Abstract
AbstractTheory predicts that males and females should often join the mating pool at different times (sexual dimorphism in timing of emergence [SDT]) as the degree of SDT affects female mating success. We utilize an analytical model to explore (1) how important SDT is for female mating success, (2) how mating success might change if either sex's mortality (abruptly) increases, and (3) to what degree evolutionary responses in SDT may be able to mitigate the consequences of such mortality increase. Increasing male pre‐mating mortality has a non‐linear effect on the fraction of females mated: The effect is initially weak, but at some critical level a further increase in male mortality has a stronger effect than a similar increase in female mortality. Such a change is expected to impose selection for reduced SDT. Increasing mortality during the mating season has always a stronger effect on female mating success if the mortality affects the sex that emerges first. This bias results from the fact that enhancing mortality of the earlier emerging sex reduces female–male encounter rates. However, an evolutionary response in SDT may effectively mitigate such consequences. Further, if considered independently for females and males, the predicted evolutionary response in SDT could be quite dissimilar. The difference between female and male evolutionary response in SDT leads to marked differences in the fraction of fertilized females under certain conditions. Our model may provide general guidelines for improving harvesting of populations, conservation management of rare species under altered environmental conditions, or maintaining long‐term efficiency of pest‐control measures.
Highlights
A shared attribute of changing environmental conditions—often a consequence of human interference—is the intended or unintended impact on population dynamics (Shea 1998)
Theory predicts that males and females should often join the mating pool at different times as the degree of sexual dimorphism in timing of emergence” (SDT) affects female mating success
We utilize an analytical model to explore (1) how important SDT is for female mating success, (2) how mating success might change if either sex’s mortality increases, and (3) to what degree evolutionary responses in SDT may be able to mitigate the consequences of such mortality increase
Summary
A shared attribute of (rapidly) changing environmental conditions—often a consequence of human interference—is the intended or unintended impact on population dynamics (Shea 1998). For semelparous (reproduction once in a lifetime) species, SDT is known to have an effect on the fraction of females that successfully mate (Wiklund and Fagerstro€m 1977, Zonneveld and Metz 1991, Morbey 2002, Kokko et al 2006, Larsen et al 2012, Degen et al 2015), and that SDT can increase the fraction of females that mate This funding is of general relevance as most annual animals, many insects, some Coleoidea, and a few vertebrates such as fish (e.g., pacific salmon, freshwater eels, and capelin, which are all examples of important commercial target species) and mammals (only in a few didelphid and dasyurid) are semelparous species (Cole 1954, Braithwaite and Lee 1979, Cortez et al 1995, Murphy and Rodhouse 1999, Gjøsæter et al 2002). Matters are further complicated by the fact that the evolutionary perspectives of females and males in this matter are similar but not necessarily identical (Zonneveld and Metz 1991, Degen et al 2015); the level of SDT is an evolutionarily stable strategy (ESS) (1) for females if it minimizes the risk of mating failure—waiting cost hypothesis —and (2) for males if an invasive male with a different mean time of emergence or arrival achieves less access to mating partners—mate opportunity hypothesis (Zonneveld and Metz 1991, Morbey and Ydenberg 2001)
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