Interactions of microbiota and invasive molluscan crop pests: impacts on food security and ecosystem services in a changing world.

Invasive species significantly impact ecosystem services and food security. With the banning of molluscicides, resilience to control measures and high intrinsic rates of increase, molluscs are now regarded as major crop pests. They are omnivorous vectors of important plant pathogens, and both hybridise with and drive out endemic species. The arrival of invasive slugs associates with declines in local biodiversity, with profound implications for food security and ecosystem stability. The extent to which invasive traits, resulting in enormous ecological and agricultural costs, are species-specific, a consequence of hybridization/introgression or carriage/introduction of native-range microbiota remain unknown.
Invasive large arionid slugs, particularly Arion vulgaris, Moquin-Tandon, 1855, are prominent agricultural pests in Europe. Their widespread distribution and high intrinsic rate of increase make them a significant component of biomass in local ecosystems1. To understand their threat and predict consequences for food security, it is necessary to elucidate the drivers of invasion dynamics. Consequently, there is an urgent strategic requirement to facilitate future work on invasive slugs quantifying phenotypic, genotypic and microbial consequences of their interactions, allowing experimental investigation of the underlying cause(s) of invasions. Findings from this tractable system are of general relevance, and may offer novel biocontrol measures.
You will integrate taxon-specific anatomical, morphometric and colormetric traits with cutting edge molecular markers (SNPs) derived from NGS ‘genotyping-by-sequencing‘ approaches and mitochondrial sequencing to make the first objective definition of each large arionid taxon, using individuals from native-range centres. This will provide markers to assess introgression, quantifying assimilation of endemic genomes and hence their contribution to invasion.
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The UK has two invasive taxa: Arion flagellus, Collinge, 1893, and A. vulgaris. Few taxonomists specialize in this group, composed of many sibling species, whose frequent hybridization1 and facultatively self-fertile breeding system confound identification. Such reproductive strategies, unusual amongst animals, characterise invasive plants; where genetic diversity partitions into sibling taxa, which exhibit ecological replacement and enhanced microbial exchange. Hybridization of sibling taxa stimulates evolution and spread of invasive traits producing rapid range expansion, with aggressive hybrids occupying novel niches and habitats. Taxonomic confusion of arionids and lack of high resolution molecular tools means their colonization history, distributions and genetic interaction of invasive forms with endemics and succeeding invasion waves remain poorly known1. Dissent amongst UK specialists about the accuracy of national records of A. vulgaris from the 1950s onwards reflects the uncertainty surrounding the limits and integrity of taxa; but all agree reported biomass increases of invasive arionids and widespread range expansion.
You will quantify traits contributing to invasive potential (fecundity, longevity, survival during development, movement characteristics, temperature, desiccation and pathogen tolerance and markers of microbiome diversity), and estimate QTLs from backcrosses of endemic A. a. ater with invasive A. vulgaris and A. flagellus. You will assess the contributions of heterosis (extreme genetic variability), microbiota, and development of transgressive hybrids (possessing qualities superior to either parent) to invasions, using contemporary and historic material from longitudinal samples spanning 35 years from first contact. These data, and that derived from GIS, will be incorporated into ecological theory-based models to compare actual and predicted spread of invasive forms under different climate scenarios.
Arionids have the potential to acquire and exploit plant pathogenic bacteria as gut commensals, aiding digestion of plant material. The extent these derive from native-ranges, their admixture with endemic microbiota and subsequent ecosystem dispersal is unknown. Hence, there is a need to assess the differential potential of invasive and endemic arionids to gain selective advantage from carriage and admixture of microbiota, and their ability to act as vectors of plant pathogenic bacteria, such that invasive hybrids may pose novel ecological and agricultural threats. Increasing size and frequency of pathogen contact networks invariably increases virulence, making slug proliferation, persistence and invasion of new habitats a major concern. You will determine association of plant pathogens with taxa and level of introgression by qPCR based approaches developed by a PI2,3; obtain information vital to models of plant pathogen spread by assessing the contribution of selected pathogens to invasive traits using a backcross population; quantify the acquisition and spread of microbiota by recording the movements of radiotagged individuals in mesocosms responding to meteorological conditions, to provide novel and invaluable data for modelling plant pathogens epidemiology, indicating their utility as sentinels.