Pure-Reptiles

Zitat

The infrared organs of boas, pythons, and pit vipers are true eyes that function not by a photochemical reaction but on the basis of heat generated in the receptors (called terminal nerve masses, TNMs), by electromagnetic radiation. In the pythons and pit vipers, the pit opening acts as the aperture of a pinhole camera, a virtual lens that permits the receptors to encode the movements of an infrared source sufficiently for the brain to form an image. Many boid snakes possess TNMs identical to those of the pythons but lack an opening that could serve as a lens. All TNMs are irrigated by a dense capillary network that serves as a heat regulator, mimicking the role of the photochemical cycle in the lateral eyes. Thus, the pits are an integral part of the snakes' visual system, which makes use of the longer waves of the electromagnetic spectrum for which there are no appropriate photoreceptive pigments in nature; they do everything the eyes do. They are definitely not, as they have often been treated, a “sixth sense,” useful only for the detection and acquisition of prey. Just as the world that most insects see includes both the visual and the ultraviolet spectra, so the world that boas, pythons, and pit vipers see includes both the visual and the infrared spectra.

Zitat

In an era of rapidly changing environments and greater human mobility and penetration into wild areas, organisms are being discovered in increasingly unexpected places. One such finding is a road-killed juvenile gartersnake (Thamnophis) outside of Haines, Alaska, in August 2005. The poor condition of the specimen prevented a positive identification based on morphology alone. Furthermore, no snakes are known to be native to this region. We therefore undertook a molecular approach to determine the species and geographic origin of the individual. We sequenced two partial loci of mitochondrial DNA (cytochrome b and NADH subunit 2) from the Alaska specimen and seven specimens from localities in the lower northwestern United States. Phylogenetic reconstruction using our sequences and additional GenBank samples unambiguously revealed that the Alaska specimen is Thamnophis ordinoides and that it shares a haplotype with the northernmost sampled Washington population of T. ordinoides. In light of these analyses, we assess the likelihood that the specimen represents a relict population, a recent natural colonization, or a fresh introduction.