Reproductive and feeding ecology of two sympatric Dionda (Cyprinidae) in the Rio Grande Basin, Texas
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The genus Dionda consists of at least 12 species, all of which inhabit groundwater-dominated streams within the western Gulf slope drainages of North America but with some slight differences in habitat preferences. The purpose of this study was to assess the influence of spring or river habitat selection on reproductive characters and feeding of two sympatric Dionda in the Devils River (TX) and between two Dionda diaboli populations taken from riverine habitats in the Devils River and from spring habitats in Pinto Creek (TX). The two species and three populations of Dionda were short lived (<3 years of age), produced multiple batches of oocytes in a spawning season, and primarily consumed algae and amorphous detritus. Dionda diaboli, which were taken from riverine habitats in the Devils River but were constrained to spring habitats in Pinto Creek, had a life span of 1 to 2 years and a six month spawning season. Individuals taken from Pinto Creek generally had narrower diet breadths, consumed more amorphous detritus, had a higher trophic position, and spawned earlier than those taken from river habitats in the Devils River. Dionda argentosa, which were taken from spring habitats in the Devils River, had a longer life span, higher growth rates, a more protracted spawning season (8 to 12 months), and intermediate diet breadths when compared to the two populations of D. dionda. Differences in reproductive characters between the spring and river Dionda species were consistent with theory that stenothermal waters of springs lack terminating cues to induce gonadal quiescence in fishes. However, a protracted spawning season was not observed in D. diaboli taken from springs of Pinto Creek. This suggests that protracted spawning is an adaptive trait, but findings were inconclusive in that low spring outflows in Pinto Creek produced more riverine-type environments rather than the more stenothermal environments normally associated with spring habitats. Likewise, differences in diets between the two populations of D. diaboli were attributed to low spring outflows and declining environmental conditions within Pinto Creek.