No abstract

All organisms are home to numerous microbes. The relationship between hosts and their microbial communities (microbiota) can play a role in key host functions (Archie & Theis, 2011; Brucker

14Resident microbes (microbiota) can shape host organismal function and adaptation in the face 15 of environmental change. Invasion of new habitats exposes hosts to novel selection pressures, 16 but the impacts on microbiota and their relationship with hosts after this transition (e.g., how 17 rapidly symbioses are formed, whether microbes influence invasion success) are unclear. We 18 used high-throughput 16S rRNA sequencing of New Zealand (native) and European (invasive) 19 populations of the freshwater snail Potamopyrgus antipodarum to find that while invaders do 20 carry over some core microbial taxa from New Zealand, most of their microbial community is 21 distinct. This finding highlights that invasions can result in the formation of novel symbioses. 22We further show that the native microbiome is composed of fewer core microbes than invasive 23 snails, suggesting that the microbiota is streamlined to essential members. Together, our 24 findings demonstrate that microbiota comparisons across native and invasive populations can 25 reveal the impact of a long coevolutionary history and specialization of microbes in the native 26 host range, as well as new associations occurring after invasion. 27 28

Potamopyrgus antipodarum is a New Zealand freshwater snail that is invasive worldwide. While native P. antipodarum populations are characterized by frequent coexistence between obligately sexual and obligately asexual individuals, only the asexual snails are known to invade other ecosystems. Despite low genetic diversity and the absence of sex, invasive asexual P. antipodarum are highly successful. Here, we quantified variation in three key life-history traits across invasive P. antipodarum lineages and compared this variation to already documented variation in these same traits in asexual native lineages to provide a deeper understanding of why some lineages become invasive. In particular, we evaluated 1) if invasive lineages of P. antipodarum could be successful because they represent life-history variation from native ancestors that could facilitate invasion, and 2) if invasive populations with higher genetic variation would display relatively high phenotypic variation. We found that invasive snails displayed a non-representative sample of native diversity, with invasive snails growing more slowly and maturing more rapidly than their native counterparts. These results are consistent with expectations of a scenario where invasive lineages represent a subset of native variation that is beneficial in the setting of invasion. Nevertheless, there was no evidence for a relationship between genetic and phenotypic variation, indicating that increased genetic variation does not necessarily translate into greater phenotypic variation, and consistent with earlier studies suggesting an important role for phenotypic plasticity in the P. antipodarum invasion. Together, these results help illuminate the mechanisms driving the worldwide expansion of invasive populations of these snails.