Abstract
Long-term studies of individual animals in nature contribute disproportionately to our understanding of the principles of ecology and evolution. Such field studies can benefit greatly from integrating the methods of molecular genetics with traditional approaches. Even though molecular genetic tools are particularly valuable for species that are difficult to observe directly, they have not been widely adopted. Here, we used molecular genetic techniques in a 10-year radio-telemetric investigation of the western diamond-backed rattlesnake (Crotalus atrox) for an analysis of its mating system and to measure sexual selection. Specifically, we used microsatellite markers to genotype 299 individuals, including neonates from litters of focal females to ascertain parentage using full-pedigree likelihood methods. We detected high levels of multiple paternity within litters, yet found little concordance between paternity and observations of courtship and mating behavior. Larger males did not father significantly more offspring, but we found evidence for size-specific male-mating strategies, with larger males guarding females for longer periods in the mating seasons. Moreover, the spatial proximity of males to mothers was significantly associated with reproductive success. Overall, our field observations alone would have been insufficient to quantitatively measure the mating system of this population of C. atrox, and we thus urge more widespread adoption of molecular tools by field researchers studying the mating systems and sexual selection of snakes and other secretive taxa.
Highlights
The long-term study of individual organisms in nature plays a central role in our understanding of ecology and evolution [1]
We found males between 700-900 mm snout-vent length (SVL) increased in length 35 mm per year, but male growth slowed at about 900 mm SVL, and males greater than 900 SVL increased in length 11 mm per year
Our analysis was unable to show that fathers were larger than non-fathers, which may be due to sample size, we found limited evidence for size-specific male mating strategies
Summary
The long-term study of individual organisms in nature plays a central role in our understanding of ecology and evolution [1]. Long-term investigations are necessary to interpret the processes affecting survival and reproduction played out over the course of multiple years, or even decades [2]. Such studies are few and there is a strong taxonomic bias. All of the studies cited in Clutton-Brock and Sheldon [1] concern mammals and birds. This bias toward endotherms is most likely related to the fact that these species can be observed in nature more . In our view, long-term studies on these taxa may disproportionately benefit from techniques that allow researchers to infer patterns of intraspecific interactions that are difficult or not possible to document by way of direct observation
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