A blog post highlighting the article by
Written by Magdalena Sorger
When I was asked to join a team to conduct a biodiversity survey of ancient church forests in Ethiopia, I was pretty excited. There were plant experts, beetle experts, fly experts and two ant experts – myself and Mark Moffett. However, our first big ant discovery was unexpected and frankly a bit alarming (yet I won’t deny that it was also exciting): We found a single ant species – everywhere. Well, almost everywhere.
The species, later identified as Lepisiota canescens, exhibited characteristics common in invasive species such as Argentine ants (Linepithema humile) including supercolony formation. Argentine ants are worldwide invasives and pose a significant threat to local biodiversity wherever they go. If the ant we found in Ethiopia was capable of anything like Argentine ants are capable of, then that was a very good reason to worry – and to pay attention.
Church forests surround Orthodox churches some of which are over 1,500 years old. The forests range in size from only a few hectares to more than 400 ha and are considered relictual oases within largely barren land and agricultural fields. We discovered Lepisiota canescens to be numerous, first in the most degraded church forest (Zhara Church forest = 8 ha) but then also around the church forest, in agricultural fields, along the paved road and in a more urban setting in the city of Bahir Dar. The species exhibited many characteristics reminiscent of invasive species, such as ecological dominance, general nesting and diet, and, most interestingly supercolony-formation.
Supercolonies are colonies that extend beyond just a single nest. The colony spans many nests and can sometimes cover many thousands of kilometers (see Argentine ants for the most famous example). The strongest basis for describing a large colony as a supercolony is its capacity to expand its range without constraints.
In this study we conducted behavioral experiments to show the extent of supercolonies. And we found several supercolonies, the largest one spanning a mighty 38 km. We also conducted molecular analyses to test whether 1) the species showed the genetic signature of an invasive species and 2) if supercolonies corresponded to genetic identity (i.e. more closely related ants were part of the same supercolony). And – surprisingly – we found that the species shows the genetic signature of a native species and that genetic identity does not correspond to supercolony identity.
These results are significant for a two main reasons: 1) supercolony formation in ants is a rare trait, there are only about 20 species with documented supercolonies, even fewer with really large supercolonies, and 2) other species in the Lepisiota genus have recently made headlines as worrisome invasive species, one in Kruger National Park and another one was reason for shutting down Darwin port (Australia) for several days.
The species we found in Ethiopia may have a high potential of becoming a (globally) invasive species, especially with tourism to this region in Ethiopia on the rise. It is important to have a record of what a species does in its native habitat because rarely do we know anything about the biology of a species BEFORE it becomes invasive.
We believe this species, while native to the general region, is moving into disturbed habitat locally like the degraded forest, feeding on honeydew excreted by insects that occur on a locally invasive plant which only appeared with the construction of the road and other urban structures. Maybe a native species invading disturbed habitat locally is a first step before it “goes international” and it’s worth keeping an eye on.