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.

Phenotypic consequences of nest-site selection in black rat snakes (Elaphe obsoleta)

Nest-site selection is the only behaviour that can be considered parental care in most oviparous reptiles because eggs are abandoned after laying and because incubation conditions resulting from nest-site selection can have profound effects on offspring. During a 7-year study of black rat snakes, Elaphe obsoleta (Say in James, 1823), we investigated phenotypic effects of incubation temperature on hatchlings, monitored temperatures in nests, and determined the preferred nesting temperature. Temperatures of communal nests were higher than those of single-female nests. In the laboratory, females preferred to nest at temperatures most similar to those of communal nests. Hatchlings from eggs incubated at temperatures similar to those in the warmer communal nests hatched faster, were longer, swam faster, were less aggressive, and had fewer scale anomalies than hatchlings from eggs incubated at temperatures similar to those in single nests. A possible disadvantage of communal nests is that eggs in communal nests may be at greater risk to parasitism by Nicrophorus pustulatus (Herschel, 1807). The incubation experiment allowed a test of a key assumption of a model proposed to explain environmental sex determination. Contrary to that assumption, we found no evidence that incubation temperature affected males and females differently. Our results might explain why temperature-dependent sex determination appears not to occur in snakes.

Implications of movement patterns for gene flow in black rat snakes (Elaphe obsoleta)

Gene flow is fundamental to evolutionary processes but knowledge about movements of individuals and their offspring necessary for gene flow is scant. We investigated potential ecological components of genetic connectivity within a population of black rat snakes (Elaphe obsoleta) by radio-tracking 82 individuals. Because adult black rat snakes are highly faithful to their hibernaculum, gene flow between hibernaculum populations has to occur through mating between members of different hibernacula or through juvenile dispersal. The present study was the first to assess the spatial dispersion of a complete network of hibernacula. The mean distance between the nearest-neighbour hibernacula was 811 m, which was less than the mean distances that reproductive males and females were found from their hibernacula during the mating season. Estimates of maximum distances individuals were from their hibernacula during the mating season indicated that, on average, a female was likely to mate with males that came from two hibernacula away from the female's own hibernaculum. Both males and females appeared to contribute actively to gene flow by moving more and increasing their distance from their hibernacula during the mating season. In addition, on average, females nested closer to a hibernaculum other than the one they attended, thereby potentially increasing the likelihood that their offspring would join hibernacula other than their mothers'. Thus, spatial and movement patterns of male and female black rat snakes are consistent with genetic evidence of extensive out-breeding among local hibernaculum populations.