The ecology of overwintering among turtles: where turtles overwinter and its consequences

Turtles are a small taxon that has nevertheless attracted much attention from biologists for centuries. However, a major portion of their life cycle has received relatively little attention until recently - namely what turtles are doing, and how they are doing it, during the winter. In the northern parts of their ranges in North America, turtles may spend more than half of their lives in an overwintering state. In this review, I emphasise the ecological aspects of overwintering among turtles, and consider how overwintering stresses affect the physiology, behaviour, distributions, and life histories of various species.Sea turtles are the only group of turtles that migrate extensively, and can therefore avoid northern winters. Nevertheless, each year a number of turtles, largely juveniles, are killed when trapped by cold fronts before they move to safer waters. Evidently this risk is an acceptable trade-off for the benefits to a population of inhabiting northern developmental habitats during the summer.Terrestrial turtles pass the winter underground, either in burrows that they excavate or that are preformed. These refugia must provide protection against desiccation and lethal freezing levels. Some burrows are extensive (tortoise genus Gopherus), while others are shallow, or the turtles may simply dig into the ground to a safe depth (turtle genus Terrapene). In the latter genus, freeze tolerance may play an adaptive role.Most non-marine aquatic turtles overwinter underwater, although Clemmys (Actinemys) marmorata routinely overwinters on land when it occurs in riverine habitats, Kinosternon subrubrum often overwinters on land, and several others may overwinter terrestrially on occasion, especially in more southern climates. For northern species that overwinter underwater, there are two physiological groupings, those that are anoxia-tolerant and those that are relatively anoxia-intolerant. All species fare well physiologically in water with a high partial pressure of oxygen (PO2). A lack of anoxia tolerance limits the types of habitats that a freshwater turtle may live in, since unlike sea turtles, they cannot travel long distances to hibernate.Hatchlings of some species of turtles spend their first winter in or below the nest cavity, while hatchlings of other species in the same area, including northern areas, emerge in the autumn and presumably hibernate underwater. All hatchlings are relatively anoxia-intolerant, and there are no studies to date of where hatchling turtles that do not overwinter in or below the nest cavity spend their first winter. Equally little is known of the ontogeny of anoxia tolerance, other than that adults of all species are more anoxia-tolerant than their hatchlings, probably because of their better ossified shells, which provide adults with more buffer reserves and a larger site in which to sequester lactate. The northern limits of turtles are most likely determined by reproductive limitations (time for egg-laying, incubation, and hatching) than by the rigors of hibernation.Mortality is typically lower in turtle populations during hibernation than it is during their active periods. However, episodic mortality events do occur during hibernation, due to freezing, prolonged anoxia, or predation.     

Morphogenesis of extraembryonic membranes and placentation in Mabuya mabouya (Squamata, Scincidae)

Topological and histological analyses of Mabuya mabouya embryos at different developmental stages showed an extraembryonic membrane sequence as follows: a bilaminar omphalopleure and progressive mesodermal expansion around the whole yolk sac at gastrula stages; mesodermal split and formation of an exocoelom in the entire embryonic chamber at neurula stages; beginning of the expansion of the allantois into the exocoelom to form a chorioallantoic membrane at pharyngula stages; complete extension of the allantois into the exocoelom between limb-bud to preparturition stages. Thus, a placental sequence could be enumerated: bilaminar yolk sac placenta; chorioplacenta; allantoplacenta. All placentas are highly specialized for nutrient absorption from early developmental stages. The bistratified extraembryonic ectoderm possesses an external layer with cuboidal cells and a microvillar surface around the whole yolk sac, which absorbs uterine secretions during development of the bilaminar yolk sac placenta and chorioplacenta. During gastrulation, with mesodermal expansion a dorsal absorptive plaque forms above the embryo and several smaller absorptive plaques develop antimesometrially. Both structures are similar histologically and are active in histotrophic transfer from gastrula stages until the end of development. The dorsal absorptive plaque will constitute the placentome and paraplacentome during allantoplacental development. At late gastrula-early neurula stages some absorptive plaques form chorionic concavities or chorionic bags that are penetrated by a long uterine fold and seem to have a specialized histotrophic and/or metabolic role. The extraembryonic mesoderm does not ingress into the yolk sac and neither an isolated yolk mass nor a yolk cleft are formed. This derived pattern of development may be related to the drastic reduction of the egg size and obligatory placentotrophy from early developmental stages. Our results show new specialized placentotrophic structures and a novel arrangement of extraembryonic membrane morphogenesis for Squamata.     

Effects of Geomorphology and Primary Productivity on Amazonian Leaf Litter Herpetofauna

The Amazon Basin, representing the largest expanse of intact tropical rain forest on the planet, harbors the largest diversity of amphibians and reptiles in the world. Limited elevation and climate differences across the Basin belie one major division of upland forests – geomorphological soil age and induced nutrient levels. We hypothesized that secondary consumers in the leaf litter herpetofauna community on ancient soils of Central Amazonia would exhibit reduced biomass compared with those found on younger soils of Western Amazonia, and that population densities on ancient soils could be driven below viable thresholds, reducing species richness. We found overall herpetofauna abundance, biomass and richness on young soils in Ecuador were significantly greater than those on ancient soils in the Brazilian Amazon. Separately, amphibians were only slightly more abundant, but their biomass on younger soils was twice that on ancient soils. Even more impressive was the variation exhibited by lizards: abundance was not significantly different, but biomass was five times greater on younger soils. Diversity of both taxa was greater on young soils. The most important driver of differences in herpetofauna biomass, abundance and possibly diversity across Amazonia may be the underlying geomorphologic differences. Reduced primary productivity on ancient soils appears to reverberate up the food chain, leaving fewer resources for higher trophic levels. We suggest that conservation initiatives must compensate for reduced biomass on ancient soils through increased reserve size, especially as forest fragmentation escalates. This study highlights the importance of including biomass as a standard measure in herpetofauna sampling.     

Diversification rates are more strongly related to microhabitat than climate in squamate reptiles (lizards and snakes)

Patterns of species richness among clades can be directly explained by the ages of clades or their rates of diversification. The factors that most strongly influence diversification rates remain highly uncertain, since most studies typically consider only a single predictor variable. Here, we explore the relative impacts of macroclimate (i.e., occurring in tropical vs. temperate regions) and microhabitat use (i.e., terrestrial, fossorial, arboreal, aquatic) on diversification rates of squamate reptile clades (lizards and snakes). We obtained data on microhabitat, macroclimatic distribution, and phylogeny for >4000 species. We estimated diversification rates of squamate clades (mostly families) from a time‐calibrated tree, and used phylogenetic methods to test relationships between diversification rates and microhabitat and macroclimate. Across 72 squamate clades, the best‐fitting model included microhabitat but not climatic distribution. Microhabitat explained ～37% of the variation in diversification rates among clades, with a generally positive impact of arboreal microhabitat use on diversification, and negative impacts of fossorial and aquatic microhabitat use. Overall, our results show that the impacts of microhabitat on diversification rates can be more important than those of climate, despite much greater emphasis on climate in previous studies.     

What was the ancestral sex‐determining mechanism in amniote vertebrates?

Amniote vertebrates, the group consisting of mammals and reptiles including birds, possess various mechanisms of sex determination. Under environmental sex determination (ESD), the sex of individuals depends on the environmental conditions occurring during their development and therefore there are no sexual differences present in their genotypes. Alternatively, through the mode of genotypic sex determination (GSD), sex is determined by a sex‐specific genotype, i.e. by the combination of sex chromosomes at various stages of differentiation at conception. As well as influencing sex determination, sex‐specific parts of genomes may, and often do, develop specific reproductive or ecological roles in their bearers. Accordingly, an individual with a mismatch between phenotypic (gonadal) and genotypic sex, for example an individual sex‐reversed by environmental effects, should have a lower fitness due to the lack of specialized, sex‐specific parts of their genome. In this case, evolutionary transitions from GSD to ESD should be less likely than transitions in the opposite direction. This prediction contrasts with the view that GSD was the ancestral sex‐determining mechanism for amniote vertebrates. Ancestral GSD would require several transitions from GSD to ESD associated with an independent dedifferentiation of sex chromosomes, at least in the ancestors of crocodiles, turtles, and lepidosaurs (tuataras and squamate reptiles). In this review, we argue that the alternative theory postulating ESD as ancestral in amniotes is more parsimonious and is largely concordant with the theoretical expectations and current knowledge of the phylogenetic distribution and homology of sex‐determining mechanisms.     

Ecological importance of sedges: a survey of the Australasian Cyperaceae genus Lepidosperma

Background

Sedges (Cyperaceae) form an important ecological component of many ecosystems around the world. Sword and rapier sedges (genus Lepidosperma) are common and widespread components of the southern Australian and New Zealand floras, also occurring in New Caledonia, West Papua, Borneo, Malaysia and southern China. Sedge ecology is seldom studied and no comprehensive review of sedge ecology exists. Lepidosperma is unusual in the Cyperaceae with the majority of species occurring in dryland habitats.

Scope

Extensive review of ecological literature and field observations shows Lepidosperma species to be important components of many ecosystems, often dominating understorey and sedge-rich communities. For the first time, a detailed ecological review of a Cyperaceae genus is presented.

Conclusions Lepidosperma

species are long-lived perennials with significant abundance and persistence in the landscape. Speciation patterns in the genus are of considerable interest due to complex biogeographical patterns and a high degree of habitat specificity. Potential benefits exist for medicinal products identified from several Lepidosperma species. Over 178 organisms, including 26 mammals, 42 birds, six reptiles, five amphibians, eight arachnids, 75 insects, three crustaceans and 13 fungi, are found to be dependent on, or making use of, Lepidosperma species. A significant relationship exists between Lepidosperma species and the moth genus Elachista. Implications for the conservation and ecology of both sedges and associated species are discussed.     

Comparative study of the corneal epithelium in some reptiles inhabiting different environments

El‐Bakry, A.M. 2011. Comparative study of the corneal epithelium in some reptiles inhabiting different environments. —Acta Zoologica (Stockholm) 92 : 54–61. The vertebrate cornea functions in either aquatic or aerial environments and in some cases in both. In terrestrial and aerial vertebrates, the cornea contributes most of the refractive powers of the eye because of the large variation in refractive index between the air and the cornea. The present study aimed to examine and compare the main features of the corneal epithelial surface of three reptilian species related to three different families (Caretta caretta, Varanus griseus and Mabuya quinquetaeniata) and inhabiting different environment, by light, scanning (SEM) and transmission electron microscopy. The mean epithelial cell densities of the species of the study were 8.670 ± 3.134, 5.945 ± 2.144 and 2.124 ± 713 respectively. The corneal epithelium of the three species observed by SEM showed a similarity to one another indicating that the apical cell surfaces possess regular polygonal cells with varieties of microprocesses. These microprocesses were represented by microplicae, numerous microvilli and some long microridges in C. caretta, microplicae and minute microholes in V. griseus and microplicae intermingled with short microvilli in M. quinquetaeniata. According to the densities of these microprocesses, three polymorphic cell types (light, medium and dark) appeared in C. caretta, light and medium cell types were observed in V. griseus and medium and dark cell types were noticed in M. quinquetaeniata. Different types of tight adhesions were observed by transmission electron microscopy between the cell borders of the epithelial cells which differ according to environment where the species occupy. In conclusion, variation in the structure of the corneal epithelial cells appears to be related to the living environment, such as aerial, terrestrial and aquatic ones, which is occupied by every species.     

Dangerous food: lacking venom and constriction,how do snake‐like lizards (Lialis burtonis,Pygopodidae) subdue their lizard prey?

Snakes are renowned for their ability to subdue and swallow large, often dangerous prey animals. Numerous adaptations, including constriction, venom, and a strike-and-release feeding strategy, help them avoid injury during predatory encounters. Burton's legless lizard ( Lialis burtonis Gray, Pygopodidae) has converged strongly on snakes. It is functionally limbless and feeds at infrequent intervals on relatively large prey items (other lizards) capable of inflicting a damaging bite. However, L. burtonis possesses neither venom glands, nor the ability to constrict prey. We investigated how L. burtonis subdues its prey without suffering serious retaliatory bites. Experiments showed that lizards modified their strike precision according to prey size; very large prey were always struck on the head or neck, preventing them from biting. In addition, L. burtonis delayed swallowing large lizards until they were incapacitated, whereas smaller prey were usually swallowed while still struggling. Lialis burtonis also displays morphological adaptations protecting it from prey retaliation. Its long snout prevents prey from biting, and it can retract its lidless eyes out of harm's way while holding onto a food item. The present study further clarifies the remarkable convergence between snakes and L. burtonis , and highlights the importance of prey retaliatory potential in predator evolution.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 91 , 719–727.     

Scaling down distribution maps from atlas data: a test of different approaches with virtual species

Aim Conservation managers are increasingly looking for modelled projections of species distributions to inform management strategies; however, the coarse resolution of available data usually compromises their helpfulness. The aim of this paper is to delineate and test different approaches for converting coarse‐grain occurrence data into high‐resolution predictions, and to clarify the conceptual circumstances affecting the accuracy of downscaled models. Location We used environmental data from a real landscape, southern Africa, and simulated species distributions within this landscape. Methods We built 10 virtual species at a resolution of 5 arcmin, and for each species we simulated atlas range maps at four decreasing resolutions (15, 30, 60, 120 arcmin). We tested the ability of three downscaling strategies to produce high‐resolution predictions using two modelling techniques: generalized linear models and generalized boosted models. We calibrated reference models with high‐resolution data and we compared the relative reduction of predictive performance in the downscaled models by using a null model approach. We also estimated the applicability of downscaling procedures to different situations by using distribution data for Mediterranean reptiles. Results All reference models achieved high performance measures. For all strategies, we observed a reduction of predictive performance proportional to the degree of downscaling. The differences in evaluation indices between reference models and downscaled projections obtained from atlases at 15 and 30 arcmin were never statistically significant. The accuracy of projections scaled down from 60 arcmin largely depended on the combination of approach and algorithm adopted. Projections scaled down from 120 arcmin gave misleading results in all cases. Main conclusions Moderate levels of downscaling allow for reasonably accurate results, regardless of the technique used. The most general effect of scaling down coarse‐grain data is the reduction of model specificity. The models can successfully delineate a species’ environmental association up until a 12‐fold downscaling, although with an increasing approximation that causes the overestimation of true distributions. We suggest appropriate procedures to mitigate the commission error introduced by downscaling at intermediate levels (approximately 12‐fold). Reductions of grain size > 12‐fold are discouraged.     

海南岛爬行动物的八个月调查（图版Ⅺ，Ⅻ）

1964年3至11月,作者受原四川医学院院长、已故刘承钊学部委员（院士）的派遣,率领一个小组到海南岛进行为期八个月的两栖爬行动物调查。当时海南岛隶属广东省,设海南行政公署管辖,该署卫生处派工作人员萧汉绮同志全程陪同调查。按照分工,调查结果的两栖动物部分已由刘承钊、胡淑琴等发表于《动物学报》1973年19卷4期;爬行动物部分则仅先后发表了2个新种和1个中国新纪录种（《动物学报》1975年21卷4期）和另1个新种（Asiatic Herpetological Research,1997年第7卷）。该次采集共得爬行动物标本1909号,计76种,分隶56属16科2目。本文报道该次采集的爬行动物,其中大部分物种的部分标本在野外曾进行长度和体重的测量,文中一并加以报道。目前发表此文,谨以之奉献给组织和领导此次调查的刘承钊院士和胡淑琴教授,和自始至终参加八个月调查工作的王宜生先生,他们均已先后逝世。