Temporal and spatial dynamics of competitive parapatry in chewing lice

Abstract: We synthesize observations from 1979 to 2016 of a contact zone involving two sub‐ species of pocket gophers (Thomomys bottae connectens and T. b. opulentus) and their respective chewing lice (Geomydoecus aurei and G. centralis) along the Río Grande Valley in New Mexico, U.S.A., to test predictions about the dynamics of the zone. Historically, the natural flood cycle of the Rio Grande prevented contact between the two subspecies of pocket gophers. Flood control measures completed in the 1930s permitted contact, thus establishing the hybrid zone between the pocket gophers and the contact zone between their lice (without hybridization). Since that time, the pocket gopher hybrid zone has stabilized, whereas the northern chewing louse spe‐ cies has replaced the southern louse species at a consistent rate of ~150 m/year. The 0.2–0.8 width of the replacement zone has remained constant, reflecting the con‐ stant rate of chewing louse species turnover on a single gopher and within a local pocket gopher population. In contrast, the full width of the replacement zone (north‐ ernmost G. centralis to southernmost G. aurei) has increased annually. By employing a variety of metrics of the species replacement zone, we are better able to understand the dynamics of interactions between and among the chewing lice and their pocket gopher hosts. This research provides an opportunity to observe active species re‐ placement and resulting distributional shifts in a parasitic organism in its natural setting.

Data Availability Statement:: 1. Chewing louse microsatellite genotypes and R‐scripts are available in Dryad, https://doi.org/10.5061/dryad.9sv4q00. 2. Parasite voucher specimens and frozen tissue samples from pocket gophers are stored at −80°C at the University of Northern Iowa and at Louisiana State University. 3. Pocket gopher voucher specimens are housed at the Louisiana State University Museum of Natural Science (LSUMZ), the Museum of Southwestern Biology, University of New Mexico (MSB), Museum of Vertebrate Zoology, University of California (MVZ), or the Biodiversity Research and Teaching Collections at Texas A&M University (BRTC). 4. Current and future research directions of the team may be found at https://louselab.uni.edu/homepage.