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At least 811 records · Page 45Linked to original sources
PubMed1997

Sperm storage in the spermatheca of the red-back salamander, Plethodon cinereus (Amphibia: Plethodontidae).

In northern Indiana, the mating season of Plethodon cinereus occurs after hibernation from March until June, when oviposition begins. During the mating season, a female stores sperm in its spermatheca, a compound tubular gland in the roof of the cloaca. The apical cytoplasm of the spermathecal epithelium is filled with large secretory vacuoles whose product is released while sperm are stored. Females induced to oviposit in June and July by injections of human chorionic gonadotropin (hCG) still retain much sperm 1 month after oviposition, but secretory vacuoles are absent in all specimens sacrificed in July and August. Instead, some sperm are embedded in the spermathecal epithelium with resultant spermiophagy involving lysosomes. A female sacrificed in September 2 months after oviposition possesses scant sperm, but spermiophagy alone does not seem extensive enough to account for the decrease in sperm numbers. Females sacrificed in October prior to hibernation lack sperm in their spermathecae; some secretory vacuoles are present, but they are not as numerous or as enlarged as in specimens collected in March and May. Inter- and intrafamilial differences in the cytology of sperm storage may not be phyletically informative at the family level but related to species-specific reproductive adaptations.

Animal Structures↗
PubMed1997

Expression pattern of an axolotl floor plate-specific fork head gene reflects early developmental differences between frogs and salamanders.

Gastrulation is one of the most important stages of animal development and, as such, tends to be remarkably conserved. Therefore it is interesting to see that the two amphibian species, Xenopus laevis (frog) and Ambystoma mexicanum (axolotl), are different in the arrangement of cell types just before and during gastrulation. In Xenopus, the cells that will form dorsal mesoderm are located deep in the dorsal marginal zone, while in the axolotl, these are on the surface of the embryo. In this study we investigated whether homologous genes known to be involved in the formation of dorsal structures show a different pattern of expression in these two species. For this purpose, we isolated a fork head gene (AxFKH 1) from the axolotl, which is likely to be the homologue of the Xenopus fork head gene, XFKH 1 (Pintallavis, XFD-1). We find that AxFKH 1 and XFH 1 have a similar pattern of expression, but there are some important differences. In early gastrulae, transcripts are detected in the organizer region of both species. In late gastrulae, the transcripts in Xenopus are located in both the superficial and deep layers, but they are only found in the superficial layer of axolotl embryos. During neurulation, XFKH 1 is expressed in notochord and neural floor plate, whereas AxFKH 1 is expressed in the neural floor plate only. We propose that the differences in expression pattern of these two genes are due to a difference in formation of dorsal structures between these two species. Furthermore, the expression pattern of these two genes early in gastrulation is consistent with the idea that at least some of the neural floor plate cells are already determined at this time.

Ambystoma mexicanum↗
PubMed2001

Caudal vertebral development and morphology in three salamanders with complex life cycles (Ambystoma jeffersonianum, Hemidactylium scutatum, and Desmognathus ocoee).

We describe caudosacral and caudal vertebral morphology across life history stages in three caudate amphibians: Ambystoma jeffersonianum (Ambystomatidae), Desmognathus ocoee (Plethodontidae: Desmognathinae), and Hemidactylium scutatum (Plethodontidae: Plethodontinae). All three species have aquatic larvae, but adults differ in habitat and predator defense strategy. Predator defense includes tail autotomy in D. ocoee and H. scutatum but not A. jeffersonianum. Of the species that autotomize, H. scutatum has a specialized constriction site at the tail base. We investigated whether aquatic larvae exhibit vertebral features similar to those previously described for aquatic adults and examined the effect of metamorphosis, if any, on vertebral morphology and the ontogeny of specialized vertebral features associated with tail autotomy. Interspecific comparisons of cleared-and-stained specimens indicate that vertebral morphology differs dramatically at hatching and that caudosacral and caudal vertebrae undergo continuous ontogenetic change throughout larval, metamorphic, and juvenile periods. Larvae and juveniles of H. scutatum do not exhibit adult vertebral features associated with constricted-base tail autotomy. The pond-type larvae of A. jeffersonianum and H. scutatum have tapering centrum lengths posterior to the sacrum. This pattern is functionally associated with aquatic locomotion. The stream-type larvae of D. ocoee undergo enhanced regional growth in the anterior tail such that the anterior caudal centra become longer than the preceding caudosacral centra. With the exception of the first two caudal vertebrae, a similar growth pattern occurs in H. scutatum adults. We hypothesize that enhanced growth of the anterior caudal segments is associated with tail elongation and autotomy.

Ambystoma↗