RESUMO
INTRODUCTION: The phenomenon of sexual conflict has been well documented, and in populations with biased operational sex ratios the consequences for the rarer sex can be severe. Females are typically a limited resource and males often evolve aggressive mating behaviors, which can improve individual fitness for the male while negatively impacting female condition and fitness. In response, females can adjust their behavior to minimize exposure to aggressive mating tactics or minimize the costs of mating harassment. While male-male competition is common in amphibian mating systems, little is known about the consequences or responses of females. The red-spotted newt (Notophthalmus viridescens) is a common pond-breeding amphibian with a complex, well-studied mating system where males aggressively court females. Breeding populations across much of its range have male-biased sex ratios and we predicted that female newts would have behavioral mechanisms to mitigate mating pressure from males. We conducted four experiments examining the costs and behavioral responses of female N. viridescens exposed to a male-biased environment. RESULTS: In field enclosures, we found that female newts exposed to a male-biased environment during the five-month breeding season ended with lower body condition compared to those in a female-biased environment. Shorter-term exposure to a male-biased environment for five weeks caused a decrease in circulating total leukocyte and lymphocyte abundance in blood, which suggests females experienced physiological stress. In behavioral experiments, we found that females were more agitated in the presence of male chemical cues and females in a male-biased environment spent more time in refuge than those in a female-biased environment. CONCLUSIONS: Our results indicate that male-biased conditions can incur costs to females of decreased condition and potentially increased risk of infection. However, we found that females can also alter their behavior and microhabitat use under a male-biased sex ratio. Consistent with surveys showing reduced detection probabilities for females, our research suggests that females avoid male encounters using edge and substrate habitat. Our work illustrates the integrated suite of impacts that sexual conflict can have on the structure and ecology of a population.
RESUMO
Testosterone (T) mediates aggression in a wide range of species. In some species, however, aggressive behavior persists or increases during the non-breeding season when T levels are relatively low. Animals that do not display a positive correlation between aggression and gonadal steroids suggest the need for further investigation of alternative neuroendocrine mechanisms mediating seasonal aggression. Siberian hamsters (Phodopus sungorus) are an ideal study system because they display increased territorial aggression during the non-breeding season which may be independent of circulating T levels. The goals of the present study were to: 1) explore the role of T in the aggression of reproductive males, and 2) test the hypothesis that the adrenal steroid dehydroepiandrosterone (DHEA) acts as an endocrine regulator of seasonal aggression. In Experiment 1, individuals were housed in long day (breeding) photoperiod and received castrations, exogenous T capsules or both manipulations. In Experiment 2, animals were housed in either long or short days (non-breeding) photoperiod and received DHEA or empty capsules. In both experiments, serum hormone levels and aggressive behavior were assessed. In Experiment 1, castration did not reduce aggression whereas exogenous T actually inhibited aggressive behavior. In Experiment 2, short-day individuals were more aggressive than long-day animals but DHEA treatment did not affect aggressive behavior, regardless of photoperiod. The present study supports the hypothesis that circulating gonadal steroids are not necessary to activate aggressive behavior in adult male hamsters. Further, seasonal changes in territorial aggression appear independent of circulating levels of DHEA in Siberian hamsters.
