Molecular systematics of the New World clingfish genus Gobiesox (Teleostei: Gobiesocidae) and the origin of a freshwater clade.

The phylogenetic relationships between marine and freshwater members of the New World clingfish genus Gobiesox are investigated using both mitochondrial and nuclear sequence data. Phylogenetic hypotheses are derived from Bayesian and maximum parsimony analyses of a six-gene concatenated data set (2 mitochondrial and 4 nuclear markers; 4098bp). Gobiesox is paraphyletic, due to the inclusion of Pherallodiscus, in phylogenetic hypotheses resulting from all analyses and its two included species are reassigned to Gobiesox. Within the expanded genus Gobiesox, the freshwater species (G. cephalus, G. juradoensis, G. mexicanus and G. potamius) represent a monophyletic group that is nested inside of a paraphyletic marine group. Based on the monophyly of the freshwater clingfishes, a habitat transition from marine to freshwater is inferred to have occurred only once in the evolutionary history of the group (potentially in the mid-Miocene). Gobiesox is obtained as part of a larger clade of New World clingfishes, including also members of Acyrtops, Acyrtus, Arcos, Rimicola, Sicyases and Tomicodon equivalent to the subfamily Gobiesocinae. The phylogenetic hypotheses obtained are discussed briefly in relation to the two alternative classifications currently in use simultaneously for the Gobiesocidae. A rediagnosis and list of included species is provided for Gobiesox.

Trophic analysis of the fish community in the Ciénega Churince, Cuatro Ciénegas, Coahuila.

Fish diets were analyzed to evaluate the dynamic trophs of the fish community in the Churince wetland system of the Cuatro Ciénegas, where the fauna consists of nine species: endemic, native and introduced. In nine sampling events (between February 2011 and May 2014) 556 specimens of all nine species were collected. Stomach contents were analyzed and the Relative Importance Index (IRI) was calculated. The feed coefficient (Q) of the diets and the accumulated trophic diversity (Hk), as well as the amplitude of the trophic niche were evaluated. Feeding strategies in the fish community were found to be eurifagic. The main foods in general were insects, crustaceans, gastropods, plants and teleosts. According to the average linkage method, four functional trophic groups were defined, with no higher consumption species; nevertheless all were regulators, mainly invertebrates. Therefore, the chain reaction in food control was higher from top to bottom, meaning a downwards dietary control.

Have superfetation and matrotrophy facilitated the evolution of larger offspring in poeciliid fishes?

Superfetation is the ability of females to simultaneously carry multiple broods of embryos, with each brood at a different developmental stage. Matrotrophy is the post-fertilization maternal provisioning of nutrients to developing embryos throughout gestation. Several studies have demonstrated that, in viviparous fishes, superfetation and matrotrophy have evolved in a correlated way, such that species capable of bearing several simultaneous broods also exhibit advanced degrees of post-fertilization provisioning. The adaptive value of the concurrent presence of both reproductive modes may be associated with the production of larger newborns, which in turn may result in enhanced offspring fitness. In this study, we tested two hypotheses: (1) species with superfetation and moderate or extensive matrotrophy give birth to larger offspring compared to species without superfetation or matrotrophy; (2) species with higher degrees of superfetation and matrotrophy (i.e. more simultaneous broods and increased amounts of post-fertilization provisioning) give birth to larger offspring compared to species with relatively low degrees of superfetation and matrotrophy (i.e. fewer simultaneous broods and lesser amounts of post-fertilization provisioning). Using different phylogenetic comparative methods and data on 44 species of viviparous fishes of the family Poeciliidae, we found a lack of association between offspring size and the combination of superfetation and matrotrophy. Therefore, the concurrent presence of superfetation and moderate or extensive matrotrophy has not facilitated the evolution of larger offspring. In fact, these traits have evolved differently. Superfetation and matrotrophy have accumulated gradual changes that largely can be explained by Brownian motion, whereas offspring size has evolved fluidly, experiencing changes that likely resulted from selective responses to the local conditions.