Invasive predators induce plastic and adaptive responses during embryo development in a threatened frog

Invasive predators can strongly affect native populations. If alien predator pressure is strong enough, it can induce anti-predator responses, including phenotypic plasticity of exposed individuals and local adaptations of impacted populations. Furthermore, maternal investment is an additional pathway that could provide resources and improve performance in the presence of alien predators. We investigated the potential responses to an alien predator crayfish (Procambarus clarkii) in a threatened frog (Rana latastei) by combining field observations with laboratory measurements of embryo development rate, to assess the importance of parental investment, origin and exposure to the crayfish cues. We detected a strong variation in parental investment amongst frog populations, but this variation was not related to the invasion status of the site of origin, suggesting that mothers did not modulate parental investment in relation to the presence of alien predators. However, cues of the invasive crayfish elicited plastic responses in clutches and tadpoles development: embryos developed faster when exposed to the predator. Furthermore, embryos from invaded sites reached Gosner’s development stage 25 faster than those from non-invaded sites. This ontogenetic shift can be interpreted as a local adaptation to the alien predator and suggests that frogs are able to recognise the predatory risk. If these plastic responses and local adaptation are effective escape strategies against the invasive predator, they may improve the persistence of native frog populations.

Facial threat affects trust more strongly than facial attractiveness in women than it does in men

Trust is essential in initiating social relationships. Due to the differential evolution of sex hormones as well as the fitness burdens of producing offspring, evaluations of a potential mating partner’s trustworthiness likely differ across sexes. Here, we explore unknown sex-specific effects of facial attractiveness and threat on trusting other-sex individuals. Ninety-three participants (singles; 46 women) attracted by the other sex performed an incentivized trust game. They had to decide whether to trust individuals of the other sex represented by a priori-created face stimuli gradually varying in the intensities of both attractiveness and threat. Male and female participants trusted attractive and unthreatening-looking individuals more often. However, whereas male participants’ trust behavior was affected equally by attractiveness and threat, female participants’ trust behavior was more strongly affected by threat than by attractiveness. This indicates that a partner’s high facial attractiveness might compensate for high facial threat in male but not female participants. Our findings suggest that men and women prioritize attractiveness and threat differentially, with women paying relatively more attention to threat cues inversely signaling parental investment than to attractiveness cues signaling reproductive fitness. This difference might be attributable to an evolutionary, biologically sex-specific decision regarding parental investment and reproduction behavior.

Inferring Preferred Mating Strategies Through Body Fat and Sex-Typical Body Features

Identifying reproductive opportunities and intrasexual rivals has necessitated the evolution of sensitivity to features diagnostic of mate value. In determining the presence of good genes through physical features, individuals may additionally infer targets’ short- and long-term mating motives. This study tested how individuals perceive men and women’s mating intentions through physical features conducive to reproductive goals. Participants evaluated preferred mating strategies of male and female targets varying in size of sex-typical features (i.e., muscles or breasts) and adiposity. Greater adiposity connoted long-term mating interest. Large muscles and breasts connoted short-term mating interests. We frame results from an affordance management framework with respect to inferences regarding parental investment and intrasexual competition.

Parental Care System and Brood Size Drive Sex Difference in Reproductive Allocation: An Experimental Study on Burying Beetles

Life-history theory predicts that increased resource allocation in current reproduction comes at the cost of survival and future reproductive fitness. In taxa with biparental care, each parent can adjust investment on current reproduction according to changes in their partner’s effort, but these adjustments may be different for males and females as they may have different reproductive strategies. Numerous theoretical and empirical studies have proposed the mechanism underlying such adjustments. In addition, the value of the brood or litter (brood size) has also been suggested to affect the amount of care through manipulation of brood size. While the two conditions have been studied independently, the impact of their interplay on potential sex-dependent future reproductive performance remains largely unknown. In this study, we simultaneously manipulated both care system (removal of either parent vs. no removal) and brood size in a burying beetle (Nicrophorus vespilloides) to understand their joint effect on reproductive allocation and trade-off between current and future reproduction. Our results show that males compensated for mate loss by significantly increasing the level of care regardless of brood size, while females exhibited such compensation only for small brood size. Additionally, with an increase in allocation to current reproduction, males showed decreased parental investment during the subsequent breeding event as a pair. These findings imply a dual influence of parental care system and brood size on allocation in current reproduction. Moreover, the impact of such adjustments on sex-dependent differences in future reproduction (parental care, larvae number, and average larval mass at dispersal) is also demonstrated. Our findings enhance the understanding of sex roles in parental investment and highlight their importance as drivers of reproductive allocation.

Number and Size of Offspring

Offspring number and size are two of the most variable life-history traits. Among species, much of this variability can be attributed to genetic, developmental, physiological, or structural constraints. Some trait combinations are not possible because of differences associated with a species’ evolutionary history. Substantial variation in propagule number and size can exist among populations of the same species, generating questions concerning the adaptive significance of this variability. The most influential models are those attributed to Lack on clutch size and to Smith and Fretwell on offspring size. Fundamental to both sets of models is a trade-off between offspring number and parental investment per offspring. When offspring survival or fitness continuously varies with offspring size, the fitness of the parent depends on both offspring size and the number of offspring of that size that the parent can produce. If offspring survival is independent of offspring size, parental fitness is maximized when individuals maximize the production of minimally sized propagules.

Evolutionary Perspectives on Maternal Parenting

This chapter focuses on maternal care, including the specialized psychological mechanisms designed to shape maternal solicitude and the various factors to which these mechanisms are sensitive. It identifies factors that influence levels of maternal parental investment. Maternal factors that lead to increased investment include the amount of resources available, potential for future mating opportunities and maternal age, and number of offspring. Child factors that lead to greater investment include reproductive value, age of the child, sex, offspring need, and relatedness to the mother. Although there has been an abundance of research on maternal parental investment, most of the studies have focused on individual factors that influence parental investment levels with only a few investigating interactive models. Therefore, more research investigating interactive models is necessary to better understand under which circumstances mothers would be more or less likely to invest in their offspring.