Male age mediates reproductive investment and response to paternity assurance

Abstract

Theory predicts that male response to reduced paternity will depend on male state and interactions between the sexes. If there is little chance of reproducing again, then males should invest heavily in current offspring, regardless of their share in paternity. We tested this by manipulating male age and paternity assurance in the burying beetle Nicrophorus vespilloides. We found older males invested more in both mating effort and parental effort than younger males. Furthermore, male age, a component of male state, mediated male response to perceived paternity. Older males provided more prenatal care, whereas younger males provided less prenatal care, when perceived paternity was low. Adjustments in male care, however, did not influence selection acting indirectly on parents, through offspring performance. This is because females adjusted their care in response to the age of their partner, providing less care when paired with older males than younger males. As a result offspring, performance did not differ between treatments. Our study shows, for the first time, that a male state variable is an important modifier of paternity–parental care trade-offs and highlights the importance of social interactions between males and females during care in determining male response to perceived paternity.

Age‐dependent variation in the terminal investment threshold in male crickets

“…Specifically, old males produced significantly fewer offspring than young males in control treatments, but elevated their reproductive success to similar levels as young males after treatment (young males did not alter their reproductive effort across treatments). In addition to age (Sanz et al 2001;Copeland and Fedorka 2012;González-Tokman et al 2013), other studies provide support for context-dependent terminal investment through significant interactions between treatment levels of a terminal investment trigger (e.g., immune stimulation) with a number of other factors, including genotype (Chadwick and (Krams et al 2015), and paternity assurance (Benowitz et al 2013). In our study, old males show terminal investment, but young males do not.…”

Biparental care is predominant and beneficial to parents in the burying beetleNicrophorus orbicollis(Coleoptera: Silphidae)

“…At dispersal, larvae were counted and weighed individually to 1 mg. At each check, we recorded the location of the parent. Cessation of parental care by a beetle is characterized by its continuous absence at a location away from the carcass, and is a readily recognizable behaviour regardless of the type of observation chamber used (Benowitz et al, 2013(Benowitz et al, , 2015Hopwood et al, 2015;Parker et al, 2015). As in these previous studies, when a beetle was observed to be away from the carcass for three consecutive observations, and thus persistently absent over a 24-h period, we defined it as abandoned.…”

Variation in parent-offspring kinship in socially monogamous systems with extra-pair reproduction and inbreeding

“…Our analyses emphasize that the differences in total allelic metrics between current and future broods are compound quantities, which depend not only on the relative degrees of female extra-pair reproduction and consequent paternity loss, but also on brood sizes and on the kinship between the male and his socially-paired females and her extra-pair males. Four variables consequently affect the relative allelic metrics of males' current versus future broods, even without considering the male's probability of surviving to future reproductive events, or any other dimension of variation in offspring value stemming from differential life-history trade-offs or environmental or maternal genetic effects (e.g., Westneat and Sherman 1993;Eliassen and Kokko 2008;Benowitz et al 2013). Although a male's own f also influences allelic metrics, f is a fixed property of an individual male and therefore cannot contribute to within-male variation in brood values.…”

“…Meanwhile, a male's kinship with his socially-paired female's current versus future extra-pair males will depend on the female's extra-pair reproductive strategy and on the availability of male relatives of the focal male, which will in turn depend on the male's previous within-pair and extra-pair reproductive success and that of his relatives (e.g., Reid et al 2015b). It may therefore be difficult for individual males to "predict" the total allelic value or carrier probability of future versus current broods and modulate paternal care accordingly, unless key causal variables vary systematically with predictable aspects of male state such as age (e.g., Benowitz et al 2013). Future analyses should quantify the pattern and magnitude of variation in total allelic metrics across consecutive broods reared by individual males in song sparrows and other systems.…”

“…Furthermore, paternal care might be reduced through behavioral plasticity within or among males when individuals expect to gain higher reproductive value from future breeding attempts than from investing in a current brood in which paternity has been lost (Westneat and Sherman 1993;Houston and McNamara 2002;Sheldon 2002;Alonzo and Klug 2012). The form and magnitude of such plasticity is predicted to be complex, and to depend on male assessment of paternity and on multiple dimensions of within-and among-individual life-history variation that shape current versus future reproductive value (Westneat and Sherman 1993;Kokko 1999;Houston and McNamara 2002;Holen and Johnstone 2007;Eliassen and Kokko 2008;Alonzo 2010;Benowitz et al 2013). However, any reduction in paternal care that occurs following any degree of female extra-pair reproduction, and that reduces the fitness of the female's offspring, will impose negative selection against extra-pair reproduction (Arnqvist and Kirkpatrick 2005).…”