Museum Specimens of Western Diamond-Backed Rattlesnakes (Viperidae: Crotalus atrox) Reveal Trends in Body Size, Diet, and Endoparasites over the Last 75 Years

Climate projections for the Southwestern United States predict increases in temperature, drought intensity and frequency, and wildfire intensity and frequency. Such climatic change is expected to impact communities and species of the region, including Crotalus atrox (western diamond-backed rattlesnake) and its helminth communities. We hypothesized that C. atrox in New Mexico has experienced measurable changes in body size, diet composition, and helminth communities over the past century. We examined specimens of C. atrox from 3 time periods: 1947-1960 (1950s, n = 34), 1980-1990 (1980s, n = 53), and 2011-2021 (2010s, n = 57). We dissected specimens of C. atrox and recorded snout-vent length (SVL), sex, age class (juvenile or adult), prey items from gastrointestinal (GI) contents, and helminth prevalence. We then tested for differences in body size, diet, and helminth prevalence between sexes of C. atrox and across time periods. To better understand the environmental breadth of the helminths in C. atrox, we also performed a literature search to reconstruct in what coarse-scale habitat conditions the helminths identified in our study have previously been reported. Over the 3 time periods we studied, body size and diet composition have remained stable; however, helminth community composition appears to have shifted significantly. Kalicephalus inermis, Mesocestoides sp., and a nematode in the family Pharyngodonidae were recovered from snakes from the 1950s, followed by Hexametra boddaertii, Mesocestoides sp. and Oochoristica osheroffi from the 1980s. Finally, only O. osheroffi was recovered from snakes from the 2010s. We also found that O. osheroffi appears to tolerate areas that often lack reliable moisture levels. We suggest 3 hypotheses explaining the observed shift in helminth community composition: changes to climate, undetected changes in the diet of C. atrox, or other untested factors. Museum vouchers of both the hosts and the helminths recovered herein are available for verification, additional analyses or in-depth species reevaluations.