Andrew T. Holycross

Variation in the Diet of Sistrurus catenatus (Massasauga), with Emphasis on Sistrurus catenatus edwardsii (Desert Massasauga)

Abstract We describe the diet of Desert Massasauga, Sistrurus catenatus edwardsii, in Arizona, Colorado, and New Mexico using fecal remains and gut contents obtained from field encounters and museum specimens. From these, 165 prey were identified, including 97 (58.8%) lizards, 51 (30.9%) mammals, 15 (9.1%) centipedes (Scolopendra sp.), one (0.6%) anuran, and one (0.6%) snake. Analyses of geographic, sexual and ontogenetic variation within S. c. edwardsii suggest diet is homogeneous among populations and between the sexes but that juveniles consume significantly more lizards and fewer mammals than adults. We assess rangewide variation in diet of Sistrurus catenatus using our data from Arizona, Colorado, and New Mexico (S. c. edwardsii) and previously published studies of populations in Wisconsin (Sistrurus catenatus catenatus), Michigan (S. c. catenatus), Missouri (Sistrurus catenatus tergeminus) and Texas (S. c. tergeminus) as well as new data from Texas (S. c. tergeminus). Significant geographic variation in diet parallels ecological and behavioral variation across the range of S. catenatus. Sistrurus c. edwardsii are xeric grassland-adapted snakes dependent on lizard and centipede prey, whereas both eastern subspecies favor more mesic environs and prey primarily on small mammals with juveniles occasionally feeding on snakes or lizards.

Diet of Crotalus lepidus klauberi (Banded Rock Rattlesnake)

Abstract We describe the diet of Crotalus lepidus klauberi (Banded Rock Rattlesnake) using samples collected in the field and from museum specimens, as well as several records from unpublished reports. Most records (approximately 91%) were from the northern Sierra Madrean Archipelago. Diet consisted of 55.4% lizards, 28.3% scolopendromorph centipedes, 13.8% mammals, 1.9% birds, and 0.6% snakes. Sceloporus spp. comprised 92.4% of lizards. Extrapolation suggests that Sceloporus jarrovii represents 82.3% of lizard records. Diet was independent of geographic distribution (mountain range), sex, source of sample (stomach vs. intestine/feces), and age class. However, predator snout–vent length differed significantly among prey types; snakes that ate birds were longest, followed in turn by those that ate mammals, lizards, and centipedes. Collection date also differed significantly among prey classes; the mean date for centipede records was later than the mean date for squamate, bird, or mammal records. We found no difference in the elevation of collection sites among prey classes.

Reproduction in Northern Populations of the Ridgenose Rattlesnake, Crotalus willardi (Serpentes: Viperidae)

Abstract We describe the reproductive biology of northern populations of Crotalus willardi using data gathered from four long-term field studies, histological examination of museum specimens, and literature records. Spermiogenesis occurs summer to early autumn. All male C. willardi examined contained sperm in the vas deferens (June–September) and had enlarged kidney sexual segments (June–October). Parturition occurs from late July through August (n = 17). Postpartum females appear to remain reproductively inactive prior to hibernation. Secondary yolk deposition (vitellogenesis) commences in the late spring or early summer, one or more years after parturition. Ovulation and fertilization probably occur early in the spring, followed by 4–5 months gestation. Copulation occurs in midsummer to early fall (n = 10). Repeated observations of marked females over several years, proportion of adult gravid females (60% Crotalus willardi obscurus, 40% Crotalus willardi willardi, 51% pooled), observations on captive animals, and histological observations collectively suggest frequency of reproduction is facultative but typically biennial or longer in wild snakes. Litter size averaged 5.4 ± 1.6 SD (n = 25, range 2–9). Regression analysis of 20 litters revealed an allometric relationship where litter size increased as an approximately cubic function of maternal SVL (litter size = e−14.64 SVL2.66). Forty-two neonates measured 167.2 ± 7.4 mm SD (range 150–182) and 43 neonates weighed 6.8 ± 1.2 g SD (range 5.0–9.0). The shortest reproductively active specimens measured 406 mm (male) and 402 mm (female) SVL.

Nowhere to Go but Up: Impacts of Climate Change on Demographics of a Short-Range Endemic (Crotalus willardi obscurus) in the Sky-Islands of Southwestern North America

Biodiversity elements with narrow niches and restricted distributions (i.e., ‘short range endemics,’ SREs) are particularly vulnerable to climate change. The New Mexico Ridge-nosed Rattlesnake (Crotalus willardi obscurus, CWO), an SRE listed under the U.S. Endangered Species Act within three sky islands of southwestern North America, is constrained at low elevation by drought and at high elevation by wildfire. We combined long-term recapture and molecular data with demographic and niche modeling to gauge its climate-driven status, distribution, and projected longevity. The largest population (Animas) is numerically constricted (N = 151), with few breeding adults (Nb = 24) and an elevated inbreeding coefficient (ΔF = 0.77; 100 years). Mean home range (0.07km2) is significantly smaller compared to other North American rattlesnakes, and movements are within, not among sky islands. Demographic values, when gauged against those displayed by other endangered/Red-Listed reptiles [e.g., Loggerhead Sea Turtle ( Caretta caretta )], are either comparable or markedly lower. Survival rate differs significantly between genders (female<male) and life history stages (juvenile<adult) while a steadily declining population trajectory (r = -0.20±0.03) underscores the shallow predicted-time-to-extinction (17.09±2.05 years). Core habitat is receding upwards in elevation and will shift 750km NW under conservative climate estimates. While survival is significantly impacted by wildfire at upper elevations, the extinction vortex is driven by small population demographics, a situation comparable to that of the European Adder (Vipera berus), a conservation icon in southern Sweden. Genetic rescue, a management approach successfully employed in similar situations, is ill advised in this situation due to climate-driven habitat change in the sky islands. CWO is a rare organism in a unique environment, with a conserved niche and a predisposition towards extinction. It is a bellwether for the eventual climate-driven collapse of the Madrean pine-oak ecosystem, one of Earth’s three recognized megadiversity centers.

Conservation Genetics of the Desert Massasauga Rattlesnake (Sistrurus catenatus edwardsii)

Abstract Populations of the Desert Massasauga Rattlesnake (Sistrurus catenatus edwardsii) have declined rapidly as desert grassland communities have become reduced and fragmented. To provide information useful for management of remaining populations, the genetic characteristics (based on microsatellite DNA loci) of the last demonstrably extant population in the state of Arizona were compared to a population in the Rio Grande Valley of New Mexico. Results indicated that genetic diversity was relatively high in both populations, with statistically significant heterozygote deficiencies detected at only one of six loci in each population. Contingency tests, Wrights F-statistics, and Bayesian clustering algorithms all indicated substantial subdivision between populations in Arizona and New Mexico, but only contingency tests supported differentiation within the Arizona population. A preliminary hierarchical analysis of variance (incorporating both our data and published microsatellite data for the Eastern Massasauga) indicated that 73% of the total molecular variance was explained by variation within populations, with variation between the two subspecies accounting for 15% of the total variance. Results support the high conservation value of individual populations, as well as the need for further population genetic studies of the Desert Massasauga Rattlesnake.

Ecology of a Population of the Narrow-Headed Garter Snake (Thamnophis rufipunctatus) in New Mexico: Catastrophic Decline of a River Specialist

Abstract We studied natural history and ecology of Thamnophis rufipunctatus at San Francisco Hot Springs, Catron County, New Mexico. Gee minnow traps were more effective at sampling adults than opportunistic captures. Females were larger than males in snout–vent length and mass, but males had longer tails. Although females were larger, rates of growth for juvenile males and females were similar. In 1996, the population was ca. 7.2 adult snakes/ha; however, we did not detect snakes in subsequent visits. Thamnophis rufipunctatus was most likely to be captured at sites with steep riverbed slope and large rocks of uniform size. Diet was exclusively fish, of which a large proportion was the introduced Gambusia affinis. This population of T. rufipunctatus was one of the most robust in the United States and it has completely disappeared in <10 years.

The Type Localities of Sistrurus catenatus and Crotalus viridis (Serpentes: Viperidae), with the Unraveling of a Most Unfortunate Tangle of Names

Abstract The broad and imprecise type localities of Crotalinus catenatus Rafinesque, 1818 (now Sistrurus catenatus) and Crotalinus viridis Rafinesque, 1818 (now Crotalus viridis) are re-identified based on a published account of the collectors travels as well as an examination of the relationship and contacts between the collector and the author of the type description. Both type specimens are lost. Unfortunately, enhanced resolution of the type locality of S. catenatus places it within the range of S. c. tergeminus Say, 1823 (a subsequently described subspecies). Thus, the name S. c. catenatus incontrovertibly applies to the form currently recognized as S. c. tergeminus, which in turn renders the latter as a subjective junior synonym of the former, leaving the eastern form with an unfamiliar name (Crotalus messasaugus Kirtland, 1838). To conserve prevailing usage, we are preparing an appeal to the International Commission of Zoological Nomenclature (ICZN) to allow a neotype of Sistrurus catenatus to be designated from the type locality of Crotalus massassaugus. In the interim, existing use of the names should be continued.

Observations of Predation on Crotalus willardi obscurus in the Animas Mountains, New Mexico

course of an ongoing mark-recapture investigation of the ecology of a montane snake community in the Animas Mountains, Hidalgo Co., New Mexico. A male C. w. obscurus (188 g, 580 mm snout-vent length [SVL]) first captured 7 October 1998 was recaptured 2 June 1999. A miniature radio-transmitter was then surgically implanted in the body cavity and the specimen was released 3 days later at its capture location at an elevation of 2,240 m. The snake was located daily and moved an average of 23.6 m each day (SE = 7.0, range = 0-78.4) from 7 to 20 June 1999. From 14 to 20 June the snake contained an exceptionally large prey bulge. Post-prandial thermophily may have increased exposure to predators and compromised agility may have increased vulnerability (Garland and Arnold, 1983; Ford and Shuttlesworth, 1986). On 21 June at 1600 h a portion of the snake (University of New Mexico, Museum of Southwest Biology, Division of Herpetology, MSB 61426) containing the radio-transmitter was found 14 m from the snakes location the

When one phenotype is not enough - divergent evolutionary trajectories govern venom variation in a widespread rattlesnake species

Understanding the relationship between genome, phenotypic variation, and the ecological pressures that act to maintain that variation, represents a fundamental challenge in evolutionary biology. Functional polymorphisms typically segregate in spatially isolated populations [1, 2] and/or discrete ecological conditions [3-5], whereas dissecting the evolutionary processes involved in adaptive geographic variation across a continuous spatial distribution is much more challenging [6]. Additionally, pleiotropic interactions between genes and phenotype often complicate the identification of specific genotype-phenotype links [7-8], and thus of the selective pressures acting on them. Animal venoms are ideal systems to overcome these constraints: they are complex and variable, yet easily quantifiable molecular phenotypes with a clear function and a direct link to both genome and fitness [9]. Here, we use dense and widespread population-level sampling of the Mohave rattlesnake, Crotalus scutulatus, and show that genomic structural variation at multiple loci underlies extreme geographic variation in venom composition, which is maintained despite extensive gene flow. Unexpectedly, selection for diet does not explain venom variation, contrary to the dominant paradigm of venom evolution, and neither does neutral population structure caused by past vicariance. Instead, different toxin genes correlate with distinct environmental factors, suggesting that divergent selective pressures can act on individual loci independently of their genomic proximity or co-expression patterns. Local-scale spatial heterogeneity thus appears to maintain a remarkably ancient complex of molecular phenotypes, which have been retained in populations that diverged more than 1.5-2 MYA, representing an exceptional case of long-term structural polymorphism. These results emphasize how the interplay between genomic architecture and spatial heterogeneity in selective pressures may facilitate the retention of functional polymorphisms of an adaptive phenotype.