Collaborative Research: Investigating the factors shaping marine-derived freshwater fish radiations in tropical rivers of Australia and New Guinea

The vast majority of the over 30,000 species of fishes in the world occur either in marine or freshwater ecosystems, not both. However, over the course of millions of years, select lineages of fishes have crossed the boundary between marine and freshwaters, established permanent residence, and diversified in the newly colonized environment. A subset of the fish groups then underwent remarkable evolutionary expansion upon colonizing freshwaters, diversifying into an array of different species that play different ecological roles.

Australia and New Guinea are unique because their freshwater fish communities are primarily comprised of lineages derived from marine ancestors, and at least seven such lineages underwent spectacular diversification. This project will explore how varying rates of evolution, ages of different fish groups, and the interactions among fish communities have influenced the evolutionary outcomes of colonizing freshwaters in the Australia-New Guinea region.

The study also aims to determine the genetic mechanisms underlying adaptation to freshwater environments, findings of particular relevance to a changing planet. The project will train undergraduate and graduate students in modern biodiversity science, and through student exchanges, provide benefits to US and New Guinean students. High school teachers will be trained to read, interpret, and teach the evolutionary Tree of Life, skills that can be incorporated into K-12 curriculum. Finally, an electronic guide the fishes of New Guinea will be developed and made freely available.

While much progress has been achieved in identifying the drivers of adaptive radiation in relation to colonization of islands by terrestrial animals (e.g., finches, anoles) or lakes by fishes (e.g., cichlids, sticklebacks), transitions into rivers by marine groups have rarely been examined in this context. The proposed project will take advantage of a unique 'natural experiment'––the depauperate primary freshwater fish community in rivers of Australia and New Guinea––to examine the extent to which marine-to-freshwater transitions resulted in adaptive radiations.

More specifically, it aims to identify the factors that promoted or constrained lineage, phenotypic, and genomic evolution of marine-derived freshwater groups in the region. The project will integrate genomic, morphological, paleontological, and ecological data from more than 400 fish species representing 16 families in the Australia and New Guinea region to study diversification patterns associated not only with transitions across the marine-freshwater boundary but also along the benthic-pelagic axis.

Phylogenomic analyses in combination with phylogenetic comparative methods will be used to study how the chronological sequence of habitat transitions influenced the outcome of lineage diversification and morphological evolution of freshwater radiations. Comparative genomic approaches based on whole genomes will be used to identify loci related to functional adaptations, including signatures of molecular adaptation and convergence, as well as gene family expansions and contractions.

Ultimately this project will provide an evolutionary framework to help understand the factors regulating adaptive radiations across environmental gradients. It will include student training in fish biodiversity at a variety of levels.

This project is jointly funded by the Systematics and Biodiversity Science Program and the Established Program to Stimulate Competitive Research (EPSCoR).

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.