Genomic data confirms phenotypic predictions of hybridization between cryptic Hawaiian cricket species

Hybridization is increasingly recognized as an important driver of species radiations, yet its detection in morphologically cryptic taxa remains challenging. The Hawaiian crickets of the genus Laupala represent a rapid non-adaptive radiation in which species are morphologically indistinguishable but differ in acoustic mating signals. Here we report the first discovery of natural hybridization in the Laupala radiation. During field surveys on Maui, we observed crickets with intermediate pulse rates and unusually high acoustic variation at sites where the ranges of Laupala makaio (slow singer) and Laupala orientalis (fast singer) converge. We hypothesized these represented natural hybrids and tested this prediction using genomic data from genotyping-by-sequencing (GBS). Maximum likelihood phylogenetic analysis showed that fast-singing putative hybrids clustered with L. orientalis and the slow-singing ones with L. makaio, yet all putative hybrids formed a cohesive geographic group. Using 9,345 ancestry-informative markers, we calculated hybrid indices and heterozygosity values for triangle plot analysis. All hybrids showed excess L. makaio ancestry (predicted from analysis of pulse rate patterns) and were classified as later-generation hybrids or backcrosses to L. makaio, with no F1 hybrids detected. Critically, we found a strong positive correlation (R = +0.74, p = 4.1x10-) between pulse rate and hybrid index at the site with highest pulse rate variation, showing that genomic ancestry predicts pulse rate phenotype. Morphological comparisons confirmed that hybrids were cryptic, reinforcing the difficulty of detecting hybridization without genomic data. Together, our results provide the first demonstration of natural hybridization in Laupala, showing that phenotypic predictions based on acoustic intermediacy can be confirmed with genomic evidence. The discovery of natural hybridization in Laupala opens new avenues for investigating how hybridization contributes to rapid diversification in non-adaptive radiations, paralleling patterns observed in some adaptive radiations.