Highland islands: assessing gene flow among populations of an aquatic highland endemic

A variety of hierarchical gene flow models have been proposed to explain
the distribution of genetic variation in aquatic environments. These
models, including the Stream Hierarchy (SH), Death Valley (DV), Headwater
(HW), and Widespread Gene flow (WG) models, provide testable hypotheses
that focus on the degree of within-basin or within-stream network
connectivity and an organism’s dispersal abilities. We tested these models
using Tlaloc hildebrandi (Profundulidae, Cyprinodontiformes), a freshwater
fish endemic to the highlands of the Grijalva and Usumacinta River basins
in southern Mexico. Data from ultraconserved elements (UCEs) showed that
although T. hildebrandi was recovered as monophyletic, the sub-basins were
not. We generated single nucleotide polymorphisms from the UCEs to analyse
the data in a population genetic framework. These results differed between
analyses such that two (STRUCTURE analysis) or three (DAPC analysis)
genetic groupings were recovered. Overall, the results of this study
provide support for the SH model. Some individuals from the Jataté
sub-basin, however, conformed to the HW model, due to historical
connections among headwater streams and rivers of the Jataté and
Amarillo–Chenalhó clades/clusters. The greatest degree of gene flow has
occurred from the Grijlava to the Usumacinta basins, two geographically
proximate basins that have been hypothesized to have had previous
connections.