Hormonal state influences aspects of female mate choice in the Túngara Frog (Physalaemus pustulosus)

Abstract

Females alter their mate choices as they transition through different reproductive stages; however, the proximal mechanisms for such behavioral fluctuation are unclear. In many taxa, as females transition through different reproductive stages, there is an associated change in hormone levels; therefore, we examined whether fluctuation in hormone levels serves as a proximal mechanism for within-individual variation in mate choice in female túngara frogs (Physalaemus pustulosus). We manipulated hormone levels of females by administering 0, 10, 100, 500 or 1000 IU of human chorionic gonadotropin (HCG), which is a ligand for luteinizing hormone (LH) receptors and will therefore cause increased gonadal hormone production. Phonotaxis assays were conducted to measure three aspects of mate choice behavior before and after HCG administration; receptivity (response to a conspecific mate signal), permissiveness (response to a signal that is less attractive than conspecific signals) and discrimination (ability to discern signal differences). The probability of response to a conspecific and an artificial hybrid signal significantly increased at the highest HCG doses. The difference in mean response time between pre-and post-HCG tests was significantly different for both the receptivity and permissiveness tests among the five doses. Increased permissiveness, however, was not due to decreased discrimination because females could discriminate between calls even at the highest HCG doses. These hormonal manipulations caused the same behavioral pattern we reported in females as they transitioned through different reproductive stages (Lynch, K.S., Rand, A.S., Ryan, M.J., Wilczynski, W., 2005. Plasticity in female mate choice associated with changing reproductive states. Anim. Behav. 69, 689-699), suggesting that changes in hormone levels can influence the female's mate choice behavior.

Effects of estradiol on neural responses to social signals in female túngara frogs

“…In the túngara frog, a previous study showed that hCG, which stimulates production of gonadal steroids (Lynch et al, 2006;Wu et al, 2001), increases egr-1 expression in the laminar nucleus of the torus (Lynch and Wilczynski, 2008). Our findings suggest that the effect observed by Lynch and Wilczynski (2008) was mediated by estradiol and not by direct effects of gonadotropins (Yang et al, 2007) or through changes in other steroids, such as progesterone or androgens.…”

“…Furthermore, in the auditory midbrain and parts of the limbic forebrain, estradiol receptor expression is sexually dimorphic , suggesting that estradiol is an important modulator of neural circuits underlying female-typical behavior. In addition, injections of human chorionic gonadotropins (hCGs), which stimulate production of gonadal steroids (Lynch et al, 2006;Wu et al, 2001), increase neural responses to conspecific social signals in the auditory midbrain (i.e. torus semicircularis) (Lynch and Wilczynski, 2008), suggesting that one way that estradiol modulates behavioral responses to conspecific calls is through modulation of auditory responses (Lynch and Wilczynski, 2008) or through integration of auditory and motor systems (see Hoke and Pitts, 2012).…”

Computational mate choice: Theory and empirical evidence

“…For example, a study on plasticity in mating preference in Túngara frog females (Lynch et al, 2005) has shown that the probability of recognizing both a conspecific call (receptivity) and a call less attractive than a conspecific call (permissiveness) changes during the reproductive stages of females, probably because of differences in their hormonal state (Lynch et al, 2006). Receptivity and permissiveness are higher in the amplexed than in the pre-and post-amplexed stages, but the probability of discriminating between two conspecific calls of different attractiveness does not change.…”

The effects of call-like masking diminish after nightly exposure to conspecific choruses in green treefrogs (Hyla cinerea)

“…Socially induced plasticity, as with seasonal and hormonally induced plasticity, should facilitate detection and/or recognition of the conspecific vocal signals that are crucial for guiding reproduction. It is not yet clear whether these effects are mediated by socially induced hormone changes (Burmeister and Wilczynski, 2000;Lynch et al, 2006) or occur independently. Nevertheless, our data add to the evidence that the social stimulation that occurs during a breeding season is an important factor in shaping the responses of the peripheral auditory system.…”