Introgression and Habitat Segregation in a Pair of Ladybird Beetle Species in the Genus Propylea (Coccinellidae, Coccinellinae) in Northern Japan

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

True sunfishes (genus Lepomis) of North America are renowned for hybridization, although hybrids often comprise of 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 which multiple females visit. Natural hybridization occurs between redbreast (L. auritus (Linnaeus, 1758)) and pumpkinseed (L. gibbosus (Linnaeus, 1758)) sunfishes, but there is no published research into its extent and causes. In this study, we assessed the relationship of ecological variables to 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.