Evidence for an extreme founding effect in a highly successful invasive species

Abstract

The adaptive potential of invasive species is thought to decrease during founding events due to reduced genetic diversity, limiting the new population’s ability to colonize novel habitats. Barbary ground squirrels (Atlantoxerus getulus) were purportedly introduced as a single breeding pair to the island of Fuerteventura but have expanded to over a million individuals spread across the island in just over 50 years. We estimated the number of founders and measured the level of genetic diversity in this population using the mitochondrial displacement loop and microsatellite markers. Island samples (n = 19) showed no variation in the d-loop, suggesting a single founding female, while Moroccan samples (n = 6) each had unique mitochondrial haplotypes. The microsatellite data of the island population (n = 256 individuals) revealed a small effective population size, low levels of heterozygosity, and high levels of inbreeding, supporting a founding population size of two to three individuals. Our results suggest that A. getulus has undergone an intense genetic bottleneck during their colonization of the island. They are one of the few species where introduction effort does not explain invasion success, although further investigation may explain how they have avoided the worst expected effects following an extreme genetic bottleneck.

Exploring the role of life history traits and introduction effort in understanding invasion success in mammals: A case study of Barbary ground squirrels

“…Barbary ground squirrels' exceptional invasion success (despite low introduction effort, Kratzer et al 2020) is not due to a remarkable fast life history profile as their life history is comparable to other invasive species that do not have such a low introduction effort (Table 1, Fig 1). When we analysed the effects of introduction effort and life history traits further, we found that neither number of founders nor life history traits influenced invasion status of introduced squirrel species.…”

“…The semifossorial Barbary ground squirrel is a social species: adult females share sleeping burrows with other related females, and males share sleeping burrows with unrelated males and subadults of either sex (van der Marel et al 2020). We defined these sleeping burrow associations as social groups (van der Marel et al 2020). Throughout the day, both male and female groups can be active in the same area (van der Marel et al 2020).…”

“…The Barbary ground squirrel can be considered a genetic paradox of invasion (Estoup et al 2016). The invaded population was founded by 2 or 3 individuals, which has resulted in a low genetic diversity and a high level of inbreeding in the invasive population (Kratzer et al 2020). A high degree of inbreeding could lead to inbreeding depression, i.e., a high impact of deleterious alleles on the average fitness of offspring (Ralls et al 1979;Ralls and Ballou 1982).…”

“…To determine life history traits of the species, we trapped Barbary ground squirrels using live traps (Tomahawk Co., WI, U.S.A.; 13 x 13 x 40 cm) baited with peanut butter during three consecutive years (February through July 2014, January through July 2015, and January through June 2016) following the procedures described in van der Marel et al (2019Marel et al ( , 2020. Upon capture, we transferred squirrels to a conical handling bag (Koprowski 2002), where every adult .…”

“…The objective of this manuscript is three-fold. First, we investigated life history traits of the Barbary ground squirrel, Atlantoxerus getulus, a species with a remarkably low introduction effort (Machado 1979;Kratzer et al 2020). Second, we studied whether the Barbary ground squirrel's exceptional invasion success (despite low introduction effort) is due to a very fast life history profile through a comparison of these traits to other successfully invaded mammals using the dataset provided by Capellini et al (2015).…”