Mechanisms influencing reproductive success in mammalian and amphibian species: Aging and environmental ultraviolet radiation.

摘要

Due to high rates of extinction and resulting loss of biodiversity, active management of threatened and endangered populations of animals has become necessary. Captive breeding programs are important components in many wildlife management strategies, and reproductive biology research is integral in optimizing these efforts. Furthermore, investigations of decreased reproductive capacity during aging offer insights into mechanisms regulating normal reproductive processes, and increase our abilities to assist some middle-aged animals to reproduce. A second area of research aimed at the management of endangered species is the study of mechanisms which contribute to population declines. Increases solar ultraviolet (UV) radiation has been implicated as a potential factor involved in declines of amphibian populations. These diverse components, reproductive aging and solar UV, converge under the challenge of endangered species management, and represent influences which affect reproductive success.; Reproductive aging in the female rat is associated with alterations in neuroendocrine and ovarian function. While there is a temporal association with compromised reproductive output and diminished ovarian follicular reserves, the relative contributions of age and decreased follicular pool size are unclear. Young and middle-aged female rats were left intact or underwent unilateral ovariectomy (ULO) to decrease to ovarian follicular reserves. There was a direct relationship between follicular pool size and early follicular development. We also found an influence of decreased follicular pool size on proestrous LH and progesterone levels as well as on ovulation rates, suggesting an ovarian component to age-related changes in neuroendocrine function. This was not mediated, however, by alterations in patterns of estradiol release. Both age and follicular pool size influenced secondary FSH surge magnitude and inhibin production on estrus morning.; For the amphibian report, the treefrogs Hyla regilla and Hyla cadaverina, and the newt Taricha torosa were studied at natural oviposition sites to determine the effects of solar UV-B on embryonic development. Embryos from H. cadaverina and T. torosa displayed increased mortality when exposed to solar UV-B. Surviving embryos of all three species, however, displayed no alterations in rates of development when exposed to solar UV-B. Diminished hatching success may affect these species at the population level, particularly if UV-B levels increase.