RESPONSE OF THE MALE REPRODUCTIVE SYSTEM OF LIZARDS (ANOLIS CAROLINENSIS) TO UNNATURAL DAY-LENGTHS IN DIFFERENT SEASONS

Abstract

1. The reproductive system of adult male anoles was stimulated by artificially lengthened days at all seasons of the year. At least a few males were brought into full breeding condition in experiments initiated from November through August. Sperm were produced at all seasons. 2. A refractory period, such as occurs in passerine birds, did not appear to be present in Anolis. 3. A previous exposure to short days was not essential for obtaining a response to a long photoperiod. 4. Both the testes and accessory sex organs exhibited progressively greater responses in successive experiments through the fall, winter, and spring. 5. The seasonal gradient of response which produced increasingly larger testes could be accounted for by the increasingly larger number of spermatogonia at the beginning of each experiment. The gradient in response of the accessory sex organs was dependent on the normal cyclic fluctuations of their histology and the abundance of hypertrophied interstitial cells. 6. The inherent rhythms of both the gonad and accessory sex organs were not disturbed by 60 days' exposure to 9- or 6-hour photoperiods during the fall and winter. However, such exposures near or after the peak of spermatogenesis resulted in premature atrophy of all reproductive organs. 7. Comparison of the effects of 14-, 16-, and 18-hour day-lengths suggested that the longer the day-length the more rapid the response. Extremely long days, however, appeared to have detrimental effects upon some individuals. 8. Most immature lizards of less than 55 mm. snout-vent length responded poorly to the experimental conditions. All that responded well were growing rapidly. Those that grew to 60 mm. or more had reproductive organs as large or larger than older adults. 9. Captive lizards exposed to natural day-length for 60 days at any time between February and July tended to have larger testes than wild lizards sacrificed on the same date.