Conclusion
The study of invasion and of accidental or intentional introductions of
species are central to much of contemporary population and community
ecology (Davis, 2009; Lockwood, Hoopes, & Marchetti, 2013). Parasitoids
are used as insect biological control agents (Wang, Liu, Shi, Huang, &
Chen, 2019). Consequently, they are intentional introduced into both
agricultural and natural environments (Grangirard, Hoddle, Petit,
Roderick, & Davies, 2009) These introductions, however, do not persist
in the long term (Goldson et al., 2014), and if they do, their genetic
structure both bares the signature of the origin and differs from it
(Hufbauer et al., 2004). Associated symbionts brought along during the
introduction events, can impact the success story of their host
populations, by affecting the phenotypes and genotypes of their hosts
(Charlat et al., 2009; Hornett et al., 2006). We use genetic evidence to
document the trajectory of a successfully introduced parasitoid
population over 22 years. We show persistence of the wasp on the
previously uninhabited island, and spread of the transplanted genotypes
to surrounding islands, along with the associated symbiotic bacteriumWolbachia. The shuffling of the nuclear and matrilineally
inherited markers among islands suggests differential selection for the
infection-associated genotypes in the local host genetic pools under
relaxed predation pressures on an island where the hyperparasitoid
species is absent (van Nouhuys et al., 2016). The invasion by newly
introduced parasitoid genotypes might contribute to either the
persistence of the isolated island wasp populations, or the replacement
of the local wasp populations, or both. It may have also changed
environment for the pre-existing nearby isolated butterfly host
population, which previously did not have the parasitoid. Like many
other butterfly and insect species, the Glanville fritillary butterfly
is vulnerable to loss of genetic variability and extinction in the
Baltic Sea region due to habitat fragmentation, and has gone extinct
from the Turku archipelago in southwest Finland (Fountain et al., 2016).
The spread of an introduced parasitoid population can represent another
pressure for such host population, as well as any competing local
parasitoid populations (Benson, Van Driesche, Pasquale, & Elkinton,
2003; Benvenuto, Cheyppe-Buchmann, Bermond, Ris, & Fauvergue, 2012).
This is especially true if newly introduced parasitoid genotypes show
greater fitness than native genotypes (Dupas, Dubuffet, Carton, &
Poirie, 2009; Kraaijeveld, Van Alphen, & Godfray, 1998; van Nouhuys,
Niemikapee, & Hanski, 2012).