Diet was manipulated in juveniles of the snake Boa constrictor (Serpentes: Boidae) to test the hypothesis of whether prey size induces phenotypic plasticity of the head skeleton. Additionally, the onset of sexual size dimorphisms (SSDs) was determined under a feeding schedule where total prey mass consumed by snakes was held constant. Twenty-three neonatal B. constrictor from a single-sired litter were placed into two treatment groups but maintained under identical environmental conditions. Group 1 (small-food treatment) was fed weanling mice throughout the entire study; group 2 (large-food treatment) was fed weanling mice, followed by rats of increasing size as the size of the snakes increased. At the termination of the study, group 1 consumed more meals but both groups consumed an equivalent mass of rodents. The snakes were measured twice during the study (5 weeks and 58 weeks). All measurements were obtained while the snakes were under general anaesthesia. Linear measurements of the head skeleton (premaxilla–basioccipital (rostrum–occipital) length, ROL; mandible length, ML) were derived from radiographs. The remaining measurements were snout–vent length (SVL), body length (BL), tail length (TL), and body mass (BM). Treatment effects between groups were equivalent, with the exception of BM and TL (group 1>group 2), and interactions between main effects were not statistically significant. Between-group differences in ROL and ML were not significant; thus, prey size did not exert an influence on growth of the head skeleton. In contrast, significant sex effects on SVL and BL (females>males) and TL (males>females) were detected, and sex effects on BM (females>males) approached significance. Because SSDs emerged during early ontogeny under conditions where prey mass consumed was held constant, a genetic role is implicated.

Laboratory reared Culex quinquefasciatus Say, 1823 originating from the vicinity of Belem, in northern Brazil, were allowed to engorge on caimans (Caiman c. crocodilus) infected with Hepatozoon caimani (Carini, 1909) and boas (Boa constrictor) infected with H. cf. terzii (Sambon and Seligmann, 1907) both from Para State. Engorged mosquitoes killed on successive days post-feeding (p.f.) were studied by transmission electron microscopy. Images of oocysts from 13 days p.f., caiman-fed mosquitoes were also examined by scanning electron microscopy. The Hepatozoon spp. from the respective hosts differed in their ability to develop in C. quinquefasciatus. Most female mosquitoes fed on caimans, became fully engorged, and survived beyond 22 days p.f., whereas those engorged on boa became debilitated and did not survive beyond 9 days p.f. In boa-fed mosquitoes oocysts were found on the 6th day p.f. The few mosquitoes surviving to the 9th day p.f. contained either undivided oocysts or those that had already commenced sporogenic division. By 8–10 days p.f. caiman-fed mosquitoes contained uninucleate oocysts. Sporogonic divisions were observed from day 12 p.f. onwards. Although sporogenic development conformed in general with the previously reported accounts, the study allowed a more detailed examination of the plasmalemmal endocytotic system, and the consolidation of the crystalline body in specialized ‘factories’ of cystalline material. Sporozoite differentiation occasionally started on the 18th day p.f., but otherwise was observed only on day 22 p.f.