Genetic diversity and structure of one of the most endangered freshwater fish species in Mexico:Tlaloc hildebrandi(Miller, 1950) and recognition of its evolutionarily significant units

Abstract

The endangered Chiapas killifish Tlaloc hildebrandi is an endemic freshwater species that lives in four subbasins of the Grijalva and Usumacinta basins, and one of the most geographically restricted species of the Produndulidae family. The species was originally described as endemic to springs in the high limestone plateau in San Cristóbal de Las Casas in the Río Amarillo subbasin (upper Grijalva basin). However, it was recently recorded in the Jataté and Tzaconejá subbasins in the upper Usumacinta basin, thereby expanding its known distribution range. The discovery of these populations is relevant not only for the conservation of the species but also for a better understanding of its evolutionary history. Currently, the scarce populations of T. hildebrandi, found in only a few localities in the Grijalva and Usumacinta basins, are fragmented and living under unfavorable conditions. Here, we analyzed three mitochondrial (mt-atp8&6 and mt-nd2) and one nuclear (nuc-s7) marker in order to assess the genetic diversity and population structure of T. hildebrandi. We found that, in comparison with other endangered freshwater fish species from Mexico, T. hildebrandi showed a lower level of genetic diversity (mt-nd2: h = 0.469, π = 0.0009; mt-atp8&6: h = 0.398, π = 0.001; and nuc-S7: h = 0.433, π = 0.001). Moreover, the analyzed populations exhibited a strong genetic structure in accordance with their geographic distribution, and can be placed into three genetic clusters: (1) Amarillo plus Chenhaló in the upper Grijalva basin, (2) Jataté, and (3) Tzaconejá, both in the upper Usumacinta basin. On the basis of our results, we propose the recognition of at least three evolutionarily significant units (ESUs) for the species and the urgent implementation of ex situ and in situ conservation and management efforts that consider the genetic background of the species.

Trophic morphology and diet of the endangered fish Tlaloc hildebrandi (Cyprinodontiformes: Profundulidae).

“…Tlaloc hildebrandi inhabits the Fogotico River and its tributaries and in the upper reaches of the Grijalva-Usumacinta system, in Chiapas, México (Beltrán-López et al, 2021;Domínguez-Cisneros et al, 2017;Velázquez-Velázquez & Schmitter-Soto, 2004). It exhibits a restricted extent of occurrence, because the number of locations where this species occurs is limited to three, based on the recognition of at least three evolutionarily significant units (Beltrán-López et al, 2021;Velázquez-Velázquez et al, 2016).…”

Intraspecific morphological variation in shads, Dorosoma anale and D. petenense (Actinopterygii: Clupeiformes: Clupeidae), in the Mexican Grijalva and Usumacinta river basins

“…Nevertheless, the structure of the community in the upper regions of these rivers notably differs (Gómez-González et al 2015;Velázquez-Velázquez et al 2016;Soria-Barreto et al 2018). Studies of systematic, biogeography and population genetics have revealed that the upper regions of the two basins have independent evolutionary histories (Elías et al 2021;Beltrán-López et al 2021;Terán-Martínez et al 2021). The presence of relic endemic species such as the catfish of Chiapas (Lacantunia enigmatica Rodiles-Hernández, Hendrickson et Lundberg, 2005) and the livebearer (Xenodexia ctenolepis Hubbs, 1950) of the upper Usumacinta are evidence of the region's unique biogeographic history (Rodiles-Hernández et al 2005;Hrbek et al 2007;Elías et al 2021).…”