A snake of a different color: physiological color change in Arizona black rattlesnakes

Coloration may serve a variety of behavioral (e.g., crypsis, communication) and physiological (e.g., thermoregulation, protection) functions for terrestrial ectotherms. However, optimal coloration for a given function may vary over environments (spatial or temporal) or conflict with other functions. Physiological color change (rapid change due to movement of pigment granules within chromatophores) may be an adaptation to resolve conflicting selective pressures on coloration. The proximate factors related to physiological color change are well known in many animals, but few studies have investigated the ecological or evolutionary implications of this behavior. Here, we present alternative hypotheses for physiological color change and discuss biotic and abiotic factors that may have led to the maintenance and/or loss of this behavior among populations of Arizona black rattlesnakes (_Crotalus cerberus_). We discuss what is known about this behavior and propose to investigate the function and evolution of coloration and color change in _C. cerberus_

Mating systems, reproductive success, and sexual selection in secretive species: a case study of the western diamond-backed rattlesnake, Crotalus atrox.

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

Summary of individuals tracked via radio-telemetry.

1<p>Indicates the total number of consecutive calendar years in which an individual was followed via radio-telemetry.</p

Summary of genetic parents identified for all litters of genotyped neonates.

1<p>Litter sizes of one indicate a sole neonate found after dispersal from birth site.</p>2<p>CA  =  <i>Crotalus atrox,</i> UM  =  Unmarked male.</p>3<p>Parentheses after male names indicate total number of offspring fathered in litter when that number is greater than one.</p>4<p>Number of males that female was found paired with during the fall and or spring mating period preceding parturition. NA (not applicable) indicates female was not telemetered prior to parturition.</p>5<p>Of those males found paired with females in the preceding fall and or spring mating periods, the number that were genetic fathers of any offspring in the litter. See text for details.</p

Sexual behavior in <i>Crotalus atrox</i>.

<p>(a) Pair of <i>C. atrox</i> in coitus. Unknown male (left) with female CA-3, September 13, 2001. (b) Pair of <i>C. atrox</i> in courtship below a den site. The lower body and tail of unknown male is wrapped over and around tail of female CA-44 (painted rattles), March 2012. Photographs by Roger Repp.</p

Size comparisons among males.

<p>Comparisons show average size and standard error of males identified as genetic fathers versus those that were not (fathers versus non-fathers), males that were the only father identified in a litter versus those that shared paternity with other males (sole paternity verus shared paternity), males that were seen attending females during the mating season versus those that were not seen to do so (attend females versus not attend), and males that attended females for longer than one week versus those attending females less than a week (long attend versus short attend).</p