Getting here from there: testing the genetic paradigm underpinning introduction histories and invasion success

Abstract

Aim To explore the potential of genetic processes and mating systems to influence successful plant invasions, we compared genetic diversity of the highly invasive tropical treelet, Miconia calvescens, in nine invasive populations and three native range populations. Specifically, we tested how genetic diversity is partitioned in native and invaded regions, which have different invasion histories (multiple vs. single introductions). Lastly, we infer how levels of inbreeding in different regions impact invasion success. Location Invaded ranges in the Pacific (Hawaii, Tahiti, New Caledonia) and Australia and native range in Costa Rica. Methods Genetic diversity was inferred by analysing variation at nine microsatellite loci in 273 individuals from 13 populations of M. calvescens. Genetic structure was assessed using amova, isolation by distance (IBD) within regions, a Bayesian clustering approach, and principal coordinates analysis. Results Microsatellite analysis revealed that invaded regions exhibit low levels of allelic richness and genetic diversity with few private alleles. To the contrary, in the native range, we observed high levels of allelic richness, high heterozygosity and 78% of all private alleles. Surprisingly, despite evident genetic bottlenecks in all invasive regions, similarly high levels of inbreeding were detected in both invasive and native ranges (FIS: 0.345 and 0.399, respectively). Bayesian clustering analysis showed a lack of geographical structure in the Pacific and evidence of differing invasion histories between the Pacific and Australia. While Pacific populations are derived from a single introduction to the region, multiple introductions have taken place in Australia from different source regions. Main conclusions Multiple introductions have not resulted in increased genetic diversity for M. calvescens invasions. Moreover, similar inbreeding levels between native and invaded ranges suggests that there is no correlation between levels of inbreeding and levels of standing genetic diversity for M. calvescens. Overall, our results show that neither inbreeding nor low genetic diversity is an impediment to invasion success.

Do founder size, genetic diversity and structure influence rates of expansion of North American grey squirrels in Europe?

“…The observed positive effect of propagule pressure on the genetic variance of introduced species is not universal (Poulin et al ., ; Myburgh et al ., ; Le Roux et al ., ). In some cases, multiple releases can give rise to low genetic diversity if all introductions came from the same source population or there was post‐introduction selection (Tsutsui et al ., ; Grapputo et al ., ; Hardesty et al ., ). In the present data, however, grey squirrels have proven to be highly sensitive to the size of introduction events.…”

“…In our view, the main potential candidate for such a variable is habitat fragmentation, but we showed that our sampling areas have similar levels of fragmentation (Table ; Appendix S1). Also, our results are consistent with a large body of work showing that propagule pressure is related to establishment and invasion success (Veltman et al ., ; Kolar & Lodge, ; Cassey et al ., ; Lockwood et al ., ; Sol et al ., ; Dlugosch & Parker, ; Le Roux & Wieczorek, ; Hardesty et al ., ). Secondly, differences in genetic diversity could be a consequence of expansion rate differences, in addition to or instead of being their cause: faster‐expanding populations could have had shorter bottleneck times, preserving more genetic variation.…”

Mixture or mosaic? Genetic patterns in UK grey squirrels support a human‐mediated ‘long‐jump’ invasion mechanism

“…This lack of differentiation might have contributed to the limited genetic variation in the UK: multiple introductions from (likely) different sources might not have introduced new variation and different allelic patterns in the British populations. For western corn rootworm (Ciosi et al ., ) or for the velvet tree Miconia calvescens in the Pacific islands (Hardesty et al ., ), multiple introductions from the same source did not lead to an increase in genetic diversity. Our historical records do not specify the source of the introductions from North America, with the exception of the population in Woburn (New York or New Jersey) and one in West Scotland (Ontario, Canada).…”

Evolutionary Biology: Biodiversification from Genotype to Phenotype

“…While even low percentages of genotypic variation could help asexual plants to fulfill ecological demands of heterogeneous environments, the capacity to acclimatize to new conquered microhabitats after exposition to novel abiotic and biotic conditions and to environmentally induced stress seems to be related to epigenetic variation (e.g., DeWalt and Hamrick 2004;Poulin et al 2005;Hardesty et al 2012;Roiloa et al 2014). Such epigenetic fine-tuning would favor the selection of fittest genotypes possible adapted to a variety of microenvironments and the entire occupancy of niche spaces.…”