Sex Ratio, Sexual Dimorphism, and Wing Geometric Morphometrics in Species of Trypoxylon Latreille, 1796 (Hymenoptera: Crabronidae).

Studying the nesting biology of wasp and bee species provides valuable insights into the ecology and evolution of these insects, shedding light on their ecological significance and aiding in their conservation efforts. Trypoxylon Latreille, 1796 is a genus of spider-hunting wasps that provisions their brood with paralyzed preys. This study focuses on aspects of nesting biology of Trypoxylon (Trypargilum) species such as sex ratio, sexual dimorphism, and morphometric variation at both inter- and intraspecific levels. The secondary sex ratio (SR) exhibited variation among species and populations. Males predominantly emerged from the first brood cells and from trap nests with smaller diameters. In comparison, females showed significantly larger body mass and linear wing measurements than males. Procrustes ANOVA values for centroid size (CS) and wing shape (SH) indicated significant differences in both wing size and shape among the five analyzed Trypoxylon species. Sexual dimorphism indices (SDI) derived from centroid size were found to be similar to those obtained from linear measurements, while SDI values based on body mass were significantly higher. Nests containing a greater number of cells tended to produce a larger number of higher-quality males and females. This observation, along with the lower coefficient of variation for female body size and high heritability, suggests that this trait may be subject to natural selection. Further studies that estimate the size of parents and their respective offspring are necessary to confirm the fitness advantage associated with larger female sizes in Trypoxylon species.

Sex ratio of Western Bluebirds Sialia mexicana is mediated by phenology and clutch size.

Mothers may produce more of one sex to maximize their fitness if there are differences in the cost of producing each sex or there are differences in their relative reproductive value. Breeding date and clutch size are known to influence offspring sex ratios in birds through sex differences in dispersal, social behaviours, differential mortality, and available food resources. We tested if breeding date, clutch size and drought conditions influenced offspring sex ratios in a sexually size-monomorphic species, the Western Bluebird, by interrogating a 21-year dataset. After controlling for differential mortality, we found that hatch dates late in the breeding season were associated with the production of more females, suggesting that the value of producing males declines as the breeding season progresses. When clutch size was taken into account, small clutches yielded significantly more females late in the breeding season compared to the early and middle parts of the breeding season that produced significantly more males. Large clutches early in the season tended to produce more females, although this was not significant. Drought severity was not correlated with sex ratio adjustment. We propose and discuss several explanations for these patterns, including male offspring, but not female offspring, acting as helpers, increased female nestling provisioning late in the breeding season, differences in food abundance, and egg-laying order. Future work will help to uncover the mechanisms leading to these patterns. Identifying patterns and mechanisms of sex ratio skew from long-term datasets is important for informing predictions regarding life-history trade-offs in wildlife populations.

Inclusive fitness and differential productivity across the life course determine intergenerational transfers in a small-scale human society.

Transfers of resources between generations are an essential element in current models of human life-history evolution accounting for prolonged development, extended lifespan and menopause. Integrating these models with Hamilton's theory of inclusive fitness, we predict that the interaction of biological kinship with the age-schedule of resource production should be a key driver of intergenerational transfers. In the empirical case of Tsimane' forager-horticulturalists in Bolivian Amazonia, we provide a detailed characterization of net transfers of food according to age, sex, kinship and the net need of donors and recipients. We show that parents, grandparents and siblings provide significant net downward transfers of food across generations. We demonstrate that the extent of provisioning responds facultatively to variation in the productivity and demographic composition of families, as predicted by the theory. We hypothesize that the motivation to provide these critical transfers is a fundamental force that binds together human nuclear and extended families. The ubiquity of three-generational families in human societies may thus be a direct reflection of fundamental evolutionary constraints on an organism's life-history and social organization.

A synthetic biosocial model of fertility transition: testing the relative contribution of embodied capital theory, changing cultural norms, and women's labor force participation.

This article presents a biosocial model of fertility decline, which integrates ecological-economic and informational-cultural hypotheses of fertility transition in a unified theoretical framework. The model is then applied to empirical data collected among 500 women from San Borja, Bolivia, a population undergoing fertility transition. Using a combination of event history analysis, multiple regression, and structural equation modeling, we examine the pathways by which education responds to birth cohort, parental education and network ties, and how age at first birth and total fertility, in turn, respond to birth cohort, social network ties, education, expectations about parental investment, work, and contraceptive use. We find that in addition to secular trends in education, respondent's education is associated with the education of parents, the investment she received from them, and the education of older siblings. Total fertility has dropped over time, partly in response to increased education; moreover, the behavior of other women in a woman's social network predicts both initiation of reproduction and total fertility, while expected parental investment in offspring negatively predicts total fertility. Involvement in paid work that is incompatible with childcare is associated with a later age of first reproduction, but not subsequent fertility. Contraceptive use partially mediates the effect of education and birth cohort on total fertility, but is not a mediator of the effect of social network or expected parental investment on total fertility. Overall, the empirical results provide support for a biosocial model of fertility decline, particularly the embodied capital and cultural pathways.

Sex ratio and parental investment in Trypoxylon (Trypargilum) agamemnon Richards (Hymenoptera, Crabronidae) / Razão sexual e investimento parental em Trypoxylon (Trypargilum) agamemnon Richards (Hymenoptera, Crabronidae)

The life history and sex ratio data of the solitary wasp Trypoxylon agamemnon nesting in trap-nests in southern Brazil was recorded from January 2002 to December 2007. Its sex ratio is strongly female-biased, being bivoltine or multivoltine with until three generations per year. It has two alternative life histories (diapause and direct development) and overlapping generations. In addition to the conflict of interest between the sexes, it is possible that local mate competition occurs between males and may cause a greater investment in the production of females.(AU)

Dados sobre a história de vida e a razão sexual da vespa solitária Trypoxylon agamemnon, que nidifica em ninhos-armadilha, foram registrado no sul do Brasil de janeiro de 2002 a dezembro de 2007. Sua razão sexual tendeu fortemente às fêmeas sendo bivoltina ou multivoltina, com até três gerações ao ano. Ela apresenta dois tipos de historia de vida (com diapausa e com desenvolvimento direto), e sobreposição de gerações. Além do conflito de interesses entre os sexos, é possível que a competição local por parceiros ocorra entre machos provocando um maior investimento na produção de fêmeas.(AU)

Sex ratio and parental investment in Trypoxylon (Trypargilum) agamemnon Richards (Hymenoptera, Crabronidae) / Razão sexual e investimento parental em Trypoxylon (Trypargilum) agamemnon Richards (Hymenoptera, Crabronidae)

The life history and sex ratio data of the solitary wasp Trypoxylon agamemnon nesting in trap-nests in southern Brazil was recorded from January 2002 to December 2007. Its sex ratio is strongly female-biased, being bivoltine or multivoltine with until three generations per year. It has two alternative life histories (diapause and direct development) and overlapping generations. In addition to the conflict of interest between the sexes, it is possible that local mate competition occurs between males and may cause a greater investment in the production of females.

Dados sobre a história de vida e a razão sexual da vespa solitária Trypoxylon agamemnon, que nidifica em ninhos-armadilha, foram registrado no sul do Brasil de janeiro de 2002 a dezembro de 2007. Sua razão sexual tendeu fortemente às fêmeas sendo bivoltina ou multivoltina, com até três gerações ao ano. Ela apresenta dois tipos de historia de vida (com diapausa e com desenvolvimento direto), e sobreposição de gerações. Além do conflito de interesses entre os sexos, é possível que a competição local por parceiros ocorra entre machos provocando um maior investimento na produção de fêmeas.

Dietary inequalities of mother-child pairs in the rural Amazon: evidence of maternal-child buffering?

This paper explores the expected outcome of maternal nutritional "buffering," namely that children's diets will be more adequate than mothers' diets under conditions of food scarcity. Data on Amazonian mothers and their children, household demography and economics and direct, weighed measures of household food availability and dietary intakes of mother-child pairs were collected from 51 households to address the following research questions: (1) is there evidence of food scarcity in this setting?; (2) are there differences in energy and protein adequacy between children and their mothers?; and, (3) which individual and household-level factors are associated with these mother-child differences in energy and protein adequacy? In this context of food scarcity, we found that the majority of children had more adequate energy (p < 0.001) and protein (p < 0.001) intakes than their mothers. Multivariate OLS regression models showed that of the individual-level factors, child age and height-for-age were negatively associated with maternal-child energy and protein inequalities while maternal reproductive status (lactation) was positively associated with energy inequality. While there were no gender differences in dietary adequacy among children, boys had a larger advantage over their mothers in terms of protein adequacy than girls. Household food availability was related to maternal-child energy and protein inequalities in a curvilinear fashion with the lowest inequalities found in households with extremely low food availability and those with adequate food resources. This is the first study to quantify maternal-child dietary inequalities in a setting of food scarcity and demonstrates the importance of the household context and individual characteristics in understanding the degree to which mothers protect their children from resource scarcity.

Diferenças no investimento materno em função de variáveis socioambientais / Differences in maternal investment as a function of socio-environmental variables

A partir da Teoria do Investimento Parental prevê-se diminuição no investimento com a diminuição da relação benefício/custos. Investigou-se a variação no investimento materno em função de variáveis socioambientais que podem apresentar impacto na relação benefício/custo do investimento materno. Os fatores investigados apresentaram, de forma geral, efeito sobre o investimento materno no sentido esperado de acordo com a teoria: quanto maiores os custos representados pela ausência de coabitação com pai, pouca disponibilidade de renda e início precoce da vida reprodutiva, menor o investimento materno. Conclui-se que os fatores socioambientais podem promover ou inibir o investimento materno indicando a importância de políticas públicas no sentido da promoção da estabilidade destes fatores.

The Theory of Parental Investment predicts a decrement in parental investment as the benefit/cost ratio decreases. Differences in maternal investment were investigated in relation to socio-environmental variables that may have an impact on the benefit/cost ratio. The factors investigated showed, in general, effects on maternal investment in the expected direction according to the theory: as costs increased, represented by the absence of cohabitation with the father, diminished income and early reproductive age, lower levels of investment were observed. It is concluded that socio-environmental factors may promote or inhibit maternal investment, indicating the importance of public policies in promoting the stability of these variables.

Diferenças no investimento materno em função de variáveis socioambientais / Differences in maternal investment as a function of socio-environmental variables

A partir da Teoria do Investimento Parental prevê-se diminuição no investimento com a diminuição da relação benefício/custos. Investigou-se a variação no investimento materno em função de variáveis socioambientais que podem apresentar impacto na relação benefício/custo do investimento materno. Os fatores investigados apresentaram, de forma geral, efeito sobre o investimento materno no sentido esperado de acordo com a teoria: quanto maiores os custos representados pela ausência de coabitação com pai, pouca disponibilidade de renda e início precoce da vida reprodutiva, menor o investimento materno. Conclui-se que os fatores socioambientais podem promover ou inibir o investimento materno indicando a importância de políticas públicas no sentido da promoção da estabilidade destes fatores.(AU)

The Theory of Parental Investment predicts a decrement in parental investment as the benefit/cost ratio decreases. Differences in maternal investment were investigated in relation to socio-environmental variables that may have an impact on the benefit/cost ratio. The factors investigated showed, in general, effects on maternal investment in the expected direction according to the theory: as costs increased, represented by the absence of cohabitation with the father, diminished income and early reproductive age, lower levels of investment were observed. It is concluded that socio-environmental factors may promote or inhibit maternal investment, indicating the importance of public policies in promoting the stability of these variables.(AU)

Successful hatching from eggs carried by females and naturally removed from incubant males in Belostoma spp. water bugs (Heteroptera: Belostomatidae)

Within Belostomatinae water bug species (Heteroptera, Belostomatidae) it has been hitherto believed that the completion of embryonic development is successful only if eggs are incubated on male hemelytra. Nevertheless, we found egg successful hatching from a back-brooding Belostoma elegans (Mayr) and B. micantulum (Stål) females, as well as from fertilized eggs kicked off from four back-brooder B. elegans males. One "encumbered" B. elongatum Montandon female was also recorded, but eggs did not hatch after she removed them.

Se considera que el desarrollo embrionario y la emergencia de las ninfas de las especies de Belostomatinae (Heteroptera, Belostomatidae) se cumplen con éxito si los huevos son incubados sobre el espacio dorsal de machos adultos. No obstante, hemos registrado eclosiones exitosas a partir de dos hembras grávidas portando huevos sobre su dorso; una de ellas de la especie Belostoma elegans (Mayr), la otra de B. micantulum (Stål). Se registra la eclosión de huevos, previamente removidos del área de postura por los propios machos incubantes de B. elegans (N=4) y la presencia de una hembra de B. elongatum Montandon, portando huevos sobre sus hemiélitros, los cuales no eclosionaron después de haber sido removidos por la propia hembra.

Beyond the "Cinderella effect" : Life history theory and child maltreatment.

A central thesis of this paper is that understanding the nature of child maltreatment is so complex that no one disciplinary specialty is likely to be sufficient for the task. Although life history theory is the guiding principle for our analysis, we argue that an evolutionary explanation adds precision by incorporating empirical findings originating from the fields of anthropology; clinical, developmental, and social psychology; and sociology. Although evolutionary accounts of child maltreatment have been largely limited to the role of the coefficient of relatedness, the prospective reproductive value of a child, and the residual reproductive potential of parents, a case is made for expanding this basic application. An explanatory model is presented that describes how ecological conditions as well as parental and child traits interact to influence the degree of parental investment. As shown in the model, these various "marker variables" alter parental perceptions of the benefits and costs associated with child care and promote low-investment parenting, which leads to disrupted family management practices and to a downward-spiraling, self-perpetuating system of coercive family interaction, increased parental rejection of the child, and even lower parental investment. Child maltreatment is the ultimate outcome of this downward trajectory of family relations.