We tested whether the reversible effects of nutrition on spermatogenesis in sexually mature sheep were mediated by Sertoli cells. Rams were fed with diets designed to achieve a 10% increase (High), no change (Maintenance) or a 10% decrease (Low) in body mass after 65 days. At the end of treatment, testes were lighter in the Low than the High group (PP<0.05) in the expression of seven Sertoli cell-specific genes. Under-nutrition appeared to reverse cellular differentiation leading to disruption of tight-junction morphology. In conclusion, in sexually mature sheep, reversible reductions in testis mass and spermatogenesis caused by under-nutrition were associated with impairment of basic aspects of Sertoli cell function but not with changes in the number of Sertoli cells.

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The gonads of Lepidogalaxias sakzmandroides are structurally distinctive. A duct, the surface of which is ciliated, is located on the ventral surface of each ovary and may be a modification of the marian tunica. The testes are small and the majority of the testicular structure functions as a sperm storage area. Secondary requisite sex characters are present in the male and the function of a modified scale sheath in copulation is unique among tcleosts. Fertilization is internal and a viscous mucus mass secreted during copulation may serve as a copulatory plug. It is postulated that internal fertilization within this species has arisen as a response to sperm competition. KEY LVORDS:sprrm storage ~ aestivation leleost fish ~ Shannon Mud Minnow ~ Salamander fish sexual dimorphism sperm competition.

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The male reproductive cycles of three species of vespertilionid bat (Nyctophilus geoffroyi, N. major, and Vespadelus regulus) are described. Descriptions are based on the degree of testicular and cauda epididymal development estimated from ®eld captures, and for N. geoffroyi, on histological examination of ®xed specimens and assays of their testicular testosterone concentrations. All species were found to undergo a dissociated pattern of reproduction; the activity of the testes and accessory glands of reproduction were asynchronous. Spermatogenesis occurred in summer/early autumn (December±March) and testes generally regressed before mating began in autumn (March±May). Spermatozoa were stored in the cauda epididymides during the mating period. Leydig cells of N. geoffroyi involuted prior to mating but the prostate gland remained enlarged and secretory during winter (June±August), regressing in late spring (November). Testicular testosterone concentrations were greatest when Leydig cells were maximally enlarged, and concentrations were low during the mating period. The reproductive cycle of all species apparently involved asynchrony between primary and secondary sexual function, which is typical of vespertilionid bats inhabiting temperate latitudes. As mating occurs when sperm stores cannot be replenished, selection for prudent sperm allocation may be expected.