Evaluation of offspring size-number invariants in 12 species of lizard.

The optimal division of resources into offspring size vs. number is one of the classic problems in life-history evolution. Importantly, models that take into account the discrete nature of resource division at low clutch sizes suggest that the variance in offspring size should decline with increasing clutch size according to an invariant relationship. We tested this prediction in 12 species of lizard with small clutch sizes. Contrary to expectations, not all species showed a negative relationship between variance in offspring size and clutch size, and the pattern significantly deviated from quantitative predictions in five of the 12 species. We suggest that the main limitation of current size-number models for small clutch sizes is that they rely on assumptions of hierarchical allocation strategies with independence between allocation decisions. Indeed, selection may favour alternative mechanisms of reproductive allocation that avoid suboptimal allocation imposed by the indivisible fraction at low clutch sizes.

Members of opposite sex mutually regulate gonadal recrudescence in the lizard Calotes versicolor Agamidae).

Adult males and females of the seasonally breeding lizard Calotes versicolor were subjected to various social situations under semi-natural conditions to explain the role of socio-sexual factors in gonadal recrudescence. They were grouped as: (i) males and females, (ii) males and females separated by a wire mesh, (iii) same sex groups of males or females, (iv) castrated males with intact females and (v) ovariectomized (OvX) females with intact males from postbreeding to breeding phase. Specimens collected from the wild during breeding season served as the control group. Plasma sex steroid levels (testosterone in male and 17b-estradiol in female), spermatogenetic activity and vitellogenesis were the criteria to judge gonadal recrudescence. In intact males and females that were kept together, gonadal recrudescence and plasma sex steroids levels were comparable to those in wild-caught individuals. Gonadal recrudescence was at its least in all male and all female groups, and plasma sex steroids were at basal levels. Association with OvX females initiated testicular recrudescence but spermatogenetic activity progressed only up to the spermatid stage while males separated from females by wire mesh showed spermatogenetic activity for a shorter period. Females grouped with castrated males and those separated from males by wire mesh produced vitellogenic follicles. However, the total number and diameter of vitellogenic follicles, and plasma estradiol levels were lower than in the females grouped with intact males. The findings indicate that association with members of the opposite sex with progressively rising titers of sex steroids is crucial in both initiating and sustaining gonadal recrudescence in the lizard. Thus, members of the opposite sex mutually regulate gonadal recrudescence in the C. versicolor.

Pattern of plasma sex steroid hormone levels during reproductive cycles of male and female tropical lizard, Calotes versicolor.

Annual changes in gonadal activity and plasma sex steroid hormone levels in male and female Calotes versicolor [plasma testosterone (T) levels in males and 17 beta-estradiol (E(2)) and progesterone (P) levels in females] are described. In females both plasma E(2) (32.80 +/- 12.91 pg/ml) and P (1.72 +/- 0.79 ng/ml) levels are at their low levels during the postbreeding season when the gonads are regressed. With the onset of recruitment of vitellogenic follicles, E(2) levels begin to rise, reaching peak values (1306.00 +/- 407.01 pg/ml) when the follicles are preovulatory. During this time, plasma levels of P are low. Plasma E(2) levels decline (285.60 +/- 143.0 pg/ml) soon after ovulation, and circulating concentrations of P begin to rise, reaching peak value (19.24 +/- 10.03 ng/ml), during eggshell formation. In gravid females, at mid-gestation, the same pattern of E(2) secretion is found when a second set of follicles undergoes vitellogenesis. However, P levels remain low from mid-gestation (4.06 +/- 2.17 ng/ml) until oviposition. These findings suggest that high P levels are not needed for oviductal egg retention during late gestation and that low levels of P may facilitate growth of a new batch of vitellogenic follicles. In males, plasma levels of T are correlated with the spermatogenetic activity that accompanies breeding.

Plasma progesterone levels and luteal activity during gestation and prolonged oviductal egg retention in a tropical lizard, Calotes versicolor.

Plasma progesterone (P) levels and luteal and adrenal activities were studied during normal gestation and unusual prolonged period of oviductal egg retention in a polyautochronic, multiclutched lizard, Calotes versicolor. The normal gestation period (approximately 15 days) was categorized into four stages: stage I--a few hours following ovulation, stage II--eggs with shell and embryo at primitive streak, stage III--embryonic stages 16-20, and stage IV--prior to ovipostion (stages 26-27). The gravid lizards maintained in captivity retained eggs in their oviducts for 45 days. Plasma P levels were low in stage I, increased significantly during stage II, declined in stage III, and reached their lowest in stage IV of gestation. 3Beta-hydroxysteroid dehydrogenase (3beta-HSDH) activity was greater in lutein cells at stage II and was present in traces in stage IV gestation. Interestingly, plasma P titers that were high in lizards with eggs retained longer though the corpora lutea (CL) showed a trace 3beta-HSDH activity. However, 3beta-HSDH activity was greater in the adrenocortical cells in these lizards than that in lizards during a normal gestation period. The present study on C. versicolor shows that the CL remains active and secretes P only during the early part of the gestation. The drop in P level during the later part of gestation might facilitate growth of a second set of vitellogenic follicles. During unfavorable conditions when the lizards are forced to retain eggs in the oviduct, the adrenal glands seem to secrete progesterone to help in egg retention and in inhibition of oviposition.

GnRH but not warm temperature induces recrudescence of quiescent testes in the tropical lizard Calotes versicolor (Daud.) during postbreeding phase.

The effects of temperature and various doses of GnRH on testicular recrudescence were studied in Calotes versicolor during the postbreeding (December-January) resting phase. Adult lizards (n = 51) were segregated into seven groups. Group I served as the initial control. Groups II, III, and IV were maintained at room temperature (23 +/- 1 degrees, range 17.5-25.5 degrees ) and natural photoperiod (12.25 h light:11.35 h dark). Groups V, VI, and VII were maintained at 30 +/- 1 degrees in an environmental chamber with 12 h light:12 h dark. Groups II and V received 0.2 ml saline, groups III and VI received 0.1 microgram GnRH/0.2 ml saline, and groups IV and VII received 0.5 microgram GnRH/0.2 ml saline on alternate days for 30 days. In the two groups that received 0.5 microgram GnRH, there was a significant increase in the diameter of the seminiferous tubules and Leydig cell nuclei, 3beta-HSDH activity in Leydig cells, and plasma testosterone level compared to those in other groups. There was no evidence of testicular recrudescence in lizards exposed to room/high temperatures treated with saline or 0.1 microgram GnRH. This study of C. versicolor shows that during the resting phase, high temperature per se does not stimulate testicular recrudescence, whereas 0.5 microgram GnRH does so. Also, the findings suggest that either higher brain centers regulating hypothalamus or hypothalamus itself become dormant, causing testicular inactivity (inactivation of hypophysial-testicular axis) during the postbreeding resting phase.