Bigger Is Not Always Better: Females Prefer Males of Mean Body Size in Philautus odontotarsus

Abstract

Most species are believed to evolve larger body sizes over evolutionary time. Previous studies have suggested that sexual selection, through male-male competition and female choice, favors larger males. However, there is little evidence of selection against large size. The female serrate-legged small treefrogs (Philautus odontotarsus) must carry passive males from leks to breeding grounds over relatively long distances after amplexus to find a suitable place to lay eggs. The costs of large male size may therefore decrease mating success due to reduced agility and/or higher energy requirements. Thus, we hypothesized that selection would not favor larger males in P. odontotarsus. Females can assess male body size on the basis of the dominant frequency of male calls in frogs. To assess female P. odontotarsus preferences for a potential mate’s body size, male calls of high, average and low dominant frequency were played back to the females in phonotaxis experiments. Results showed that most females prefer the advertisement call with average dominant frequency. In addition, we compared the body mass distribution of amplectant males with that of single males in nature. The body masses of amplectant males are more narrowly distributed in the intermediate range than that of single males. The phonotaxis results and the data of actual female preferences in the field show that females strongly prefer potential mates of mean body sizes, consistent with the view that, in this species at least, larger males are not always perceived as better by females. In the present study, P. odontotarsus provides an example of an amphibian species in which large size does not have an advantage in mating success for males. Instead, our results provide evidences that stabilizing selection favors the optimal intermediate size of males.

Multivariate phenotypic selection on a complex sexual signal

“…Across anurans, it is often assumed that females have strong preferences for low‐frequency calls, creating a mating advantage for larger males, but this general view is not well supported by the present study and data from other frogs (e.g., Zhu et al. ; reviewed in Gerhardt and Schwartz ). Indeed, gray treefrogs represent an important and cautionary counterexample to the notion that, in anurans broadly, females prefer to mate with larger males that produce low‐frequency calls.…”

“…Historically, the preferences of female frogs for calls with lower frequencies have been of interest from the perspective of sexual selection favoring larger (and hence older) males (Ryan 1980;Morris 1989;Morris and Yoon 1989). Across anurans, it is often assumed that females have strong preferences for low-frequency calls, creating a mating advantage for larger males, but this general view is not well supported by the present study and data from other frogs (e.g., Zhu et al 2016;reviewed in Gerhardt and Schwartz 2001). Indeed, gray treefrogs represent an important and cautionary counterexample to the notion that, in anurans broadly, females prefer to mate with larger males that produce low-frequency calls.…”

Male-male competition and female choice are differentially affected by male call acoustics in the serrate-legged small treefrog,Kurixalus odontotarsus

“…If the female still failed to approach a speaker, no choice was recorded. We observed the behavior of the females on a monitor using a wide-angle lens video system with an infrared light source (also see Zhu et al, 2016b ). The frogs were returned that night to their original habitat after the tests were completed.…”

“…In some anuran species, males produce a single type of sexual signal, while in others highly complex and graded sexual signals have evolved which enable males to attract females and compete with rivals ( Narins & Capranica, 1978 ; Greer & Wells, 1980 ; Rand & Ryan, 1981 ; Schwartz & Wells, 1984 ; Schwartz & Wells, 1985 ; Berglund, Bisazza & Pilastro, 1996 ; Zhu et al, 2016a ; Zhu et al, 2016b ). For example, males in two Panamanian species, Dendropsophus ebraccatus and D. microcephalus , which exhibit graded variation in both advertisement and aggressive calls, can adjust the relative aggressiveness and attractiveness of their calls in a graded fashion, depending on the proximity of their opponents ( Wells & Schwartz, 1984 ; Wells & Bard, 1987 ; Wells, 1989 ).…”

Sexual selection constrains the body mass of male but not female mice

“…These four hypotheses include pressures due to both natural (1 and 2) and sexual (3 and 4) selection; however, supporting evidence in vertebrates has been difficult to obtain for the two sexual selection hypotheses. Specifically, within vertebrates, costs associated with relatively large body size, in the context of male sexual selection, have only been demonstrated in the pied flycatcher (Ficedula hypoleuca) and serratelegged small treefrogs (Philautus odontarsus) (Alato & Lundberg, 1986;Zhu et al, 2016).…”