Abstract:
Axolotls (Ambystoma mexicanum) are aquatic salamanders that are widely used in
research. Axolotls have been bred in laboratories for nearly 150 years, yet little is known
about the basic biology of reproduction in these animals. We investigated the effects of
changing day length, time of year, and food availability on levels of circulating estradiol
and androgens in adult female and male axolotls, respectively. In addition, we examined
the effects of these variables on the mass of ovaries, oviducts, and eggs in females and
on mass of testes in males relative to each individual's body weight, to calculate a form
of gonadosomatic index (GSI). In both sexes, GSI was not correlated with levels of
circulating steroids. In female axolotls, estradiol levels were influenced by food
availability, changes in day length, and season, even when animals were held at a
constant temperature and day length was decorrelated with calendar date. In addition,
the mass of ovaries, oviducts, and eggs varied seasonally, peaking in the winter months
and declining during the summer months, even though our animals were not breeding
and shedding eggs. In males, levels of androgens appeared to vary independently of
external conditions, but GSI varied dramatically with changes in day length. These
results suggest that reproduction in axolotls may vary seasonally, as it does in many
other ambystomid species, although both male and female axolotls are capable of
reproducing several times each year. The physiological basis of this ability remains
enigmatic, given the indications of seasonality contained in our data.
Description:
Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in General and Comparative Endocrinology 176 (2012): 472-480, doi:10.1016/j.ygcen.2011.12.034.
