Sensory Cues, Association Preferences, and Social Interactions of the San Marcos Salamander
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I studied the sensory communication, association preference, and social interactions of the threatened San Marcos salamander (Eurycea nana) in the laboratory. Eurycea nana (Plethodontidae) is endemic to the headwaters of the spring-fed San Marcos River (Texas). Within the geographic distribution of this species, temperature, chemical properties, and nutrient concentrations of the water are fairly constant. I expected that this stable habitat and year-round breeding would affect their communication and social behavior.
In chapter II, I examined the additive and multiplicative effectiveness of different sensory cues in the association preference of males and females of E. nana. The mode and effectiveness of signals depends on the environmental conditions and activity patterns of animal species. Visual cues frequently are involved in social interactions, although in nocturnal species, chemical and acoustic cues are more important. Multiple cues, however, can increase the accuracy of communication. Therefore, I examined association preferences of male and female salamanders based on conspecific (1) chemical cues, (2) visual cues, and (3) chemical & visual cues when simultaneously exposed to one individual of each sex. Both sexes significantly preferred to associate with the opposite sex when exposed to both chemical, and chemical and visual cues. There was no significant preference for either sex with visual cues alone. The simultaneous inclusion of both chemical and visual cues did not increase male or female preference for the opposite sex, thus chemical cues alone were sufficient to identify sex. I further tested male association preference for the chemical and visual cues of gravid versus non-gravid females. Males did not significantly prefer either type of female. Overall, my results suggest that although chemosensory communication is sufficient for females and males to distinguish between the sexes at close range, the ability of males to discriminate between females of different gravidity may require a different sensory modality.
In chapter III, I examined aspects of social interactions in E. nana. Social interactions of conspecifics are a function of the complex relationships among resource defense, anti-predatory tactics, and mate acquisition. Individuals often associate non-randomly with conspecifics in their habitats, where spatial distributions of adults range from territorial spacing to aggregations, depending on the habitat conditions and breeding status of the interacting individuals. I examined the cohabitation patterns of intrasexual and intersexual pairs of salamanders under artificial shelters across a 20-day period. I also examined individual affinity to the two shelters as a measure of site tenacity. None of the salamanders exhibited significant affinity to a particular shelter. In fact, males in the intrasexual pair treatment affiliated with both shelters equally often, indicating that they move frequently. Female pairs and intersexual pairs were found cohabiting more often than expected from random, whereas pairs of males cohabited in a pattern not significantly different from random. These results demonstrate that females of E. nana preferred to cohabit with individuals of both sexes, and males did not cohabit with other males, which could be a non-aggressive tactic to reduce competition or an indication that males move more frequently than females.
CitationThaker, M. (2004). Sensory cues, association preferences, and social interactions of the San Marcos salamander (Unpublished thesis). Texas State University-San Marcos, San Marcos, Texas.
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