Behavioral and physiological female responses to male sex ratio bias in a pond-breeding amphibian

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.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.The sex ratio of a population can play an important and complex role in the ecology of a species. A bias in the operational sex ratio (OSR) of a population, the ratio of reproductively active males to females, can lead to intense mate competition in the more common sex and therefore, increased sexual selection on traits that improve mating success [1]. These traits include behaviors that increase the number of mating opportunities and the likelihood of successful mating attempts [2,3]. Males often evolve coercive behaviors, such as forced copulations or harassment, which can decrease female fitness [4]. Male harassment can be a consequence of sexual conflicts over the optimal number of matings, which is predicted to be larger for males than for females [5], and can result in increased female acceptance of mat