Elaphe Obsoleta Research Articles

Occurrence and molecular characterization of Giardia spp. in snakes from China

Giardia intestinalis is a major diarrhea-causing parasite that colonizes the proximal small intestine of humans and various other mammalian species, including pets and livestock. Despite its global occurrence, there is limited information about the epidemiology of Giardia in reptiles, particularly snakes. The aim of this study was to amplify the beta-giardin (bg) gene of Giardia by polymerase chain reaction (PCR), followed by a comparative evolutionary tree analysis to determine the occurrence and molecular characterization of Giardia in snakes. We collected 603 asymptomatic samples from 26 provinces in China, representing species such as Pantherophis guttatus, Pantherophis obsoletus, Pituophis melanoleucus, Thamnophis sirtalis, Lampropeltis getula, and Heterodon nasicus. Ultimately, a occurrence of Giardia infection of 4.15 % was detected in these snakes, with corn snakes (Pantherophis guttatus) having a significantly higher occurrence than other species. Molecular analysis identified assemblage F as the predominant genotype, and also identified an assemblage B that can infect humans and a variety of mammals. The results of this study illustrate the potential risk of transmission of Giardia from snakes to humans, especially in environments where close contact occurs. The present epidemiological study examines epidemiological investigations of Giardia in reptiles, provides data to understand the zoonotic risk of Giardia, and emphasizes the need for targeted surveillance, stringent hygiene measures, and public awareness campaigns to reduce these risks.

Cryptosporidium spp. in captive snakes from 26 provinces in China: Prevalence, molecular characterization, and symptoms.

Snakes are sometimes regarded as pets and are used in traditional Chinese medicine. Cryptosporidium spp. are frequently identified in snakes, representing an important pathogen and causing gastrointestinal diseases. Current data indicate that risk factors for infection and patterns of clinical symptom presentation may differ among Cryptosporidium spp. To better understand the infection status by Cryptosporidium spp., fecal samples were collected from 603 asymptomatic and 147 symptomatic snakes in 26 provinces of China. These samples came from Elaphe guttata, Elaphe obsoleta, Pituophis melanoleucus, Thamnophis sirtalis, Lampropeltis getulus, and Heterodon nasicus. The partial small subunit (SSU) rRNA gene was amplified using nested polymerase chain reaction (PCR) to investigate the infection rate of Cryptosporidium spp., and to assess evolutionary relationships and genetic characterization. A prevalence of 20% was recorded in asymptomatic snakes, with age identified as a significant risk factor. In contrast, 70% of symptomatic snakes were positive for Cryptosporidium spp., with Cryptosporidium serpentis and Cryptosporidium varanii (syn. C. saurophilum). Further analysis revealed a potential association between C. serpentis and regurgitation, and C. varanii and diarrhea, while neither species was linked to flatulence. To our knowledge, this is the first study to report Cryptosporidium spp. and associated clinical signs in symptomatic snakes in China. This study aims to enhance the understanding of Cryptosporidium infections, risk factors, and clinical manifestations in snakes, providing data crucial for the control and prevention of cryptosporidiosis.

Factors Influencing Activity and Detection of Species in a Cross Timbers Snake Assemblage

The Cross Timbers of North America is an ecotone between the eastern deciduous forests and central grasslands and exhibits a diverse composite snake fauna. Over a 3-yr period, we performed repeated nocturnal road surveys of snakes across three transects in Wise County, Texas, and evaluated species composition, relative abundances, vehicular mortality, detection probability, and the influence of environmental variables on snake activity. Sixteen taxa and 406 observations were recorded over 250 surveys, and the three most frequently encountered species had detection probabilities of approximately 0.20: Pantherophis obsoletus, Agkistrodon laticinctus, and Nerodia rhombifer. Only the two species of Agkistrodon present at our study area showed significant differences in count frequencies across the three transects. Covariate effects on overall snake activity were subtle, with barometric pressure, ordinal date, and ambient temperature better explaining variation in combined snake counts than humidity, wind speed, or lunar phase. Furthermore, peak snake activity corresponded closely to the timing of peak warm-season precipitation in the study area, suggesting that snake activity coincides with rainfall periodicity in the Cross Timbers region. However, results of site-occupancy models indicated that covariate effects were different across species, and that several common species did not show clear responses to any of the survey covariates.

Scaling relationships of maximal gape and prey size of snakes for an egg‐eating specialist (Dasypeltis gansi) and a dietary generalist (Pantherophis obsoletus)

AbstractThe size of both predators and prey can profoundly affect the foraging ecology of animals. This is especially true for snakes which consume prey whole. Although their gape imposes an anatomical limit on prey size, different snake species have a wide variety of prey types, prey sizes, and dietary breadth. To test whether a dietary specialist that only consumes bird eggs (Dasypeltis gansi) differed from a generalist that occasionally eats eggs (Pantherophis obsoletus), I quantified and compared the scaling relationships between overall size, cranial dimensions, and maximal gape and the orientation and mobility of relevant bones. Compared to P. obsoletus with a given overall size, D. gansi had maximal gape areas approximately 3–4 times greater and a significantly larger relative contribution to gape by the intermandibular (IM) soft tissues (50% vs. 19%). The greater distensibility of the IM soft tissues also allowed much greater lateral displacement of the distal end of the lower jaw in D. gansi versus P. obsoletus, but at maximal gape, the bones of these species had unexpectedly similar orientations in lateral view. The large gape of D. gansi was attained despite having a significantly shorter head than P obsoletus for a given snout–vent length. As a result of their large gape and more slender build, the predicted values of relative prey masses (RPM) for D. gansi at maximal gape vastly exceeded those of P. obsoletus for a given prey type. Although eggs are much stouter than rats, values of RPM at maximal gape for D. gansi eating eggs greatly exceeded those for P. obsoletus eating rats. Perhaps, Dasypeltis has the greatest size‐corrected gape and potential values of RPM (for a given prey shape) of any snake taxon as these values of D. gansi exceed those from all previously studied species with similar data.

Central projections of auditory nerve fibers in the western rat snake (Pantherophis obsoletus).

Despite the absence of tympanic middle ears, snakes can hear. They are thought to primarily detect substrate vibration via connections between the lower jaw and the inner ear. We used the western rat snake (Pantherophis obsoletus) to determine how vibration is processed in the brain. We measured vibration-evoked potential recordings to reveal sensitivity to low-frequency vibrations. We then used tract tracing combined with immunohistochemistry and Nissl staining to describe the central projections of the papillar branch of the VIIIth nerve. Applications of biotinylated dextran amine to the basilar papilla (homologous to the organ of Corti of mammals) labeled bouton-like terminals in two first-order cochlear nuclei, a rostrolateral nucleus angularis (NA) and a caudomedial nucleus magnocellularis (NM). NA formed a distinct dorsal eminence, consisted of heterogenous cell types, and was parvalbumin positive. NM was smaller and poorly separated from the surrounding vestibular nuclei. NM was distinguished by positive calbindin label and included fusiform and round cells. Thus, the atympanate western rat snake shares similar first-order projections to tympanate reptiles. Auditory pathways may be used for detecting vibration, not only in snakes but also potentially in atympanate early tetrapods.

Considering admixture when producing draft genomes: an example in North American ratsnakes (Pantherophis alleghaniensis/Pantherophis obsoletus).

The number of reference genomes of snakes lags behind several other vertebrate groups (e.g. birds and mammals). However, in the last two years, a concerted effort by researchers from around the world has produced new genomes of snakes representing members from several new families. Here, we present a high-quality, annotated genome of the central ratsnake (Pantherophis alleghaniensis), a member of the most diverse snake lineage, Colubroidea. Pantherophis alleghaniensis is found in the central part of the Nearctic, east of the Mississippi River. This genome was sequenced using 10X Chromium synthetic long reads and polished using Illumina short reads. The final genome assembly had an N50 of 21.82 Mb and an L50 of 22 scaffolds with a maximum scaffold length of 82.078 Mb. The genome is composed of 49.24% repeat elements dominated by long interspersed elements. We annotated this genome using transcriptome assemblies from 14 tissue types and recovered 28,368 predicted proteins. Finally, we estimated admixture proportions between two species of ratsnakes and discovered that this specimen is an admixed individual containing genomes from the western (Pantherophis obsoletus) and central ratsnakes (P. alleghaniensis). We discuss the importance of considering interspecific admixture in downstream approaches for inferring demography and phylogeny.

Prevalence of Ophidiomycosis (Snake Fungal Disease) at a High Disturbance Remediated Landfill and at a Low-Impacted Forest Research Site in East Tennessee, USA

Ophidiomycosis (snake fungal disease; SFD) is a disease of conservation concern caused by the fungus Ophidiomyces ophidiicola that threatens the health of snake populations worldwide. Gaps exist in our knowledge about the prevalence of this disease across landscapes. In our study, we compared the prevalence of ophidiomycosis between a low-impacted forest site (n = 93) and a highly disturbed remediated landfill (n = 53) in Anderson County, Tennessee, USA. Free-ranging snakes were examined for the presence of skin lesions that are consistent with ophidiomycosis and were swabbed to detect O. ophidiicola DNA using quantitative PCR (qPCR). Apparent ophidiomycosis (qPCR-positive and skin lesions present) was diagnosed at both sites, but there was no significant difference in prevalence between the two sites (24.7% at the forest site; 22.6% at the landfill site). Apparent ophidiomycosis was most prevalent in Racers (38%; Coluber constrictor) and Ring-Necked Snakes (26%; Diadophis punctatus). There was no difference in ophidiomycosis status between sites for the most-sampled species: Racers, Black Rat Snakes (Pantherophis obsoletus), and Ring-necked Snakes (Diadophis punctatus). Our study represents the first report of ophidiomycosis at focal sites in Tennessee. The findings suggest that O. ophidiicola may be ubiquitous across the landscape and point to the need for further study of diverse habitat types for the prevalence of O. ophidiicola.

Southeastern US Snake Species are Vulnerable to Egg Predation by Red Imported Fire Ants (Solenopsis invicta)

Invasion and spread of Red Imported Fire Ants (RIFA; Solenopsis invicta) is cited as a possible cause for enigmatic reptile declines in the southeastern United States. Reptiles are negatively affected by RIFA through predation of eggs, hatchlings, and adults. We used short-term (12-h) field trials early in incubation to evaluate whether RIFA could successfully depredate intact eggs from six species of native terrestrial oviparous snakes: North American Racer (Coluber constrictor), Speckled Kingsnake (Lampropeltis holbrooki), Prairie Kingsnake (L. calligaster), Rough Greensnake (Opheodrys aestivus), Black Ratsnake (Pantherophis obsoletus) and Great Plains Ratsnake (P. emoryi). Then we used an artificial nest field experiment at the end of incubation to test whether RIFA predation differed between a species that has apparently declined in areas of its range where RIFA has invaded (L. holbrooki) and a species that has apparently not declined (C. constrictor). We measured pip–hatch and incubation time for each species in the laboratory to determine whether differences in time between pipping and hatching (pip–hatch time) could account for interspecific differences in RIFA predation on eggs. Overall, RIFA predation rates on snake eggs were high for all species (25–67% during early trials, 50–100% at end of incubation), although P. obsoletus was only depredated after hatching in the field. Coluber constrictor had significantly shorter pip–hatch times than other species, but probability of predation by RIFA did not differ for C. constrictor and L. holbrooki. Our study provides novel observations of RIFA predation and suggests that time spent in nest, eggshell characteristics, and nest microhabitat may be more important than pip–hatch time in mediating vulnerability of snake eggs to RIFA predation.

Spatiotemporal Patterns of Snake Captures and Activity in Upland Pine Forests

Patterns of species' occurrences across space and time are fundamental components to understanding their ecology, as this variation often reflects responses to local environmental gradients. We built species-specific models to understand the spatial and temporal factors predicting captures and activity of five snake species in upland pine forests: copperhead (Agkistrodon contortrix), racer (Coluber constrictor), coachwhip (Masticophis flagellum), western ratsnake (Pantherophis obsoletus), and western ribbonsnake (Thamnophis proximus). From mid-May to mid-July across 3 y (2018, 2019, 2020), we monitored boxtraps in two upland pine forests experiencing different management regimes: (1) subjected to frequent thinning and prescribed burning, and (2) subjected to infrequent thinning and prescribed burning. Significantly more copperheads and western ribbonsnakes were captured at the infrequently thinned and burned forest, whereas significantly more racers were captured at forest subjected to frequent thinning and burning. As the summer progressed, captures decreased each subsequent month for both racers and western ratsnakes, with the fewest captures in July. Western ratsnakes were the only species to exhibit a response to the weather in that activity decreased with increasing rainfall. No variables were significant predictors of coachwhip captures. The variation in captures across space may be attributed to the physiological tolerances of each species based on their habitat preferences or differences in prey availability at each forest. Interactions between the physiological tolerances, foraging behaviors, or their reproductive phenology may be underlying the temporal variation in activity patterns.

Additional comments on the types and nomina of several North American ratsnakes (Pantherophis obsoletus complex, Colubridae, Serpentes)

Here, we provide updates to our recent paper reviewing the taxonomy and nomenclature of the Eastern ratsnakes (Pantherophis obsoletus complex, Colubridae, Serpentes). Specifically, we clarify that Coluber alleghaniensis Holbrook, 1836 is a subjective, rather than objective, senior synonym of Elaphis holbrookii Duméril, Bibron & Duméril, 1854. Contrary to our statement that USNM 1733–4 were syntypes of Scotophis lindheimerii Baird & Girard, 1853, the former is the holotype and the latter is the paratype. The holotype is lost and the paratype is in poor condition, but no neotype designation is warranted at present. We note that USNM 248870, which we designated as the lectotype of Coluber obsoletus lemniscatus Cope, 1888, was originally cataloged as USNM 4710. This catalog number was shared with the type of the salamander Amblystoma tenebrosum Baird & Girard, 1852, and the snake was re-cataloged as USNM 248870 in 1985. Finally, we originally treated C. reticulatus La Cépède, 1789 and C. reticularis Daudin, 1803 as senior subjective synonyms of C. corais Boie, 1827, but here corroborate recent authors in designating it a senior subjective synonym of C. obsoletus Say in James, 1823. As the Commission suppressed C. reticulatus La Cépède, 1789 (an exoplonym), this subsequently rendered C. reticularis Daudin, 1803 (an exoploneonym) unavailable as well.

Is There Always a Need for Speed? Testing for Differences in the Striking Behavior of Western Ratsnakes (Pantherophis obsoletus) When Encountering Predators and Prey

Prior to both offensive and defensive striking, snakes can display notable differences in prestrike behaviors between offensive and defensive contexts. However, few studies have investigated strike movements during the different scenarios with which snakes are faced. To better understand how snakes strike, we measured the strikes of Western Ratsnakes (Pantherophis obsoletus; N = 11) presented with two different targets: one simulated predator (a gloved human hand) and one prey (pre-killed mice). For each strike, we recorded strike distance, duration, velocity (average and peak), acceleration (average and peak), and time to start mouth gape. In both encounters, ratsnakes displayed similar time to the initiation of a mouth gape while all peak performances were significantly different between strike types with performances being higher in defensive strikes. Defensive strikes took longer (mean = 122 ± 13 ms), reached greater distances (mean = 15.1 ± 1.7 cm), had higher maximum velocities (mean = 1.80 ± 0.11 ms-1), and maximum accelerations (mean = 101.4 ± 15.2 ms-2). Offensive strikes had much shorter durations (mean = 49 ± 5 ms), distances (mean = 4.3 ± 0.6 cm), maximum velocities (mean = 1.06 ± 0.10 ms-1), and maximum accelerations (mean = 81.4 ± 18.9 ms-2). The results for average performance measurements are similar to those for the maximum performance comparisons. Our results show that snakes can recognize and differentiate prey from threats and respond differently in each situation. Our results also show that predatory and defensive strikes are quantitatively and situationally distinct, should be treated as separate behaviors, and therefore should be evaluated and analyzed separately from one another.

Characterization of the Leucistic Texas Rat Snake Pantherophis obsoletus

Albinism and leucism are phenotypes resulting from impaired melanin pigmentation in the skin and skin appendages. However, melanin pigmentation of eyes remains unaffected in leucism. Here, using transmission electron microscopy, we show that the leucistic morph of the Texas rat snake (Pantherophis obsoletus lindheimeri) lacks both melanophores and xanthophores in its skin and exhibits a uniform ivory white color generated by iridophores and collagen fibers. In addition, we sequenced the full genome of a leucistic individual and obtained a highly-contiguous near-chromosome quality assembly of 1.69 Gb with an N50 of 14.5 Mb and an L50 of 29 sequences. Using a candidate-gene approach, we then identify in the leucistic genome a single-nucleotide deletion that generates a frameshift and a premature termination codon in the melanocyte inducing transcription factor (MITF) gene. This mutation shortens the translated protein from 574 to 286 amino acids, removing the helix-loop-helix DNA-binding domain that is highly conserved among vertebrates. Genotyping leucistic animals of independent lineages showed that not all leucistic individuals carry this single-nucleotide deletion. Subsequent gene expression analyses reveal that all leucistic individuals that we analyzed exhibit a significantly decreased expression of MITF. We thus suggest that mutations affecting the regulation and, in some cases, the coding sequence ofMITF, the former probably predating the latter, could be associated with the leucistic phenotype in Texas rat snakes.MITFis involved in the development and survival of melanophores in vertebrates. In zebrafish, a classical model species for pigmentation that undergoes metamorphosis, larvae and adults of homozygousmitfamutants lack melanophores, show an excess of iridophores and exhibit reduced yellow pigmentation. On the contrary, in the leucistic Texas rat snake, a non-metamorphic species, only iridophores persist. Our results suggest that fate determination of neural-crest derived melanophores and xanthophores, but not of iridophores, could require the expression ofMITFduring snake embryonic development.

Resolving spatial complexities of hybridization in the context of the gray zone of speciation in North American ratsnakes (Pantherophis obsoletus complex).

Inferring the history of divergence between species in a framework that permits the presence of gene flow has been crucial for characterizing the "gray zone" of speciation, which is the period of time where lineages have diverged but have not yet achieved strict reproductive isolation. However, estimates of both divergence times and rates of gene flow often ignore spatial information, for example when considering the location and width of hybrid zones with respect to changes in the environment between lineages. Using population genomic data from the North American ratsnake complex (Pantherophis obsoletus), we connected phylogeographic estimates of lineage structure, migration, historical demography, and timing of divergence with hybrid zone dynamics. We examined the spatial context of diversification by linking migration and timing of divergence to the location and widths of hybrid zones. Artificial neural network approaches were applied to understand how landscape features and past climate have influenced population genetic structure among these lineages. We found that rates of migration between lineages were associated with the overall width of hybrid zones. Timing of divergence was not related to migration rate or hybrid zone width across species pairs but may be related to the number of alleles weakly introgressing through hybrid zones. This research underscores how incomplete reproductive isolation can be better understood by considering differential allelic introgression and the effects of historical and contemporary landscape features on the formation of lineages as well as overall genomic estimates of migration rates through time.

SEASONAL ACTIVITY AND POPULATION FLUCTUATIONS OF A FREE-RANGING POPULATION OF THE RAT SNAKE PANTHEROPHIS OBSOLETUS INHABITING THE DALLAS ZOO, TEXAS

In 1989 a mark–recapture study of a free-ranging urban population of Pantherophis obsoletus inhabiting the 38.5-ha grounds of the Dallas Zoo (Dallas, Texas) was undertaken and has continued until the present time. Seasonal activity occurred from late February through December. To understand and evaluate further the geographic variation of the seasonal activity of the eastern rat snake complex, we combined data on the seasonal activity of P. obsoletus from our long-term study with those from five other populations previously studied in Texas, Illinois, Kansas, and Maryland and Ontario, Canada. There was a highly significant linear reduction in length of the activity season with increasing latitude. We also describe significant changes in population size and body condition of the snakes during a 26-year study period at the Dallas Zoo and discuss possible factors causing the changes.

Molecular characterization and novel genotypes of Enterocytozoon bieneusi in pet snakes in Beijing, China.

Little is known regarding the Enterocytozoon bieneusi genotypes in snakes worldwide. In the present study, a total of 273 fecal samples were collected from pet snakes in Beijing, China. They were then tested for the presence of E. bieneusi by PCR amplification of the internal transcribed spacer (ITS) gene. The overall infection rate of E. bieneusi was 4.4% (12/273), with the highest infection rate (20%, 1/5) of E. bieneusi was found in the Black rat snake (Pantherophis obsoletus), whereas no positive samples were detected from both Milk (0/22) and Coast garter snakes (0/2). Eight genotypes were identified, including four known genotypes: EbpA (n = 1), EbpC (n = 5), Henan-III (n = 1), and SHR1 (n = 1), and four novel genotypes: CRep-5 (n = 1), CRep-6 (n = 1), CRep-7 (n = 1), and CRep-8 (n = 1). Among them, EbpC (41.7%, 5/12) was the predominant genotype. Phylogenetic analysis showed that seven genotypes belonged to group 1, while genotype SHR1 belonged to group 2. Genotypes EbpA, EbpC, and Henan-III have been previously reported in humans. This suggests that pet snakes are a potential source of zoonotic microsporidiosis transmission in China.

Preliminary evaluation of complete blood count and diurnal variation of hematological parameters in black rat snake (Pantherophis obsoletus)

Introduction. The purposes of this study were to determine the presence of daily variations in hematological parameters of the black rat snake (Pantherophis obsoletus) and to compare them with the reference interval values of its subspecies, yellow rat snake (Pantherophis obsoleta quadrivittata). Materials and Methods. Blood from four black rat snakes was collected in the morning and in the evening, and after each collection, blood smears, packed cell volume (PCV), red blood cell count (RBC) and hemoglobin concentration (HGB) were determined, while erythrocyte indices of mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH) and mean corpuscular hemoglobin concentration (MCHC) were calculated and differential leukocyte counts were evaluated. Results and Conclusions. There were no statistically significant differences in any of the blood parameters in the morning and in the evening. Most of the complete blood count values in the black rat snakes were lower, but still within the reference range of those found in the literature for the yellow rat snake. The results of hematological parameters of the black rat snake could be beneficial for further research of physiological and pathological variations in complete blood count of these snakes, for diagnosing health conditions and for detecting various diseases.

The scaling of terrestrial striking performance in western ratsnakes (Pantherophis obsoletus).

In many organisms, juveniles have performance capabilities that partly offset their disadvantageous sizes. Using high-speed video recordings and imaging software, we measured the scaling of head morphology, axial morphology, and defensive strike performance of Pantherophis obsoletus across their ontogeny to understand how size and morphology affect performance. Head measurements were negatively allometric whereas the cross-sectional area (CSA) of epaxial muscles displayed positive allometry. The greater relative muscle CSA of larger ratsnakes allows them to produce higher forces relative to their mass, and those forces act on a relatively smaller head mass when it is thrust forward during striking. Maximum strike accelerations of 70-273.8 ms-2 and velocities of 1.08-3.39 ms-1 scaled positively with body mass but differed from the geometric predictions. Velocity scaled with mass0.15 and acceleration scaled with mass0.17 . Larger snakes struck from greater distances (range = 4.1-26 cm), but all snakes covered the strike distances with similarly short durations (84 ± 3 ms). The negatively allometric head size, isometry of anterior mass, and positively allometric muscle CSA enable larger P. obsoletus to strike with higher velocities and accelerations than smaller individuals. Our results contrast with the scaling of strike performance in an arboreal viper, whose strike distance and velocity were independent of body mass. When strike distance is modulated, all other performance capacities are affected because of the interdependence of acceleration, velocity, duration, and distance.

PREDATION ON NORTHERN BOBWHITE AND SCALED QUAIL BY SNAKES IN TEXAS, USA

Snakes are a known predator of quail; however, the influence of snake predation on quail populations is unknown. We used a long-term data set collected by eight radiotelemetry studies in Texas, encompassing 23 years (1994–2017) and 5,369 quail, to quantify snake predation on quail. We documented that northern bobwhite (Colinus virginianus) and scaled quail (Callipepla squamata) mortalities were caused by three species: western diamondback rattlesnakes (Crotalus atrox), prairie rattlesnakes (Crotalus viridis viridis), and Texas rat snakes (Pantherophis obsoletus). This study is the first to document predation of quail (Odontiphoridae) by the latter two species. We found 30 mortalities (0.6%) attributable to western diamondback rattlesnakes. We found 1 mortality (0.03%) attributable to a prairie rattlesnake and 2 mortalities (0.06%) attributable to Texas rat snakes of the 3,206 quail exposed to predation by those two species. We concluded that snakes are not major predators of adult quail, but that they will prey opportunistically upon them.

Geographic variation in body size and sexual size dimorphism of North American Ratsnakes (Pantherophis spp. s.l.)

Because body size affects nearly all facets of an organism’s life history, ecologists have long been interested in large-scale patterns of body-size variation, as well as why those large-scale patterns often differ between sexes. We explored body-size variation across the range of the sexually dimorphic Ratsnake complex (species of the genus Pantherophis Fitzinger, 1843 s.l.; formerly Elaphe obsoleta (Say in James, 1823)) in North America. We specifically explored whether variation in body size followed latitudinal patterns or varied with climatic variables. We found that body size did not conform to a climatic or latitudinal gradient, but instead, some of the populations with the largest snakes occurred near the core of the geographic range and some with the smallest occurred near the northern, western, and southern peripheries of the range. Males averaged 14% larger than females, although the degree of sexual size dimorphism varied between populations (range: 2%–25%). There was a weak trend for male body size to change in relation to temperature, whereas female body size did not. Our results indicate that relationships between climate and an ectotherm’s body size are more complicated than linear latitudinal clines and likely differ for males and females.

Eastern Bluebirds (Sialia sialis) do not abandon their chosen nest site in response to a single visit by a nest predator

ABSTRACT We investigated whether visual cues of a nest predator at the nest site prior to the completion of nest building would induce Eastern Bluebirds (Sialia sialis) to abandon their nesting attempt and switch to another box 10 m away. Upon detecting the onset of nest building in one of the paired boxes, we presented the birds with either a visual predator cue (a rubber black rat snake (Pantherophis obsoletus) or a visual control cue (a model Northern Cardinal (Cardinalis cardinalis) on the active nest box for 15 min and recorded the responses of the resident pair of bluebirds. We returned 1 week later to determine whether the presentation of the snake or cardinal resulted in no change, a switch to the other box, or abandonment of the box pair. Although the bluebirds seemed to respond more negatively to the model snake, we found no significant difference in their propensity to abandon the box pair (vs. remain in one of the paired boxes). We found a similar majority of bluebirds continued to nest in the...