Chad E. Montgomery

Wet- and Dry-Season Steroid Hormone Profiles and Stress Reactivity of an Insular Dwarf Snake, the Hog Island Boa (Boa constrictor imperator)

Field endocrine studies providing new comparisons for inference into the evolutionary and ecological factors shaping organismal physiology are important, often yielding novel physiological insights. Here, we explored factors associated with the sex steroid hormone concentrations and adrenocortical response to capture stress in Hog Island boas (Boa constrictor imperator) in the Cayos Cochinos archipelago of Honduras to generate comparative field hormone data from a tropical reptile and test the island tameness hypothesis. Baseline concentrations of testosterone, corticosterone, estradiol, and progesterone were measured during the wet and dry seasons, and an acute stressor of 1 h in a cloth bag was used to assess the stress response. Plasma steroid concentrations in these snakes were generally low in comparison to other taxa. Higher testosterone concentrations in males and higher estradiol and corticosterone concentrations in females were observed during the wet season compared to the dry season, which may be indicative of mating activities and vitellogenesis during this period. Snakes displayed a 15-fold increase in corticosterone concentrations in response to capture stress, a rise that was not impacted by whether a snake had been captured during previous years. The adrenocortical stress response was greater in males and positively related to body temperature. We suggest that this system merits future inquiries into the physiology and behavior of B. c. imperator, particularly as a model for studying insular impacts on diverse life history characters.

Divergence in morphology, but not habitat use, despite low genetic differentiation among insular populations of the lizard Anolis lemurinus in Honduras

Studies of recently isolated populations are useful because observed differences can often be attributed to current environmental variation. Two populations of the lizard Anolis lemurinus have been isolated on the islands of Cayo Menor and Cayo Mayor in the Cayos Cochinos Archipelago of Honduras for less than 15000 y. We measured 12 morphometric and 10 habitat-use variables on 220 lizards across these islands in 2 y, 2008 and 2009. The goals of our study were (1) to explore patterns of sexual dimorphism, and (2) to test the hypothesis that differences in environment among islands may have driven divergence in morphology and habitat use despite genetic homogeneity among populations. Although we found no differences among sexes in habitat use, males had narrower pelvic girdles and longer toe pads on both islands. Between islands, males differed in morphology, but neither males nor females differed in habitat use. Our data suggest that either recent selection has operated differentially on males despite low genetic differentiation, or that they display phenotypic plasticity in response to environmental variation. We suggest that patterns may be driven by variation in intrapopulation density or differences in predator diversity among islands.

Natural history of the Massasauga, Sistrurus catenatus edwardsii, in southeastern Colorado

Abstract Studies of natural history are important for determining baseline information, particularly for species that might be threatened or endangered. We collected 254 (141M:94F:19UNK) massasauga, Sistrurus catenatus edwardsii, from May 1995 through October 1996. The average snoutvent length (SVL ± SD) for adult males (355 ± 45 mm) was not significantly different than the SVL of adult females (364 ± 24 mm). Habitat descriptions indicate that the massasauga in Colorado is a semiarid grassland species that utilizes areas of relatively open shortgrass prairie. Massasaugas were active between 14 and 30°C, with an average ambient temperature during activity of 22.1 ± 2.5°C. The time of observed activity shifted through the season, with primarily diurnal activity during the cooler months (April and late September to October) and primarily early evening activity during the hotter months (May through August). Massasaugas in Colorado gave birth to litters of 5 to 7 young between late August and late September, and reproduction appeared to be biennial. Populations of S. c. edwardsii in Colorado are scattered but population size appeared to be relatively large based on number of captures and low recapture rates, particularly in Lincoln County. However, due to habitat loss and fragmentation resulting from agricultural expansion, these populations might become increasingly threatened in the future.

Ontogenetic Shift in Height of Sleeping Perches of Cope's Vine Snake, Oxybelis brevirostris

Abstract In Omar Torrijos National Park, Coclé Province, Panama, we visually located Copes vine snakes Oxybelis brevirostris at night along trails and streams. Of 203 O. brevirostris located, we documented height of perch for 185 individuals during March 2005–March 2007. All sleeping snakes encountered were on vegetation rather than on the ground. There was no significant difference in height of perch between males (170.1 cm) and females (148.7 cm). There, however, was a significant positive relationship between snout–vent length and height of perch. Longer snakes perched on branches significantly more often than small snakes, which tended to perch on herbaceous leaves.

Communal Nesting in the Anoline Lizard Norops lionotus (Polychrotidae) in Central Panama

Abstract We examined nesting in Norops lionotus to describe nesting sites and to determine if nesting aggregations were by multiple females or repeated deposition of eggs by the same female. We also described eggs during incubation and the subsequent hatchlings. We collected eggs from nests along streams at Omar Torrijos National Park in central Panama and incubated them until they hatched. We located seven nests (six active, one inactive) containing 47 eggshells (2 depredated; 45 hatched) and 67 unhatched eggs. All nests were on the downstream side of large boulders covered by moss and herbaceous vegetation. Estimated minimum number of females using each nest was one to five, depending on assumptions of the estimate. Estimates indicated that nesting aggregations were a combination of multiple females nesting communally and repeated deposition of eggs by the same female. Hatchlings averaged 2.66 cm in snout–vent length, 4.60 cm in length of tail, and 0.42 g in mass, with no significant difference between males and females or among nests. Overall sex ratio for hatchlings was not significantly different from 1∶1.

Pattern-Class D of Parthenogenetic Aspidoscelis tesselata (Sauria: Teiidae) in Las Animas County, Colorado

Abstract The diploid, parthenogenetic, whiptail lizard Aspidoscelis tesselata is represented by two distinctive variants of color pattern in southeastern Colorado. Pattern-class C has been recorded from several sites in the canyonlands of Otero, Las Animas, and Baca counties and D has been recorded from four sites north of the Purgatoire River near Higbee, Otero County. We report a specimen of A. tesselata D collected in 2008 south of the Purgatoire River in Las Animas County, which represents a significant range extension for this distinctive parthenogen.

Crotalus horridus (Timber Rattlesnake) Maternal Scent Trailing by Neonates

Abstract Intraspecific chemical communication among related and unrelated conspecifics may play an important role in social organization and kin recognition within snakes. We monitored the movements of 7 adult Crotalus horridus (Timber Rattlesnake) and 22 of their neonates from May 2008 to October 2010. Our objective was to determine if neonates follow their mothers to suitable den sites in North Central Missouri. Mothers tended to move away from the rookery between parturition and ingress, but neonates stayed in the vicinity of their release site for up to a week after the dispersal of their mother. Despite the loss of radiotransmitters, we were able to follow 6 neonates to ingress: 5 overwintered in the same den as their mother and 1 overwintered in a known den of a conspecific female. Our observations support the hypothesis that Timber Rattlesnake neonates follow their mother or, at the very least, follow conspecifics to suitable den sites in the ir first year.

Recent northward range expansion of the parthenogenetic lizard Aspidoscelis tesselatus in Colorado and the distributional enigma posed by pattern-classes C and D at the northern range periphery

Abstract The range of the parthenogenetic lizard Aspidoscelis tesselatus extends from eastern Chihuahua, Mexico, to southeastern Colorado, USA. In Colorado, pattern-class D, source of the neotype of the species, is syntopic with the more widely distributed pattern-class C only in Ninemile Valley of the Purgatoire River, beyond which, in all directions, these pattern classes are allopatric. We identify a recent northward range expansion of pattern-class C to the same northern latitude attained by pattern-class D, thereby establishing a latitudinal baseline for the species. The two northern arrays of pattern-class C, reported herein, occupied open habitats of sparsely distributed shrubs on rocky slopes, whereas the northernmost arrays of pattern-class D were using juniper woodland. Although this allopatric arrangement suggests ecological segregation of pattern classes, we provide an example of pattern-class C in juniper woodland only ca. 11 km south of the new records, which suggests that other factors could be involved.

Natural history of the black-chested spiny-tailed iguanas, Ctenosaura melanosterna (Iguanidae), on Cayo Cochnino Menor, Honduras

Abstract We examined aspects of natural history and ecology of the black-chested spiny-tailed iguana, Ctenosaura melanosterna, on Cayo Cochino Menor, Honduras, over 6 years to provide baseline data to assist in management of this critically endangered species. Size of territory is resource-dependent, and the species seems to prefer habitats with open canopy. Mating occurred between March and June, with emergence of hatchlings from June to August. Ctenosaura melanosterna is an omnivore that feeds on a variety of vegetation, invertebrates, vertebrates, and food-scraps. The threats to this population include predation by Boa constrictor, competition with an increasing population of Iguana iguana, and potential poaching of adults and eggs for food.