Interspecific Variation in the Female Sexual Attractiveness Pheromone

of Garter Snakes

Emily Uhrig

Mentors: Dr. Robert Mason, Oregon State University

Dr. Michael LeMaster, Western Oregon University

Interspecific Variation:

Prezygotic Isolation

+Species 1 Species 2

Prevents production of hybrids (inviable or reduced fitness…)

Benefit?

Black-chinned Mountain Tanager(Anisognathus notabilis)

Blue-winged Mountain Tanager(Anisognathus somptuosus)

Coloration

Vocalizations

• Frequency

• Duration

Interspecific Variation:

Eastern Gray Tree Frog

Hyla versicolor

Cope’s Gray Tree Frog

Hyla chrysoscelis

Interspecific Variation:

Chemical

Essex Y moth

(Cornutiplusia circumflexa)

Silver Y moth

(Autographa gamma)

(Z)-7-dodecenyl acetate (Z)-7-dodecen-1-ol

Pheromone:

A chemical cue produced by an individual that affects the physiology and/or behavior of a member of the same species.

Introduction:

Interspecific Variation:

General Question

Do vertebrate pheromone systems exhibit the interspecific variation necessary for pheromones to function as mechanisms of reproductive isolation?

The Red-sided Garter SnakeThamnophis sirtalis parietalis

Model System:

Vomeronasal Organ:

Model System:

Female Sexual Attractiveness Pheromone of the Red-sided Garter Snake, Thamnophis sirtalis parietalis

Model System:

Potential variation:

• Quantity

• Absence/presence

• Relative concentrations

Question

Does the female sexual attractiveness pheromone vary between garter snake species?

Interspecific Variation:

Interspecific Variation:

Red-sided Garter Snake(Thamnophis sirtalis parietalis)

Red-spotted Garter Snake(Thamnophis sirtalis concinnus)

Plains Garter Snake(Thamnophis radix)

Northwestern Garter Snake(Thamnophis ordinoides)

Subspecies

Sympatric Sympatric

Allopatric

Courtship Preference Tests

Behavior Trials:

Male red-sided garter snakes preferentially courted red-sided and red-spotted females over northwestern and plains females.

Interspecific Variation:

Hypothesis

The chemical profile of the female sexual attractiveness pheromone will exhibit

interspecific variation.

Relatively little difference between the pheromone profiles of red-sided and red-spotted.

Significant difference between the pheromone profiles of red-sided and plains.

Significant difference between the pheromone profiles of red-spotted and northwestern.

Predictions

Collection

Hexane Wash

Fractionation

Extraction

GC/MS

Interspecific Variation - Chemical Analysis:

Measures of Pheromone Variation:

1) Quantitative 2) Qualitative

# of CompoundsPresent

Relative[individual compounds]

= mg

% MK (of total lipids)

(?)

(?) (?)

Interspecific Variation - Chemical Analysis:

= mg

Results:

Interspecific Variation in Pheromone Quantity:Relative Amount of Pheromone Expressed on Surface of Females

Results:

Interspecific Variation in Pheromone Quality:Number of Unique Methyl Ketones Expressed

Results:

Interspecific Variation in Pheromone Quality: Relative Concentrations of Individual Methyl Ketones

Results:

Non-metric multi-dimensional scaling plotof individual pheromone profiles

Thamnophis sirtalis parietalis

Thamnophis sirtalis concinnus

Thamnophis radix

Thamnophis ordinoides

Conclusion:

Predictions

Red-sided vs. red-spotted: little difference

Red-sided vs. plains: significant difference

Red-spotted vs. northwestern: significant difference

Pheromone Quantity

• Red-sided significantly different from other species Newly emerged…

Pheromone Quality

• Significant differences between all four species

Conclusion:

Do vertebrate pheromone systems exhibit the interspecific variation necessary for pheromones

to function as mechanisms of reproductive isolation?

Future Work

Include behavioral tests with males of other species

Are they “fine-tuned” enough to recognize the variation?

Acknowledgements:

Dr. Robert Mason

Dr. Michael LeMaster

Dr. Kevin Ahern

HHMI

Chelsey Miller

Rocky Parker

Chris Friesen

Everyone in the Mason lab