Summary
The testicular regression that is caused by photorefractoriness inZonotrichia leucophrys gambelii (white-crowned sparrow) appears to be a delayed response to photostimulation that may be timed by counting of days or summing of daylengths. Our results demonstrate that time of onset of testicular regression inZ. l. gambelii on four photoperiodic treatments is an inverse function of daylength. Onset of regression is apparently fixed relatively early in gonadal growth and is not affected by changes in photoregimen after the end of logarithmic phase of testicular growth. The rate of testicular regression appears to be constant regardless of daylength. Our data on timing of testicular regression cannot be rationalized by a simple mechanism that counts days after onset of photostimulation. Of several possible timing mechanisms for the summation of hours of light, simple summation of total hours of light received appears to rationalize our data most readily. However, because our results indicate that this summation can only occur during the early phase of gonadal growth, further experiments are necessary to evaluate this mechanism fully.
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Abbreviations
- 8L 16D :
-
8 h light, 16 h dark, etc.
- L3S :
-
cycle consisting of 1 long followed by 3 short days
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Moore, M.C., Schwabl, H. & Farner, D.S. Biochronometry of testicular regression in white-crowned sparrows (Zonotrichia leucophrys gambelii). J. Comp. Physiol. 153, 489–494 (1983). https://doi.org/10.1007/BF00612603
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DOI: https://doi.org/10.1007/BF00612603