Ecogeographic variation of body size of the semidesertic amphibian Rhinella atacamensis
The causes of intraspecific geographic variation of body size in ectothermic vertebrates have generally been attributed to environmental variables (e.g. temperature, precipitation) that act on ecological time scale. In amphibians, the research of the last decades has favored mechanisms that involve...
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| Tipo de recurso: | tesis de maestría |
| Estado: | Versión publicada |
| Fecha de publicación: | 2020 |
| País: | Chile |
| OAI Identifier: | oai:repositorio.anid.cl:10533/249985 |
| Acceso en línea: | https://hdl.handle.net/10533/249985 |
| Access Level: | acceso abierto |
| Palabra clave: | Ciencias Naturales Otras Ciencias Naturales |
| Sumario: | The causes of intraspecific geographic variation of body size in ectothermic vertebrates have generally been attributed to environmental variables (e.g. temperature, precipitation) that act on ecological time scale. In amphibians, the research of the last decades has favored mechanisms that involve the water availability as explanation of geographic variation of body size. However, there are few studies of terrestrial species that inhabit desert or semi-desert environments, where water scarcity is more likely to create important restrictions on physiological and ecological aspects. This study describes the geographic variation in body size of the semi-desert amphibian Rhinella atacamensis. This species is distributed for more than 750 km through a latitudinal aridity gradient that constitutes the transition between the southern tip of the Atacama Desert and the Mediterranean region of central Chile. The snout-vent length (SVL) of 315 adults of the species from 11 representative localities of its entire distribution (25 - 32 ° S) was measured and a theoretical information modeling approach was used to assess the support of the data for different ecogeographic hypotheses. The modeling was explicitly based on eight hypotheses proposed in the literature, involving precipitation, temperature, potential evapotranspiration and primary productivity. The pattern of variation was adjusted to a Bergmann body size cline: the mean SVL of populations consistently increases towards higher latitudes. The two best models, together with the hierarchical partition analysis, showed that most of the evidence supports precipitation mean annual as predictor of body size, favoring the converse water availability hypothesis. It is proposed that the decrease in body size at lower latitudes would be the result of less foraging activity in response to the decrease in precipitation levels in areas that also have lower productivity (availability of resources). This constitutes one of the few examples in amphibians at intraspecific level that cannot be attributed to water economy since it does not involve an increase in body size in response to decrease in precipitation. We suggest that the unusual pattern found in the Atacama toad could be attributed to an adaptive response to conditions of lower water availability, made possible by the age of the aridity gradient that characterizes the current distribution of the species. |
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