External nasal gland morphology of Eurycea bislineata (Amphibia, Urodela, Plethodontidae)

Abstract

Plethodontid salamanders possess numerous courtship glands. Previous studies have shown that the glands are more prominent in male individuals than females, and often experience periods of atrophy and hypertrophy throughout the year that correlate to the nonmating and mating seasons, respectively. We sampled male and female Eurycea bislineata throughout the year to test the hypothesis that external nasal glands are courtship glands. External nasal glands are paired, branched tubular glands that extend from excretory ducts dorsal to the nares to terminal secretory units posterior to the eyes. We found that the glands hypertrophy and stain/react more intensely with histochemical procedures during the mating season. Hypertrophy of the glands is more pronounced in males, and seasonal variation in epithelial height of external nasal glands of males is significantly correlated to that of seasonal variation in mental gland epithelial height, a known courtship gland found in males, when compared throughout the year. This correlation was not as strong in females, confirming sexual dimorphism of external nasal glands in terms of seasonal variation. We found no ultrastructural differences between male and female external nasal glands. In all specimens, the glandular tubules were lined by a simple, columnar epithelium that was packed with secretory granules that often obscured other cytoplasmic contents.

Sexually Dimorphic Biofluorescence of the Postcloacal Gland in the Terrestrial Salamander, Plethodon cinereus

“…We found that fluorescence in males peaked in October, declined through late fall, and was at its lowest in March and April. This peak in fluorescence falls within the extended mating season reported by other researchers (Sayler, 1966; Werner, 1969; Sever, 1997; Sever and Siegel, 2006) which lasts from October to April, and corresponds to the pattern of hypertrophy in the breeding season and atrophy outside the breeding season in courtship glands in other plethodontids (Rupp and Sever, 2018; Trame et al, 2022). Perhaps more importantly, a study examining seasonal variation in testosterone levels in Eastern Red-backed Salamanders found that levels peaked in September and October (Church and Okazaki, 2002) which corresponds to our peak in fluorescence of the PCG.…”

“…Note also that it is the orangecolored glands that fluoresce in both sexes. Our data suggest that, in P. cinereus, the PCG of males is made up of larger S1 glands than that of females, a size difference found in other glands in related species (Rollins and Staub, 2017;Trame et al, 2022). Additionally, because we found large differences in the numbers of fluorescent glands between the sexes (discussed in the following), our data also suggest that either females have fewer S1 glands in the tail, or fewer of their S1 glands fluoresce.…”