The evolution of scale sensilla in the transition from land to sea in elapid snakes.
Scale sensilla are small tactile mechanosensory organs located on the head scales of many squamate reptiles (lizards and snakes). In sea snakes and sea kraits (Elapidae: Hydrophiinae), these scale organs are presumptive scale sensilla that purportedly function as both tactile mechanoreceptors and potentially as hydrodynamic receptors capable of sensing the displacement of water. We combined scanning electron microscopy, silicone casting of the skin and quadrate sampling with a phylogenetic analysis to assess morphological variation in sensilla on the postocular head scale(s) across four terrestrial, 13 fully aquatic and two semi-aquatic species of elapids. Substantial variation exists in the overall coverage of sensilla (0.8-6.5%) among the species sampled and is broadly overlapping in aquatic and terrestrial lineages. However, two observations suggest a divergent, possibly hydrodynamic sensory role of sensilla in sea snake and sea krait species. First, scale sensilla are more protruding (dome-shaped) in aquatic species than in their terrestrial counterparts. Second, exceptionally high overall coverage of sensilla is found only in the fully aquatic sea snakes, and this attribute appears to have evolved multiple times within this group. Our quantification of coverage as a proxy for relative 'sensitivity' represents the first analysis of the evolution of sensilla in the transition from terrestrial to marine habitats. However, evidence from physiological and behavioural studies is needed to confirm the functional role of scale sensilla in sea snakes and sea kraits.
School of Biological Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia jenna.crowe-riddell@adelaide.edu.au.
Jenna M
JM
Crowe-Riddell
Brain Function Research Group, School of Physiology, University of the Witwatersrand, Johannesburg, Gauteng 2193, South Africa.
Edward P
0000-0002-8985-8737
EP
Snelling
School of Biological Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia.
Amy P
AP
Watson
School of Biological Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia.
Anton Kyuseop
AK
Suh
School of Animal Biology and Oceans Institute, University of Western Australia, Crawley, Western Australia 6009, Australia.
Julian C
JC
Partridge
School of Biological Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia.
Kate L
KL
Sanders
D000818:Animals; D005075:Biological Evolution; D017753:Ecosystem; D017815:Elapidae / Q000145:classification / Q000502:physiology*; D010802:Phylogeny; D058618:Sensilla / Q000502:physiology*; D013045:Species Specificity
elapid; hydrodynamic; mechanoreceptor; sea snake; sensilla; sensory