Female Amazon mollies, Poecilia formosa, are a unisexual species that reproduce by gynogenesis. They must coexist and mate with males of other species (usually the mollies Poecilia latipinna or Poecilia mexicana) to induce embryogenesis, but inheritance is strictly maternal. We examined the mating preference of the male sailfin molly, P. latipinna, for female sailfin mollies versus Amazon mollies, P. formosa. We compared the mating preferences of sympatric and allopatric populations collected throughout the Gulf Coast of North America. Male P. latipinna from six populations sympatric with Amazon mollies showed a significantly greater strength of preference for conspecific sailfin females than males from five populations that were allopatric with Amazon mollies. These results provide strong evidence for reproductive character displacement of male mate choice in sympatry. Furthermore, the large geographical range of populations that we tested revealed variation among populations within sympatry and allopatry, indicating that it is important to evaluate a large number of populations when examining reproductive character displacement.
In some species, females sequentially mate with different males within a single mating period, store sperm until the eggs are eventually fertilized, and gain no other resources from the males. Halliday hypothesized that, for such species, a female could ensure fertilization of her eggs by mating with the first male that she encounters; thereafter, she can maximize the quality of her progeny by sampling further males and by mating only with males of higher quality than previously mated males. This hypothesis predicts that females' choosiness will increase as the breeding season progresses. We tested this prediction of Haffiday's hypothesis by examining mate choice by female smooth newts (THturui vuigaris vuigaris). Males of this species develop a dorsal crest during the courtship season. Crest height varies between males and is potentially an indicator of male quality. Initially, female smooth newts were equally willing to mate with males with low or high crests. However, in their second mating, females remated only with high-crested males. These results support our prediction and are consistent with HaOiday's hypothesis. If crest height in smooth newts is an indicator of quality, this change in females' mate choice criterion allows females both to initiate egg-laying very early in the season and, subsequently, to mate preferentially with higher quality mates.
Anthropogenic disturbances have been implicated in the rapid decline of amphibians. Disturbances, such as disease and poor water quality, might cause changes in the physiology of amphibians resulting in chronic stress, which can result in decreased growth and development as well as immunosuppression. In amphibians, corticosterone (CORT) is the main hormone released in response to Stressors. We took the first steps towards validating a new, non-invasive, technique to assay CORT in amphibians using a water-borne collection method previously used only with fish. In validation of this technique, we found a significant positive correlation between release rates of water-borne CORT and levels of CORT in circulating plasma in adults of the San Marcos salamander, Eutycea nana, and the common midwife toad, Alytes obstetricans. These results indicate that water-borne CORT can be used as a proxy for plasma CORT. Additionally, we examined basic background information on the physiological states of these two species. We found that captive-reared salamanders had significantly lower release rates of CORT than field-collected salamanders. Field-collected salamanders had significantly higher CORT release rates 24 h after capture and transfer to the laboratory. For tadpoles, we found that field-collected tadpoles did not have significantly different CORT release rates than those maintained in the laboratory for four months. Our research indicates that this method of water-bome hormone collection should be viable for many species of amphibians; however, further validation via adrenocorticotropic hormone (ACTH) challenges is required. This method can be a useful tool for assessing tbe physiological state of laboratory and field populations of amphibians and the effects of urbanization, pesticides and diseases. An important benefit of this method is that it allows for repeated measures of the same individuals and can be less stressful than drawing blood.
Effective and efficient predator recognition and avoidance are essential for the persistence of prey populations, especially in habitats where non‐native predators have been introduced. Predator recognition studies are commonly couched within a learned or innate dichotomous framework; however, characteristics of some systems or species could favor innate recognition combined with the ability to alter avoidance responses based on experience with predators. Eurycea nana is a fully aquatic salamander inhabiting a system with a diverse, yet temporally stable, community of native and non‐native opportunistically foraging fish predators. To examine predator recognition, we examined avoidance responses (decreased activity) of predator‐naïve (first‐generation, captive‐reared) and predator‐experienced (recently collected) E. nana to the chemical cues of a native predator, a non‐native predator, a non‐predator, and a blank control. Both predator‐naïve and predator‐experienced E. nana significantly lowered activity in response to the native fish predator when compared with a blank control. Interestingly, predator‐naïve E. nana decreased activity in response to the non‐native fish predator while predator‐experienced E. nana did not. These results indicate that while there is an innate component to predator recognition in E. nana, experience and risk assessment may also be important.
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