Zoologists uncover new example of rapid evolution -- meet the Sulawesi Babblers

Date:
October 8, 2020
Source:
Trinity College Dublin
Summary:
Zoologists have discovered that male and female Sulawesi Babblers
(Pellorneum celebense, a species of bird) have evolved to attain
different sizes on small islands, and in quick-fire time. They
believe this is most likely due to evolutionary pressure favoring
such 'dimorphism' because the birds are able to reduce competition
with each other by feeding on different, scarce resources.



FULL STORY ========================================================================== Zoologists from Trinity College Dublin, working in tropical Southeast
Asia, have uncovered a modern-day example of rapid evolution in action.


==========================================================================
The zoologists have discovered that male and female Sulawesi Babblers (Pellorneum celebense, a species of bird) have evolved to attain different sizes on small islands, and in quick-fire time. They believe this is
most likely due to evolutionary pressure favouring such "dimorphism"
because the birds are able to reduce competition with each other by
feeding on different, scarce resources.

The research, completed with the support of the Irish Research Council
and collaborators in Universitas Halu Oleo, is published today in the
journal Biotropica. The research shows that the males of the Sulawesi
Babbler grow to be up to 15% larger than the females -- with this
difference particularly marked on the smaller islands.

Fionn O' Marcaigh, first author on the paper and a PhD Candidate in
Trinity's School of Natural Sciences, said: "Tropical regions are home to
more species of plants and animals than anywhere else, but many of these
remain poorly understood even as they face imminent extinction. This is especially true of relatively non-descript species like the babblers,
which are shy birds that feed in dense bushes all over the islands of
Southeast Asia.

"Because male and female babblers have the same dull brown plumage,
unlike familiar birds such as pheasants or peacocks, scientists previously thought that they did not show sexual dimorphism. Our discovery proves
this wrong and provides another timely reminder that we have so much
more to learn about tropical species if we are to understand how they
are evolving on all the world's marvellous and diverse islands.

"We can't protect them if we don't understand them." The kind of sexual dimorphism in size displayed by the babblers is important because it
enables the males and females to fill different "niches" in the ecosystem.

There is an evolutionary theory stating that dimorphic species are
likely to become more strongly dimorphic on islands than they are
on the mainland, as it prevents them having to compete for scarcer
resources. However, this is usually seen on very isolated islands where
there has been ample time for populations to evolve separately.

Fionn O' Marcaigh added: "Our research is significant for showing the same process to have occurred on much younger islands, which were connected
to the mainland by land-bridges only 30,000 years ago. This means that
the difference in sexual dimorphism between mainland and island birds
must have evolved quite rapidly, showing its importance for the ecology
of the species."

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


========================================================================== Journal Reference:
1. Fionn O' Marcaigh, David J. Kelly, Kangkuso Analuddin, Adi Karya,
Naomi
Lawless, Nicola M. Marples. Cryptic sexual dimorphism reveals
differing selection pressures on continental islands. Biotropica,
2020; DOI: 10.1111/btp.12852 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201008104229.htm

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