Annual Reproductive Patterns in Three Species of Marine Snakes from the Central Phillippines

Abstract

Monthly samples of three tropical snakes, Acrochordus granulatus, Cerberus rhynchops and Laticauda colubrina from a limited collecting area where they are syntopic in the central Phillippines reveal pronounced diversity in reproductive seasonality. Both sexes of A. granulatus are highly seasonal and synchronized in their reproductive activity. Testis size, spermatogenic activity and plasma androgen levels declined precipitously in the non-breeding season to the same extent as observed in typical temperate species of snakes. Spermatogenesis and androgen secretion occur concomittantly and are prenuptial, coinciding with the appearance of enlarging yolked follicles in females. Gestation time (5-8 months) in this species may repesent one of the longest for a reptile, and females probably do not breed annually. C. rhynchops is also seasonal but to a lesser extent than Acrochordus. In males, testis weight, spermatogenesis and androgen secretion show a significant increase at certain times of year, but testis regression is only partial; there is some spermatogenic activity and epididymal sperm storage in all months. Gestation periods in this ovoviviparous species are probably much shorter (perhaps 3 months) than in Acrochordus, ovulation occurs over a broader season and females probably reproduce annually. In contrast, extensive evidence for male L. colubrina and limited observations on females indicate that this oviparous species is probably completely aseasonal in its reproductive biology. A review of reproductive data on other tropical marine snakes suggests that seasonality is probably the rule with the exception of L. colubrina (and some other species of Laticauda), the only oviparous species examined. Information on climatic conditions in the study area sugests that declining photoperiod and/or temperature may be responsible for testicular regression in Cerberus and Acrochordus. Data for plasma sex steroids (testosterone, estradiol and progesterone) suggest greater variability in ovarian function than previously reported for snakes.