High elevation increases the risk of Y chromosome loss in Alpineskink populations with sex reversal
The view that has genotypic sex determination and environmental sex determination as mutually exclusive states in fishes and reptiles has been contradicted by the discovery that chromosomal sex and environmental influences can co-exist within the same species, hinting at a continuum of intermediate states. Systems where genes and the environment interact to determine sex present the opportunity for sex reversal to occur, where the phenotypic sex is the opposite of that predicted by their sex chromosome complement. The skink Bassiana duperreyi has XX/XY sex chromosomes with sex reversal of the XX genotype to a male phenotype, in laboratory experiments, and in field nests, in response to exposure to cold incubation temperatures. Here we studied the frequency of sex reversal in adult populations of B. duperreyi in response to climatic variation, using elevation as a surrogate for environmental temperatures. We demonstrate sex reversal in the wild for the first time in adults of a reptile species with XX/XY sex determination. The highest frequency of sex reversal occurred at the highest coolest elevation location, Mt Ginini (18.46%) and decreased in frequency to zero with decreasing elevation. We model the impact of this under Fisher’s frequency-dependent selection to show that, at the highest elevations, populations risk the loss of the Y chromosome and a transition to temperature-dependent sex determination. This study contributes to our understanding of the risks of extinction from climate change in species subject to sex reversal by temperature, and will provide focus for future research to test on-the-ground management strategies to mitigate the effects of climate in local populations.
Source: Dissanayake, D.S.B., Holleley, C.E., Deakin, J.E. et al. High elevation increases the risk of Y chromosome loss in Alpine skink populations with sex reversal. Heredity (2021). https://doi.org/10.1038/s41437-021-00406-z
Genome Subtarction:Identification of Y chromosome markers in the eastern three-lined skink using in silico whole genome subtraction.
Homologous sex chromosomes can differentiate over time because recombination is suppressed in the region of the sex determining locus, leading to the accumulation of repeats, progressive loss of genes that lack differential influence on the sexes and sequence divergence on the hemizygous homolog. Divergence in the non-recombining regions leads to the accumulation of Y or W specific sequence useful for developing sex-linked markers. Here we use in silico whole-genome subtraction to identify putative sex-linked sequences in the scincid lizard Bassiana duperreyi which has heteromorphic XY sex chromosomes.The sex of B. duperreyi can be reversed by low temperatures (XX genotype reversed to a male phenotype). We have developed sex-specific markers to identify the underlying genotypic sex and its concordance or discordance with phenotypic sex in wild populations of B. duperreyi. Our pipeline can be applied to isolate Y or W chromosome-specific sequences of any organism and is not restricted to sequence residing within single-copy genes. This study greatly improves our knowledge of the Y chromosome in B. duperreyi and will enhance future studies of reptile sex determination and sex chromosome evolution.
Source: Dissanayake, D.S.B., Holleley, C.E., Hill, L.K. et al. Identification of Y chromosome markers in the eastern three-lined skink (Bassiana duperreyi) using in silico whole genome subtraction. BMC Genomics 21, 667 (2020). https://doi.org/10.1186/s12864-020-07071-2
Viviparous Reptile Regarded to Have Temperature-Dependent Sex Determination Has Old XY Chromosomes
The water skinks Eulamprus tympanum and Eulamprus heatwolei show thermally induced sex determination where elevated temperatures give rise to male offspring. Paradoxically, Eulamprus species reproduce in temperatures of 12–15 °C making them outliers when compared with reptiles that use temperature as a cue for sex determination. Moreover, these two species are among the very few viviparous reptiles reported to have thermally induced sex determination. Thus, we tested whether these skinks possess undetected sex chromosomes with thermal override. We produced transcriptome and genome data for E. heatwolei. We found that E. heatwolei presents XY chromosomes that include 14 gametologs with regulatory functions. The Y chromosomal region is 79–116 Myr old and shared between water and spotted skinks. Our work provides clear evidence that climate could be useful to predict the type of sex determination systems in reptiles and it also indicates that viviparity is strictly associated with sex chromosomes.
Source: Paola Cornejo-Páramo, Duminda S B Dissanayake, Andrés Lira-Noriega, Mónica L Martínez-Pacheco, Armando Acosta, Ciro Ramírez-Suástegui, Fausto R Méndez-de-la-Cruz, Tamás Székely, Araxi O Urrutia, Arthur Georges, Diego Cortez, Viviparous Reptile Regarded to Have Temperature-Dependent Sex Determination Has Old XY Chromosomes, Genome Biology and Evolution, Volume 12, Issue 6, June 2020, Pages 924–930, https://doi.org/10.1093/gbe/evaa104
Morphology and Molecular Characterization of Parabronema smithii (Cobbold, 1882) (Nematoda: Habronematidae) from Wild Asian Elephant (Elephas maximus maximus) of Sri Lanka
The aim of the present study was to carry out a detailed study of morphological features and to determine the phylogenetic position of a Parabronema smithii (Cobbold, 1882) found in wild elephants in Sri Lanka. Adult worms were collected from stomach ulcers at the postmortem examination of wild elephants in the Udawalawe National Park, Sri Lanka. Fifteen morphological characteristics were investigated. All P. smithii isolated from wild elephants were similar in their key morphological features. Furthermore, the present study provides a comparison of morphology and morphometrics of Parabronema species that occur in different hosts. Here we present first evidence and have clariﬁed the phylogenetic positions of P. smithii isolates using the second internal transcribed spacer region (ITS2), and portions of the large subunit ribosomal DNA (28S) and cytochrome c oxidase subunit 1(cox1). All samples analysed were identical in their nucleotide sequences. Phylogenetic analysis of the selected genes revealed that P. smithii in the present study is closely associated with P. skrjabini and Habronema spp. Findings of the present study enhance our understanding of the biology and taxonomy of P. smithii in wild elephant in Sri Lanka and will contribute to future phylogeographic studies.
Source: Thewarage, L.D., Dissanayake, D.S.B., Perera, U.S. et al. Morphology and Molecular Characterization of Parabronema smithii (Cobbold, 1882) (Nematoda: Habronematidae) from Wild Asian Elephant (Elephas maximus maximus) of Sri Lanka. Acta Parasit. 65, 504–517 (2020). https://doi.org/10.2478/s11686-020-00193-3
Nesting behaviour and ecology of the White-browed Fantail Flycatcher (Rhipidura aureola) in Sri Lanka
he White-browed Fantail Flycatcher (Rhipidura aureola) is a widely distributed species in tropical regions of the Indian subcontinent and in Southeast Asia. We determined the breeding biology and nest site characteristics of R. aureola in Sri Lanka during 2012 to 2017. All the nests observed were small cup-shaped and without a ‘tail’ extending below the nest base. Both male and female R. aureola built their nests within 9–13 days with an average mean external diameter, mean internal diameter, and mean depth of, respectively, 6.4 ± 0.32, 5.6 ± 0.22, and 2.9 ± 0.21 cm. The R. aureola we found used various habitats such as home gardens, forest boundaries, sanctuaries, man-made tanks/water bodies, stream banks, tea plantations and road edges to build their nests. We did not find any change in clutch size (2–3 eggs) with different elevation gradients. The eggs were oval-shaped with the ground colour of pale warm yellow-brown to pink and lots of spots or
blotches in dark gray-brown. More than 60% of nests were built in a high to medium range of visibility to predators, without a specific location or tree preference, which resulted in nest failure due
to predation by domestic cats or birds of prey. Also, we found nest failure due to washing away by abundant rains. Detailed studies on ecological and environmental parameters with respect to nesting
or breeding success will help to better understand the species.
Source: Dissanayake, D.S., Thewarage, L.D., & Mohan, M.A. (2019). Nesting behaviour and ecology of the White-browed Fantail Flycatcher (Rhipidura aureola) in Sri Lanka. Zoology and ecology, 29, 3-6.
The Venom of Spectacled Cobra (Elapidae: Naja naja): In Vitro Study from Distinct Geographical Origins in Sri Lanka
everal countries residing envenomation due to Naja naja had revealed a disparity in the venom composition according to their geographic location and Sri Lankan cobra still lacks the evidence to support this. Therefore, the current study was focused on addressing relationship between the histopathological changes according to geographic variation of Sri Lankan N. naja venom. The histopathological changes in vital organs and muscle tissues following intramuscular administration of venom of N. naja were studied using BALB/c mice. The median lethal dose of venom of N. naja in the present study was determined to be 0.55, 0.66, 0.68, 0.62, and 0.7 mg/kg for North (NRP), Central (CRP), Western, Southern, and Sabaragamuwa Regional Population venoms, respectively. Histopathological changes were observed in different levels in vital organs and muscle tissues of mice. NRP accompanied significantly higher infiltration of inflammatory and necrotic cells into skeletal muscle and CRP venom demonstrated high level of cardiotoxic effects comparing to other regions. This study revealed a certain extent of variations in the pathological effects of N. naja venom samples according to their geographical distribution.
Source: Dissanayake, D.S.B., Thewarage, L.D., Waduge R.N., Ranasinghe J.S.G., Kularatne S.A.M., Rajapaksea, R.P.V.J. The Venom of Spectacled Cobra (Elapidae: Naja naja): in vitro study from distinct geographical origins in Sri Lanka. Journal of Toxicology, Article ID 7358472, 14 pages.
Hematological and plasma biochemical parameters in a wild population of Naja naja (Linnaeus, 1758) in Sri Lanka
Hematological studies of any animal species comprise an important diagnostic method in veterinary medicine and an essential tool for the conservation of species. In Sri Lanka, this essential technique has been ignored in studies of many species including reptiles. The aim of the present work was to establish a reference range of hematological values and morphological characterization of wild spectacled cobras (Naja naja) in Sri Lanka in order to provide a diagnostic tool in the assessment of health condition in reptiles and to diagnose diseases in wild populations. Blood samples were collected from the ventral caudal vein of 30 wild-caught Naja naja (18 males and 12 females). Hematological analyses were performed using manual standard methods. Several hematological parameters were examined and their mean values were: red blood cell count 0.581 ± 0.035 × 106/μL in males; 0.4950 ± 0.0408 × 106/μL in females; white blood cell count 12.45 ± 1.32 × 103/μL in males; 11.98 ± 1.62 × 103/μL in females; PCV (%) in males was 30.11 ± 1.93 and in females was 23.41 ± 1.67; hemoglobin (g/dL) was 7.6 ± 0.89 in males and 6.62 ± 1.49 in females; plasma protein (g/dL) was 5.11 ± 0.75 in males and 3.25 ± 0.74 in females; whereas cholesterol (mg/mL) was 4.09 ± 0.12 in males and 3.78 ± 0.42 in females. There were no significant differences in hematological parameters between the two genders except for erythrocyte count, thrombocyte count, hematocrit, hemoglobin, plasma protein, percentage of azurophil and heterophil. Intracellular parasites were not found in any of the studied specimens. Hematological and plasma biochemical parameters indicated a difference between geographically isolated populations and some values were significantly different between the two genders. These hematological results provide a reference range for Sri Lankan population of adult Naja naja.
Source: Dissanayake, D.S.B., Thewarage, L.D., Manel Rathnayake, R.M.P. et al. Hematological and plasma biochemical parameters in a wild population of Naja naja (Linnaeus, 1758) in Sri Lanka. J Venom Anim Toxins Incl Trop Dis 23, 8 (2017). https://doi.org/10.1186/s40409-017-0098-7
A breeding colony of the brown bat (Myotis hasseltii) from Sri Lanka
Myotis hasseltii (Temminck, 1840) variously known as the brown bat, Van Hasselt’s bat, Van Hasselt’s mouse-eared bat, or lesser large-footed myotis in the vernacular is a patchily distributed species; aside from Sri Lanka, within the Indian Subcontinent it is found only in West Bengal (Bates et al., 2008). The study was conducted in the Knuckles region, Illukkumbura area (7°32'11.51''–7°32'18.16''N, 80°46'14.73''–80°46'26.95''E, alt. ~470m a.s.l.) Central Province of Sri Lanka. The study area was 2 km² in extent and encompassed altitudes between 420–480m. The area’s vegetation was predominantly lowland semi-evergreen forest and there were hamlets along the Thelgamuwa Oya (stream), the observation site, involved in paddy and chena cultivation.This is the first confirmed breeding colony of M. hasseltii found in Sri Lanka in over 80 years.
Source: Wellappulli-Arachchi S. M., Edirisinghe W. G. M., Dissanayake D. S. B., Mapatuna Y & Wickramasinghe S, 2014. A breeding colony of the brown bat (Myotis hasseltii) from Sri Lanka. Taprobanica, 2014. 6(1) 68–71.
Dietary habits and the predators of the Bengal Monitor Varanus bengalensis in Sri Lanka
The Bengal monitor (Varanus bengalensis) is the second largest lizard species in Sri Lanka, and is well adapted to living in a variety of terrestrial habitats. Varanus bengalensis is a diurnal generalist predator, but sometimes function as a scavenger. Given the ecological plasticity and generalist foraging strategy of V. bengalensis, its feeding ecology and role in trophic networks could vary among different environments. Thus, in this study we documented the prey and natural predators of V. bengalensis across different landscapes along the urban-rural gradient and geo-climatic zones of Sri Lanka through field observations, literature surveys, and personal communications with other biologists. We documented 82 species of vertebrate prey in the diet of V. bengalensis, which included 20 mammals, 21 birds, 20 reptiles, 14 amphibians, and seven fishes.
Source: Karunarathna S.U., Surasinghe T., Dissanayake D., Boutejue M., Gabadage D. & Madawala M., 2017. Dietary habits and the predators of the Bengal Monitor Varanus bengalensis in Sri Lanka. Biawak, 11: 28–39
Habitat preferences of the endemic shrub frog Pseudophilautus regius (Manamendra-Arachchi and Pethiyagoda 2005) at Mihintale Sanctuary, Sri Lanka
—Mihintalae is situated in the dry zone of the North Central Province of Sri Lanka, at an elevation of 108 m, and is an under studied site of the habitat of the endemic shrub frog Pseudophilautus regius. Six different habitat types which included forest edge, seasonal pond, rock,
shrub, grassland, and home garden habitats were selected and systematically sampled to identify the habitat preference of P. regius. During the survey, a total of 143 P. regius individuals were counted. The highest percentage (53%) of individuals were recorded from the forest edge habitats, 23% from shrub land habitats, 20% from home gardens, and 2% from grassland and seasonal ponds. No individuals were found in the rocky areas. The number of observed individuals of P. regius increased with the rainfall in forest habitats and simultaneously decreased in the home gardens. During the dry season the overall turnout of the number of individuals increased in home gardens. However, more extensive and systematic studies, over a longer period of time, are required to estimate the population size and document the fluctuation of P. regius and implement suitable
conservation measures, if necessary.
Source: Dissanayake DSB, Wellapuli-Arachchi SM. 2012. Habitat preferences of the endemic shrub frog Pseudophilautus regius (Manamendra-Arachchi and Pethiyagoda 2005) at Mihintale Sanctuary, Sri Lanka. Amphibian & Reptile Conservation 5(2):114-124 (e57).