Genetic diversity of a widespread annual killifish from coastal Tanzania

Veronika Bartáková,Matej Polačik,Martin Reichard,Hieromin Lamtane,Radim Blažek,Béla Nagy

doi:10.1186/s12862-019-1549-2

Abstract

BackgroundAfrican annual killifishes (Nothobranchius spp.) are adapted to seasonally desiccating habitats (ephemeral pools), surviving dry periods as dormant eggs. Given their peculiar life history, geographic aspects of their diversity uniquely combine patterns typical for freshwater taxa (river basin structure and elevation gradient) and terrestrial animals (rivers acting as major dispersal barriers). However, our current knowledge on fine-scale inter-specific and intra-specific genetic diversity of African annual fish is limited to a single, particularly dry region of their distribution (subtropical Mozambique). Using a widespread annual killifish from coastal Tanzania and Kenya, we tested whether the same pattern of genetic divergence pertains to a wet equatorial region in the centre of Nothobranchius distribution.ResultsIn populations of Nothobranchius melanospilus species group across its range, we genotyped a part of mitochondrial cytochrome oxidase subunit 1 (COI) gene (83 individuals from 22 populations) and 10 nuclear microsatellite markers (251 individuals from 16 populations). We found five lineages with a clear phylogeographic structure but frequent secondary contact. Mitochondrial lineages were largely congruent with main population genetic clusters identified on microsatellite markers. In the upper Wami basin, populations are isolated as a putative Nothobranchius prognathus, but include also a population from a periphery of the middle Ruvu basin. Other four lineages (including putative Nothobranchius kwalensis) coexisted in secondary contact zones, but possessed clear spatial pattern. Main river channels did not form apparent barriers to dispersal. The most widespread lineage had strong signal of recent population expansion.ConclusionsWe conclude that dispersal of a Nothobranchius species from a wet part of the genus distribution (tropical lowland) is not constrained by main river channels and closely related lineages frequently coexist in secondary contact zones. We also demonstrate contemporary connection between the Ruvu and Rufiji river basins. Our data do not provide genetic support for existence of recently described cryptic species from N. melanospilus complex, but cannot resolve this issue.

Highlights

African annual killifishes (Nothobranchius spp.) are adapted to seasonally desiccating habitats, surviving dry periods as dormant eggs
Small coastal basins of Mkuza and Mbezi harboured individuals from the third lineage (Mbezi, green) that locally coexisted with the Ruvu lineage in the lower Ruvu basin
The putative N. prognathus was represented by the fourth lineage (Wami, orange), from pools within the upper Wami River basin (Tendigo swamp)

Summary

Introduction

African annual killifishes (Nothobranchius spp.) are adapted to seasonally desiccating habitats (ephemeral pools), surviving dry periods as dormant eggs. Given their peculiar life history, geographic aspects of their diversity uniquely combine patterns typical for freshwater taxa (river basin structure and elevation gradient) and terrestrial animals (rivers acting as major dispersal barriers). Small cladocerans often produce resting stages that are dispersed by wind and, Temporary freshwater pools are common in highly seasonal environments, including African savanna Their specialised fauna includes widespread invertebrate species with specific dispersal stage (e.g. crustaceans and aquatic insects) as well as specialised killifish species that are extremely poor dispersers [3, 4]. Nothing is known on how such contrasting conditions affects connectivity of populations and their genetic diversity and phylogeographic structure

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