Seasonal Dynamics of Head Shape in Eurycea chamberlaini (Caudata, Plethodontidae, Spelerpini)
Males of some species of Eurycea exhibit gross morphological shape changes of their heads throughout the year because of hypertrophy of jaw musculature during the mating season, although glandular swelling of the integument has not been rejected for all taxa. We assessed head shape variation of a species from the Eurycea quadridigitata complex, E. chamberlaini, throughout the year to examine seasonal variation in head shape in a diminutive species where this has never been reported. We found that male specimens differed from females in terms of morphospace and, similar to other species of Eurycea, male heads were wider posterior to the orbital region relative to anterior. Interestingly, we also recovered the same result for females, demonstrating that head shape varies seasonally in both sexes of E. chamberlaini. Collectively, these results indicate that hypertrophy and atrophy of jaw muscles, or potentially integumentary glands, not only occurs in males and females of the Eurycea bislineata complex, but also may be more ubiquitous within the genus. The previous lack of this observation within the E. quadridigitata complex is most likely the result of difficulty in observing head shape variation in a diminutive species similar to E. chamberlaini without the use of large datasets and morphometric analysis.
Landmarks used for geometric morphometric analysis of dorsal cranial view of heads from male and female Eurycea chamberlaini (male pictured). Dorsal landmarks include the anterior-most point on the head (20), left posterior distal aspect of jaw (1), right posterior distal aspect of jaw (30), and 36 pseudolandmarks assigned using a fractional semilandmark shape template.
Canonical variates histogram depicting sexual dimorphic head shape variation between males and females (df = 74, F = 6.12, P < 0.0001). Orange indicates overlap between the sexes.
Canonical variates histogram depicting head shape variation between mating and non-mating females designated by collection season (df = 814, F = 2.28, P < 0.0001). Orange indicates overlap between mating and non-mating individuals.
Canonical variates ordination depicting morphospace separation among mating males, mating females, non-mating males, and non-mating females. Confidence ellipses are shown as 90% confidence of the means. Transformation grids elucidate shape variation at poles of CV1 and CV2. Results here indicate separation in morphospace between males and females along CV1 and separation in morphospace between mating conditions within sex along CV2.
Canonical variates histogram depicting head shape variation between mating and non-mating males designated by collection season (df = 814, F = 5.12, P < 0.0001). Orange indicates overlap between mating and non-mating individuals.
Contributor Notes
Associate Editor: W. L. Smith.