Abstract
Sex differences in parental care are thought to arise from differential selection on the sexes. Sexual dimorphism, including sexual size dimorphism (SSD), is often used as a proxy for sexual selection on males. Some studies have found an association between male-biased SSD (i.e., males larger than females) and the loss of paternal care. While the relationship between sexual selection on males and parental care evolution has been studied extensively, the relationship between female-biased SSD (i.e., females larger than males) and the evolution of parental care has received very little attention. Thus, we have little knowledge of whether female-biased SSD coevolves with parental care. In species displaying female-biased SSD, we might expect dimorphism to be associated with the evolution of paternal care or perhaps the loss of maternal care. Here, drawing on data for 99 extant frog species, we use comparative methods to evaluate how parental care and female-biased SSD have evolved over time. Generally, we find no significant correlation between the evolution of parental care and female-biased SSD in frogs. This suggests that differential selection on body size between the sexes is unlikely to have driven the evolution of parental care in these clades and questions whether we should expect sexual dimorphism to exhibit a general relationship with the evolution of sex differences in parental care.
Highlights
Female parental care is generally more common than male care (Darwin 1874; Bateman 1948; Trivers 1972; Clutton-Brock 1991; Queller 1997; Kokko and Jennions 2003, 2008)
Ecology and Evolution published by John Wiley & Sons Ltd
To determine whether or not there is a difference in body size and female-biased sexual size dimorphism (SSD) between species that provide parental care and those that do not, we ran a phylogenetic generalized least square model (PGLS) on the presence or absence of parental care using a phylogeny containing approximately 40 species that do not provide parental care and 32 that do
Summary
Female parental care is generally more common than male care (Darwin 1874; Bateman 1948; Trivers 1972; Clutton-Brock 1991; Queller 1997; Kokko and Jennions 2003, 2008). Because females typically invest more per gamete than do males, female fitness is argued to be limited by the number of gametes produced while male fitness is limited by access to females (Bateman 1948). In species where females are larger than males, it is often assumed that fecundity selection (i.e., natural selection acting in favor of larger clutch or egg sizes) on females is stronger than sexual selection on male size (Shine 1979; Andersson 1994). In species where males are larger than females, it is typically assumed that sexual selection favoring larger males is stronger than selection on female a 2014 The Authors.
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