Historically Isolated Tamarisk Beetle Species Meet Again on the Rio Grande and Pecos River
Amanda Stahlke1*, Ellyn Bitume2,3, Zeynep Ozsoy4, Levi Jamison5, Dan Bean6, Ruth Hufbauer3, Matt Johnson7, Paul Hohenlohe1
1Institute for Bioinformatics and Evolutionary Studies (IBEST), University of Idaho, Moscow, Idaho, USA; astahlke@idaho.edu, hohenlohe@uidaho.edu
2Exotic and Invasive Weeds Research Unit, U.S. Department of Agriculture – Agricultural Research Service, Albany, CA; Ellyn.Bitume@ars.usda.gov
3Bioagricultural Science and Pest Management, Colorado State University, Fort Collins, CO, USA; Ruth.Hufbauer@colostate.edu
4Biological Sciences, Colorado Mesa University, Grand Junction, CO, USA; aozsoy@coloradomesa.edu
5EcoPlateau Research, Flagstaff, AZ, USA; levisor7@hotmail.com
6Colorado Department of Agriculture, Palisade, CO, USA; dan.bean@state.co.us
7Colorado Plateau Research Station, Northern Arizona University, Flagstaff, AZ, USA; Matthew.Johnson@nau.edu
Since 2001, six populations of four cryptic tamarisk leaf beetle species have been introduced to North America as biological control agents of the tamarisk (or saltcedar; Tamarix spp.): Diorhabda carinata from Uzbekistan, D. carinulata from China and Kazakhstan, D. elongata from two sites in Greece, and D. sublineata from Tunisia. As original introduction populations grew and individuals dispersed naturally, they were also intentionally redistributed anthropogenically. Today this biocontrol agent has come to occupy much of the southwest US, though it is unknown which populations ultimately established, spread, and interbred – and how interactions among and evolution of these populations may impact efficacy and risk of the biological control program. With our newly assembled draft reference genome for D. carinulata and RADseq (restriction-site associated DNA-sequencing), we assessed hybridization status of over 500 individuals over multiple time points from the native range, introduced range, and laboratory cultures. In this talk, we focus on populations at novel contact zones in N. America: Along the Rio Grande, where southward range expansion of D. carinulata met northward expansion of possible hybrids; and along the Pecos River, where all four species were released. Using genome-wide sampling, we find widespread hybridization where all four species were released, especially among D. sublineata and D. carinata, and even three-way hybrids. A comparatively low level of hybridization along the Rio Grande suggests little or no connectivity between these river corridors despite geographical proximity. Instead, the Rio Grande populations are likely the result of dispersal and range expansion along contiguous habitat through Big Bend, TX. Complex patterns of dispersal and hybridization among Diorhabda spp. may lead to rapid evolution in the introduced populations and consequences for the further spread and ecological impacts of this biocontrol agent. Being able to predict these effects depends on understanding gene flow among these populations and species.