Cloacal morphology in Bolitoglossa nicefori (Caudata: Plethodontidae): Variation during the reproductive cycle

Male and female plethodontid salamanders have specialized cloacal glands associated with the reproductive activity. The reproductive cycle in Bolitoglossa nicefori is characterized by males that are potentially reproductive throughout the year, and females that are reproductive only for a few months. To determine whether morphological and histochemical variation occur in cloacal structures related to reproductive activity, the cloacal region of male and female specimens of B. nicefori was studied in different stages of their annual reproductive cycle using light microscopy and compared with features reported in other plethodontid salamanders. The main anatomy and histology of the male and female cloacal regions of B. nicefori are similar to those of other salamanders; however, in comparison to other Bolitoglossa previously studied, B. nicefori has a relatively larger cloacal tube and a tubular rather than acinar spermatheca. As a common trait, the spermatheca has a common tube that diverges into two tubules, before branching into spermathecal tubules, horizontally arranged on frontal planes. The secretions of the spermathecal glands differed between reproductive and nonreproductive adult females. This secretory product consists of prevailing neutral carbohydrates that were related to the increase in ovarian follicular size during the breeding season. Sperm was found only in the spermatheca of reproductive periovulatory females, suggesting that the reproductive cycle involves a no long-term storage of sperm. Although males can produce sperm throughout the year, spermatophores, namely specialized structures involved in sperm transport, were found in their cloaca only during the breeding season. In these males, some of the cloaca-associated glands were seen to undergo change their secretory activity and their secretory products were related to spermatophore formation.

Comparative spermatogenesis, spermatocytogenesis, and spermatozeugmata formation in males of viviparous species of clinid fishes (Teleostei: Clinidae, Blennioidei)

Spermatogenesis and spermatocytogenesis in 16 species of viviparous clinid fishes (Clinidae, Blennioidei) from various localities were followed for the first time by means of light and electron microscopy. The testes of the studied species are of the lobular type, with germinal stem cells situated at the apical ends of the lobules and a vas efferens along the internal margin. Maturation of the spermatides takes place in spermatocysts formed by Sertoli cells around the B-spermatogonia. The gradual condensation and relocation of the chromosomes along the nuclei membranes are highly prominent in this process, which can be divided into several stages. Anisodiametric and slightly flattened sperm heads are eventually formed, 0.4-0.5 microm in diameter and 7.5 +/- 1 microm long, bearing 80 +/- 15 microm long flagella. The sperms are packed into spermatozeugmata within the spermatocysts, enveloped and penetrated by the mucotic material of the Sertoli cells. With division of the germ cells and maturation of the spermatids, the spermatocyst dimensions increase, attaining 40 +/- 8 microm in diameter in the smaller species of Heteroclinus, and up to 90 +/- 10 microm in the larger males of Clinus superciliosus and C. cottoides. Accordingly, the volume of the maturing spermatocysts attains ca. 1,300 +/- 100 microm(3) in the smaller species, and ca. 6,500 +/- 300 microm(3) in the larger ones. As sperm head volume is ca. 2.24 microm(3), the number of sperm in the smallest mature spermatocysts reaches ca. 440 and in the largest over 2,900. Upon release from the cysts, the spermatozeugmata are transported along the sperm ducts to the posterior ampullae where they are stored in the epididymis. During copulation, the sperms are transported from there to the female via the intromittent organ. The sperm formation parameters and their structure and numbers are discussed.

Visualization of sperm by immunohistochemistry: application of alternative counterstains

The aim of this study was to evaluate the application of hematoxylin, safranin, light green and picric acid as counterstain in sperm immunohistochemistry. This is important to visualize the best staining procedure and to determine the advantage of picric acid as a counterstain in some situations. Picric acid used for counterstaining in the immunohistochemical procedure gives the best image of reaction on sperms when DAB was used as a chromogen.

Multiple paternity in a natural population of a salamander with long-term sperm storage

Sperm competition appears to be an important aspect of any mating system in which individual female organisms mate with multiple males and store sperm. Post-copulatory sexual selection may be particularly important in species that store sperm throughout long breeding seasons, because the lengthy storage period may permit extensive interactions among rival sperm. Few studies have addressed the potential for sperm competition in species exhibiting prolonged sperm storage. We used microsatellite markers to examine offspring paternity in field-collected clutches of the Ocoee salamander (Desmognathus ocoee), a species in which female organisms store sperm for up to 9 months prior to fertilization. We found that 96% of clutches were sired by multiple males, but that the majority of females used sperm from only two or three males to fertilize their eggs. The high rate of multiple mating by females suggests that sperm competition is an important aspect of this mating system. Comparison of our data with those of other parentage studies in salamanders and newts reveals that multiple mating may be common in urodele amphibians. Nevertheless, the number of males siring offspring per clutch in D. ocoee did not differ appreciably from that in other species of urodeles with shorter storage periods.

Ultrastructure of the annual cycle of female sperm storage in spermathecae of the torrent salamander, Rhyacotriton variegatus (Amphibia: Rhyacotritonidae)

This study is the first report on the ultrastructure of the sperm storage glands (spermathecae) in the salamander Rhyacotriton variegatus. The population studied is associated with cold-water, rocky streams of the redwood (Sequoia) zone in northern California. Males possess sperm in their vasa deferentia and undergo spermiation throughout the year, but mating is seasonal. Most females with large, vitellogenic follicles (2.0-3.9 mm mean dia.) collected from February-June contain sperm in their spermathecae, although some females with large follicles lack sperm. Other mature-size females collected during this period have small ovarian follicles (0.9-1.2 mm mean dia.) and lack stored sperm. All females collected from September-November have small follicles (0.6-1.6 mm mean dia.) and lack sperm, except in one instance in which a female collected in November had a small amount of degraded sperm, apparently retained from the previous breeding season. The spermathecae consist of simple tubulo-alveolar glands in which the neck tubules produce a mucoid secretory product, and the distal bulbs, where sperm are stored, contain secretory vacuoles of uniform density that stain positively for glycosaminoglycans. In specimens containing sperm, some bulbs have abundant sperm and others lack sperm, but the ultrastructure is similar in both conditions. The acini contain columnar epithelial cells with wide intercellular canaliculi, and a merocrine process releases the secretion. Spermiophagy occurs. In specimens from spring and summer with small ovarian follicles, the neck tubules are similar to those of breeding females, but the distal bulbs are reduced to cords of cells lacking a discernible lumen. Secretory activity in the distal bulbs is initiated in the fall. Spermathecae of R. variegatus are most similar to those of a stream-dwelling plethodontid, Eurycea cirrigera.

Female sperm storage in amphibians

The three orders of extant amphibians are Gymnophiona, Anura, and Urodela. Although all gymnophionans apparently have internal fertilization and many are viviparous, female sperm storage is unknown. Internal fertilization has convergently evolved in a few anurans, but females of just one species, Ascaphus truei, are known to possess oviductal sperm storage tubules (SSTs). The SSTs of A. truei are similar anatomically to such glands in squamate reptiles. This similarity is convergence due to similar functional adaptations and/or internal design constraints. In salamanders and newts (Urodela), absence of sperm storage in females is the ancestral condition (three families). In the derived condition, sperm storage occurs in cloacal glands called spermathecae, and their possession is a synapomorphy for females in the suborder Salamandroidea (seven families). Salamandroids are the only vertebrates with cloacal sperm storage glands. In this paper, a phenetic analysis of variation in spermathecal characters reveals patterns of convergence in certain spermathecal characters in unrelated taxa that breed in similar habitats. In the family Salamandridae, a role in sperm nutrition for the spermathecal epithelium is questioned, and the widespread occurrence of spermiophagy is related to other reproductive strategies. I propose how the packaging of sperm in structurally different types of spermathecae may influence male paternity.

Sperm storage in the oviduct of the internal fertilizing frog Ascaphus truei

This study provides the first descriptions of sperm storage at the tissue and cellular levels in a female frog or toad. Oviducal anatomy was studied by light and electron microscopy in Ascaphus truei from north coastal California. Ascaphus truei is one of the few species of anurans in which fertilization is internal. Unlike other anurans with internal fertilization, however, mating in A. truei consists of a unique combination of amplectic and copulatory mechanisms that we term "copulexus." Posterior to a short, aglandular infundibular region, the oviduct possesses: 1) a proximal, convoluted ampullary region where intrinsic tubular glands secrete gelatinous envelopes around eggs; 2) a middle ovisac region where fertilization occurs; and 3) a distal oviducal sinus formed by medial junction of the ovisacs. Sperm storage tubules (SSTs) occur in the anterior portions of the ovisacs and consist of simple tubular glands. SSTs and the rest of the oviducal lining stain positively with the periodic acid-Schiff's procedure for neutral carbohydrates and this reaction is especially intense in reproductively active females. Sperm were found in the SSTs of gravid females as well as some nonvitellogenic females. The sperm are in orderly bundles in the SSTs, and although occasionally sperm nuclei were embedded in the epithelium, no evidence for spermiophagy was found. Oviducal sperm storage in A. truei is homoplastic, with closest structural similarities to squamate reptiles. Oviduct/sperm design constraints appear to limit the options for expression of features associated with oviducal sperm storage.