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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.

The characiform fish Astyanaxmexicanus comes in two forms, a surface-dwelling morph which lives in the rivers of North and Central America and a blind, depigmented cave-dwelling morph which inhabits caves in Mexico. In recent years, this species has arguably become among the most influential model system for the study of evolutionary development and genomics in cave biology. While recent articles have analysed in great detail Astyanax genetics, development, physiology, phylogeny and behaviour, there have been comparatively few recent studies concerning its ecology and in particular its biogeography. Mitchell et al. (1977) reported the species inhabiting 29 caves in the Sierra de El Abra region. Despite the elapsing of over 40 years and the latest surge of interest in the model, not a single new cave locality had been described for the species. We describe here a new and 30th cave locality, Chiquitita Cave, inhabited by troglomorphic A.mexicanus. Their morphology, eye histology, 16S rRNA DNA sequence, and smelling capabilities are analysed. This cave represents the southernmost extension for the cave morph’s habitat within the Sierra de El Abra. Its name, Chiquitita Cave (Tiny Cave), was chosen in reference to a potential hydrologic connection to “Chica Cave” (small cave), which is among the most studied populations of Astyanax.

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.

The "thysanuran" (Zygentoma: Nicoletiidae) Speleonycta ozarkensis is the only troglobiotic nicoletiid from the Ozark Highlands. It was originally described with only four specimens from four different cave systems in Arkansas and Oklahoma. The scarcity of available specimens has made it difficult to determine whether morphological variation among populations represents intraspecific or interspecific variation. We examined molecular (16S rRNA) variation among populations and found no evidence that they represent a species complex. Because of its limited distribution and lack of ecological and life history data, S. ozarkensis may be a species of conservation concern. We therefore conducted a conservation status assessment. We bioinventoried 44 caves in Arkansas and Oklahoma to determine the distribution of S. ozarkensis. A new locality in Adair Co., Oklahoma, was discovered and new specimens were collected to better assess morphological variation among populations. Data on ecology and life history was gathered. We determined the conservation status of the species and identified potential threats to existing populations. Despite being known from a few localities, S. ozarkensis has a broad distribution approaching 10,000 km2. Molecular data suggest S. ozarkensis is capable of considerable dispersal and is primarily an epikarstic species, perhaps explaining why it has been infrequently collected from caves. Conservation assessments revealed that S. ozarkensis is at a slight risk of extinction. We identified seven threats impacting populations that vary in scope and severity, but only recreational caving (three caves) and development associated with urbanization (one cave) have the greatest potential to immediately impact populations.

The hydrogeology of the El Abra region has a very dynamic history. Surface and underground rivers have broadly changed their paths throughout time. A simple model for estimating the age of caves by assessing rates of uplift/erosion is proposed. It is likely that not a single one of the river caves that currently house Astyanax populations had been formed when the original wave of colonization occurred 4.6-1.12 mya (million years ago). Colonization had to occur at higher-level caves. As the zone uplifted and eroded, deeper-level cave passages formed. Capture and sequestration of the underground streams allowed the ancestral population(s) to migrate to their current localities.