Natural history and trophic ecology of three populations of the Mexican cavefish, Astyanax mexicanus

The Mexican cavefish, Astyanax mexicanus (Characidae), has become an important model in evolutionary physiology and developmental biology, providing insights into the evolution of sensory systems, pigmentation, and metabolism. In contrast, comparatively little is known about the natural history and trophic ecology of this elusive cave inhabitant. We investigated cavefish from three independently colonized cave systems (Pachón, Tinaja, and Sabinos), which are located in the Sierra de El Abra of northeastern Mexico. Samples were collected multiple times throughout the year to investigate variation in body size, sex ratios, proportions of individuals with empty guts, and diet composition. We found consistent differences in body size among caves, and sex ratios were generally female biased, although to varying degrees. Gut content analyses indicated that cavefish consume food throughout the year, and diets are dominated by detritus, plant materials, and aquatic invertebrates. Especially in the Pachón cave, where we had the densest sampling, there was evidence for seasonal changes in diet composition that coincided with the rainy and dry seasons. Our findings potentially suggest that the cave environments in this system are characterized by continual nutrient limitation, rather than intermittent periods of starvation.