Experimental manipulation of DNA methylation in invasive cane toads causes long-term, intergenerational, and regionally differential effects on ecologically-relevant traits

Invasive species often rapidly adapt to their introduced environments, even when genetic diversity is low. Phenotypic variance may be generated by environmentally-induced epigenetic changes (e.g., shifts in DNA methylation) and, where heritable, these changes could affect evolution, especially in genetically depauperate populations. To investigate the role of such changes during invasion, I have studied introduced cane toads in Australia. Since their introduction in 1935, toads have accumulated significant phenotypic variation in their morphological, physiological, and behavioural traits across their range, despite low levels of genetic diversity. Here, I employed a common-garden framework to manipulate levels of DNA methylation in offspring of pairs of toads collected from range-core and range-edge localities and assessed how treatments impacted phenotype across toads’ invasive range, life-stages and generations. I manipulated DNA methylation using two methods: exposure to a DNA methylation inhibitor (zebularine) and exposure to conspecific alarm cues. I found that exposure to either treatment affected phenotype and DNA methylation patterns in cane toads. I identified interactions between the effects of experimental manipulations and population of origin on development and behaviour across larval and adult life-stages. I also identified more differentially methylated regions in response to these treatments in range-edge tadpoles compared to those from the range-core. Importantly, some of the effects of the DNA methylation manipulations I used were transmitted to the second generation and improved the fitness of those individuals. This suggests that changes to DNA methylation in wild toads have the potential to drive phenotypic changes that promote invasion. I identified genes that respond to these manipulations, and that are linked to functions that plausibly assist invaders encountering challenges in their new environment. Overall, my thesis indicates that exposure to a DNA methylation inhibitor affects ecologically-relevant phenotypes that may assist invasion, that exposure to congeneric alarm cues affects both DNA methylation and phenotype, and that some of the effects of these treatments are transmitted to the next generation. Together, these findings highlight the potential for heritable, epigenetic changes to affect evolution during invasion, and suggest that further investigation of this topic is warranted

Effect of Climate Change on Invasion Risk of Giant African Snail (Achatina fulica Férussac, 1821: Achatinidae) in India

The Giant African Snail (Achatina fulica) is considered to be one the world’s 100 worst invasive alien species. The snail has an impact on native biodiversity, and on agricultural and horticultural crops. In India, it is known to feed on more than fifty species of native plants and agricultural crops and also outcompetes the native snails. It was introduced into India in 1847 and since then it has spread all across the country. In this paper, we use ecological niche modeling (ENM) to assess the distribution pattern of Giant African Snail (GAS) under different climate change scenarios. The niche modeling results indicate that under the current climate scenario, Eastern India, peninsular India and the Andaman and Nicobar Islands are at high risk of invasion. The three different future climate scenarios show that there is no significant change in the geographical distribution of invasion prone areas. However, certain currently invaded areas will be more prone to invasion in the future. These regions include parts of Bihar, Southern Karnataka, parts of Gujarat and Assam. The Andaman and Nicobar and Lakshadweep Islands are highly vulnerable to invasion under changed climate. The Central Indian region is at low risk due to high temperature and low rainfall. An understanding of the invasion pattern can help in better management of this invasive species and also in formulating policies for its control

Integrative Taxonomic Approach for Describing a New Cryptic Species of Bush Frog (Raorchestes: Anura: Rhacophoridae) from the Western Ghats, India

A new cryptic species of bush frog Raorchestes honnametti sp. nov. is described from the south-eastern part of the Western Ghats, India. This newly described species belongs to the Charius clade and is morphologically similar to other clade members—R. charius and R. griet. Therefore, an integrative taxonomic approach based on molecular and bioacoustic analysis along with morphology was used to delimit the new species. Raorchestes honnametti sp. nov., is currently known only from Biligiri Rangaswamy Temple Tiger Reserve, a part of Biligiri Rangaswamy horst mountain range (a mountain formed due movement of two faults) formed during the Late Quaternary period (1.8–2.58 Ma). Discovery of cryptic species from a highly speciose and well-studied genus Raorchestes hints at the possible existence of several more cryptic species in this genus. We discuss the possible reasons for crypsis and emphasize the need for continued systematic surveys of amphibians across the Western Ghats

Percent number of records of <i>A</i>.<i>fulica</i> invasion along the altitudinal gradient.

<p>Percent number of records of <i>A</i>.<i>fulica</i> invasion along the altitudinal gradient.</p

Environmental Data used for ENM for <i>A</i>. <i>fulica</i>.

<p>The highlighted variables were included in the model after testing for correlation between variables.</p

Pearson’s correlation between number of <i>A</i>. <i>fulica</i> records and climatic factors.

<p>*P<0.05,</p><p>**P<0.01,</p><p>df = 10</p><p>Pearson’s correlation between number of <i>A</i>. <i>fulica</i> records and climatic factors.</p

Potential distribution of <i>A</i>.<i>fulica</i> under current, and three climate change scenario (RCP 4.5, 6.0 and 8.0) a) for mainland India and b) Andaman and Nicobar Islands.

<p>Legend: Blue to red colour indicates unsuitable to highly suitable areas</p

Area under curve for training and test points under different scenarios.

<p>Area under curve for training and test points under different scenarios.</p

Top 10 Indian states with >0.50% probability of invasion risk from <i>A</i>. <i>fulica</i> under present and future climate change scenarios.

<p>The values in table are in percentage.</p

Relative contribution of different bioclimatic variables to MaxEnt model for <i>A</i>. <i>fulica</i>.

<p>Percent contribution values are averages over 10 replicate runs.</p