Long live the alien: studying the fate of the genomic diversity along the long-term dynamics of an extremely successful invader, the crested porcupine.

Pre-print version of the paper is available on bioRxiv (doi: http://dx.doi.org/10.1101/016493 )

Abstract

Describing long-term evolutionary trajectories of alien species is a fundamental, although

rarely possible, step to understand the pivotal drivers of successful invasions. Here, we

tackled this task by investigating the genetic structure of the crested porcupine (Hystrix

cristata), whose invasion of Italy started about 1500 years ago. Using genome-wide RAD

markers, we explored the demographic processes that shaped, and are shaping, the gene pool

of the expanding invasive populations and compared their genetic diversity with that of native

and invasive populations of both African porcupine species (crested and Cape, H.

africaeaustralis). Through coalescence-based demographic reconstructions, we demonstrated

that bottleneck at introduction was mild and did not severely affect the reservoir of genetic

diversity. Our data also highlighted a marked geographic structure in the invasive populations,

indicating that they are likely the results of multiple introduction events. Nevertheless, both

the invasive populations and its source show a lower level of diversity relative to other native

populations from Sub-Saharan and South Africa, suggesting that demographic history before

introduction may have played a role in forging a successful invader. Finally, we showed that

the current spatial expansion at the northern boundary of the range is following a leading-edge

model characterized by a general reduction of genetic diversity towards the edge of the

expanding range. Consistently, random fixation of alleles through gene-surfing seems a more

likely explanation than adaptive divergence for the distribution of the few outlier loci with

highly divergent frequencies between core and newly colonized areas.