Low Temperature Dormancy Affects the Quantity and Quality of the Female Sexual Attractiveness Pheromone in Red-sided Garter Snakes

Abstract

Low temperature dormancy is a necessary requirement of the annual cycle of most nonmigratory, temperate vertebrates. The red-sided garter snake, Thamnophis sirtalis parietalis, overwinters in communal dens during its prolonged winter dormancy (8 mo), and upon emergence, reproductive behavior of both sexes is maximal. Previous work on this species showed that male courtship behavior is maximally induced after simulated low temperature dormancy. The purpose of this study was to determine whether low temperature dormancy affects the pheromone profiles of individual female red-sided garter snakes. We collected females in the fall at den sites in Manitoba, Canada, and extracted pheromones from individuals at three different time points: fall (field), winter (lab), and spring (lab). Total skin lipid and pheromone fraction masses increased from fall to spring, and pheromone profiles were distinctly different in the fall and spring. Pheromone profiles became dominated by the long-chain, unsaturated methyl ketone components of the blend by the time snakes emerged in the spring. Further, the amounts of both saturated and unsaturated components increased from fall to spring, suggesting significant sex pheromone synthesis was induced by low temperature dormancy.

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“…There is interesting variability within groups, especially among females, and this corroborates findings from other studies on the composition of the red-sided garter snake sex pheromone (e.g. LeMaster and Mason, 2002;Parker and Mason, 2009). Previous work has shown that pheromone profiles can differ in their ratios of unsaturated (U) to saturated (S) methyl ketones (U:S) and that males rely on this ratio to make mate choice decisions (LeMaster and Mason, 2002;Parker and Mason, 2009).…”

“…Pheromone profiles were analyzed with the Multi Response Permutation Procedure (MRPP) followed by Bray-Curtis analysis using Sorenson distance for multiple comparisons [R statistical computing software (McCune et al, 2002)]. This method for pheromone analysis was also used in previous publications (Parker and Mason, 2009;Mason and Parker, 2010). We also generated the coordinates for non-metric multidimensional scaling (NMS) plots using the vegan package in R. All graphics were produced with SigmaPlot 8.0 (SysStat Software, Inc.).…”

“…E2 males differed from Sham males in their total pheromone compositions, both quantitatively (A0.2876, 0.2506, P<0.001; Fig.2B) and qualitatively (Fig.2C). When female pheromone extract data from another study (Parker and Mason, 2009) …”

“…LeMaster and Mason, 2002;Parker and Mason, 2009). Previous work has shown that pheromone profiles can differ in their ratios of unsaturated (U) to saturated (S) methyl ketones (U:S) and that males rely on this ratio to make mate choice decisions (LeMaster and Mason, 2002;Parker and Mason, 2009). We analyzed the U:S ratios for E2 vs Sham males and found that E2 males had much greater U:S ratios than Sham males (Mann-Whitney, U98.0, P<0.001; Fig.3A).…”

“…The composition of the pheromone relays several key pieces of information to males: species (Mason, 1993), population , sex (Mason et al, 1989), season Parker and Mason, 2009), reproductive condition (Shine et al, 2003), and age (LeMaster and Mason, 2002). More interesting is that male red-sided garter snakes can be deceived into courting other males that naturally produce small amounts of female sex pheromone ('she-males').…”