Like matryoshka dolls: One insect species introduced decades ago to a
small island had an effect on several insect populations

Date:
August 2, 2021
Source:
University of Helsinki
Summary:
Researchers thought 30 years ago that they just introduced some
Glanville fritillary butterfly larvae on a small island in the
AAland islands, Finland. Little did they know that within the
butterfly larvae there nested two other insect species and a
bacterial symbiont. This created a unique opportunity to study how
a local accidental introduction of insects can affect the dynamics
and genetics of the neighbouring populations.



FULL STORY ========================================================================== Larvae of the Glanville fritillary butterfly, Melitaea cinxia, were
introduced to the island of Sottunga in the AAland Islands, Finland, in
1991. The original research project for which this introduction was aimed failed. However, although the island was previously free of the butterfly,
the relocated species persisted, offering the ground for investigating how
an entire insect community could be affected by one introduction event.


========================================================================== "What the researchers did not know 30 years ago was that the larvae
carried along with them the butterfly parasitoid wasp Hyposoter
horticola. The parasitoid then carried its hyperparasitoid wasp
Mesochorus stigmaticus, and a mum-to-offspring transmitted bacterial
symbiont Wolbachia pipientis that somehow increases the susceptibility
of the host H. horticola to M.

stigmaticus," says Academy research fellow at the University of Helsinki,
Dr.

Anne Duplouy.

Thanks to yearly survey of the AAland butterfly population, researchers
from the University of Helsinki and the Cornell University, USA, have
shown that the butterfly population introduced to Sottunga has faced
several bottle necks since 1991. It consequently is genetically quite diminished and faces a high risk of extinction.

"If local butterfly populations are small and unstable their parasitoids
must be mobile enough to find hosts elsewhere. We have been able to show
that the parasitoid H. horticola is dispersive in AAland. Furthermore,
it has persisted and shows less genetic structure than the butterfly
host. This probably explains their genetic mixing with populations on
nearby island after introduction to Sottunga. Introduced genotypes have potentially kept nearby populations from extinction during host population declines," Anne Duplouy says.

The hyperparasitoid M. stigmaticus isn't quite as mobile and has a
smaller population size, so it suffers from inbreeding and is absent
from some islands.

Where the hyperparasitoid is absent, the parasitoid lineages with
Wolbachia can flourish.

"The genetic signature of introduced wasp lineages gives us a window
into what has happened in an island archipelago over the 25 years since
their accidental introduction, including persistence through population bottlenecks, dispersal and interbreeding, as well as sorting among
lineages depending on a hyperparasitoid and bacterial symbiont," says
Dr. Saskya van Nouhuys from Cornell University, USA, who has studied
the parasitoid populations in AAland since 1998.

The researchers are excited to see how genetic methods can complement ecological studies and be useful in studying and making inferences about
a population introduced decades ago.

"We have integrated population genetic and population ecology methods to
find exciting insights about host and parasitoid ecology, as well as the influence of their bacterial symbionts over such short period of time," concludes University Researcher Dr. Abhilash Nair from the University
of Helsinki.

========================================================================== Story Source: Materials provided by University_of_Helsinki. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Anne Duplouy, Abhilash Nair, Toshka Nyman, Saskya Nouhuys.

Long‐term spatiotemporal genetic structure of an accidental
parasitoid introduction, and local changes in prevalence of its
associated Wolbachia symbiont. Molecular Ecology, 2021; DOI:
10.1111/ mec.16065 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210802115002.htm

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