Biology subjects

Baxter, S. W.

Publications and source records attributed to Baxter, S. W..

3 recordsLinked to original sources

bioRxiv2018

Assessing genomic admixture between cryptic Plutella moth species following secondary contact

Cryptic species are genetically distinct taxa without obvious variation in morphology and are occasionally discovered using molecular or sequence datasets of populations previously thought to be a single species. The world-wide Brassica pest, Plutella xylostella (diamondback moth), has been a problematic insect in Australia since 1882, yet a morphologically cryptic species with apparent endemism (P. australiana) was only recognized in 2013. Plutella xylostella and P. australiana are able to hybridize under laboratory conditions, and it was unknown whether introgression of adaptive traits could occur in the field to improve fitness and potentially increase pressure on agriculture. Phylogenetic reconstruction of 29 nuclear genomes confirmed P. xylostella and P. australiana are divergent, and molecular dating with 13 mitochondrial genes estimated a common Plutella ancestor 1.96{+/-}0.175 MYA. Sympatric Australian populations and allopatric Hawaiian P. xylostella populations were used to test whether neutral or adaptive introgression had occurred between the two Australian species. We used three approaches to test for genomic admixture in empirical and simulated datasets including i) the f3 statistic at the level of the population, ii) pairwise comparisons of Neis absolute genetic divergence (dXY) between populations and iii) changes in phylogenetic branch lengths between individuals across 50 kb genomic windows. These complementary approaches all supported reproductive isolation of the Plutella species in Australia, despite their ability to hybridize. Finally, we highlight the most divergent genomic regions between the two cryptic Plutella species and find they contain genes involved with processes including digestion, detoxification and DNA binding.

evolutionary biology↗

bioRxiv2017

A global Brassica pest and a sympatric cryptic ally, Plutella australiana (Lepidoptera: Plutellidae), show strong divergence despite the capacity to hybridize

The diamondback moth, Plutella xylostella, has been intensively studied due to its ability to evolve insecticide resistance and status as the worlds most destructive pest of brassicaceous crops. The surprise discovery of a cryptic ally, Plutella australiana Landry & Hebert, with apparent endemism to Australia, immediately raised questions regarding the extent of ecological and genetic diversity between these two species, whether gene flow could occur, and ultimately if specific management was required. Here, we show that despite sympatric distributions and the capacity to hybridize in controlled laboratory experiments, striking differences in genetic and phenotypic traits exist that are consistent with contrasting colonization histories and reproductive isolation after secondary contact. Almost 1500 Plutella individuals were collected from wild and cultivated brassicaceous plants at 75 locations throughout Australia. Plutella australiana was commonly found on all Brassica host types sampled except commercial vegetables, which are routinely sprayed with insecticide. Bioassays using four commonly-used insecticides found that P. australiana was 19-306 fold more susceptible than P. xylostella. Genome-wide SNPs derived from RADseq revealed substantially higher levels of genetic diversity across P. australiana compared with P. xylostella nuclear genomes, yet both species showed limited variation in mtDNA. Infection with a single Wolbachia subgroup B strain was fixed in P. australiana, suggesting that a selective sweep contributed to low mtDNA diversity, while a subgroup A strain infected just 1.5 % of P. xylostella. Although P. australiana is a potential pest of brassica crops, it is of secondary importance to P. xylostella.

genetics↗

bioRxiv2017

Genome-Wide SNP Discovery In Field And Laboratory Colonies Of Australian Plutella Species

Understanding dispersal and gene flow is an important focus of evolutionary biology, conservation biology and pest management. The diamondback moth, Plutella xylostella, is a worldwide pest of Brassica vegetable and oilseed cropping systems. This insect has high dispersal ability, which has important consequences for population dynamics and the potential spread of insecticide resistance genes. Population genetic studies of the diamondback moth have found little evidence of population structure, suggesting that frequent intermixing occurs within regions, however the patterns of local and regional dispersal remain to be identified. For this and many other pest species, understanding dispersal is crucial for developing integrated management tactics such as forecasting systems and insecticide resistance management plans. In recent years, next generation sequencing (NGS) methods have provided previously unparalleled resolution for population genetic studies in a wide range of species. Here, we assessed the potential of NGS-derived molecular markers to provide new insights about population structure in the diamondback moth. We use restriction-site-associated DNA sequencing (RAD-Seq) to discover hundreds to thousands of single nucleotide polymorphism (SNP) markers in nine field and laboratory-reared populations collected from Australia. Genotypic data from RAD-Seq markers identified a cryptic species, P. australiana, among individuals collected from a wild host, Diplotaxis sp., indicating strong divergence in the nuclear genomes of two Australian Plutella lineages. Significant genetic differentiation was detected among populations of P. xylostella used in our study, however this could be explained by reduced heterozogosity and genetic drift in laboratory-reared populations founded by relatively few individuals. This study demonstrates that RAD-Seq is a powerful method for generating SNP markers for population genetic studies in this species.

ecology↗