among urban than rural monkeys; urban individuals delayed their escape compared to rural individuals. We found no relationship between FID and sex and age class, but FID was positively correlated with group size in both settings; urban monkeys live in smaller groups than monkeys in rural areas. As FID and group size are important predictors of predation risk perception in primates, results suggest that, despite probable effects of habituation, vervet monkeys in Uganda adjust their antipredator behaviour when coping with novel environments within human settlements. Our findings are consistent with some previous studies of risk perception in animals, and indicate that FID could be used as an alternative measure for predation risk in primates.