Comparative Morphology of Some Plethodontid Salamander Spermatozoa

Abstract

Spermatozoa of 28 species of the Plethodontidae, including 11 genera representing both subfamilies and all tribes in the Plethodontinae, were collected from vasa deferentia, spot-smeared on lightly albuminized slides, fixed in 95% ethyl alcohol, stained and examined at 400X to 1,000X. Lengths of the head with acrosome, neck piece and whole spermatozoa; nature of the head-neck piece junction; location and appearance of the cytoplasmic droplet; and shape of the acrosomal barb were determined. A cytoplasmic droplet containing dense bodies was found on spermatozoa of all 28 species. Members of the Desmognathinae have a flat, but oblique head-neck piece junction; it is flat and perpendicular to the long axis in all plethodontines examined except in Aneides, in which the neck piece appears to fit into a slight concavity of the head. Desmognathine sperm have short heads (x = 48.2-69.5 Mtm); hemidactyliines have long neck pieces (x = 10.8-17.8 jum). Heads with acrosomes were shortest in Desmognathus aeneus (x = 48.2 jum) and longest in Bolitoglossa subpalmata (x = 150.4 M/m), neck pieces shortest in D. aeneus (x = 3.1 jum) and longest in Chiropterotriton multidentatus (x = 18.9 jum), and whole spermatozoa shortest in D. aeneus (x = 388 Mum) and longest in Aneides aeneus (x = 777 Mjm). Among seven species of Desmognathus, mean lengths of sperm heads ranged from 48.2 (D. aeneus) to 69.5 !um (D. fuscus-Ohio, and D. brimleyorum), mean lengths of sperm neck pieces from 3.1 (D. aeneus) to 8.4 jum (D. quadramaculatus), and mean lengths of whole sperm from 388 (D. aeneus) to 507 ,um (D. ochrophaeus-Wayah Bald). Eastern and western species of Plethodon formed two groups based on head lengths (x = 74.5-85.0 versus 97.6-113.9 Mam, respectively) and neck piece lengths (x = 6.7-8.4 versus 8.5-9.8 Mtm) and, except for P. vandykei (x = 506 jum), on length of whole sperm (x = 430-546 versus 577-627 jum). A few species difficult to distinguish on external body traits may be identified by spermatozoan dimensions, for example Desmognathus aeneus and D. wrighti (by all dimensions), Plethodon cinereus and P. dorsalis (by head length), and Pseudotriton ruber and P. montanus (by head and whole sperm lengths). Geographic variation in sperm dimensions is suggested in Desmognathus ochrophaeus, D. fuscus, Aneides aeneus and Eurycea longicauda.