MECHANISMS OF SPECIATION AND REINFORCEMENT IN THE AMEEREGA BASSLERI SPECIES GROUP

Author

• BreAnn Geralds, Southern Illinois University CarbondaleFollow

Date of Award

5-1-2026

Degree Name

Doctor of Philosophy

Department

Zoology

First Advisor

Brown, Jason

Abstract

The Ameerega bassleri species group (ABSG), consists of four closely related montane poison frog species (A. bassleri, A. kuriinti, A. pepperi, and A. yoshina; Dendrobatidae). The species occur throughout regions in Central Peru and are differentiated by distinct morphology, male advertisement calls, and geographic ranges. Historical hybridization has occurred among members of this species group, and despite these fundamental morphological differences, it underscores their complex evolutionary history. This species group constitutes a robust model for investigating the interplay of geographic isolation, sexual isolation, and speciation mechanisms that promote and maintain species boundaries. Here, I describe a new poison frog, previously misidentified as the Yellow morph of Ameerega bassleri, and formally establish the Ameerega bassleri species group with the addition of A. kuriinti. Using extensive sampling of this group and genomic-wide sequencing of the nuclear genome from 91 individuals across all known populations, I demonstrate that A. bassleri sensu lato is polyphyletic. The nominal Chrome-green and black morphs form a clade that is sister to A. pepperi, while the distinctive (and previously misclassified) Yellow morph is sister to A. yoshina. Observed color-pattern variation and quantitative analyses of male advertisement call traits (note-rate and dominant frequencies) reveal consistent differences among all four species, confirming their status as independent evolutionary lineages. Furthermore, through multiple population genetic and phylogenetic analyses, including mitochondrial genomic data, a robust reconstruction of the evolutionary history of the ABSG uncovered a complex speciation history marked by recurrent admixture with profound evolutionary consequences. Ameerega bassleri originated through hybrid speciation approximately 1.5 million years ago, resulting from historic gene flow between the ancestors of A. kuriinti and A. pepperi. Finally, mixed landscape genetic models demonstrated that speciation correlated strongly with Andean topographic complexity and regionally heterogeneous montane climates characterizing each species’ distributions. Each species occupies a significantly distinct Grinnellian niche, creating fragmented connectivity through time that promoted ecological divergence and reinforced reproductive isolation despite historical gene flow.