HORMONAL CONTROL OF OVIPOSITION AND PARTURITION IN LIZARDS

Abstract

The steroid hormones estradiol-17,8, progesterone, and testosterone induce hy- pertrophy of the oviducts (uterus) of lizards. Once ovulation occurs, eggs remain within the oviducts for a period of time characteristic of each species, after which oviposition of shelled eggs (in oviparous lizards) or young (in viviparous species) occurs. Oviposition or parturition is accomplished by rhythmic contractions of the oviducts. The neurohypophysial hormone arginine vasotocin (AVT) causes premature oviposition or parturition when injected into gravid or preg- nant lizards in several species. Furthermore, oviducts of several species contract in response to AVT in vitro. Natural regression of corpora lutea, as well as surgical deluteinization, is correlated with premature oviposition in oviparous species, suggesting that luteal steroid hormones may inhibit AVT secretion. In Anolis carolinensis, unilateral inhibition of oviducal contraction is accomplished by nonsystematic delivery of a substance from the corpus luteum to the ipsilateral oviduct, possibly via small utero-ovarian blood vessels. The role of corpora lutea in timing parturition in viviparous lizards is less clear, possibly because there are species differences in the time of luteal regression during pregnancy. There is limited evidence that the adenohypoph- ysis plays a role in corpus luteum function and, therefore, in the timing of oviposition or par- turition. Recent evidence suggests that the sympathetic nervous system, through activation of beta-adrenergic receptors in oviducal smooth muscle, can delay oviposition or parturition. Thus, the sympathetic nervous system may mediate environmental influences on the occurrence of oviducal contraction. Behaviors associated with oviposition or parturition include lateral compression and flexure of the trunk, lowering of the rostral portion of the body, leg-stretching, tail-raising, rapid and deep breathing, and reflexive contraction of the abdomen. In addition, several lizard species exhibit maternal behaviors associated with oviposition or parturition, and the motivation for these behaviors could be under hormonal control.