Disrupting evolutionary processes: The effect of habitat fragmentation on collared lizards in the Missouri Ozarks

Humans affect biodiversity at the genetic, species, community, and ecosystem levels. This impact on genetic diversity is critical, because genetic diversity is the raw material of evolutionary change, including adaptation and speciation. Two forces affecting genetic variation are genetic drift (which decreases genetic variation within but increases genetic differentiation among local populations) and gene flow (which increases variation within but decreases differentiation among local populations). Humans activities often augment drift and diminish gene flow for many species, which reduces genetic variation in local populations and prevents the spread of adaptive complexes outside their population of origin, thereby disrupting adaptive processes both locally and globally within a species. These impacts are illustrated with collared lizards (Crotaphytus collaris) in the Missouri Ozarks. Forest fire suppression has reduced habitat and disrupted gene flow in this lizard, thereby altering the balance toward drift and away from gene flow. This balance can be restored by managed landscape burns. Some have argued that, although human-induced fragmentation disrupts adaptation, it will also ultimately produce new species through founder effects. However, population genetic theory and experiments predict that most fragmentation events caused by human activities will facilitate not speciation, but local extinction. Founder events have played an important role in the macroevolution of certain groups, but only when ecological opportunities are expanding rather than contracting. The general impact of human activities on genetic diversity disrupts or diminishes the capacity for adaptation, speciation, and macroevolutionary change. This impact will ultimately diminish biodiversity at all levels.

Influence of a cratering device on close-in populations of lizards /

"PNE-224F."

The horned lizards of California and Nevada of the genera Phrynosoma and Anota,

Mode of access: Internet.

Temperature and the respiratory properties of whole blood in two reptiles, Pogona barbata and Emydura signata

We investigated the capacity of two reptiles, an agamid lizard Pogona barbata and a chelid turtle Emydura signata, to compensate for the effects of temperature by making changes in their whole blood respiratory properties. This was accomplished by measuring the P-50 (at 10, 20 and 30 degrees C), hematocrit (Hct), haemoglobin concentration ([Hb]) and mean cell haemoglobin concentration (MCHC) in field acclimatised and laboratory acclimated individuals. The acute effect of temperature on P50 in P barbata, expressed as heat of oxygenation (Delta H), ranged from -16.8 +/- 1.84 to -28.5 +/- 2.73 kJ/mole. P-50 of field acclimatised P barbata increased significantly from early spring to summer at the test temperatures of 20 degrees C (43.1 +/- 1.2 to 48.8 +/- 2.1 mmHg) and 30 degrees C (54.7 +/- 1.2 to 65.2 +/- 2.3 mmHg), but showed no acclimation under laboratory conditions. For E. signata, Delta H ranged from -31.1 +/- 6.32 to -48.2 +/- 3.59 kJ/mole. Field acclimatisation and laboratory acclimation of P-50 did not occur. However, in E. signata, there was a significant increase in [Hb] and MCHC from early spring to summer in turtles collected from the wild (1.0 +/- 0.1 to 1.7 +/- 0.2 mmol/L and 4.0 +/- 0.3 to 6.7 +/- 0.7 mmol/L, respectively). (C) 2005 Published by Elsevier Inc.

Origin, colonization, adaptive radiation, intrainsular evolution snd species substitution processes in the fossil and living lizards of the Canary Islands

[EN] The Canary lsland lizards constitute a monophyletic group which separated from the rest of the family shortly after the first islands of the archipelago emerged. Five living and at least one recently extinct species belong to the genus Gallotia. In addition, two of the living species, Gallotia simonyi and Gallotia stehlini have become extinct on Gomera and Tenerife, respectively. Juveniles of all species present tricuspid teeth. This character is preserved in the adults with changes to one degree or another in G. galloti, G. caesaris, G. simonyi and G. goliath. In G. atlantica there are only two cuspids and G. stehlini has 4 or more.

The relationship between cranial structure, biomechanical performance and ecological diversity in varanoid lizards

This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Skull structure is intimately associated with feeding ability in vertebrates, both in terms of specific performance measures and general ecological characteristics. This study quantitatively assessed variation in the shape of the cranium and mandible in varanoid lizards, and its relationship to structural performance (von Mises strain) and interspecific differences in feeding ecology. Geometric morphometric and linear morphometric analyses were used to evaluate morphological differences, and finite element analysis was used to quantify variation in structural performance (strain during simulated biting, shaking and pulling). This data was then integrated with ecological classes compiled from relevant scientific literature on each species in order to establish structure-function relationships. Finite element modelling results showed that variation in cranial morphology resulted in large differences in the magnitudes and locations of strain in biting, shaking and pulling load cases. Gracile species such as Varanus salvadorii displayed high strain levels during shaking, especially in the areas between the orbits. All models exhibit less strain during pull back loading compared to shake loading, even though a larger force was applied (pull =30N, shake = 20N). Relationships were identified between the morphology, performance, and ecology. Species that did not feed on hard prey clustered in the gracile region of cranial morphospace and exhibited significantly higher levels of strain during biting (P = 0.0106). Species that fed on large prey clustered in the elongate area of mandible morphospace. This relationship differs from those that have been identified in other taxonomic groups such as crocodiles and mammals. This difference may be due to a combination of the open 'space-frame' structure of the varanoid lizard skull, and the 'pull back' behaviour that some species use for processing large prey.

Colour change on different body regions provides thermal and signalling advantages in bearded dragon lizards

Many terrestrial ectotherms are capable of rapid colour change, yet it is unclear how these animals accommodate the multiple functions of colour, particularly camouflage, communication and thermoregulation, especially when functions require very different colours. Thermal benefits of colour change depend on an animal's absorptance of solar energy in both UV–visible (300-700 nm) and near-infrared (NIR; 700-2600 nm) wavelengths, yet colour research has focused almost exclusively on the former. Here, we show that wild-caught bearded dragon lizards (Pogona vitticeps) exhibit substantial UV–visible and NIR skin reflectance change in response to temperature for dorsal but not ventral (throat and upper chest) body regions. By contrast, lizards showed the greatest temperature-independent colour change on the beard and upper chest during social interactions and as a result of circadian colour change. Biophysical simulations of heat transfer predicted that the maximum temperature-dependent change in dorsal reflectivity could reduce the time taken to reach active body temperature by an average of 22 min per active day, saving 85 h of basking time throughout the activity season. Our results confirm that colour change may serve a thermoregulatory function, and competing thermoregulation and signalling requirements may be met by partitioning colour change to different body regions in different circumstances.

Concordance in phylogeography and ecological niche modelling identify dispersal corridors for reptiles in arid Australia

Aim: Using the rock-specialist agamid Ctenophorus caudicinctus as a model, we test hypothesized biogeographical dispersal corridors for lizards in the Australian arid zone (across the western sand deserts), and assess how these dispersal routes have shaped phylogeographical structuring. Location: Arid and semi-arid Australia. Methods: We sequenced a c. 1400 bp fragment of mtDNA (ND2) for 134 individuals of C. caudicinctus as well as a subset of each of the mtDNA clades for five nuclear loci (BDNF, BACH1, GAPD, NTF3, and PRLR). We used phylogenetic methods to assess biogeographical patterns within C. caudicinctus, including relaxed molecular clock analyses to estimate divergence times. Ecological niche modelling (Maxent) was employed to estimate the current distribution of suitable climatic envelopes for each lineage. Results: Phylogenetic analyses identified two deeply divergent mtDNA clades within C. caudicinctus - an eastern and western clade - separated by the Western Australian sand deserts. However, divergences pre-date the Pleistocene sand deserts. Phylogenetic analyses of the nuclear DNA data sets generally support major mtDNA clades, suggesting past connections between the western C. c. caudicinctus populations in far eastern Pilbara (EP) and the lineages to the east of the sand deserts. Ecological niche modelling supports the continued suitability of climatic conditions between the Central Ranges and the far EP for C. c. graafi. Main conclusions: Estimates of lineage ages provide evidence of divergence between eastern and western clades during the Miocene with subsequent secondary contact during the Pliocene. Our results suggest that this secondary contact occurred via dispersal between the Central Ranges and the far EP, rather than the more southerly Giles Corridor. These events precede the origins of the western sand deserts and divergence patterns instead appear associated with Miocene and Pliocene climate change.

Color change for Thermoregulation versus camouflage in free-ranging lizards

Animal coloration has multiple functions including thermoregulation,camouflage, and social signaling, and the requirementsof each function may sometimes conflict. Many terrestrial ectothermsaccommodate the multiple functions of color through color change.However, the relative importance of these functions and how colorchangingspecies accommodate themwhen they do conflict are poorlyunderstood because we lack data on color change in the wild. Here, weshow that the color of individual radio-tracked bearded dragon lizards,Pogona vitticeps, correlates strongly with background color andless strongly, but significantly, with temperature. We found no evidencethat individuals simultaneously optimize camouflage and thermoregulationby choosing light backgrounds when hot or dark backgroundswhen cold. In laboratory experiments, lizards showed both UV-visible(300–700 nm) and near-infrared (700–2,100 nm) reflectance changesin response to different background and temperature treatments, consistentwith camouflage and thermoregulatory functions, respectively,but with no interaction between the two. Overall, our results suggestthat wild bearded dragons change color to improve both thermoregulationand camouflage but predominantly adjust for camouflage, suggestingthat compromising camouflage may entail a greater potentialimmediate survival cost.