南亚和东南亚巨蜥居群的种间亲缘和越南─新种描述

１９９２年１１月１５日从云南省河口县城自由市场的一位越南人手中买得一雌性巨蜥,经鉴定为一新种,定名为越南巨蜥Ｖａｒａｎｕｓｖｉｅｔｎａｍｅｎｓｉｓ。鉴别特征：新种背部鳞片光滑,仅在后半部插有极少的起棱鳞片,不同于Ｖ．ｎｅｂｕｌｏｓｕｓ（Ｂｏｕｌｅｎｇｅｒ,１８８５,１８９０;Ｔａｙｌｏｒ,１９６３）;新种不同于Ｖ．ｓａｌｖａｔｏｒ在于其背部没有眼斑状横斑带（ｏｃｅｌｌｉｍａｒｋｓ）（Ｇｕｅｎｔｈｅｒ,１８６４;Ｈａｒｒｉｓｏｎ等,１９５７;Ｐｏｐｅ,１９３５）;不同于Ｖ．ｉｒｒａｗａｒｄｉｃｕｓ（Ｙａｎｇ等,１９８７）,Ｖ．ｇｒｉｓｅｕｓ和Ｖ．ｍｏｎｉｔｏｒ（Ｓｍｉｔｈ,１９３５）在于有６─７个横向扩大的眼上鳞。文中运用了１５个外部性状对产于南亚,东南亚大陆及岛屿共９个种（含新种）的种间亲缘关系进行了研究,结果认为,种间亲缘关系的亲疏与分布地区相距的远近成正相关。     

Temperature effects on bioenergetics of growth, assimilaton efficiency and thyroid activity in juvenile varand lizards

When varanid lizards, Varanus niloticus, were allowed to select their preferred body temperature (c. 34°C) they exhibited swifter growth, larger food intake and superior efficiency of conversion when compared with animals restricted to a maximum body temperature of 24°C. At the higher temperature the animals also exhibited a higher metabolic rate and increased thyroid activity, while those at the lower temperature lostproportionately more energy via respiration. A complete energy budget over a period of 6 weeks is presented.     

Phenetic relationships among varanid lizards based upon comparative electrophoretic data and karyotypic analyses

Comparative electrophoretic phenotypes of 18 of the 32 species of the lizard genus Varanus have been determined for four proteins. The animals studied were representative of species from Africa, Israel, Southeast Asia and Australia. Malate dehydrogenase (A₂) exhibited a single phenotype throughout. Lactate dehydrogenase (B₄) showed four distinctive electrophoretic forms which grouped the various subgenera as follows: (1) Polydaedalus, Empagusia (African); (2) Psammosaurus (Israel); (3) three species of Varanus, V. gouldii, V. spenceri, V. mertensi (Australian); (4) Dendrovaranus, Indovaranus (Southeast Asian), other Varanus species, Odatria (Australian). Electrophoretic and previously reported karyotypic data were used to interpret the phylogenetic relationships as well as the mode and direction of evolution of these animals. In particular, the results questioned the reality of the subgenus Varanus as a taxonomic unit, since four distinct karyotypic forms and two LDH-B₄ phenotypes were observed for these animals, of which one belongs to another subgenus. Serum albumin and carbonic anhydrase phenotypes were of little use in deciding phenotypic groupings.     

A trophic cascade initiated by an invasive vertebrate alters the structure of native reptile communities

Invasive vertebrates are frequently reported to have catastrophic effects on the populations of species which they directly impact. It follows then, that if invaders exert strong suppressive effects on some species then other species will indirectly benefit due to ecological release from interactions with directly impacted species. However, evidence that invasive vertebrates trigger such trophic cascades and alter community structure in terrestrial ecosystems remains rare. Here, we ask how the cane toad, a vertebrate invader that is toxic to many of Australia's vertebrate predators, influences lizard assemblages in a semi‐arid rangeland. In our study area, the density of cane toads is influenced by the availability of water accessible to toads. We compared an index of the abundance of sand goannas, a large predatory lizard that is susceptible to poisoning by cane toads and the abundances of four lizard families preyed upon by goannas (skinks, pygopods, agamid lizards and geckos) in areas where cane toads were common or rare. Consistent with the idea that suppression of sand goannas by cane toads initiates a trophic cascade, goanna activity was lower and small lizards were more abundant where toads were common. The hypothesis that suppression of sand goannas by cane toads triggers a trophic cascade was further supported by our findings that small terrestrial lizards that are frequently preyed upon by goannas were more affected by toad abundance than arboreal geckos, which are rarely consumed by goannas. Furthermore, the abundance of at least one genus of terrestrial skinks benefitted from allogenic ecosystem engineering by goannas where toads were rare. Overall, our study provides evidence that the invasion of ecosystems by non‐native species can have important effects on the structure and integrity of native communities extending beyond their often most obvious and frequently documented direct ecological effects.     

An experimental test of the thermoregulatory hypothesis for the evolution of endothermy

The thermoregulatory hypothesis proposes that endothermy in mammals and birds evolved as a thermoregulatory mechanism per se and that natural selection operated directly to increase body temperature and thermal stability through increments in resting metabolic rate. We experimentally tested this hypothesis by measuring the thermoregulatory consequences of increased metabolic rate in resting lizards (Varanus exanthematicus). A large metabolic increment was induced by feeding the animals and consequent changes in metabolic rate and body temperature were monitored. Although metabolic rate tripled at 32 degrees C and quadrupled at 35 degrees C, body temperature rose only about 0.5 degrees C. The rate of decline of body temperature in a colder environment did not decrease as metabolic rate increased. Thus, increasing the visceral metabolic rate of this ectothermic lizard established neither consequential endothermy nor homeothermy. These results are inconsistent with a thermoregulatory explanation for the evolution of endothermy.     

Vertebrate evolution reflected in the evolution of nuclear ribosomal internal transcribed spacer 2

In eukaryotes, mature rRNA sequences are produced from single large (45S) precursor (pre-rRNA) as the result of successive removal of spacers through a series of rapid and intricate actions of endo- and exonucleases. The excision of internal transcribed spacer (ITS2), a eukaryotic-specific insertion, remains the most elusive processing step. ITS2 is the element mandatory for all eukaryotic pre-rRNAs that contain at least three processing cleavage sites for precise 5.8S and 28S formation. Conserved core sequences (cis-elements) binding to trans-factors provide for precise rRNA processing, whereas rapidly diverging regions between the core sequences preserve internal complementarity, which guarantees the spatial integrity of ITS2. Characteristic differences in the formation of such insertions during evolution should reflect the relationships between taxa. The phylogeny of the reptiles and the relationships between taxa proposed by scientists are controversial. To delineate the structural and functional features preserved among reptilian ITS2s, we cloned and sequenced 58 ITS2s belonging to four reptile orders: Squamata, Crocodilians, Aves, and Testudines. We studied the subsequent alignment and folding of variable regions. The sizes and packing of the loop–stems between conserved consensus segments in reptiles vary considerably between taxa. Our phylogenetic trees constructed on the basis of the reptile ITS2s primary structural alignments revealed a split between Iguania clade and all other taxa. True lizards (suborder Scleroglossa) and snakes (suborder Serpentes) show sister relationships, as well as the two other reptilian orders, Crocodilia + Aves and Testudines. In summary, our phylogenetic trees exhibit a mix of specific features deduced or, to the contrary, rejected earlier by other authors.     

Activity areas and daily movements of an arboreal monitor lizard,Varanus tristis (Squamata: Varanidae) during the breeding season

During the breeding season, in the western Great Victoria Desert, Western Australia, male Varanus tristis move greater daily distances (186.5 m) than females (99.7 m) and have larger activity areas (40.3 ha vs 3.7 ha). V. tristis retreat predominantly to live and dead upright Eucalyptus gongylocarpa (marble gum) trees that have hollows in their trunks and limbs. There is no observable difference between males and females in their preferred habitat, but females are found more frequently in a lesser number of preferred retreats during the breeding season.     

Taking the bait: Developing a bait delivery system to target free‐ranging crocodiles and varanid lizards with a novel conservation strategy

In tropical Australia, conditioned taste aversion (CTA) can buffer vulnerable native predators from the invasion of a toxic prey species (cane toads, Rhinella marina). Thus, we need to develop methods to deploy aversion‐inducing baits in the field, in ways that maximize uptake by vulnerable species (but not other taxa). We constructed and field‐tested baiting devices, in situ with wild animals. Apparatus were set next to waterbodies and baited concurrently at multiple locations (over water, water''s edge, and on the bank). Baits were checked and replaced twice daily during the trial; remote cameras recorded visitation by native predators. Bait longevity was compared at sun‐exposed and shaded locations over 12 h. The strength required to remove baits from apparatus was measured in varanids and crocodiles. The device promoted high rates of bait uptake by freshwater crocodiles (47% baits consumed), varanid lizards (19% baits consumed), and non‐target taxa (34% baits consumed). Targeting specific predators can be achieved by manipulating bait location and time of deployment, as well as the force required to dislodge the bait. Crocodiles were best targeted with over‐water baits, whereas varanid lizards preferred baits located at the edges of waterbodies. When testing bait longevity in ambient conditions, during the daytime baits desiccated fully within 12 h, and faster in the sun than in the shade. Based on studies using captive animals, the “pulling force” strength of reptilian predators scaled with body size and was greater in crocodiles than in varanid lizards. We present the first conservation baiting protocol designed specifically for reptiles. Our results demonstrate the feasibility of widespread and taxon‐specific deployment of aversion‐inducing baits to buffer the impacts of invasive cane toads, and our methods are applicable (with modification) to other research and management programs globally.