Current research on the behavioral neuroendocrinology of reptiles

Selected reptilian species have been the targets of investigations in behavioral neuroendocrinology for many years. Reptiles offer a particularly powerful set of traits that facilitate comparisons at multiple levels, including those within and between individuals of a particular species, between different environmental and social contexts, as well as across species. These types of studies, particularly as they are considered within the framework of results from other vertebrates, will enhance our understanding of the genetic and hormonal influences regulating changes in the structure and function of the nervous system. Work on the hormonal and environmental factors influencing courtship and copulatory behaviors in green anoles, including the development and maintenance of the neuromuscular structures critical for their display, is highlighted. Some very recent work on other model systems is also discussed to provide a context for suggested future research directions.     

Normally occurring intersexuality and testosterone induced plasticity in the copulatory system of adult leopard geckos

The copulatory neuromuscular system of lizards is highly sexually dimorphic. Adult males possess bilateral penises called hemipenes, which are independently controlled by two muscles, the retractor penis magnus (RPM) and transversus penis (TPN). These structures are not obvious in adult females. However, in adult female leopard geckos (Eublepharis macularius), testosterone induces hemipene growth. We investigated whether these structures develop de novo in adulthood or are histologically present as rudimentary structures in the female leopard gecko. We also investigated the extent of sexual dimorphisms and plasticity in the associated neuromuscular components. To do this, we compared copulatory morphology (sizes of hemipenes, RPM and TPN muscle fibers, and associated motoneurons, as well as motoneuron and RPM fiber number) in adult females treated with testosterone, control females, and control males. All of the geckos possessed hemipenes, RPMs and TPNs, but these structures were indeed vestigial in control females. Testosterone induced striking increases in hemipene and copulatory muscle fiber size in females, but not to levels equivalent to control males. In parallel, males with increased levels of androgenic activity had larger hemipenes, suggesting naturally occurring steroid-induced plasticity. Copulatory motoneurons were not sexually dimorphic in size or number, and these measures did not respond to testosterone. The data demonstrate that the copulatory system of leopard geckos, in which gonadal sex is determined by egg incubation temperature, differs from that of many species (both reptilian and mammalian) with genotypic sex determination. Indeed, the system is remarkable in that adult females have normally occurring intersex characteristics and they exhibit substantial steroid-induced morphological plasticity in adulthood.     

Size and structure of populations of Oedura reticulata (Reptilia: Gekkonidae) in woodland remnants: Implications for the future regional distribution of a currently common species

Abstract The gecko Oedura reticulata is restricted in distribution to the southwest of Western Australia. Within this region O. reticulata occurs mainly in smooth-barked eucalypt woodland habitat, much of which has become fragmented by clearing. In this study, demographic characteristics of nine populations of O. reticulata that currently persist in eucalypt woodland remnants are assessed and compared with those of populations in three nature reserves. The remnants cover a range of sizes but are similar in age, tree species composition and vegetation structure. Population sizes vary considerably among remnants and are poorly correlated with remnant size or the number of smooth-barked eucalypts. Population size does not appear to be limited by habitat availability in most remnants. The number of adults of breeding age is small in most populations suggesting that they may be susceptible to stochastic extinction pressures. The poor dispersal ability of this species between remnants means that the possibility of recolonization of a remnant following an extinction event is unlikely. As a result, the occupancy rate of O. reticulata in remnant woodland is likely to decline.     

Ultrastructure and distribution of chromatophores in the skin of the leopard gecko (Eublepharis macularius)

The aim of this study was to describe the ultrastructure and arrangement of pigment cells in the leopard gecko (Eublepharis macularius) skin to explain how wild‐type coloration is formed. The study also attempted to explain, on a morphological level, how skin colour changes occur. Samples of leopard gecko skin were collected from wild‐type coloration adult specimens. The morphology of pigmented cells was determined using light microscopy on haematoxylin and eosin (H&E) stained sections and in transmission electron microscopy. These studies indicate that skin of E. macularis contains xanthophores and melanophores but lacks iridophores and that this is probably related to nocturnal activity. The number and distribution of xanthophores and melanophores determines the skin colour and pigmentation pattern. The colour changes depend on the arrangement of characteristic protrusions of melanophores and the degree of filling them with melanosomes.     

Histology and histochemistry of the gekkotan notochord and their bearing on the development of notochordal cartilage

The persistence of the notochord into the skeletally mature life stage is characteristic of gekkotans, but is otherwise of rare occurrence among amniotes. The taxonomic diversity of Gekkota affords the opportunity to investigate the structure and development of this phylogenetically ancestral component of the skeleton, and to determine its basic characteristics. The gekkotan notochord spans almost the entire postcranial long axis and is characterized by a moniliform morphology with regularly alternating zones of chordoid and chondroid tissue. Chordoid tissue persists in the region of intervertebral articulations and occupies the cavitations that lie between the centra of the amphicoelous vertebrae. Chondroid tissue is restricted to zones in which the diameter of the notochord is reduced, corresponding to mid‐vertebral locations. In the tail, these zones of chondroid tissue are associated with the autotomic fracture planes. Chondroid tissue first manifests during late embryogenesis, appears to differentiate from pre‐existing chordoid tissue, and has the histological and histochemical characteristics of cartilage. Our observations lend support to the hypothesis that cartilage can be derived directly from notochordal tissue, and suggest that the latter may be an evolutionary and developmental precursor to chordate cartilage. The persistence of chordoid tissue in the intervertebral regions of amphicoelous vertebrae is consistent with a suite of paedomorphic traits exhibited by gekkotans and suggests that the typical hydrostatic nature of notochordal tissue may play a role in mechanically governing patterns of displacement between adjacent amphicoelous vertebrae that lack extensive centrum‐to‐centrum contact. Morphol., 2012. © 2012 Wiley Periodicals, Inc.     

Organising pest control by contract

Abstract

The Otago Regional Council uses contractors for control of both possums and rabbits. There is now a much greater emphasis on involving farmers in control work.

In Central Otago, rabbit poisoning operations are carried out under negotiated contracts; landholders provide much of the labour, and Council staff the 1080 and job supervision. This year we are trying a pilot programme for possum control, under which the Council will buy the skins and pay a bonus if a 75% reduction in possum numbers is achieved over a defined area in a certain time.

This paper discusses the details of the various contracts and the practical changes made to improve the job management programme.     

Tetranucleotide microsatellites in the gecko Oedura reticulata isolated from an enriched library

Ten tetranucleotide microsatellite loci were isolated from an enriched library for the gecko Oedura reticulata. The species is endemic to the southwest of Western Australia, known to be a habitat specialist, and exposed to severe habitat fragmentation in the Western Australian wheatbelt. These highly polymorphic markers (two to 25 alleles) will facilitate the population genetic analyses of this species. In particular, they will enable estimates of gene flow between remnant populations — a critical element in assessing extinction dynamics in fragmented populations.     

Kinematic Analysis and Experimental Verification on the Locomotion of Gecko

This paper presents a kinematic analysis of the locomotion of a gecko,and experimental verification of the kinematicmodel.Kinematic analysis is important for parameter design,dynamic analysis,and optimization in biomimetic robot research.The proposed kinematic analysis can simulate,without iteration,the locomotion of gecko satisfying the constraint conditionsthat maintain the position of the contacted feet on the surface.So the method has an advantage for analyzing the climbing motionof the quadruped mechanism in a real time application.The kinematic model of a gecko consists of four legs based on 7-degreesof freedom spherical-revolute-spherical joints and two revolute joints in the waist.The motion of the kinematic model issimulated based on measurement data of each joint.The motion of the kinematic model simulates the investigated real gecko’smotion by using the experimental results.The analysis solves the forward kinematics by considering the model as a combinationof closed and open serial mechanisms under the condition that maintains the contact positions of the attached feet on the ground.The motions of each joint are validated by comparing with the experimental results.In addition to the measured gait,three othergaits are simulated based on the kinematic model.The maximum strides of each gait are calculated by workspace analysis.Theresult can be used in biomimetic robot design and motion planning.     

大壁虎两种群的求偶鸣叫变异

大壁虎Gekko gecko俗称蛤蚧,可分为黑蛤蚧和红蛤蚧.黑蛤蚧主要分布在中国的广东、广西和越南的东北部,而红蛤蚧则主要分布在东南亚地区,包括越南南部、老挝、泰国等.本文对这两种蛤蚧种群的求偶鸣叫进行了定性和定量研究.经比较分析结果表明这两个种群蛤蚧的求偶鸣叫声学特征存在明显差异.大壁虎的求偶鸣叫由一系列的音节组成,可分为3段:第一段由0～5个脉冲串组成,每个脉冲串含多个脉冲(7～10);第二段由4～10个双音节组成;第三段由1～3个单音节组成,只有红蛤蚧的求偶鸣叫具有第三段.此外,黑蛤蚧和红蛤蚧的求偶鸣叫差异也表现在第二段,即双音节的结构上.黑蛤蚧的双音节呈现出复杂的频率调节模式,且第一音节和第二音节之间有明显的沉默间隔.红蛤蚧的求偶鸣叫很少或基本没有频率调节,第一音节和第二音节之间没有沉默间隔.结合这两种蛤蚧在形态、染色体和基因结构方面的显著差异,推测传统认为的大壁虎可能由两个不同的物种以及一个亚种组成.