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assortative mating; body size; mark–recapture; mate choice; sexual selection; Syngnathidae
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.
