Reproductive skipping as an optimal life history strategy in the southern elephant seal, Mirounga leonina.

Blaine D Griffen

doi:10.1002/ece3.4408

Abstract

Intermittent breeding by which organisms skip some current reproductive opportunities in order to enhance future reproductive success is a common life history trade‐off among long‐lived, iteroparous species. The southern elephant seal Mirounga leonina engages in intermediate breeding when body condition is low. While it is anticipated that this strategy may increase the lifetime reproductive output of this species, the conditions under which reproductive skipping are predicted to occur are not clear. Here I develop a dynamic state variable model based on published data that examines when southern elephant seals are predicted to optimally skip reproduction in order to maximize lifetime reproductive output as a function of current body mass, maternal age, and survivorship. I demonstrate that the optimal reproductive strategy for this species can include reproductive skipping, and that the conditions where this is optimal depend on patterns of mass‐dependent adult female survival. I further show that intermittent breeding can increase lifetime reproductive output, and that the magnitude of this benefit increases with the ability of individual animals to replenish depleted body mass through foraging. Finally, I show that when the environment is variable and foraging is reduced in bad years, the benefit of adopting an optimal strategy that includes reproductive skipping increases asymptotically with the frequency of bad years. These results highlight the importance of characterizing the pattern of adult survival in this species, as well as the need to identify other factors that may influence the prevalence and benefits of reproductive skipping.

Highlights

Reproduction is a central process for all organisms, and there is strong evolutionary pressure to optimize reproductive performance (Smith, 1978; Tuomi, Hakala, & Haukioja, 1983)
Does the optimal strategy for elephant seal lifetime reproductive output include instances of reproductive skipping? Second, could mass-dependent adult female mortality risk influence the combination of maternal age and body mass where reproductive skipping may be optimal? Third, how might lifetime reproductive output be influenced by adopting a strategy that includes reproductive skipping as opposed to reproducing every year? Fourth, do the consequences of reproductive skipping on lifetime reproductive output for seals depend on their persistent individual quality or body condition? Fifth, do the consequences of reproductive skipping on lifetime reproductive output for seals depend on annual variation in environmental quality and the frequency of bad years?
I used dynamic state variable modeling to examine the conditions that are predicted to lead to reproductive skipping in southern elephant seals (Clark & Mangel, 2000; Houston & McNamara, 1999; Mangel & Clark, 1988)

Summary

| INTRODUCTION

Reproduction is a central process for all organisms, and there is strong evolutionary pressure to optimize reproductive performance (Smith, 1978; Tuomi, Hakala, & Haukioja, 1983). Previous work demonstrates the link between intermittent breeding and several ecological and individual factors, including individual age (in fur seals: Beauplet, Barbraud, Dabin, Küssener, & Guinet, 2006; ibex: Rughetti, Demetteis, Meneguz, & Festa- Bianchet, 2014; and seabirds: Zhang, Rebke, Becker, & Bauwuis, 2015), body condition (in birds: Calladine & Harris, 1997; Chastel, Weimerskirch, & Jouventin, 1995), previous reproductive experience (in birds: Desprez, Pradel, Cam, Monnat, & Gimenez, 2011; Pradel, Choquet, & Béchet, 2012), population density (in birds: Coulson, Duncan, & Thomas, 1982; and mountain goats: Hamel, Côté, & Festa-Bianchet, 2010), and environmental conditions (in fish: Jørgensen & Fiksen, 2006). Does the optimal strategy for elephant seal lifetime reproductive output include instances of reproductive skipping? Second, could mass-dependent adult female mortality risk influence the combination of maternal age and body mass where reproductive skipping may be optimal? Third, how might lifetime reproductive output be influenced by adopting a strategy that includes reproductive skipping as opposed to reproducing every year? Fourth, do the consequences of reproductive skipping on lifetime reproductive output for seals depend on their persistent individual quality or body condition (i.e., the “heterogeneity class” from Desprez et al, 2017)? Fifth, do the consequences of reproductive skipping on lifetime reproductive output for seals depend on annual variation in environmental quality and the frequency of bad years?

| METHODS

Findings

| DISCUSSION