Terrestrial fishes: rivers are barriers to gene flow in annual fishes from the African savanna

Abstract

Aim We compared the genetic variability and phylogeographical structure of three sympatric clades of annual killifishes (the Nothobranchius furzeri complex, N. orthonotus complex and N. rachovii complex) inhabiting annually desiccating savanna pools. Hypotheses on the mechanisms affecting intraspecific structure and speciation were tested. Location Temporary pools in Mozambique (Africa). Methods The study is based on spatially detailed samples covering the entire range of all three species complexes. A set of 12–13 microsatellites (1638 individuals, 96 populations) and cytochrome b sequences (463 fish, 152 populations) were used as genetic markers. Phylogenetic and population genetic approaches were used to describe the spatial genetic structure and to test the respective roles of river channels and river basins on diversification. Results Profound genetic differentiation among populations was evident; some populations located only a few kilometres apart were genetically very distinct, suggesting a significant role of genetic drift and low dispersal ability. Large rivers (Zambezi, Save, Limpopo) formed major barriers to gene flow, with minor differences among the three complexes. Further, the demographic expansion of previously isolated lineages was often limited by the river channel, and rivers were also confirmed as factors affecting speciation events. River basins and elevational gradient had a smaller, but non‐negligible, role in population structuring. Main conclusions River channels are the main barriers to gene flow in Nothobranchius fishes. The study demonstrated low dispersal ability and congruence in the phylogeographical pattern of all three complexes. Cases where Nothobranchius appear to have crossed river channels result from the dynamics of river morphology rather than from rare dispersal events. This conclusion is supported by simultaneous crossing events across lineages. A further division, also consistent among the three complexes, was detected between drier inland and wetter coastal areas. The phylogeographical pattern of Nothobranchius is unique in that it combines features of both aquatic and terrestrial taxa.

Local variation in embryo development rate in annual fish

“…and Table ). Similarly, nuclear markers indicate genetic separation between N. kadleci populations from the north and south, with northerly regions receiving more rainfall than those in the south (Bartáková et al, ; Fig. and Table ).…”

“…Embryo development in annual fishes reflects the unpredictable nature of the temporary pools they inhabit. Evolution of a local adaptation can sometimes be prevented by substantial inter‐population gene flow (Rytkönen & Orell, ), though this is not the case in the well‐isolated study populations (Bartáková et al, , ). The Nothobranchius spp.…”

Patterns of morphological variation among populations of the widespread annual killifish Nothobranchius orthonotus are independent of genetic divergence and biogeography

“…Here, we analyse morphological variation in a freshwater fish species with wide distribution, where separation into two species has been suggested by molecular phylogenetic data using both mitochondrial and nuclear markers (Bartáková et al. ). We ask whether genetic distinctiveness among metapopulations is driven by historical separation and ensuing phylogeographic structure without morphological diversification, or whether there is morphological evidence for the existence of separate species.…”

“…Additionally, large rivers constitute major barriers to gene flow, often isolating populations from opposite banks (Bartáková et al. ). Contemporary dispersal appears limited to temporary connections between pools due major flooding after intensive precipitation (Bartáková et al.…”

“…Contemporary dispersal appears limited to temporary connections between pools due major flooding after intensive precipitation (Bartáková et al. , ). Range fragmentation and limited dispersal ability contribute to pronounced genetic differentiation of Nothobranchius populations (Dorn et al.…”