Translocation of cave fish (Poecilia mexicana) within and between natural habitats along a toxicity gradient

Abstract

During ecological speciation, diverging taxa have the potential to remain in close spatial proximity (i.e., sympatry or micro-allopatry) theoretically allowing for continued contact and gene flow. In a system where incipient speciation of populations of the Atlantic molly (Poecilia mexicana) appears to be driven by abiotic factors, we investigated whether one of these factors, hydrogen sulphide (H 2 S) toxicity, also constitutes an effective barrier to slow migration within and between habitats. We addressed this experimentally by translocating individuals from high toxicity to lower toxicity within a toxic cave and by translocating individuals from the toxic cave to a nontoxic surface habitat. Using a stepwise-backwards Cox regression, we found that overall mortality was low, but statistically significant mortality occurred when individuals were transferred from higher toxicity to lower toxicity. In addition, only males were negatively affected by being transferred from low levels of toxicity to nontoxic, surface waters. This indicates that in addition to abiotic factors, other mechanisms, like predation and sexual selection, must be important in maintaining population separation.

Gradient Evolution of Body Colouration in Surface- and Cave-DwellingPoecilia mexicanaand the Role of Phenotype-Assortative Female Mate Choice

“…The latter can be explained by exposure to constant hypoxia resulting in the downregulation of cellular oxidative stress protection mechanisms [66]. However, reciprocal translocation experiments between the surface (El Azufre) and the Cueva del Azufre did not find increased mortality rates [8, 67], and other reproductive isolation barriers must account for the observed reduction of gene flow between El Azufre and the Cueva del Azufre. Aquatic heteropterans ( Belostoma sp.…”

Microhabitat use, population densities, and size distributions of sulfur cave-dwellingPoecilia mexicana

“…After meandering for approximately 1.5 km, it eventually drains into the Río Oxolotán, which is part of the Río Grijalva drainage system. Despite the gradual oxidation of H 2 S to sulfate and elemental sulfur with increasing distance from the sulfide sources, which increases the water turbidity, and despite the influx of some smaller clear water affluents, El Azufre still has a remarkably high H 2 S concentration of up to ∼40 µMol ( Tobler et al, 2006 ; Schlupp et al, 2013 ).…”