Cranial Courtship Glands of Eurycea chamberlaini
Besides studies on mental glands, research regarding cranial integumentary glands potentially involved in courtship of plethodontid salamanders is scarce. In this study, we examined the cranial glands of Eurycea chamberlaini. Scattered amongst typical mucous and serous glands of the integument, we found simple alveolar glands that reacted positively with the periodic acid-Schiff procedure along the lateral sides of the heads of only male E. chamberlaini during the putative mating season. These glands were identical to the lateral head courtship glands previously described in E. bislineata. External nasal glands of E. chamberlaini were also identical in morphology and histology to those previously described in E. bislineata, with the bulk of the secretory terminals residing behind the orbital cavities and extending anteriorly to where their excretory ducts empty through the integument dorsal to the external nares. We measured external nasal gland length, width, height, and volume and found that the means were greater in males when compared to females except for width, which was not sexually dimorphic. We compared external nasal gland tubular diameter to mental gland tubular diameter (a known secondary sexual structure) throughout the year and found a direct correlation that was significant in males but not for females; thus, hypertrophy of external nasal glands occurs at the same time pheromone production increases in mental glands, supporting a previously proposed hypothesis that external nasal glands are also secondary sexual structures in Eurycea. In culmination, Eurycea from two different complexes possess the same suite of cranial integumentary glands that may be involved in courtship, providing evidence that these glands are possibly ubiquitous across Eurycea.
Lateral head courtship gland and external nasal gland histology. (A) Gross image of the dorsal surface of a male E. chamberlaini from December (scale bar = 1,000 µm). (B) Gross image of a dissected dorsal surface of the head from the same specimen depicted in A. (C) Complete transverse section of the head of a male E. chamberlaini from December at the approximate plane of section indicated by a dashed line labeled c in image A (hematoxylin and eosin; scale bar = 700 µm). (D) High magnification image from the dashed box labeled d in micrograph C highlighting a lateral head courtship gland (hematoxylin and eosin; scale bar = 200 µm). (E) Complete transverse section of the head of a male E. chamberlaini from June at the approximate plane of section indicated by a dashed line labeled e in image B (hematoxylin and eosin; scale bar = 500 µm). (F) High magnification image from the dashed box labeled f in micrograph E highlighting an external nasal gland (hematoxylin and eosin; scale bar = 200 µm). Eng, external nasal gland; Lcg, lateral head courtship gland; Og, orbital gland.
External nasal gland height, length, and width by sex. Lines inside boxes indicate medians, boxes indicate 25th and 75th percentiles, bars indicate 1.5x interquartile range, and points are individual measurements.
Joinpoint analysis for mean mental gland tubular diameter (A), mean male external nasal gland tubular diameter (B), and mean female external nasal gland tubular diameter (C).
Contributor Notes
Associate Editor: W. L. Smith.