Reproductive Signals of Female Lizards: Pattern of Trait Expression and Male Response

Abstract

Relative to the volume of studies concerning the function and evolution of male‐biased sexually dimorphic traits, instances of female‐biased sexual dimorphisms remain largely unstudied, especially in species with conventional sex roles. I investigated the signal function of a female‐specific ornamental trait using the striped plateau lizard (Sceloporus virgatus, Phrynosomatidae) as a model system. During the reproductive season, female S. virgatus develop orange color on their throats that is absent in conspecific males. I established the relationship between color expression and female reproductive state, and determined male response to female color. I show that dynamic changes occurring within the color patch can potentially identify each stage of the female reproductive cycle, largely because of a lag in patch growth relative to color intensification. Sexual receptivity is associated with intense patches rapidly growing in size; ovulation occurs near peak color expression; and the unreceptive period is associated with large patches fading in intensity. Because females express orange color during both the receptive and unreceptive periods, the pattern of color expression is consistent with the courtship‐stimulation and courtship‐rejection hypotheses of signal function. Males may preferentially associate with females that have more highly developed color patches during the courtship season, and/or ignore such females when they are unreceptive. An examination of male behavior towards unfamiliar females indicates that female color has a role in courtship stimulation but has little, if any, role in courtship rejection. During the pre‐mating season, males maintained significantly closer affiliation with, and tended to perform more social behavior towards females with more intense color. During the post‐mating season, female color had no apparent effect on male behavior. The evolution and current function of female ornaments may vary among taxonomically‐related species as a result of differences in ecology, social system, and life‐history.

Effect of stress on female-specific ornamentation

“…Though sample size of non-reproductive females was small in this study, the pattern detected was expected as the ornament is known to develop and fade in concert with the ovarian cycle (Weiss, 2002), thereby serving as a signal of reproductive state as well as phenotypic quality. Also expected was the increased rate of reproductive suppression among C-IMP females, as it seems selectively advantageous for limited energy resources to be shunted to survival rather than reproduction in the face of an anabolic challenge.…”

“…Reproductive state was also included in our final statistical models as ornament expression is known to vary with reproductive state (Weiss, 2002) and C-IMP females were significantly less likely than other females to produce a clutch of eggs (χ 2 3 =9.04, P=0.03; Table2). Of the females that failed to produce a clutch, ~53% were C-IMP females (N=8), ~20% were autotomized (N=3) and ~13% were in each of the two control groups (N=2 per control group).…”

“…Females develop orange throat patches during the ovarian cycle, with peak ornament size and color occurring around the time of ovulation (Weiss, 2002). Though all reproductive females express some orange color, the extent of ornamentation at peak expression varies among individuals and that variation may function as an honest signal of female phenotype as well as the quality of her eggs and her future offspring (Weiss, 2006;Weiss et al, 2009;Weiss et al, 2011).…”

The evolution of female ornaments and weaponry: social selection, sexual selection and ecological competition

“…Weiss [199] reptile Uta stansburiana latter viewpoint and West-Eberhard's [12] definition of social selection, wherein sexual selection is a special form of social selection [41]. Placing aspects of fitness within this framework is necessarily somewhat subjective.…”

The yellow cheek-patches of the Hermann's tortoise (Reptilia, Chelonia): Sexual dimorphism and relationship with body condition

“…Most of these studies reported a relationship between female colourations and reproductive state (Ferguson 1976;Cooper et al 1983;Watkins 1997;Cuadrado 2000;LeBas & Marshall 2000;Hager 2001;Weiss 2002;Baird 2004); for example, the throat colouration of female Sceloporus virgatus changes seasonally and the colour intensity peaks near the time of ovulation (Weiss 2002(Weiss , 2006. In some cases, males have been shown to respond to female ornaments by increasing courtship towards ovulating females while reducing courtship to non-receptive females (Baird 2004).…”