Pitviper Embryology: The Development of the Loreal Pit Organ in the Brazilian Pitviper Bothrops jara
Wouters, Roel M.
de Bakker, Merijn A.G. Richardson, Michael K. Animal Sciences & Health Institute of Biology Leiden Leiden University Leiden, Netherlands
Pitvipers (Crotalinae) are a subfamily of venomous snakes, which are characterized by an infra-red sensing organ called the loreal pit organ. The loreal pit organ is bilaterally located between the eye and nostril and consists of a posterior (inner) chamber and an anterior (outer) chamber septated by a heavily innervated membrane. By detecting infra-red radiation on the pit membrane, the loreal pit organ functions in prey acquisition and behavioural thermoregulation. Here, we study the developmental biology of the loreal pit organ in a rare embryo-series of the Brazilian pitviper Bothrops [Bothropoides] jararaca and the Malayan pitviper Calloselasma rhodostoma. The embryos have been stained with phosphotungstic acid before being scanned using X-ray microcomputed tomography (Micro-CT). The scans were used for 3D reconstruction. Afterwards, several embryos were selected and sectioned for paraffin histology. All together these resulted in a time-series showing embryonic development of the loreal pit organ. We found the loreal pit organ only forms after the other sensory organs have already well developed. We also found the development of the loreal pit organ starts with an invagination of skin epidermis, forming the outer chamber. Later, posterior of the outer chamber the inner chamber forms consisting of duct-like epithelium. The innervated pit membrane consists of connective mesenchyme and grows thinner during development. Our findings suggest that the outer and inner chamber have different origins with the pit membrane connecting them. We are still investigating whether the inner chamber is part of the lacrimal system. Our study contributes to a better understanding of the complex developmental and evolutionary origins of the loreal pit organ in pitvipers.