A novel methodological approach for group classification during fission of a semi-free-ranging group of Japanese macaques (Macaca fuscata)

The self-initiated split of a social group, known as fission, is a challenge faced by many group-living animals. The study of group fission and the social restructuring process in real time provides insights into the mechanism of this biologically important process. Previous studies on fission in Japanese macaques (Macaca fuscata) assigned individuals to newly reorganized groups mainly using behavioral observations and group attendance records based on periods before or after fission itself. Here, we present a novel framework for group classification during the process of fission that uses quantifiable behavioral variables and statistical analyses. The framework was tested on a group fission process at Affenberg Landskron (Austria), a park that housed around 160 semi-free-ranging Japanese macaques. The behavioral data were collected for 26 days during fission. We analyzed three behavioral developments recurrent in fissions in Japanese macaques, that is, independence of behavior, participation in group movements, and separation of nomadic ranges. These analyses were combined to assign individuals to different groups. Our study resulted in one main group (N = 33), one subgroup (N = 36) and 56 individuals whose group membership was still undefined. The demographic characteristics of these newly formed groups were comparable with those of fissioned groups in wild populations. Furthermore, we found that these newly forming groups showed early social dynamics of fission five months before group level movements, that is: grouping based on spatial proximity and spatial withdrawal of the subgroup to the periphery. These results underline the validity of our novel framework to study social dynamics in Japanese macaques during the process of fission. It represents an important addition to existing methods, and we recommend testing its scope in other primate societies

Sex Differences in Intergenerational Income Transmission and Educational Attainment: Testing the Trivers-Willard Hypothesis

From an evolutionary point of view, sex differences in intergenerational transmission of income may be influenced by the Trivers-Willard (T-W) effect: Low status parents should invest more in daughters, whereas high status parents are expected to invest more in sons. This bias in parental investment may result in status-dependent sex biased parental support for higher education and educational attainment and should therefore affect the level of intergenerational income transmission for the sons and daughters. We used the data from the Wisconsin Longitudinal Study (WLS) to model the effect of parental financial investment on the child's income and educational attainment controlling for the number of siblings. The observed sex differences in intergenerational income transmission demonstrate that sons profited more from parental income and education in terms of their own income than daughters. Furthermore, we showed that fathers with a high socioeconomic index (SEI) invest more in their sons' education in terms of completed years of education and financial support during college. In contrast daughters of low SEI fathers completed more years of education and received more financial support than sons of low SEI fathers. However, the pattern in intergenerational income transmission might be better explained as a product of sociological factors and reproductive trade-offs in later life rather than as a consequence of the T-W effect

Sex Differences in Intergenerational Income Transmission and Educational Attainment: Testing the Trivers-Willard Hypothesis

From an evolutionary point of view, sex differences in intergenerational transmission of income may be influenced by the Trivers-Willard (T-W) effect: Low status parents should invest more in daughters, whereas high status parents are expected to invest more in sons. This bias in parental investment may result in status-dependent sex biased parental support for higher education and educational attainment and should therefore affect the level of intergenerational income transmission for the sons and daughters. We used the data from the Wisconsin Longitudinal Study (WLS) to model the effect of parental financial investment on the child's income and educational attainment controlling for the number of siblings. The observed sex differences in intergenerational income transmission demonstrate that sons profited more from parental income and education in terms of their own income than daughters. Furthermore, we showed that fathers with a high socioeconomic index (SEI) invest more in their sons' education in terms of completed years of education and financial support during college. In contrast daughters of low SEI fathers completed more years of education and received more financial support than sons of low SEI fathers. However, the pattern in intergenerational income transmission might be better explained as a product of sociological factors and reproductive trade-offs in later life rather than as a consequence of the T-W effect.status: publishe

Effects of Individual Mortality Experience on Out-of-Wedlock Fertility in Eighteenth- and Nineteenth-Century Krummhorn, Germany

Life history theory predicts that exposure to high mortality in early childhood leads to faster and riskier reproductive strategies. Individuals who grew up in a high mortality regime will not overly wait until they find a suitable partner and form a stable union because premature death would prevent them from reproducing. Cox proportional hazard models were used to determine whether women who experienced sibling death during early childhood (0-5 years) reproduced earlier and were at an increased risk of giving birth to an illegitimate child, with illegitimacy serving as a proxy for risky sexual behavior. Furthermore, we investigate whether giving birth out of wedlock is influenced by individual mortality experience or by more promiscuous sexual behavior that is clustered in certain families. Models are fitted on pedigree data from the eighteenth- and nineteenth-century Krummhörn population in Germany. The results show a relationship between sibling death in early childhood and the risk of reproducing out of wedlock, and reproductive timing. The risk of giving birth out of wedlock is linked to individual mortality experience rather than to family-level effects. In contrast, adjustments in connubial reproductive timing are influenced more by family-level effects than by individual mortality experience.status: publishe