Equivocal species Equivocal species boundaries in desert fishes: Gila (Cyprinidae) in the Upper Colorado River Basin

Authors: Tyler K Chafin, Marlis R Douglas, Michael E Douglas

Year: 2016 (xlviii)

Abstract

Contemporary stream hierarchy of the Colorado Plateau reflects a volatile drainage evolution shaped by tectonism and climate. These provided alternating periods of drainage segregation and amalgamation, and thus a complex evolutionary theater for fish lineages to isolate, adapt, or merge. The resulting phylogenetic histories are reticulated and thus evolutionary processes remain difficult to segregate and infer. However, increased affordability of genomic approaches allows for alternative scenarios of lineage diversification to be statistically evaluated. We used reduced-representation genomic methods to examine patterns of admixture among three divergent lineages of Gila endemic to the Upper Colorado River: Roundtail chub (Gila robusta), Humpback chub (Gila cypha), and Ponytail (Gila elegans). A hypothesis-testing framework was employed to: (a) infer biogeographic and demographic processes driving lineage evolution; (b) evaluate historical and contemporary introgression among inter-specific populations; and (c) characterize intra-specific differentiation. Our analyses highlight the porous nature of ‘species boundaries’ and extend conservation initiatives by clarifying intra- and inter-specific delineations.