Abstract
Size-assortative mating is a nonrandom association of body size between members of mating pairs and is expected to be common in species with mutual preferences for body size. In this study, we investigated whether there is direct evidence for size-assortative mating in two species of pipefishes, Syngnathus floridae and S. typhle, that share the characteristics of male pregnancy, sex-role reversal, and a polygynandrous mating system. We take advantage of microsatellite-based “genetic-capture” techniques to match wild-caught females with female genotypes reconstructed from broods of pregnant males and use these data to explore patterns of size-assortative mating in these species. We also develop a simulation model to explore how positive, negative, and antagonistic preferences of each sex for body size affect size-assortative mating. Contrary to expectations, we were unable to find any evidence of size-assortative mating in either species at different geographic locations or at different sampling times. Furthermore, two traits that potentially confer a fitness advantage in terms of reproductive success, female mating order and number of eggs transferred per female, do not affect pairing patterns in the wild. Results from model simulations demonstrate that strong mating preferences are unlikely to explain the observed patterns of mating in the studied populations. Our study shows that individual mating preferences, as ascertained by laboratory-based mating trials, can be decoupled from realized patterns of mating in the wild, and therefore, field studies are also necessary to determine actual patterns of mate choice in nature. We conclude that this disconnect between preferences and assortative mating is likely due to ecological constraints and multiple mating that may limit mate choice in natural populations.
Highlights
Assortative mating is nonrandom mating based on similarity (Burley 1983; Jiang et al 2013) and may arise via sexual selection when either one or both partners evolve preferences for mates with trait values similar to their own (Crespi 1989; Arnqvist et al 1996; H€ardling and Kokko 2005)
Ecology and Evolution published by John Wiley & Sons Ltd
We found no evidence of size-assortative mating in S. floridae and S. typhle in our field collections, and no evidence that either order of mating or number of eggs transferred by females affected pairing patterns in the wild
Summary
Assortative mating is nonrandom mating based on similarity (Burley 1983; Jiang et al 2013) and may arise via sexual selection when either one or both partners evolve preferences for mates with trait values similar to their own (Crespi 1989; Arnqvist et al 1996; H€ardling and Kokko 2005). Organisms use a wide range of phenotypic traits for assortative mating, including body size (Arnqvist et al 1996), ornamentation (Andersson et al 1998; Hancox et al 2010), and major histocompatibility complex genotype (Milinski 2006). Such nonrandom patterns of mating should be especially common in natural populations when traits used in mate choice confer a fitness advantage or reflect variation in genotypic quality (Arnqvist 2011).
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