Elaphe

Abstract: A general model in thermal ecology predicts that ectotherms should stop thermoregulating when the costs outweigh the benefits. Support for this model comes from studies of warm-temperate species, but the extent to which the model can be extrapolated to species living in climatic extremes is unknown, because of the lack of information regarding the thermoregulatory behavior of such species. We tested the applicability of this cost-benefit model using data for black rat snakes (Elaphe obsolete obsoleta) studied at the northern extreme of their range in Ontario. During 1997-1999, we used automated temperature-sensitive radiotelemetry to collect -150000 body temperatures from 53 free- ranging rat snakes. Simultaneously, we used physical models of snakes to measure the environmental operative temperatures available to black rat snakes, and we determined their preferred body temperature range in a laboratory thermal gradient. The mostly forested habitats inhabited by rat snakes in Ontario were more thermally challenging than the habitats of other species studied to date. The preferred body temperature ranges of male, nongravid female, and gravid female black rat snakes were not significantly different (preferred body temperature averaged across all individuals, 28. 1C). However, free-ranging gravid females tended to maintain higher body temperatures in order to thermoregulate more effectively as well as exploit their thermal environment more than males and nongravid females. This difference was most pronounced during the day and prior to egg laying, and constituted the first documentation of such a phenomenon in an oviparous snake. Black rat snakes had indices of thermoregulation effectiveness similar to other species but tended to exploit opportunities for thermoregulation less. Overall, our data provided support that was at best ambiguous for the current cost-benefit thermoregulation model, suggesting that this model may generally be less applicable to species inhabiting climatic extremes. We propose that, for species in extreme climates, the costs associated with thermoconformity may be more important than previously recognized. We identified several problems associated with the index of thermoregulation effectiveness used by previous researchers, and we propose a mathematically simpler alternative that circumvents these problems. We also make rec- ommendations regarding the future use of the various indices of thermoregulation developed in recent years.

Abstract: Radio transmitters embedded in silicone rubber in elongate, oval, smooth-surfaced packages 50 x 21 x 14 mm or a little larger, were forcefed to 67 snakes of eight species (a 68th snake had an abdominally implanted transmitter), which were then trailed on a day to day basis. Forty per cent of all snakes located had made no movement since the previous day. Average distances, in meters covered per day, were: 142, Pituophis melanoleucus; 51.3, Elaphe obsoleta; 44.7, Crotalus horridus; 28.5, Coluber constrictor; 10, Thamnophis sirtalis; 8, Agkistrodon contortrix; 7, Lampropeltis calligaster; 3.7, Natrix sipedon. Movements were irregular and erratic. For periods of 15-30 days the trailed snakes usually moved progressively farther from their starting points. Three displaced snakes exhibited no homing ability. One female N. sipedon made short, irregular movements typical of resident individuals. A displaced male A. contortrix made an unusually long movement the first night, then settled down to a pattern of short, irregular movements like those of residents. A displaced female C. horridus moved away from the release point but did not travel toward its place of origin approximately 10 km distant.

Abstract: Thermoregulation is thought to be the most important factor influencing habitat selection by terrestrial ectotherms, at least in temperate climates. The cost-benefit model of thermoregulation predicts that ectotherms should invest more in thermoregulation when the costs of doing so are low (when the thermal quality of the habitat is high). However, the extent to which ectotherms vary their thermoregulatory behaviour according to the thermal quality of habitats is currently unknown. We studied the relationship between habitat use and thermoregulation in 53 black rat snakes using temperature-sensitive radio-transmitters. Among the habitats available to black rat snakes, edges had the highest thermal quality, retreat sites and forest were intermediate, and open habitats had the lowest thermal quality. Black rat snakes experienced more favourable body temperatures while in barns (retreat sites) than in edges, and in edges than in forest. During the day, the effectiveness and the extent of thermoregulation by the snakes were equal in barns and forest, but much lower in edges. In fact, black rat snakes selected thermally favourable microhabitats less than their availability while in edges. Therefore, more favourable body temperatures were not necessarily achieved in thermally superior habitats by increased thermoregulation, but simply because favourable temperatures were encountered more often in those habitats. This result is contrary to the central prediction of the cost-benefit model of thermoregulation and we suggest that this model should be modified to put more emphasis on other costs of thermoregulation, such as increased predation risk or lost foraging opportunities.

Abstract: The phylogenetic relationships of the Holarctic ratsnakes (Elaphe auct.) are inferred from portions of two mitochondrial genes, 12S rRNA and COI. Elaphe Fitzinger is made up of ten Palaearctic species. Natrix longissima Laurenti (type species) and four western Palaearctic species (hohenackeri, lineatus, persicus, and situla) are assigned to Zamenis Wagler. Its phylogenetic affinities with closely related genera, Coronella and Oocatochus, remain unclear. The East Asian Coluber porphyraceus Cantor is referred to a new genus. This taxon and the western European Rhinechis scalaris have an isolated position among Old World ratsnakes. Another new genus is described for four Oriental species (cantoris, hodgsonii, moellendorffi, and taeniurus). New World ratsnakes and allied genera are monophyletic. Coluber flavirufus Cope is referred to Pseudelaphe Mertens and Rosenberg. Pantherophis Fitzinger is revalidated for Coluber guttatus L. (type species) and further Nearctic species (bairdi, obsoletus, and vulpinus). Senticolis triaspis is the sister taxon of New World ratsnakes including the genera Arizona, Bogertophis, Lampropeltis, Pituophis, and Rhinocheilus. The East Asian Coluber conspicillatus Boie and Coluber mandarinus Cantor form a monophyletic outgroup with respect to other Holarctic ratsnake genera and are referred to Euprepiophis Fitzinger. Three Old World species, viz. Elaphe (sensu lato) bella, E. (s.l.) frenata, and E. (s.l.) prasina remain unassigned. The various groups of ratsnakes (tribe Lampropeltini) show characteristic hemipenis features.