The Fundulus diaphanus Species Complex: A Case Study of Convergent Evolution?

Abstract

The Fundulus diaphanus (banded killifish) species complex of Eastern North Carolina streams and Carolina bays provides a possible case study of convergent evolution with important conservation implications. It was originally believed that the Fundulus in Lake Phelps were Fundulus waccamensis that had been introduced from Lake Waccamaw—a very distinctive putative sister species of F. diaphanus and a federal species of concern and state endangered species. It is now hypothesized that these two species/populations independently evolved shallow, terete body shapes due to similar environmental and selection pressures. The specific aim in this study was to test the hypothesis that the terete F. diaphanus (in Lake Phelps) and F. waccamensis (in Lake Waccamaw) are independently derived from ancestral stream F. diaphanus, with their similar forms a result of convergent evolution. I sampled the two lake populations and a stream population adjacent to each, extracted DNA from fin clips and/or livers, and sequenced the resulting DNA using a pooled approach. These sequences were compared to a representative Fundulus genome and evolutionary relationships were examined for the four populations. I found that the Lake Phelps and Scuppernong River populations were most closely related, supporting convergent evolution. The Lake Waccamaw population was more closely related to Lake Phelps and Scuppernong River than it was to Waccamaw River, suggesting that the divergence between the Waccamaw River population and the three other populations preceded the diversification of the other populations. Due to the limited range of both F. waccamensis, and the Phelps population, this study highlights the importance of managing both these distinctive Carolina bay populations.