Abstract
BackgroundGeographic variation in body size and condition can reveal differential local adaptation to resource availability or climatic factors. Body size and condition are related to fitness in garter snakes (Thamnophis), thus good body condition may increase survival, fecundity in females, and mating success in males. Phylogenetically related species in sympatry are predicted to exhibit similar body condition when they experience similar environmental conditions. We focused on interspecific and geographical variation in body size and condition in three sympatric Mexican garter snakes from the highlands of Central Mexico.MethodsWe assessed SVL, mass, and body condition (obtained from Major axis linear regression of ln-transformed body mass on ln-transformed SVL) in adults and juveniles of both sexes of Thamnophis eques, T. melanogaster, and T. scalaris sampled at different locations and ranges from 3–11 years over a 20-year period.ResultsWe provide a heterogeneous pattern of sexual and ontogenic reproductive status variations of body size and condition among local populations. Each garter snake species shows locations with good and poor body condition; juvenile snakes show similar body condition between populations, adults show varying body condition between populations, and adults also show sex differences in body condition. We discuss variations in body condition as possibly related to the snakes’ life cycle differences.
Highlights
Organisms usually respond to differences in environmental conditions by exhibiting local adaptation in phenotypic traits
To understand the complex evolution of body condition, we studied interspecific and geographical variation in traits known to be associated with body condition in three sympatric Mexican garter snakes (Thamnophis sp.) inhabiting five sites from the highlands of Central Mexico
Thamnophis melanogaster was slightly larger than T. scalaris (T. melanogaster: snout-vent length (SVL) 29.17 ± 41 cm [range 14.40–66.0], mass 19.10 ± 23.3 g [range 1.62–196.0], n = 686; T. scalaris: SVL 28.70 ± 9.21 cm [range 12.10–53.0], mass 16.44 ±12.59 g [range 1.30–60.70], n = 80)
Summary
Organisms usually respond to differences in environmental conditions by exhibiting local adaptation in phenotypic traits. Geographic variation in phenotypic traits associated with body size and condition can reveal differential adaptation of local populations to local biotic and abiotic fluctuations as presence of related species, resource availability, or climatic factors (Bronikowski & Arnold, 1999; Bronikowski, 2000; Miller et al, 2011). Geographic variation in body condition comes from many causes, including phenotypic plasticity (Krause, Burghardt & Gillingham, 2003) or microevolutionary change among natural populations (Bronikowski, 2000) These population differences may arise from geographic variation in food resources (Bronikowski & Arnold, 1999), climate (Ashton, 2001), or intra-inter species interactions (e.g., Kurzava & Morin, 1994). We discuss variations in body condition as possibly related to the snakes’ life cycle differences
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