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97 results for “Monitor lizard”
Competition and geography underlie speciation and morphological evolution in Indo-Australasian monitor lizards
<p>How biotic and abiotic factors act together to shape biological diversity is a major question in evolutionary biology. The recent availability of large datasets and development of new methodological approaches provide new tools to evaluate the predicted effects of ecological interactions and geography on lineage diversification and phenotypic evolution. Here, we use a near complete phylogenomic-scale phylogeny and a comprehensive morphological dataset comprising more than a thousand specimens to assess the role of biotic and abiotic processes in the diversification of monitor lizards (Varanidae). This charismatic group of lizards shows striking variation in species richness among its clades and multiple instances of endemic radiation in Indo-Australasia (i.e., the Indo-Australian Archipelago and Australia), one of Earth's most biogeographically complex regions. We found heterogeneity in diversification dynamics across the family. Idiosyncratic biotic and geographic conditions appear to have driven diversification and morphological evolution in three endemic Indo-Australasian radiations. Furthermore, incumbency effects partially explain patterns in the biotic exchange between Australia and New Guinea. Our results offer insight into the dynamic history of Indo-Australasia, the evolutionary significance of competition, and the long-term consequences of incumbency effects.</p>
Figure 4 in Skeletochronology in long tubular bones of the Javan water monitor lizard, Varanus salvator bivittatus in the juvenile stage (Lacertilia: Varanidae)
Figure 4. Cross sections of the diaphysis fibula bone in four individuals with SVLs between 14.4 cm to 25.0 cm. Dotted arrow: endosteal bone; black solid arrow: LAG; red solid arrow: resorption line (RL); yellow solid arrow: additional resting Line (AdL). The scale bar is equal to 200 m.
Figure 1 in Skeletochronology in long tubular bones of the Javan water monitor lizard, Varanus salvator bivittatus in the juvenile stage (Lacertilia: Varanidae)
Figure 1. Measurement of bone cross section. d: the longest part of the marrow cavity; D: the longest part of the bone diameter; MP: the widest point of bone thickness.
Figure 3 in Skeletochronology in long tubular bones of the Javan water monitor lizard, Varanus salvator bivittatus in the juvenile stage (Lacertilia: Varanidae)
Figure 3. Cross section of the seven long tubular bones of a juvenile female Varanus salvator bivittatus with one LAG (SVL: 22.2 cm). MC: marrow cavity; dotted arrow: endosteal bone; red solid arrow: LAG.
Figure 2 in Skeletochronology in long tubular bones of the Javan water monitor lizard, Varanus salvator bivittatus in the juvenile stage (Lacertilia: Varanidae)
Figure 2. Cross section of the seven long tubular bones of juvenile male Varanus salvator bivittatus with zero LAG (SVL: 14.4 cm). MC: marrow cavity; dotted arrow: endosteal bone.
Competition and geography underlie speciation and morphological evolution in Indo-Australasian monitor lizards
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Raw data accompanying: Ground reaction forces in monitor lizards (Varanidae) and the scaling of locomotion in sprawling tetrapods
<p>Geometric scaling predicts a major challenge for legged, terrestrial locomotion.<b> </b>Locomotor support requirements scale identically with body mass (α M<sup>1</sup>), while force generation capacity should scale α M<sup>2/3</sup> as it depends on muscle cross-sectional area. Mammals compensate with more upright limb postures at larger sizes, but it remains unknown how sprawling tetrapods deal with this challenge. Varanid lizards are an ideal group to address this question because they cover an enormous body size range while maintaining a similar bent-limb posture and body proportions. This study reports the scaling of ground reaction forces and duty factor for varanid lizards ranging from 7 g 37 kg. Impulses (force x time) scaled roughly as predicted by the inverted pendulum model (α M<sup>0.99-1.34</sup>) while peak forces (α M<sup>0.73-1.00</sup>) scaled higher than expected. Duty factor scaled α M<sup>0.04 </sup>and was higher for the hindlimb than the forelimb. The proportion of vertical impulse to total impulse increased with body size, and impulses decreased while peak forces increased with speed. These results provide valuable data into how locomotor forces vary with body size and suggest how other, extinct, sprawling tetrapods may have dealt with the biomechanical challenges associated with generating sufficient locomotor forces at larger body sizes.</p>
Use of road underpasses by mammals and a monitor lizard in eastern Australia and consideration of the prey-trap hypothesis
<p class="MsoNormal"><span>Road networks continue to expand globally with predictable effects on ecological systems. Research into the effectiveness of road underpasses and overpasses for wildlife has been concentrated in North America and Europe. In Australia, most studies of underpasses have been of relatively short duration and without reference sites to give context to the measured rates of use. We studied 5–7 road underpasses at two locations in eastern Australia over 2–3 years, comparing camera trap detections of animals in underpasses with those at nearby forest sites. Three species of large macropod (wallabies and kangaroos) were frequently detected in the underpasses, with some underpasses traversed 1–4 times per week, and in many cases exceeded detections in the forest. The lace monitor (<em>Varanus various</em>) was detected in all underpasses, often once per week during spring and summer, and infrequently in the forest. At each location a different small macropod species, including one regionally threatened, showed a higher probability of detection in one underpass compared to several of the forest sites. The vulnerable koala (<em>Phascolartos cinereus</em>) was detected infrequently in underpasses and in the adjoining forest. The short-beaked echidna (<em>Tachyglossus aculeatus</em>) had a high probability of detection in a single underpass. The 'prey-trap hypothesis' postulates that predators will exhibit increased activity at underpasses as a consequence of prey being funnelled. We found the red fox (<em>Vulpes vulpes</em>) had high activity in some underpasses. However, its activity coincided less than expected with the activity of the mammals most at risk to it. Our results provide no consistent support for the 'prey-trap hypothesis'. Instead, our study confirms the generic value of underpasses for a range of medium-large mammals as well as one large reptile. Habitat adjoining underpasses exerts a strong influence on their use and requires greater consideration to maximise underpass use. </span></p>
Use of road underpasses by mammals and a monitor lizard in eastern Australia and consideration of the prey-trap hypothesis
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Raw data accompanying: Ground reaction forces in monitor lizards (Varanidae) and the scaling of locomotion in sprawling tetrapods
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Data and code from: Integrating genomics, collections, and community science to delimit species clarifies the taxonomy of a variable monitor lizard (<em>Varanus tristis</em>)
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Phylogenomics of monitor lizards and the role of competition in dictating body size disparity
<p>Organismal interactions drive the accumulation of diversity by influencing species ranges, morphology, and behavior. Interactions vary from agonistic to cooperative and should result in predictable patterns in trait and range evolution. However, despite a conceptual understanding of these processes, they have been difficult to model, particularly on macroevolutionary timescales and across broad geographic spaces. Here we investigate the influence of biotic interactions on trait evolution and community assembly in monitor lizards (<em>Varanus</em>). Monitors are an iconic radiation with a cosmopolitan distribution and the greatest size disparity of any living terrestrial vertebrate genus. Between the colossal Komodo dragon <em>Varanus komodoensis</em> and the smallest Australian dwarf goannas, <em>Varanus</em> length and mass vary by multiple orders of magnitude. To test the hypothesis that size variation in this genus was driven by character displacement, we extended existing phylogenetic comparative methods which consider lineage interactions to account for dynamic biogeographic history and apply these methods to Australian monitors and marsupial predators. Incorporating both exon-capture molecular and morphological datasets we use a combined evidence approach to estimate the relationships among living and extinct varaniform lizards. Our results suggest that communities of Australian <em>Varanus</em> show high functional diversity as a result of continent-wide interspecific competition among monitors but not with faunivorous marsupials. We demonstrate that patterns of trait evolution resulting from character displacement on continental scales are recoverable from comparative data and highlight that these macroevolutionary patterns may develop in parallel across widely distributed sympatric groups.</p>
Data from: Multilocus phylogeny and Bayesian estimates of species boundaries reveal hidden evolutionary relationships and cryptic diversity in Southeast Asian monitor lizards
Recent conceptual, technological, and methodological advances in phylogenetics have enabled increasingly robust statistical species delimitation in studies of biodiversity. As the variety of evidence purporting species diversity has increased, so too have the kinds of tools and inferential power of methods for delimiting species. Here we showcase an organismal system for a data-rich, comparative molecular approach to evaluating strategies of species delimitation among monitor lizards of the genus Varanus. The water monitors (Varanus salvator Complex), a widespread group distributed throughout Southeast Asia and southern India, have been the subject of numerous taxonomic treatments, which have drawn recent attention due to the possibility of undocumented species diversity. To date, studies of this group have relied on purportedly diagnostic morphological characters, with no attention given to the genetic underpinnings of species diversity. Using a 5-gene dataset, we estimated phylogeny and used multilocus genetic networks, analysis of population structure, and a Bayesian coalescent approach to infer species boundaries. Our results contradict previous systematic hypotheses, reveal surprising relationships between island and mainland lineages, and uncover novel, cryptic evolutionary lineages (i.e. new putative species). Our study contributes to a growing body of literature suggesting that, used in concert with other sources of data (e.g., morphology, ecology, biogeography), multilocus genetic data can be highly informative to systematists and biodiversity specialists when attempting to estimate species diversity and identify conservation priorities. We recommend holding in abeyance taxonomic decisions until multiple, converging lines of evidence are available to best inform taxonomists, evolutionary biologists, and conservationists.
FIGURE 34 in Unravelling the underestimated diversity of Philippine water monitor lizards (Squamata: Varanus salvator complex), with the description of two new species and a new subspecies
FIGURE 34. Distribution ranges of the Philippine species of the V. s a l va t o r complex according to the morphological investigations presented here: V. marmoratus = red; V. nuchalis = blue; V. palawanensis sp. nov. = green; V. rasmusseni sp. nov. = black; V. c. cumingi = yellow; and V. c. s a m a re n s i s ssp. nov. = purple. Question marks denote the water monitor populations from Mindoro, Basilan, and northern Borneo of unknown taxonomic status. The grey shaded areas indicate the paleo-shorelines of several Pleistocene aggregate island complexes, which today, form biogeographic subregions of the Philippines: I = Greater Palawan; II = Greater Luzon; III = Greater Negros–Panay; IV = Greater Mindanao; and V = Greater Sulu. Map modified after Gaulke (in press).
FIGURE 23 in Unravelling the underestimated diversity of Philippine water monitor lizards (Squamata: Varanus salvator complex), with the description of two new species and a new subspecies
FIGURE 23. Ventral view of the juvenile paratype (ZFMK 89391) of V. rasmusseni sp. nov. Photo by André Koch.
FIGURE 26 in Unravelling the underestimated diversity of Philippine water monitor lizards (Squamata: Varanus salvator complex), with the description of two new species and a new subspecies
FIGURE 26. Ventral view of the holotype (SMF 73912) of V. palawanensis sp. nov. Photo by André Koch.
FIGURE 27 in Unravelling the underestimated diversity of Philippine water monitor lizards (Squamata: Varanus salvator complex), with the description of two new species and a new subspecies
FIGURE 27. Portrait of the holotype (SMF 73912) of V. palawanensis sp. nov. Note the ill-defined temporal stripe and the dark pigmentation on the dorsal and ventral side of the tongue. Photo by André Koch.
FIGURE 20 in Unravelling the underestimated diversity of Philippine water monitor lizards (Squamata: Varanus salvator complex), with the description of two new species and a new subspecies
FIGURE 20. Ventral view of the adult holotype (ZMUC R42151) of V. rasmusseni sp. nov. Photo by André Koch.
FIGURE 19 in Unravelling the underestimated diversity of Philippine water monitor lizards (Squamata: Varanus salvator complex), with the description of two new species and a new subspecies
FIGURE 19. Dorsal view of the adult holotype (ZMUC R42151) of V. rasmusseni sp. nov. Note the lack of colour pattern. Photo by André Koch.
FIGURE 15 in Unravelling the underestimated diversity of Philippine water monitor lizards (Squamata: Varanus salvator complex), with the description of two new species and a new subspecies
FIGURE 15. Dorsal view of the subadult lectotype (ZMB 470) of V. marmoratus Wiegmann, 1834 from Luzon. Photo courtesy of Mark-Oliver Rödel and Frank Tillack.
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