Variation in Leg Color Does Not Influence Courtship Success in the
Red-legged Salamander, Plethodon shermani
Christy Baggett, Sarah Eddy, and Lynne Houck
Department of Zoology, Oregon State University, Corvallis, OR 97331
Abstract
The ritualized courtship of the Red-legged salamander, Plethodon shermani, has been studied extensively. Males and females possess brightly colored red legs, but little is known about the implications of this
coloration on mate choice. An alternative hypothesis is that coloration may be used as a warning signal to predators. Animals were collected in North Carolina and scored for leg coloration (1-10). To test the
hypothesis of mate choice, male and female animals varying in leg coloration were paired together in courtship trials and observed every 2 minutes. Linear regressions were performed on data collected to test
the predictions that (1) leg color is sexually dimorphic, (2) females prefer males with red legs, and (3) red coloration is condition-dependent. These analyses determined that none of the predictions were
sufficient support for the hypothesis of sexual selection for leg coloration; this lack of support gives strength to the alternative hypothesis of aposematic coloration by way of natural selection.
Discussion
Introduction
• In Plethodon shermani a visual display performed by the
male, foot-dancing, increases the likelihood of mating
success (Eddy 2012).
• Another visual cue in P. shermani, red leg coloration, and
the role it may play in either natural or sexual selection is
not understood.
• Research Question: Why do P. shermani have red legs?
• In three-spined sticklebacks, females prefer males based on
the intensity of red on their bodies (Milinksi & Bakker 1990),
an example of coloration due to mate choice.
• If sexual selection is responsible for red leg coloration, then
we might expect:
1. Leg color to be sexually dimorphic
2. Female preference for males with red legs
3. Red coloration to be condition-dependent
Figure 4. (A) Each male was
placed in box with one
female. Trials conducted
under low light conditions to
mimic levels in the field. (B)
40 pairs observed each trial.
Trials ran for 10 nights, with
1-2 days before the next
observation.
A
B
Figure 5. Variation in leg color
of P. shermani ranges from
very dark to bright red.
Results
Figure 1. Amount of red coloration on
legs does not vary based on sex
(β = 0.1311 ± 0.1716, p = 0.445).
Figure 2. Males with red on their
legs were no more successful in
courtship than males with darker
legs (β = -0.003963 ± 0.005563,
p = 0.481).
Figure 6. Female three-spined
stickelbacks prefer mates with more
intense color because it reveals physical
condition (Milinski & Bakker 1990).
Methods
• Animals collected from Macon Co., N.C. in August 2011.
• Biometric data collected (weight, snout-vent length, etc).
• Front and back legs assigned color score.
1 = < 10% red
4 = 70-89% red
2 = 11-39% red
5 = full sleeve, > 90% red
3 = 40-69% red
Total = front + back
• Courtship trials: each male paired with female and behavior of
male was recorded every 2 minutes.
• Results do not support the sexual selection hypothesis of red
legs as consequence of mate choice.
1. Red leg coloration is not sexually dimorphic (Figure 1).
2. Females did not preferentially mate with males who had
red legs (Figure 2).
3. Variation in red coloration did not correlate with
differences in body condition (Figure 3).
• Insufficient evidence for mate choice strengthens the
alternative hypothesis of aposematic coloration, a result of
natural selection.
• Taricha granulosa are a great example. Animals of this species
exhibit orange coloration on their ventrum as an aposematic
(warning) signal to advertise their extreme toxicity (Brodie et
al. 2005; Johnson et al. 1975).
Figure 3. Body condition
(weight/snout-vent length) was no
greater for males with red leg
coloration than for those with dark
legs
(β = -8.279 ± 11.538, p = 0.47745 ).
Figure 7. The orange color on the ventral
side of Taricha granulosa is an example of
aposematic coloration warning predators of
the newt’s lethal toxin (Brodie et al. 2005;
Johnson et al. 1975).
References
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Sperm Storage (Doctoral dissertation). Oregon State University, Corvallis, OR.
• Johnson, Judith A., and Edmund D. Brodie, Jr. 1975. The selective advantage of the defensive posture of
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