Publication: Effects of photoperiod and temperature on testicular function in amphibians
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Date
1990
Authors
Paniagua, R. ; Fraile, Benito ; Sáez, F.J.
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Publisher
Murcia : F. Hernández
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DOI
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info:eu-repo/semantics/article
Description
Abstract
Most amphibians present an annual
testicular cycle characterized by a quiescent period (late
autumn-winter) and a spermatogenic period (spring and
summer). At the end of the period of spermatogenesis
undifferentiated interstitial cells transform into
steroid-secreting Leydig cells which regress in spring
at the beginning of the new spermatogenetic cycle.
The testicular cycle is controlled by the pituitary
gonadotropin levels which are high in autumn and
winter, low in spring and increase temporarily in the
middle of summer.
Photoperiod and temperature seem to be the most
important externa1 factors involved in the regulation of
this cycle in many amphibian species since the colder the
geographic area, the longer the quiescent period and the
shorter the spermatogenic period. This suggests the
occurrence of a potentially continuous cycle in these
species, in contrast with that which occurs in other
species having an endogenous rhythm of testicular
function which is much less sensitive to environmental
factors.
Although the specific response to temperature
can vary widely between species, the most frequent
observation in amphibians with a potentiaiiy continuous
cycle is that exposure to mild temperatures (15-20° C,
according to the spring temperatures of the different
geographic areas) stimulates spermatogenesis even
during the period of testicular quiescence. If this mild
temperature is combined with a long photoperiod,
complete spermatogenesis is attained. Experiments
performed during the period of germ-cell proliferation
(development from spermatogonia to round spermatids)
indicated that low temperatures (below 11° C) as well as
short photoperiods (less than 8 h of light) hinder germcell
proliferation. Moderately high temperatures (about
30° C) do not impair this proliferation. In the newt
Offprint reqoests to: Dr. R. Paniagua, Department of Cell Biology and
Genetics, University of AlcalA de Henares, E-28871 Alcala de
Henares, Madrid, Spain
Triturus marmoratus, it has been shown that an
excessively long photoperiod (over 16 h) has the same
effect as a short photoperiod. In this species eyes are not
required for the testicular photoperiodic response.
Photoperiod appears to have no effect on spermiogenesis
(differentiation of round spermatids into
spermatozoa), because once round spermatids are
formed, spermiogenesis will occur even in total
darkness. Mild temperatures seem to be necessary for
spermiogenesis as well as for androgen biosynthesis
because neither process will take place at extreme
temperatures. Results on the effect of photoperiod in
steroidogenesis differ between species.
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