Integrating ecological and molecular data to investigate species maintenance and interspecific hybridization between the redbreast sunfish (Lepomis auritus) and the pumpkinseed sunfish (Lepomis gibbosus)

Abstract

True sunfishes (genus Lepomis Rafinesque, 1819) of North America are renowned for hybridization, although hybrids often comprise only a fraction of the sunfish population in natural systems. Species boundaries may be maintained through premating mechanisms (e.g., ethological and habitat isolation), which may be facilitated by the promiscuous sunfish mating system; primarily, singular males guard nests that multiple females visit. Natural hybridization occurs between redbreast ( Lepomis auritus (Linnaeus, 1758)) and pumpkinseed ( Lepomis gibbosus (Linnaeus, 1758)) sunfishes, but there is no published research on its extent and causes. In this study, we assessed the relationship between ecological variables and the prevalence of hybridization in a sunfish population in a freshwater lake. Nests of both species were evaluated for differences in substrate, date, water depth, temperature, and dissolved oxygen. Sequencing of one fragment of nuclear DNA (calmodulin intron 4) and one fragment of mitochondrial DNA (12S) was employed on adult males and eight offspring from each nest to determine genetic identity and hybridization direction. Nonparametric tests found a significant difference in substrate between species’ nests ( p < 0.01), warranting further investigation into nest substrate as a mechanism for species maintenance. Furthermore, we observed asymmetrical hybridization with the less abundant species (redbreast sunfish) disproportionately affected.