Photoperiodism and Related Phenomena in Plants and Animals

By Robert B. Withrow | Go to book overview

PHOTOPERIODISM IN REPTILES

GEORGE A. BARTHOLOMEW

Department of Zoology, University of California, Los Angeles

Relatively little information is available on the reproductive physiology of reptiles, and much of the experimental work on reptilian endocrinology has been a repetition of classical work done originally on mammals. As a result, the data tend to be fragmentary and out of context biologically, and usually contribute little to the understanding of the factors controlling the timing of reproduction in this group. The literature on reptilian reproduction, though limited in comparison with that on birds and mammals, is still extensive enough to be confusing. At the present time, it is difficult to generalize beyond saying that the reproductive activities of a wide variety of reptiles are seasonal and that the major patterns of pituitary-gonad relations in reptiles are qualitatively similar to those that have been worked out for other terrestrial vertebrates.

A guide to the literature on the reproduction and natural occurring reproductive cycles of reptiles can be found in papers by Evans and Clapp ( 1940), Cieslak ( 1945), Miller ( 1948), Fox ( 1952), and Kehl and Combescot ( 1955). The present paper will review the scant literature on photoperiodism in reptiles, but its main purpose is the presentation of a point of view that may help to supply an appropriate ecological orientation to the problem of relating day length to breeding season in this group.

Although it is a familiar fact that many reptiles have markedly seasonal patterns of breeding, the role of environmental factors in the determination of this periodicity has been studied in only a few species and in no case has it been possible to make an adequate synthesis of physiological and ecological data. The paucity of information on photoperiodism in reptiles and its fragmentary nature is indicated by the brevity of the literature summary which follows. Mellish ( 1936) reported that exposure to continuous light and a temperature of 35°C

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