Pheromones are chemical cues produced by organisms that affect the behavior
and/or physiology of conspecifics. The orchestration of reproductive behaviors in many
animals depends on the expression of sex pheromones. In insects, intraspecific variation
in sex pheromone expression is commonly observed and often influences social
interactions between individuals. To what extent similar variation is present in vertebrate
sex pheromone systems is not well understood. This thesis investigated the occurrence
and significance of phenotypic variation in the sexual attractiveness pheromone of the
red-sided garter snake, Thamnophis sirtalis parietalis. Composed of a homologous series
of saturated and unsaturated methyl ketones sequestered in the skin lipids of females, this
pheromone elicits male courtship behaviors during the breeding season.
Variation in the expression of the sexual attractiveness pheromone was examined
at three levels: seasonal, individual and populational. Seasonal variation in pheromone
expression was examined with respect to trailing behavior. In field experiments, males
followed female trails during the breeding season but not during the non-breeding season.
Skin lipid analysis revealed marked differences in pheromone composition between the
two seasons, suggesting a role for this pheromone in regulating male trailing behavior.
Individual variation in pheromone expression was examined with respect to mate choice.
In arena trials, males displayed a courtship preference for larger females and continued to
demonstrate this preference when visual, tactile, and behavioral cues from the females
were removed through the use of skin lipid extracts. Analysis of pheromone profiles
from individual females showed size-specific variation in composition, demonstrating
that this pheromone can function as a reliable indicator of female size. Finally,
populational variation in pheromone expression was examined with respect to sexual
isolation among hibernacula. In arena and trailing experiments, males preferred to court
and trail resident (same den) females over non-resident (distant den) females. Chemical
analysis showed significant inter-den variation in pheromone composition, suggesting
that this pheromone represents the cue that males use to identify females from their own
population. In summary, these studies demonstrate that significant variation exists in the
female sexual attractiveness pheromone of the red-sided garter snake and suggest that this
variation has functional significance for this species. / Graduation date: 2002
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/32526 |
| Date | 21 September 2001 |
| Creators | LeMaster, Michael P. |
| Contributors | Mason, Robert T. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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