Species Of Monitor Lizards Research Articles

A preliminary study of the effects of enrichment on the activity and spatial distribution of captive monitor lizards in Nakhon Ratchasima Zoo, Thailand

The monitor lizard (Varanus salvator) has the widest distribution among all extant varanids found across South and Southeast Asia. However, behavioral studies on captive monitor lizard have not been well-documented. The objective of this research was to investigate the effects of enrichment items on the activity and spatial distribution of captive monitor lizards. The study involved three adult captive Black water monitors (Hiea dam), three adult Roughnecked monitors (Ngu-hao Chang), and two adult Dumeril’s monitors (Tut-too) in outdoor enclosures. Three treatments were administered: control (no enrichment item), cone (enrichment item), and takraw (enrichment item: a rattan ball). The frequency of activity and spatial distribution of three species of monitor lizards were recorded. The results showed that the percentages of activity and spatial distribution of three species of monitor lizards were not significantly affected by the enrichment items (P > 0.05). However, there were significant differences only in lying behavior between the Hiea dam, Ngu-hao Chang, and Tut-too monitors (P < 0.05). In conclusion, the general behaviors of captive Hiea dam, Ngu-hao chang, and Tut-too monitor lizards were similar, and their spatial distribution was also similar. The behavior and spatial distribution of captive monitor lizards were not affected by the enrichment items.

Two new species of monitor lizards (Squamata: Varanus) endemic to the Louisiade and Tanimbar Archipelagos with a key to the subgenus Euprepiosaurus

ABSTRACT We describe two new species of Varanus, one each endemic to the Louisiade and Tanimbar Archipelagos in Papua New Guinea and Indonesia, respectively. The new species belong to the subgenus Euprepiosaurus and, therein, to the widely distributed and relatively species-rich Varanus indicus group. They can be distinguished from all other recognised species by scalation, colour-pattern and genetic differences. The new species from Tanimbar is most closely related to V. indicus and V. melinus, from which it can be distinguished by its dark blue/grey tongue and higher middorsal and midventral scale counts. The new species from the Louisiades can be distinguished from its phylogenetically and geographically nearest relative, V. chlorostigma, by the presence of dorsal crossbands, the mostly pink tongue mottled with grey, and higher midbody scale count. The Louisiades constitute the easternmost archipelago of Milne Bay Province in eastern Papua New Guinea, and they host a diverse herpetofauna with a high degree of endemism; Varanus louisiadensis sp. nov. increases the known number of herpetofaunal endemics in that archipelago to 60. The Tanimbar Islands are situated in the southern part of Maluku Province (Moluccas), Indonesia, and are a minor centre of vertebrate endemism; Varanus tanimbar sp. nov. increases the number of known herpetofaunal endemics there to six. http://www.zoobank.org/urn:lsid:zoobank.org:pub:E06BDE2A-0B24-4CB5-B46E-6B93476CC3EB

Invasional meltdown-under? Toads facilitate cats by removing a naïve top predator

Context Australia has been a battleground of invasive versus native species for ~200 years. Two of the most impactful invasive species to Australian animal communities are the toxic cane toad (Rhinella marina) and the predatory feral cat (Felis catus). Australia’s native fauna is evolutionarily naïve to both invaders because neither’s taxonomic group is native to the continent. Both invaders have had severe effects on Australian native animal communities including species extinctions, extirpations, and severe population declines, but until now their effects have generally been thought to be independent of one another. Aims We aimed to determine the impacts of invasive cane toads on monitor lizards and feral cats by estimating changes in relative abundance before and after the toad invasion. Methods We studied toad impacts at three sites in the Kimberley region of northern Australia. We used two methods for estimating relative abundance: camera traps and track station data. Data included greater than 4000 trap days and included 7 years over an 11-year period. Key results As expected, invading cane toads rapidly decimated populations of two species of monitor lizards (97–99% declines), including the top-order predatory Varanus panoptes. Unexpectedly, this loss was associated with a >10-fold mean increase in detection rates of cats by 5 years after the loss of V. panoptes, reflecting relative increases of 3.3–8.7 individual cats per site. Conclusions Although some unknown factor may have caused an increase in cats, their similar trophic position and niche to V. panoptes suggests that toads facilitated cats by effectively removing the lizards from the animal community. This interaction likely reflects one type of invasional meltdown, whereby a non-native species (cane toad) facilitated any aspect of another’s (feral cat) invasion (e.g. survival, reproduction, resource acquisition), but the latter has no detected influence on the former (+/0 interaction). Implications Because both invaders cause declines in animal populations and are difficult to control, the potentially synergistic tandem of cane toads and feral cats could have chronic, irreversible effects on animal communities.

Long-term Memory of a Complex Foraging Task in Monitor Lizards (Reptilia: Squamata: Varanidae)

Procedural memory allows animals to solve previously encountered tasks over weeks, months, or years efficiently. Although thoroughly documented in vertebrate clades such as mammals and birds, studies of procedural memory in squamate reptiles are lacking. Filling the gap in knowledge regarding procedural memory in squamates is important to understanding the degree to which procedural memory is unique to birds and mammals, as it is related to their unique cognitive abilities. We tested for memory of a problem-solving task in two species of monitor lizard (Varanus spp.) and a beaded lizard (Heloderma sp.) after a 20-mo hiatus in exposure, representing approximately 25% of their ages at the time of testing. All the monitor lizards had lower initial latencies to solve the task upon re-exposure posthiatus than they had as naive individuals during the prehiatus trials and reached minimum latencies in fewer trials than when previously tested. Our results indicate procedural memory of puzzle-solving behaviors on the time scales of years. Our results add to an emerging literature suggesting that squamate and other nonavian reptiles share a number of cognitive traits with birds and mammals, suggesting that such traits are far more widespread across taxa than previously recognized. We also discuss a framework for studying cognition in squamates that would allow tests of cognition across a great diversity of body forms and ecologies.

Amendment of Rostellotaenia Freze, 1963 (Cestoda: Proteocephalidae) from African monitors (Varanus spp.) and a redescription of its type-species, R. nilotica (Beddard, 1913).

Based on morphological evaluation of type-specimens and new material collected in three species of monitor lizards (Squamata: Varanidae), the diagnosis of the monotypic Rostellotaenia Freze, 1963 (Proteocephalidae: 'Acanthotaeniinae') is amended. The genus differs from Acanthotaenia von Linstow, 1903, with which it was previously synonymised, by the shape of the scolex with a wide, dome-shaped rostellum, the posterior extent of the uterus, which does not overpass the ovarian isthmus posteriorly, well-developed retractor muscles connecting the rostellum with the neck region, absence of a well-developed, ring-like vaginal sphincter, shorter and wider proglottides, and geographical distribution (Ethiopian region only). The type- and only species, R. nilotica (Beddard, 1913), is redescribed and two new definitive hosts, Varanus albigularis Daudin and V. exanthematicus (Bosc), are reported. Host specificity of R. nilotica, which exhibits remarkable morphological variability, is stenoxenous, i.e. it occurs in several congeneric species of African monitor lizards, unlike species of Acanthotaenia, which are strictly specific (oioxenous).

Latency in Problem Solving as Evidence for Learning in Varanid and Helodermatid Lizards, with Comments on Foraging Techniques

Cognition and learning have been widely studied in vertebrates, but not across much phylogenetic breadth. Non-avian reptiles, for example, have been poorly studied. Anecdotal observations and a few previous studies suggest that lizards may have strong cognitive skills owing, in part, to behaviors such as optimal foraging and territoriality. We tested four lizard species, including three species of monitor lizard (Varanus spp.) and one species of beaded lizard (Heloderma), in a longitudinal, repeated-trials experimental design using a puzzle-feeder device to evaluate learning, in the form of latency trends over time. We used a Bayesian multilevel modeling statistical method and incorporated unsuccessful trials as censored data. Collectively, all lizards showed a pattern of decreasing latencies over time. We interpret this pattern as learning among our lizards. Notable individual and inter-specific differences were evident, however, suggesting that learning abilities differed among the lizards. In this case, the monitor lizards exhibited steeper declines in latencies and greatly reduced inter-individual variation in comparison to the beaded lizards. Finally, we found differential use of the claws versus the snout among the lizards, which is consistent with a previously posed hypothesis based on different species than we measured.

Conserved sex chromosomes and karyotype evolution in monitor lizards (Varanidae).

Despite their long history with the basal split dating back to the Eocene, all species of monitor lizards (family Varanidae) studied so far share the same chromosome number of 2n = 40. However, there are differences in the morphology of the macrochromosome pairs 5-8. Further, sex determination, which revealed ZZ/ZW sex microchromosomes, was studied only in a few varanid species and only with techniques that did not test their homology. The aim of this study was to (i) test if cryptic interchromosomal rearrangements of larger chromosomal blocks occurred during the karyotype evolution of this group, (ii) contribute to the reconstruction of the varanid ancestral karyotype, and (iii) test homology of sex chromosomes among varanids. We investigated these issues by hybridizing flow sorted chromosome paints from Varanus komodoensis to metaphases of nine species of monitor lizards. The results show that differences in the morphology of the chromosome pairs 5-8 can be attributed to intrachromosomal rearrangements, which led to transitions between acrocentric and metacentric chromosomes in both directions. We also documented the first case of spontaneous triploidy among varanids in Varanus albigularis. The triploid individual was fully grown, which demonstrates that polyploidization is compatible with life in this lineage. We found that the W chromosome differs between species in size and heterochromatin content. The varanid Z chromosome is clearly conserved in all the analyzed species. Varanids, in addition to iguanas, caenophidian snakes, and lacertid lizards, are another squamate group with highly conserved sex chromosomes over a long evolutionary time.

Deep Communal Nesting by Yellow-Spotted Monitors in a Desert Ecosystem: Indirect Evidence for a Response to Extreme Dry Conditions

Abstract In oviparous reptiles with no parental care, the choice of nest site is a mother's final investment in her offspring. Although linkages between nest site choice, egg temperatures, and embryonic success have been well studied, much less is known about analogous linkages with soil moisture encompassing developing embryos. Most ground-nesting reptiles nest at depths <25 cm, with the deepest nests <1.0 m deep. Recently, however, the nests of two species of monitor lizards (Varanus panoptes and V. gouldii) have been discovered at depths of 2.3–3.0 m, suggesting that nesting at extreme depths in these species is an adaptive response to the lack of sufficient soil moisture at shallower depths. Herein, we examine this idea with V. panoptes, specifically predicting that deeper nests in a desert ecosystem compared with those in a savannah ecosystem are attributable to differences in the magnitude of rainfall. We excavated a communal nesting warren to a depth of 4 m and identified 11 fresh nests and 99 hatc...

Forensically informative nucleotide sequencing (FINS) for the first time authentication of Indian Varanus species: implication in wildlife forensics and conservation

Monitor lizards are Varanus species widely distributed, endangered reptile in the IUCN red data list. In India, based on the morphological and ecological characteristic, it is divided into four species viz. Bengal monitor lizard, Yellow monitor lizard, Desert monitor lizard and Water monitor lizard. These four species listed as Schedule I species in Indian Wildlife (Protection) Act 1972. This paper first attempt to present Forensically Informative Nucleotide Sequencing (FINS) for the Indian Varanus based on three mitochondrial genes. The molecular framework will be useful for the identification of Indian Varanus species and trade products derived from monitors and as such, have important applications for wildlife management and conservation. Here, we used known 14 individual skin pieces of four species of monitor lizards; the partial fragment of three mitochondrial genes (Cyt b, 12S rRNA, and 16S rRNA) were amplified for genetic study. In Cyt b, 12S rRNA and 16s rRNA, we observed, 5, 5 and 4 Haplotypes; 71, 69, and 43 Variables sites; 90, 89, and 50 Parsimony Informative sites within four species of Indian monitor lizards, respectively. Despite it, the nucleotide composition was T 26.4, C 32.8, A 29.2 and G11.6; T 18.8, C 29.7, A 34.0 and G 17.5; T 21.7, C 27.3, A 32.5 and G 18.5 in Cyt b, 12S rRNA and 16S rRNA, respectively. The neighbor joining phylogenetic tree and maximum parsimony tree of three mitochondrial genes, showed similar results and reveal that, there are two major clades are present in Indian monitor lizards.

Morphological characteristics of blood cells in monitor lizards: is erythrocyte size linked to actual body size?

Blood cell morphology and count are not uniform across species. Recently, between-species comparisons revealed that the size of red blood cells is associated with body size in some lizard taxa, and this finding was interpreted in the context of the metabolic theory. In the present study, we examined the numbers and the size of blood cells in 2 species of monitor lizards, the mangrove-dwelling monitor (Varanus indicus) and the savannah monitor (V. exanthematicus), and we compared these traits in individuals of different body size. The results revealed that during the course of ontogeny, the size of red blood cells increases with body mass. Because the mass-specific metabolic rate decreases with body size and the cell volume-to-surface ratio decreases with the cell size, changes in the erythrocyte size might be the result of oxygen transport adjustment.

Amphibians and Reptiles, Luzon Island, Aurora Province and Aurora Memorial National Park, northern Philippines: new island distribution records

We report 35 new amphibian and reptile distribution records for two regions within the southern Sierra Madre Mountain Range, Aurora Province, central Luzon Island, Philippines. Together with results of our previous survey work in Aurora, our new data result in a total of 82 amphibian and reptile species for the area. These results highlight the degree to which the island’s biodiversity continues to be underestimated and poorly understood. We report on observations of rarely encountered species including the skink Sphenomorphus leucospilos, the forest gecko Luperosaurus cf. cumingii, and a sensational new species of monitor lizard, Varanus bitatawa. Our recent collections clarify the conservation status of the “critically endangered” Polillo Island forest frog Platymantis polillensis, now known to be widespread, abundant, and common throughout Camarines Norte, Quezon, and Aurora Provinces on the adjacent mainland of Luzon Island. These results add to our growing understanding of many species’ distributions in the region.

A new melanistic species of monitor lizard (Reptilia: Squamata: Varanidae) from Sanana Island, Indonesia

A new species of monitor lizard endemic to Sanana Island in the northwestern Moluccas is described from a preserved specimen and field observations. This is the only melanistic member of the Varanus indicus species group, and the only taxon in the subgenus Euprepiosaurus with prominent orange-red markings. Allied to Varanus melinus of nearby Mangole and Taliabu islands in body proportions and scutellation, the new species is convergent with melanistic populations of the Varanus salvator complex from the Sula Platform, Sulawesi and Togian Islands. On Sanana the new species reaches highest densities in coastal sago palm swamps, a habitat type that is underutilized by other species in the V. indicus group elsewhere in the Moluccas.

Effect of masking the parietal eye on the diurnal activity and body temperature of two sympatric species of monitor lizards, Varanus s. salvator and Varanus b. nebulosus

Five water monitor lizards, Varanus salvator salvator, and four clouded monitor lizards, Varanus bengalensis nebulosus, were caught on Tioman island in Malaysia. A radio-thermistor transmitter was implanted into the buccal cavity of each animal, and they were released into an enclosure measuring 5.5 × 6.5 metres. The lizards were observed for 9 and 8 days, respectively, before and after the parietal eye was covered with aluminium foil. With uncovered parietal eye, both species showed a clear diurnal rhythm, being active only during day time. After covering the parietal eye, the mean locomotor activity of five V. s. salvator decreased from 791 to 107 min · day–1 but remained unchanged around 850 min · day–1 for V. b. nebulosus. The mean duration of locomotor activity decreased in V. s. salvator and V. b. nebulosus after the parietal eye was covered, but V. b. nebulosus maintained its locomotor activity by increasing the number of locomotor bouts. The water monitor spent very little time on thermoregulation. Its body temperature ranged between 26.3 and 28.4 °C, which decreased after the parietal eye was covered. The clouded monitor thermoregulated around 28.8–36.0 °C, which remained unchanged after the parietal eye was covered. In both species, there was a strong correlation between body temperature and ambient temperature. Behavioural abnormalities were recorded among V. s. salvator with covered parietal eye. They were often observed to be active by night and often slept outside a burrow. The circadian rhythm of V. b. nebulosus appeared unaffected by shielding of its parietal eye. Captivity combined with shielded parietal eye induced agonistic behaviour in both species.