Potential Contribution of Ancient Introgression to the Evolution of a Derived Reproductive Strategy in Ricefishes

Area of Science:

• Evolutionary biology
• Genetics
• Ichthyology

Background:

• Parental care transitions, like the evolution of pelvic brooding in Sulawesi ricefishes, involve significant life history, behavioral, and morphological changes.
• Pelvic brooding, where females carry eggs on their belly, evolved independently in distantly related lineages of Adrianichthys and Oryzias ricefishes.
• Previous studies suggested independent evolution due to a lack of direct gene flow, despite shared traits.

Purpose of the Study:

• To investigate the role of interspecific gene flow and ancient standing genetic variation in the convergent evolution of pelvic brooding.
• To analyze gene-tree-species-tree incongruencies using a multispecies coalescent model and D-statistics.
• To evaluate gene flow not only between pelvic brooding lineages but also with other Sulawesi ricefish lineages.

Main Methods:

• Multispecies coalescent modeling
• D-statistics analysis
• Phylogenetic analysis of gene flow and introgression

Main Results:

• Confirmed a general network-like evolutionary pattern in Sulawesi ricefishes.
• Detected no direct gene flow between the pelvic brooding lineages of Adrianichthys and Oryzias.
• Identified hybridization between the ancestor of brooding Oryzias and the Lake Poso Oryzias ancestor, with signs of introgression near a pelvic brooding quantitative trait locus.

Conclusions:

• Convergent evolution of pelvic brooding in Oryzias likely involved ancient standing genetic variation and hybridization, rather than solely de novo evolution.
• The findings suggest a complex evolutionary history in Sulawesi ricefishes, with hybridization playing a role in the spread of adaptive traits.
• Further research into the genetic basis of pelvic brooding is warranted.