THE EVOLUTION OF REPRODUCTIVE EFFORT IN LIZARDS AND SNAKES

Life history theory suggests that the optimal evolved level of reproductive effort (RE) for an organism depends upon the degree to which additional current reproductive investment reduces future reproductive output. Future reproduction can be decreased in two ways, through (i) decreases in the organism's survival rate, and/or (ii) decreases in the organism's growth (and hence subsequent fecundity). The latter tradeoff–that is, the “potential fecundity cost”—should affect the evolution of RE only in species with relatively high survival rate, a relatively high rate of fecundity increase with body size, or a relatively high reproductive frequency per annum. Unless these conditions are met, the probable benefit in future fecundity obtained from decreasing present reproductive output is too low for natural selection to favor any reduction in RE below the maximum physiologically possible. Published data on survival rate, reproductive frequency and relative clutch mass (RCM) suggest that many lizard species fall well below the level at which natural selection can be expected to influence RE through such “potential fecundity” tradeoffs. Hence, the relative allocation of resources between growth and reproduction is unlikely to be directly optimized by natural selection in these animals. Instead, energy allocation should influence the evolution of RE only indirectly, via effects on an organism's probability of survival during reproduction. Survival costs of reproduction may be the most important evolutionary determinants of RE in many reptiles, and information on the nature and extent of such costs is needed before valid measures of reptilian RE can be constructed.     

Reptiles from Len?óis Maranhenses National Park,Maranh?o,northeastern Brazil

We are presenting a list of the reptile species from Lençóis Maranhenses National Park (LMNP), Maranhão, Brazil, obtained during 235 days of field work. The study area is located in the contact zone between three major Neotropical ecosystems: Amazonia, Caatinga, and Cerrado. The PNLM encompasses the largest dune fields in Brazil, wide shrubby areas (restingas), lakes, mangroves, and many freshwater lagoons. We have recorded 42 species of reptiles in the area: 24 snakes, 12 lizards, two worm lizards, three turtles, and one alligator. About 81 % of the recorded species occurred only in restinga areas. Our data highlights the uniqueness of the PNLM in the context of the biomes that surround it and shows the importance of efforts to improve the conservation of reptiles living in the restinga, which currently comprise only about 20 % of the total area protected by the park, but which are the mesohabitat containing most of the reptile species in the Lençóis Maranhenses complex of habitats.     

Determination of Age from Cemental Incremental Lines for Forensic Dentistry

Determination of age from cemental incremental lines was evaluated in intact teeth obtained from 17 individuals aged 23-77 years. Mineralized 100 μm cross sections were subjected to one of three treatments: unstained, stained with Villanueva's blood stain, and stained with acridine orange. Ideal areas were selected by light microscopy and photographed. Countability of incremental lines from photographic enlargements were evaluated. The average number of years required for the eruption of a particular tooth was added to the incremental lines count to determine the estimated age for that individual. Results obtained from unstained mineralized 100 μm thick cross sections using differential interference microscopy (Nomarsky) provided the most countable lines. The accuracy and repeatability of the method is not dependent on tooth type or location, but on the average obtained from making as many counts as possible. This method can be applied to general populations regardless of systemic or periodontal health.     

爬行动物肾性节的研究概述

肾性节是一种雄性副性结构,主要存在于爬行动物双孔亚纲Diapsida鳞龙下纲Lepidosauria,尤其是有鳞目的雄性,由肾脏的集合管前端或肾单位的远曲小管末端膨大特化而成.肾性节的细胞由柱状上皮细胞组成,胞质中充满电子致密的分泌颗粒.组织化学研究表明,肾性节呈ACP、AKP、糖原、糖蛋白、脂类和蛋白质等反应阳性,且存在种间差异.肾性节的细胞大小和超微结构具有明显的年周变化,并与生殖腺的发育密切相关.此外,某些蛇和蜥蜴的雄性幼体具有肾性节,而在某些种类的雌性也具有类似的结构.有关这一结构的生理功能尚不完全清楚,曾有学者提出几种假设:具有支持和激活精子的作用,形成交配栓,与精液形成有关或提供求爱信息素等.