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Phylogeny, ecology, and heart position in snakes
Gabriel E A Gartner1, James W Hicks, Paulo R Manzani
1Department of Biology, University of California, Riverside, California 92521, USA. ggart001@ucr.edu
Physiological and Biochemical Zoology : PBZ
|December 9, 2009
Summary
Snake heart position is influenced by gravity, habitat, and evolutionary history. Contrary to previous beliefs, arboreal snakes tend to have more posterior heart placement, suggesting complex adaptations to gravity.
Area of Science:
- Cardiovascular Physiology
- Evolutionary Biology
- Herpetology
Background:
- Gravitational pressure gradients significantly impact animal cardiovascular systems, varying with organismal traits, behavior, and habitat.
- Previous research suggested arboreal snakes have anterior hearts to mitigate hydrostatic pressure during vertical postures, unlike aquatic species.
Purpose of the Study:
- To investigate the influence of phylogeny, habitat, and body size on heart position in Alethinophidia (snakes).
- To re-evaluate the hypothesis of anterior heart placement in arboreal snakes concerning gravitational effects.
Main Methods:
- Analysis of heart position data from 155 snake species across five major families of Alethinophidia.
- Application of conventional and phylogenetically informed statistical models, including general linear models and Ornstein-Uhlenbeck models.
- Comparison of model fit using likelihood ratio tests and Akaike Information Criterion.
Main Results:
- Snake heart position scales isometrically with snout-vent length (SVL).
- Phylogenetic models provided a better fit than nonphylogenetic models, indicating evolutionary influence.
- The best-fit model revealed arboreal snakes tend to have more posterior heart positions, contradicting prior findings.
Conclusions:
- Snake heart position is shaped by both habitat and evolutionary clade.
- The adaptation to gravitational pressure gradients in snakes likely involves a combination of cardiovascular and behavioral strategies, with relative heart location playing a nuanced role.
- Phylogenetic signal is significant in snake heart position, both within and across major snake groups.
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