Evolutionary modifications of Astyanax larval prey capture (LPC) in a dark environment.

Feeding strategies of an organism depend on the multimodal sensory processing that most efficiently integrates available visual, chemosensory, and/or mechanoreceptive cues as part of their environmental adaptation. The blind cavefish morph of Astyanax mexicanus has developed sensory-dependent behaviors to find food more efficiently than their eyed, surface-morph counterparts while in darkness. In the absence of light, adult cavefish have evolved enhanced behaviors, such as vibration attraction behavior (VAB), and changes in feeding angle. Here, we identified evolved differences in cavefish larval prey capture (LPC) behavior. In the dark, LPC is more efficient in cavefish than in surface fish. Furthermore, different cave populations express laterality in their LPC and strike towards prey preferentially located on their left or right sides. This suggests the occurrence, to some extent, of divergent LPC evolution among cave populations. While LPC can be triggered exclusively by a vibration stimulus in both surface and cavefish, we provide evidence that LPC is, at least partially, a multimodal sensory process different from adult VAB. We also found that a lack of food may exacerbate the laterality of LPC. Thus, we proposed a mathematical model for explaining laterality based on a balance between: (1) enlarged range of foraging field (behavioral or perceptive) due to asymmetry, (2) food abundance, and (3) disadvantages caused by laterality (unequal lateral hydrodynamic resistance when swimming, allocation of resources for the brain and receptors, and predator escape).

Miocene divergence for Texoreddellia? An important component of the cave-adapted fauna of Texas and northern Mexico.

The genus Texoreddellia (Zygentoma; Nicoletiidae) is an important component of the cave-adapted fauna of Texas and northern Mexico. Specimens are often found in caves in central Texas. They are less common in western Texas and Coahuila, Mexico. We describe a new species, Texoreddellia chihuahuensis n. sp., from Chihuahua, Mexico, greatly expanding the range for the genus. The new species is found in an isolated karstic zone, far removed from the other cave forming areas inhabited by Texoreddellia spp. Phyletic analyses show the species to be the most basal and earliest to diverge within the genus. When compared to a calibrated molecular clock of the 16S rRNA for nicoleiids, its sequence supports a divergence of roughly 20 mya. Such a date is congruent with the geological origins of the Rio Grande and the Pecos River. Structural deformations coupled with long term erosion and downcutting through major river basins may have contributed in forming biological barriers that influenced speciation and isolation, especially between the western and eastern species of Texoreddellia.

Mc1r gene in Astroblepus pholeter and Astyanax mexicanus: Convergent regressive evolution of pigmentation across cavefish species.

Cave-adapted organisms are often characterized by a reduction in pigmentation, eyesight, and enhanced mechanosensory functions. Previous studies have described the genetic basis for a depigmented phenotype in multiple independent populations of the Blind Mexican Tetra, Astyanax mexicanus; the reduction in melanin content (brown; Mc1r). At least seven wild populations express the brown phenotype. In three populations, there are two different coding sequence alterations affecting Mc1r and the remaining four populations show the accumulation of sequence mutations affecting the 5' regulatory region. Thus, the Mc1r gene has been the repeated and independent location of mutations in Astyanax. As such, it would appear that this gene is a target during regressive evolution of cave adapted organisms. If this is the case, it would be expected that other cave adapted fish would have mutations in the same gene. We study here the stygobitic catfish Astroblepus pholeter, a depigmented fish found within some river caves in Ecuador. A. pholeter displays mutations in ultra-conserved areas of the pigment-controlling gene, Mc1r, that have been linked to pigment regulation in other organisms. It is thus concluded that Mc1r, a gene known to control pigment variation in many organisms, may be the target of cavernicole regressive evolution across species in different families of fish.