Genetic identification and reiterated captures suggest that the Astyanax mexicanus El Pachón cavefish population is closed and declining.

The sizes of Astyanax mexicanus blind cavefish populations of North-East Mexico are demographic parameters of great importance for investigating a variety of ecological, evolutionary, and conservation issues. However, few estimates have been obtained. For these mobile animals living in an environment difficult to explore as a whole, methods based on capture-mark-recapture are appropriate, but their feasibility and interpretation of results depend on several assumptions that must be carefully examined. Here, we provide evidence that minimally invasive genetic identification from captures at different time intervals (three days and three years) can give insights into cavefish population size dynamics as well as other important demographic parameters of interest. We also provide tools to calibrate sampling and genotyping efforts necessary to reach a given level of precision. Our results suggest that the El Pachón cave population is currently very small, of an order of magnitude of a few hundreds of individuals, and is distributed in a relatively isolated area. The probable decline in population size in the El Pachón cave since the last census in 1971 raises serious conservation issues.

Nutritional regulation of glucose metabolism-related genes in the emerging teleost model Mexican tetra surface fish: a first exploration.

Astyanax mexicanus has gained importance as a laboratory model organism for evolutionary biology. However, little is known about its intermediary metabolism, and feeding regimes remain variable between laboratories holding this species. We thus aimed to evaluate the intermediary metabolism response to nutritional status and to low (NC) or high (HC) carbohydrate diets in various organs of the surface-dwelling form of the species. As expected, glycaemia increased after feeding. Fish fed the HC diet had higher glycaemia than fish fed the NC diet, but without displaying hyperglycaemia, suggesting that carbohydrates are efficiently used as an energy source. At molecular level, only fasn (Fatty Acid Synthase) transcripts increased in tissues after refeeding, suggesting an activation of lipogenesis. On the other hand, we monitored only moderate changes in glucose-related transcripts. Most changes observed were related to the nutritional status, but not to the NC versus HC diet. Such a metabolic pattern is suggestive of an omnivorous-related metabolism, and this species, at least at adult stage, may adapt to a fish meal-substituted diet with high carbohydrate content and low protein supply. Investigation to identify molecular actors explaining the efficient use of such a diet should be pursued to deepen our knowledge on this species.

Astyanax transgenesis and husbandry: how cavefish enters the laboratory.

Astyanax mexicanus, a teleost fish comprising both sighted river-dwelling and blind cave-dwelling morphs, is becoming increasingly used in the field of developmental and evolutionary biology. Thus, new experimental and technological tools are needed on this emerging fish model by the expanding scientific community. Here, we describe Astyanax husbandry and egg spawning habits, a prerequisite to the successful establishment of Astyanax transgenic lines. We then compare two different transgenesis methods on both surface and cave Astyanax. Both meganuclease (I-SceI)- and transposase (Tol2)-mediated transgenesis are equivalently efficient, resulting in ∼40% mosaic transgenic fish in F0. Furthermore, the transmission rate was analyzed in F1 in the case of the I-SceI method and was found to be 16%. Finally, the transgene was found stable up the F3 generation, demonstrating the feasibility of generating stable transgenic lines in Astyanax and opening a wide range of possibilities for this fish model.

Differences in chemosensory response between eyed and eyeless Astyanax mexicanus of the Rio Subterráneo cave.

BACKGROUND: In blind cave-dwelling populations of Astyanax mexicanus, several morphological and behavioral shifts occurred during evolution in caves characterized by total and permanent darkness. Previous studies have shown that sensory systems such as the lateral line (mechanosensory) and taste buds (chemosensory) are modified in cavefish. It has long been hypothesized that another chemosensory modality, the olfactory system, might have evolved as well to provide an additional mechanism for food-searching in troglomorphic Astyanax populations. FINDINGS: During a March 2013 cave expedition to the Sierra de El Abra region of San Luís Potosi, Mexico, we tested chemosensory capabilities of the Astyanax mexicanus of the Rio Subterráneo cave. This cave hosts a hybrid population presenting a wide range of troglomorphic and epigean mixed phenotypes. During a behavioral test performed in situ in the cave, a striking correlation was observed between the absence of eyes and an increased attraction to food extract. In addition, eyeless troglomorphic fish possessed significantly larger naris size than their eyed, nontroglomorphic counterparts. CONCLUSIONS: Our findings suggest that chemosensory capabilities might have evolved in cave-dwelling Astyanax mexicanus and that modulation of naris size might at least partially underlie this likely adaptive change.

A developmental staging table for Astyanax mexicanus surface fish and Pachón cavefish.

Every model species requires its own developmental table. Astyanax mexicanus, a teleost fish comprising both sighted river and blind cave populations, is becoming more and more important in the field of developmental and evolutionary biology. As such, a developmental staging table is increasingly necessary, particularly since comparative analysis of early developmental events is widely employed by researchers. We collected freshly spawned embryos from surface fish and Pachón cavefish populations. Embryos were imaged every 10-12 min during the first day of development, and less frequently in the following days. The results provide an illustrated comparison of selected developmental stages from one cell to hatching of these two populations. The two morphs show an essentially synchronous development regarding major events such as epiboly, neurulation, somitogenesis, heart beating, or hatching. We also present data on particular morphological characters appearing during larval development, such as eye size, yolk regression, swim bladder, and fin development. Some details about the development of F1 Pachón cave×surface hybrids are also given. Comparisons are made with Danio rerio (zebrafish) development.

Lhx9 and lhx9alpha: differential biochemical properties and effects on neuronal differentiation.

The Lhx9 LIM-homeodomain transcription factor and its truncated isoform Lhx9alpha are generated by alternative splicing of the Lhx9 gene. Here we investigated the differential functional properties of these two isoforms. Lhx9alpha, which lacks parts of the homeodomain, was unable to bind DNA in EMSA experiments, but was able to associate with CLIM cofactors in GST pull-down assays. In transfection experiments in PC12 cells, Lhx9alpha fusion constructs systematically showed a nuclear localization, as opposed to Lhx9 fusion constructs, which also localized to the cytoplasm. Moreover, Lhx9 increased NGF-induced neuronal differentiation of PC12 cells. Lhx9alpha, on the other hand, did not significantly increase neuronal differentiation but had an effect on the morphology of PC12 cells. Finally, as tested by RT-PCR experiments on transfected PC12 cells, Lhx9 was not able to induce the transcription of Lhx9alpha. Our results show significantly different functional properties for Lhx9 and Lhx9alpha, and suggest that Lhx9alpha can compete away limiting amounts of nuclear CLIM cofactors. Thus, Lhx9 and Lhx9alpha isoforms could be implicated in regulating various aspects of neuronal differentiation.