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Social environment profoundly influences the fitness of animals, affecting their probability of survival to adulthood, longevity, and reproductive output. The social conditions experienced by parents at the time of reproduction can predict the social environments that offspring will face. Despite clear challenges in predicting future environmental conditions, adaptive maternal effects provide a mechanism of passing environmental information from parent to offspring and are now considered pervasive in natural systems. Maternal effects have been widely studied in vertebrates, especially in the context of social environment, and are often mediated by steroid hormone (SH) deposition to eggs. In insects, although many species dramatically alter phenotype and life‐history traits in response to social density, the mechanisms of these alterations, and the role of hormone deposition by insect mothers into their eggs, remains unknown. In the experiments described here, we assess the effects of social environment on maternal hormone deposition to eggs in house crickets (Acheta domesticus). Specifically, we tested the hypotheses that variable deposition of ecdysteroid hormones (ESH) to eggs is affected by both maternal (a) social density and (b) social composition. We found that while maternal hormone deposition to eggs does not respond to social composition (sex ratio), it does reflect social density; females provision their eggs with higher ESH doses under low‐density conditions. This finding is consistent with the interpretation that variable ESH provisioning is an adaptive maternal response to social environment and congruent with similar patterns of variable maternal provisioning across the tree of life. Moreover, our results confirm that maternal hormone provisioning may mediate delayed density dependence by introducing a time lag in the response of offspring phenotype to population size. Here we show that female crickets respond to social density in provisioning their eggs with hormones that govern hatchling growth and development. This is the first evidence that we are aware of for hormone provisioning as a mechanism for achieving delayed density dependence in a population.

Children and mothers' cortisol production in response to family psychosocial conditions, including parenting demands, family resource availability and parental conflict, has been extensively studied in the United States and Europe. Less is known about how such family dynamics relate to family members' cortisol in societies with a strong cultural emphasis on cooperative caregiving. We studied a cumulative indicator of cortisol production, measured from fingernails, among BaYaka forager children (77 samples, n = 48 individuals) and their parents (78 samples, n = 49) in the Congo Basin. Men ranked one another according to locally valued roles for fathers, including providing resources for the family, sharing resources in the community and engaging in less marital conflict. Children had higher cortisol if their parents were ranked as having greater parental conflict, and their fathers were seen as less effective providers and less generous sharers of resources in the community. Children with lower triceps skinfold thickness (an indicator of energetic condition) also had higher cortisol. Parental cortisol was not significantly correlated to men's fathering rankings, including parental conflict. Our results indicate that even in a society in which caregiving is highly cooperative, children's cortisol production was nonetheless correlated to parental conflict as well as variation in locally defined fathering quality. This article is part of the theme issue 'Multidisciplinary perspectives on social support and maternal–child health'.

In birds, reproductive success is mainly a function of skill or environmental conditions, but it can also be linked to hormone concentrations due to their effect on behavior and individual decisions made during reproduction. For example, a high prolactin concentration is required to express parental behaviors such as incubation or guarding and feeding the young. Corticosterone level, on the other hand, is related to energy allocation or stress and foraging or provisioning effort. In this study, we measured individual baseline prolactin and corticosterone between 2006 and 2012 in breeding common terns (Sterna hirundo) using blood-sucking bugs. Reproductive parameters as well as prey abundance on a local and a wider scale were also determined during this period. Baseline prolactin and corticosterone varied significantly between years, as did breeding success. At the individual level, prolactin was positively and corticosterone was negatively linked to herring and sprat abundance. At the population level, we also found a negative link between corticosterone and prey abundance, probably reflecting overall foraging conditions. High prolactin during incubation was mainly predictive of increased hatching success, potentially by supporting more constant incubation and nest-guarding behavior. It was also positively linked to a lesser extent with fledging success, which could indicate a high feeding rate of young. Corticosterone concentration was positively related to high breeding success, which may be due to increased foraging activity and feeding of young. In general, our study shows that baseline prolactin and corticosterone levels during incubation can predict reproductive success, despite the presence of an interval between sampling and hatching or fledging of young.

In cooperative breeders, aggression from dominant breeders directed at subordinates may raise subordinate stress hormone (glucocorticoid) concentrations. This may benefit dominants by suppressing subordinate reproduction but it is uncertain whether aggression from dominants can elevate subordinate cooperative behaviour, or how resulting changes in subordinate glucocorticoid concentrations affect their cooperative behaviour. We show here that the effects of manipulating glucocorticoid concentrations in wild meerkats (Suricata suricatta) on cooperative behaviour varied between cooperative activities as well as between the sexes. Subordinates of both sexes treated with a glucocorticoid receptor antagonist (mifepristone) exhibited significantly more pup protection behaviour (babysitting) compared to those treated with glucocorticoids (cortisol) or controls. Females treated with mifepristone had a higher probability of exhibiting pup food provisioning (pup-feeding) compared to those treated with cortisol. In males, there were no treatment effects on the probability of pup-feeding, but those treated with cortisol gave a higher proportion of the food they found to pups than those treated with mifepristone. Using 19 years of behavioural data, we also show that dominant females did not increase the frequency with which they directed aggression at subordinates at times when the need for assistance was highest. Our results suggest that it is unlikely that dominant females manipulate the cooperative behaviour of subordinates through the effects of aggression on their glucocorticoid levels and that the function of aggression directed at subordinates is probably to reduce the probability they will breed.

The emergence of queens and workers from solitary antecedents mark a major evolutionary transition in the history of life. The solitary progressive provisioning wasp Synagris cornuta, a member of the subfamily Eumeninae (basal to eusocial vespid wasps), alternates between behavioral states characterized as queenlike and worker-like. Akin to a queen in eusocial wasps, a S. cornuta female initiates construction of a cell into which she oviposits and then, similar to a worker, cares for the brood as it develops. The ovarian groundplan (OGP) hypothesis for caste origins predicts that these behavioral states are associated with cyclical changes in ovarian status, where females performing queenlike tasks have eggs and those performing worker-like tasks possess only small oocytes. Our findings show strong support for the OGP hypothesis: the ovaries of S. cornuta females undergo differential oogenesis depending on the behavioral phase: the largest oocyte in the ovaries of females building a cell progresses faster compared to that of females attending brood. Yet contrary to the OGP hypothesis, neither juvenile hormone nor ecdysteroids is associated with the reproductive cycle. Finally, the cuticular hydrocarbon profile showed no link with ovarian status, suggesting that fertility signals evolved subsequent to the emergence of group living.

Showing traces of eusocial behavior, Zethus miniatus is an emblematic member of the primarily solitary subfamily Eumeninae. The females of this casteless species share a common nest, but each one provisions her own brood in a progressive manner. They express dominance when reproductive (queen-like behavior) and occasionally perform tasks that benefit others when provisioning the brood (worker-like behavior). Hence, the biology of this species has long been considered as harboring traits that could mark the transition from a solitary to social lifestyle. Here, we present for the first time measurements of the juvenile hormone (JH) titer in combination with behavioral observations and data on the females’ ovarian status. Aggressive reproductives seeking to reuse or usurp brood cells were found to possess longer oocytes than provisioners of young larvae. Brood killings by reproductive cell-seekers and JH titers were both higher when the female/open-brood-cell ratio of the nest was high—an indicator of strong competition. Females lacking brood, such as those that are victims of cell usurpation attempts by other females, were found to perform tasks relating to nest defense, nest maintenance, and/or adoption of orphaned brood. Hence, we hypothesize that competition for brood cells may have shaped the reproductive physiology of this group-living species of social wasps, and that JH is critical for this competitive behavior. Furthermore, we hypothesize that JH-mediated dominance interactions in casteless groups may have preceded and contributed to the origin of reproductive castes.Significance statementHow, mechanistically, did caste phenotypes (a polyphenism with egg-layers and non-egg-laying helper females within groups) originate from solitary ancestors? Key to addressing this question can be casteless, group-living wasp species, where the females progressively feed their brood. The eumenine wasp Zethus miniatus has behavioral traits intermediate between solitary and caste-possessing wasps, and hence, has gained a model status for this transition. This is the first study of such a wasp in nature that combines data on behavior, ovarian activity, and juvenile hormone (JH) levels. The results show that the ovarian status of a Z. miniatus female is a good predictor of her behavior, and that JH titers were highest when competition for available brood cells was intense. This suggests that JH may have become linked to the origin of worker caste behaviors through its involvement in competitive interactions among nestmates.

Summary Glucocorticoid steroid hormones play a central role in regulating the metabolic state of animals, especially when they cope with unanticipated stressors in their environment. The cort‐adaptation hypothesis predicts that baseline concentrations of glucocorticoids are adjusted upward to match energetic needs and promote fitness when individuals are faced with physiological challenges, including those associated with reproduction. We tested the cort‐adaptation hypothesis in the violet‐green swallow (Tachycineta thalassina) by experimentally increasing flight costs during the offspring rearing period. Individual females were assigned to one of three treatments: light feather clipping (removal of four wing feathers), heavy feather clipping (removal of eight wing feathers) or a sham‐clip control. We measured baseline corticosterone and body mass immediately prior to implementing treatments during the offspring rearing period and then 10 days after initial manipulations took place. We also quantified risk‐taking behaviour, offspring feeding rate and the number of offspring fledged. Finally, we examined how treatments influenced offspring phenotype via measurements of nestling body mass and baseline corticosterone, as both measures have been associated with post‐fledging survival. We found that handicapped females significantly increased baseline corticosterone between the two sampling periods, with the magnitude of change in the light clipping and heavy clipping treatments 2·5× and 6·1× greater than controls, respectively. All individuals lost mass between the two sampling periods, but the degree of loss was greater for females in both clipping treatments relative to unmanipulated controls. In contrast, we found no evidence of treatment differences in female risk‐taking, offspring provisioning or in the number of offspring fledged. Offspring raised by females in both handicapped treatments did have significantly elevated baseline corticosterone relative to those in control broods, but we detected no treatment differences in offspring body mass. Our study found that handicapped females increased circulating glucocorticoids and were able to maintain critical parental care behaviours and raise a similar number of offspring as unmanipulated controls. Thus, increases in baseline cort of handicapped females appeared to have allowed them to maintain fitness despite increased physiological challenges, providing support for the cort‐adaptation hypothesis. A Lay Summary is available for this article. Lay Summary

This review aims to discuss the management approaches of zinc (Zn) fertilization and breeding efforts for quality maize production in provisioning a healthy human diet. Biofortification of Zn to a high-yielding maize variety with increased Zn content in maize grain is of great importance to the health of those feeding on these staples. Literature review was performed on the Zn fertilization in the maize plant grown in Zn-deficient soils and the breeding maize varieties with improved attributes for increasing Zn content and availability to humans. Factors regulating the Zn availability and transport from soil to plant and food to humans were identified and discussed. The health issues induced by Zn deficiency affect a large global population, particularly those relying on a maize diet. The agronomic approach is a feasible method in combatting Zn deficiency in soil. Given the wide choices available for crop fertilization, the type of fertilizers and the timing of application to specific maizes are important for a maximum yield. Clinical studies have so far indicated that genetically biofortified maize increased Zn absorption in human bodies. Both agronomic and plant breeding approaches to biofortification in maize are promising in providing adequate Zn intake for optimum body functioning.

Resource allocation and hormone provisioning during vitellogenesis has been documented for many oviparous reptiles, while viviparous species remain relatively understudied in the context of yolk composition. Squamates that have evolved viviparity have retained varying degrees of embryonic nourishment via the yolk (lecithotrophy). Very little is known about the timing of embryonic hormone production, and the degree of maternal hormone provisioning in viviparous reptiles. Viviparous species may, in principle, receive hormone exposure through some or all of three routes, viz., maternal provisioning in the yolk, transfer from the maternal circulation, and/or hormone production by the developing embryonic endocrine tissues. In toad-eating snakes, adrenal hormones may provide protection from toad toxins, supplementing genetic resistance. Additionally, one species of oviparous snake has been shown to provision its embryos with defensive toxins from toads. We hypothesized that embryonic hormone levels would increase during development and that yolk hormone levels would correspondingly decrease. We also predicted that the embryos from females administered toad toxin would have higher levels of corticosterone (CORT) in response to exposure to a toad toxin. We measured levels of CORT in the embryos and corresponding yolks of a viviparous and genetically toxin-resistant natricine, the Western Terrestrial Garter Snake (Thamnophis elegans), beginning at Zehr Stage 26. We found that embryos and their corresponding yolks had relatively higher levels of CORT in later stages. There were no measurable differences in CORT between embryos of the same stage obtained from dams treated with marinobufagenin (MBG) or no treatment. Given that yolk and embryonic CORT increase throughout the course of development, a trade-off between early maternal provisioning and the onset of adrenal function is not apparent. However, increase in adrenal production of CORT over the course of development remains relevant to both stress physiology and physiological toxin resistance.