Investigating the origins and stability of hybridization in an assemblage of Australian freshwater gudgeons

Interspecific hybridization has long been grist to the mill for evolutionary theorists seeking to define what constitutes a “species” and to understand the processes involved in their creation and destruction.  A range of ecological and evolutionary outcomes can follow hybridization including an increase or decrease in biological diversity.  For example, depending on the degree of divergence and ecological differentiation between closely related species, hybridization might result in enhancement of prezygotic barriers to reproduction and reinforce species isolation.  In other cases, a switch to parthenogenesis might be triggered, or a species assemblage might collapse into a hybrid swarm.  Many freshwater fish taxa are suspected or proven to engage in interspecific hybridization, so studies of hybridising fish lineages will lead us to a more complete understanding of the regulation of biodiversity in freshwater ecosystems.  In this study we use population genetic methods to test for patterns of hybridisation in an assemblage of gudgeon taxa (Hypseleotris: Eleotrididae) in Australian inland rivers.  Previous allozyme studies indicate that hybridization might occur among several members of this assemblage.  We use newly developed microsatellite loci to investigate the incidence of hybrid fish and their distribution within a network of ephemeral streams.  We found that hybridization was extensive and widespread in the study area and based on these results we propose new hypotheses on the role of hybridization in the maintenance of connectivity and demographic stability in this system.