Cone-like rhodopsin expressed in the all cone retina of the colubrid pine snake as a potential adaptation to diurnality

Colubridae is the largest and most diverse family of snakes, with visual systems that reflect this diversity, encompassing a variety of retinal photoreceptor organizations. The transmutation theory proposed by Walls postulates that photoreceptors could evolutionarily transition between cell types in squamates, but few studies have tested this theory. Recently, evidence for transmutation and rod-like machinery in an all cone retina has been identified in a diurnal garter snake (Thamnophis), and it appears that the rhodopsin gene at least may be widespread among colubrid snakes. However, functional evidence supporting transmutation beyond the existence of the rhodopsin gene remains rare. We examined the all cone retina of another diurnal colubrid,Pituophis melanoleucus, distantly related toThamnophis. We found thatP. melanoleucusexpresses two cone opsins (SWS1, LWS) and rhodopsin (RH1) within the eye. Immunohistochemistry localized rhodopsin to the outer segment of photoreceptors in the all-cone retina of the snake and all opsin genes produced functional visual pigments when expressedin vitro. Consistent with other studies, we found thatP. melanoleucusrhodopsin is extremely blue-shifted. Surprisingly,P. melanoleucusrhodopsin reacted with hydroxylamine, a typical cone opsin characteristic. These results support the idea that the rhodopsin-containing photoreceptors ofP. melanoleucusare the products of evolutionary transmutation from rod ancestors, and suggests that this phenomenon may be widespread in colubrid snakes. We hypothesize that transmutation may be an adaptation for diurnal, brighter-light vision, which could result in increased spectral sensitivity and chromatic discrimination with the potential for colour vision.Summary StatementThe all cone retina of the colubrid snake,Pituophis melanoleucuscontains a blue-shifted rhodopsin with cone opsin-like properties, which may have been adaptive in diurnal snakes.

Radiocarbon Dates from the Pine Snake Site (41CE467), Cherokee County, Texas

The Pine Snake site is a late 17th to early 18th century Caddo Indian archaeological site located on private land in the northwestern part of Cherokee County, Texas, in the valley of the westward-flowing Flat Creek, a tributary to the Neches River. This is an area of the Pineywoods of East Texas that contains extensive numbers of Caddo archeological sites along all major and minor streams. Post-A.D. 1400 Frankston phase and post-A.D. 1650 Historic Caddo Allen phase sites, especially cemeteries dating to either phase, are particularly abundant in this part of East Texas. However, not many of these sites in the upper Neches River basin have had radiocarbon assays obtained from charred plant remains in feature contexts, and consequently the absolute age of most of these ancestral Caddo components and phases are not well or definitively established. Fortunately, charred Carya sp. nutshells are abundant in feature contexts in habitation deposits at the Pine Snake site, and samples of these remains have been submitted to DirectAMS (Seattle, Washington) for radiocarbon dating.

Archaeological Investigations at the Pine Snake Site, an Allen Phase Settlement on Flat Creek in Northwestern Cherokee County, Texas

The Pine Snake site is a recently discovered late 17th to early 18th century Caddo Indian archaeological site located on private land in the northwestern part of Cherokee County, Texas, in the valley of a westward flowing tributary to the Neches River. This is an area of the Pineywoods of East Texas that contains extensive numbers of Caddo archaeological sites along all major and minor streams. Post-A.D. 1400 Frankston phase and post-A.D. 1650 Historic Caddo Allen phase sites, especially cemeteries dating to either phase, are particularly abundant in this part of East Texas. This article summarizes the findings from archaeological investigations we completed at the Pine Snake site in late 2008. They have produced important information on the domestic archaeological record at a well preserved Allen phase habitation site.