The Cell in Development and Heredity

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The Biology of Plethodontid Salamanders

The chapter describes sperm competition as a major factor in the sexual behavior of many species. This is clearly a major factor that has led to the evolution in males of a variety of behavior patterns, morphological features and physiological processes that serve to reduce its impact, such as mate-guarding and sexual dimorphism. The potential for sperm competition may have shaped the evolution of anuran sexual behavior. In particular, amplexus, by which males sequester and guard females has evolved as an adaptation that prevents sperm competition. Among urodeles, the necessary conditions for sperm competition, internal fertilization, multiple mating by females and sperm storage are widespread, and several recent studies provide evidence that it has been very important in the evolution of urodele sexual behavior. A female strategy that incorporates multiple mating and sperm competition imposes a strong selection on how much males invest in sperm production and in the way that males allocate sperm to individual matings. This also leads to a diverse array of behavioral patterns and other adaptations.

12 - Sperm Competition in Amphibians

Recent evidence suggests that the hypothalamic ventromedial nucleus contains a wide variety of functionally specialized neurons, some of which are located within discrete regions of the nucleus. However, regional morphologic variations in neuronal populations within the HVM have not been demonstrated. In the present report, the neurons of the HVM were studied in young adult, male rats with the electron microscope. The collection and analysis of cytologic data were systematized with reference to location on a histologic map of the HVM, which was prepared prior to fine structural study.



Neurons of the HVM were observed to exhibit regional variations in cytology. For example, cisternae of the rough endoplasmic reticulum in the anterior and dorsomedial regions of the nucleus are commonly collected into regular stacks typical of Nissl bodies. In contrast, rough cisternae in the posterior ventrolateral region of the HVM are often extremely long and pleomorphic, and form broad, loosely organized Nissl zones, in which occur myelin figures and wide varieties of cytoplasmic filamentous bodies.



Other neurons located principally in the ventrolateral and posterior regions of the nucleus are characterized by the presence of whorled bodies. Still others restricted to the lateral rim of the nucleus are conspicuous by virtue of their enormous size and massive accumulation of Nissl material.



One extremely unusual variety of HVM neuron is distinguished by the presence of large, acristic mitochondria, polysomal disaggregation, and aberrant nucleolar morphology. These cytologic features may indicate metabolic quiescence and perhaps anaerobiosis.



Possibly these region-centered variations in neuronal cytology reflect the functional parcellation of the HVM.

Cytology of neurons of the hypothalamic ventromedial nucleus in the adult male rat.

Data on cloacal anatomy were gathered for 128 species of salamanders, representing 48 genera and the nine extant families. Twenty-five characters were recognized, but after resolution of polymorphisms and elimination of autapomorphies, only 12 characters remained for use in phylogenetic analyses at the family level. Weighting the characters equally and using branch-and- bound parsimony algorithms, 15 (PAUP) or 9 (Hennig86), equally parsimonious cladograms were revealed, each with 19 steps and a consistency index of 0.63. The variation in phylogenies is due to opposing hypotheses concerning convergence or reversal in two characters: the extent of epidermal lining in the cloaca, and the presence of primary and secondary folds in the cloacal tube. The strict consensus cladogram gives the topology: Sirenidae (Hynobiidae, Cryptobranchidae (Amphiumidae (Salamandridae (Ambystomatidae, Dicamptodontinae (Rhyacotritoninae, Plethodontidae, Protei- dae))))). These results and consensus analyses with other cladograms based upon morphological data support the notion that the Salamandroidea, as defined by Duellman and Trueb (1986), is a monophyletic group and that internal fertilization evolved once, and is a synapomorphy for the suborder. Male and female cryptobranchids and hynobiids possess one type of cloacal gland that is not highly dimorphic, and may be a courtship gland that functions in the production of chemical signals during reproductive activities. In the Salamandroidea, portions of the cloacal gland mass (male dorsal and vent glands, female ventral glands) retain the ancestral anatomy and presumed function, while other portions have evolved structural and functional differences relating to sper- matophore formation (male pelvic and ventral glands) and storage of spermatozoa (female sper- mathecae). Courtship glands have been secondarily lost or reduced in some of the Salamandroidea, especially in plethodontids, in which selection apparently has led to adaptations for delivery of courtship pheromones by skin glands rather than reliance on a cloacal source.

Comparative anatomy and phylogeny of the cloacae of salamanders (Amphibia: Caudata). I, Evolution at the family level

Spermathecae of mature salamanders (Manculus quadridigitatus) were studied by light and electron microscopy. Gross morphology exhibits a complex of muscle, connective tissue and pigment cells surrounding a cluster of tubules, which empty into a ciliated central duct leading to the cloacal cavity. The tubules are composed of myoepithetial cells and secretory cells, anchored to an encompassing basal lamina. Secretion products appear to be initiated as crystalline deposits, seen in mitochondrial repositories, which are subsequently sequestered in the perinuclear region. Observations show these vesicles to be precursors of the Golgi synthesis of carboxylated polysaccharides, as determined by histochemical tests using toluidine blue, ruthenium red, and alcian blue. The secretory products are emptied into the tubule lumen. thereby bathing the stored sperm and maintaining them in a viable state for approximately 8 months. The storage tubules appear to be a complete complex of varying epithelial cells specifically designed to support viable sperm and to resorb non-functional forms.

The ultrastructure of secretion in the spermatheca of the salamander, Manculus quadridigitatus (Holbrook)

Intranuclear and cytoplasmic annulate lamellae were studied in grasshopper spermatocytes (Melanoplus) with the electron microscope. Although cytoplasmic annulate lamellae were observed in all three species examined, intranuclear annulate lamellae were found in only one species. The intranuclear annulate lamellae encompass certain nuclear material adjacent to the nuclear envelope forming a vesicle that is extruded into the spermatocyte cytoplasm. In this same species, cytoplasmic annulate lamellae are seen contiguous with granular masses of varying size. These structures were noted as being morphologically indistinguishable from the "yolk nuclei" of dragonfly oocytes (Kessel and Beams, 1969; Kessel, 1973).

Terrell R. Hoage

Papers

The ultrastructure of secretion in the spermatheca of the salamander, Manculus quadridigitatus (Holbrook)

Intranuclear and cytoplasmic annulate lamellae in grasshopper spermatocytes (genus Melanoplus).