Biology subjects

Selechnik, D.

Publications and source records attributed to Selechnik, D..

4 recordsLinked to original sources

bioRxiv2021

Brain transcriptome analysis reveals gene expression differences associated with dispersal behaviour between range-front and range-core populations of invasive cane toads in Australia

Understanding the mechanisms underlying rapid adaptation of invasive species in novel environments is key to improving our ability to manage these species. Many invaders demonstrate rapid evolution of behavioural traits involved in range expansion such as locomotor activity, exploration and risk-taking. However, the molecular mechanisms that underpin these changes are poorly understood. In 86 years, invasive cane toads (Rhinella marina) in Australia have drastically expanded their geographic range westward from coastal Queensland to Western Australia. During their range expansion, toads have undergone extensive phenotypic changes, particularly in behaviours that enhance the toads dispersal ability. Common-garden experiments have shown that some changes in behavioural traits related to dispersal are heritable. However, genetic diversity is greatly reduced across the invasive range due to a strong founder effect, and the genetic basis underlying dispersal-related behavioural changes remains unknown. Here we used RNA-seq to compare the brain transcriptomes of toads from the Hawaiian source population, as well as three distinct populations from across the Australian invasive range. We found markedly different gene expression profiles between the source population and Australian toads. By contrast, cane toads from across the Australian invasive range had very similar transcriptomic profiles. Yet, key genes with functions putatively related to dispersal behaviour showed differential expression between range-core and range-front populations. These genes could play an important role in the behavioural changes characteristic of range expansion in Australian cane toads.

genomics↗

bioRxiv2020

Inherent population structure determines the importance of filtering parameters for reduced representation sequencing analyses

As technological advancements enhance our ability to study population genetics, we must understand how the intrinsic properties of our datasets influence the decisions we make when designing experiments. Filtering parameter thresholds, such as call rate and minimum minor allele frequency (MAF), are known to affect inferences of population structure in reduced representation sequencing (RRS) studies. However, it is unclear to what extent the impacts of these parameter choices vary across datasets. Here, we reviewed literature on filtering choices and levels of genetic differentiation across RRS studies on wild populations to highlight the diverse approaches that have been used. Next, we hypothesized that choices in filtering thresholds would have the greatest impact when analyzing datasets with low levels of genetic differentiation between populations. To test this hypothesis, we produced seven simulated RRS datasets with varying levels of population structure, and analyzed them using four different combinations of call rate and MAF. We performed the same analysis on two empirical RRS datasets (low or high population structure). Our simulated and empirical results suggest that the effects of filtering choices indeed vary based on inherent levels of differentiation: specifically, choosing stringent filtering choices was important to detect distinct populations that were slightly differentiated, but not those that were highly differentiated. As a result, experimental design and analysis choices need to consider attributes of each specific dataset. Based on our literature review and analyses, we recommend testing a range of filtering parameter choices, and presenting all results with clear justification for ultimate filtering decisions used in downstream analyses.

bioinformatics↗

bioRxiv2019

Immune and environment-driven gene expression during invasion: An eco-immunological application of RNA-Seq

Host-pathogen dynamics change rapidly during a biological invasion and are predicted to impose strong selection on immune function. The invader may experience an abrupt reduction in pathogen-mediated selection ( enemy release), thereby favoring decreased investment into costly immune responses, and the extent of this reduction may depend on factors such as propagule size. Across plants and animals, there is mixed support for this prediction. Pathogens are not the only form of selection imposed on invaders; differences in abiotic environmental conditions between native and introduced ranges are also expected to drive rapid evolution. Here, we assess the expression patterns of immune and environmentally-associated genes in the cane toad (Rhinella marina) across its invasive Australian range. Transcripts encoding mediators of costly immune responses (inflammation, cytotoxicity) showed a curvilinear relationship with invasion history, with highest expression in toads from oldest and newest colonized areas. This pattern is surprising given theoretical expectations of density dynamics in invasive species, and may be because density influences both intraspecific competition and parasite transmission, generating conflicting effects on the strength of immune responses. Alternatively, this expression pattern may be the result of other evolutionary forces, such as spatial sorting and genetic drift, working simultaneously with natural selection. Our findings do not support predictions about immune function based on the enemy release hypothesis, and suggest instead that the effects of enemy release are difficult to isolate in wild populations. Additionally, expression patterns of genes underlying putatively environmentally-associated traits are consistent with previous genetic studies, providing further support that Australian cane toads have adapted to novel abiotic challenges.

ecology↗

bioRxiv2019

Invaders weather the weather: rapid adaptation to a novel environment occurs despite reduced genetic diversity

Invasive species often exhibit rapid evolution in their introduced ranges despite the genetic bottlenecks that are thought to accompany the translocation of small numbers of founders; however, some invasions may not fit this "genetic paradox." The invasive cane toad (Rhinella marina) displays high phenotypic variation across its environmentally heterogeneous introduced Australian range. Here, we used three genome-wide datasets to characterize population structure and genetic diversity in invasive toads: RNA-Seq data generated from spleens sampled from the toads native range in French Guiana, the introduced population in Hawaii that was the source of Australian founders, and Australia; RNA-Seq data generated from brains sampled more extensively in Hawaii and Australia; and previously published RADSeq data from transects across Australia. We found that toads form three genetic clusters: (1) native range toads, (2) toads from the source population in Hawaii and long-established areas near introduction sites in Australia, and (3) toads from more recently established northern Australian sites. In addition to strong divergence between native and invasive populations, we find evidence for a reduction in genetic diversity after introduction. However, we do not see this reduction in loci putatively under selection, suggesting that genetic diversity may have been maintained at ecologically relevant traits, or that mutation rates were high enough to maintain adaptive potential. Nonetheless, cane toads encounter novel environmental challenges in Australia and appear to respond to selection across environmental breaks; the transition between genetic clusters occurs at a point along the invasion transect where temperature rises and rainfall decreases. We identify loci known to be involved in resistance to heat and dehydration that show evidence of selection in Australian toads. Despite well-known predictions regarding genetic drift and spatial sorting during invasion, this study highlights that natural selection occurs rapidly and plays a vital role in shaping the structure of invasive populations. Author SummaryDespite longstanding evidence for the link between genetic diversity and population viability, the "genetic paradox" concept reflects the observation that invasive populations are successful in novel environments despite a putative reduction in genetic diversity. However, some recent studies have suggested that successful invasions may often occur due to an absence of obstacles such as genetic diversity loss or novel adaptive challenges. The recent emergence of genome-wide technologies provides us with the tools to study this question comprehensively by assessing both overall genetic diversity, and diversity of loci that underlie ecologically relevant traits. The invasive cane toad is a useful model because there is abundant phenotypic evidence of rapid adaptation during invasion. Our results suggest strong genetic divergence between native and invasive populations, and a reduction in overall genetic diversity; however, we do not see this reduction when solely assessing ecologically relevant loci. This could be for reasons that support or refute the genetic paradox. Further studies may provide perspectives from other systems, allowing us to explore how variables such as propagule size affect the fit of an invasion to the model of the paradox. Studying invasive species remains important due to their largely negative impacts on the environment and economy.

evolutionary biology↗