Interspecific variation in the female sexual attractiveness pheromone of garter snakes
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of the Red-sided Garter Snake, Thamnophis sirtalis parietalis ... Male red-sided garter snakes preferentially courted red-sided and red-spotted females ...

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Interspecific variation in the female sexual attractiveness pheromone of garter snakes l.jpg

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


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Interspecific Variation:

+

Species 1

Species 2

Prezygotic Isolation

Benefit?

Prevents production of hybrids (inviable or reduced fitness…)


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Interspecific Variation:

Cope’s Gray Tree Frog

Hyla chrysoscelis

Black-chinned

Mountain Tanager

(Anisognathus notabilis)

Blue-winged

Mountain Tanager

(Anisognathus somptuosus)

Eastern Gray Tree Frog

Hyla versicolor

Vocalizations

  • Frequency

  • Duration

Coloration


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Interspecific Variation:

Chemical

Silver Y moth

(Autographa gamma)

Essex Y moth

(Cornutiplusia circumflexa)

(Z)-7-dodecen-1-ol

(Z)-7-dodecenyl acetate


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Introduction:

Pheromone:

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


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Interspecific Variation:

General Question

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


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Model System:

The Red-sided Garter Snake

Thamnophis sirtalis parietalis


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Model System:

Vomeronasal Organ:


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Model System:

Female Sexual Attractiveness Pheromone

of the Red-sided Garter Snake, Thamnophis sirtalis parietalis

  • Potential variation:

  • Quantity

  • Absence/presence

  • Relative concentrations


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Interspecific Variation:

Question

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


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Interspecific Variation:

Red-sided Garter Snake

(Thamnophis sirtalis parietalis)

Red-spotted Garter Snake

(Thamnophissirtalisconcinnus)

Sympatric

Sympatric

Plains Garter Snake

(Thamnophis radix)

Northwestern Garter Snake

(Thamnophis ordinoides)

Subspecies

Allopatric


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Behavior Trials:

Courtship Preference Tests

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


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Interspecific Variation:

Hypothesis

The chemical profile of the female sexual attractiveness pheromone will exhibit

interspecific variation.

Predictions

  • 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.


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Interspecific Variation - Chemical Analysis:

Collection

Hexane Wash

Extraction

Fractionation

GC/MS


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Interspecific Variation - Chemical Analysis:

Measures of Pheromone Variation:

1) Quantitative

2) Qualitative

# of Compounds

Present

Relative

[individual compounds]

(?)

=

(?)

(?)

mg

=

mg

% MK (of total lipids)


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Results:

Interspecific Variation in Pheromone Quantity:

Relative Amount of Pheromone Expressed on Surface of Females


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Results:

Interspecific Variation in Pheromone Quality:

Number of Unique Methyl Ketones Expressed


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Results:

Interspecific Variation in Pheromone Quality:

Relative Concentrations of Individual Methyl Ketones


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Results:

Non-metric multi-dimensional scaling plot

of individual pheromone profiles

Thamnophis sirtalis parietalis

Thamnophis sirtalis concinnus

Thamnophis radix

Thamnophis ordinoides


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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


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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?


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Acknowledgements:

Dr. Robert Mason

Dr. Michael LeMaster

Dr. Kevin Ahern

HHMI

Chelsey Miller

Rocky Parker

Chris Friesen

Everyone in the Mason lab


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