Cichlid fishes from African Lake Tanganyika shed light on how organismal diversity arises

Date:
November 18, 2020
Source:
University of Basel
Summary:
Lake Tanganyika in Africa is a true hotspot of organismal diversity.

Approximately 240 species of cichlid fishes have evolved in this
lake in less than 10 million years. A research team has investigated
this phenomenon of 'explosive speciation' and provides new insights
into the origins of biological diversity.



FULL STORY ==========================================================================
Lake Tanganyika in Africa is a true hotspot of organismal diversity.

Approximately 240 species of cichlid fishes have evolved in this lake
in less than 10 million years. A research team from the University
of Basel has investigated this phenomenon of "explosive speciation"
and provides new insights into the origins of biological diversity,
as they report in the journal Nature.


==========================================================================
The diversity of life on Earth has been shaped by two antagonistic
processes: phases of mass extinctions and episodes characterized by
the rapid evolution of a multitude of new species. Such outbursts of
organismal diversity, also known as "adaptive radiations," are responsible
for a substantial part of the biological species on our planet.

For instance, most of the animal phyla existing today evolved over the
course of the Cambrian radiation about 540 million years ago (also known
as Cambrian explosion). What triggered these massive adaptive radiations,
and how the process of explosive speciation proceeds in detail, has been largely unknown until now.

Different stages of adaptive radiation The cichlid fishes of the African
Great Lakes Victoria, Malawi and Tanganyika are among the most impressive examples of "adaptive radiation." Using the cichlid fishes of Lake
Tanganyika as a model system, a team of scientists headed by Professor
Walter Salzburger from the University of Basel have now investigated
in detail the phenomenon of adaptive radiation. On extensive field
expeditions to Burundi, Tanzania and Zambia, they collected specimens
from virtually all approximately 240 species of cichlid fishes occurring
in Lake Tanganyika.

Based on this material, they compiled a comprehensive dataset covering information on morphology, ecology, and genetics. For example, the team analyzed body shape and jaw morphology of all species using X-ray imaging
and high-resolution computed tomography. The zoologists were particularly interested in the three-dimensional structure of the pharyngeal jaw. This second set of jaws is situated in the pharynx of cichlid fishes and is
used to masticate food, allowing the fish to specialize in very specific nutritional niches.

Because adaptation to different environments is a central component of
adaptive radiation, the researchers also quantified the "ecological niche"
used by each species. In collaboration with the Botanical Institute of the University of Basel, they measured the stable carbon and nitrogen isotope composition in the muscle tissue of the fish. These measurements allow
to determine in what habitat the fishes lived and what food resources
they used. Further, the team sequenced two complete genomes for each
and every cichlid species from Lake Tanganyika. Based on this molecular information they were able to reconstruct the complete phylogeny of the cichlids in that lake.

Based on their analyses, the scientists could demonstrate that the
evolution of cichlid fishes in Lake Tanganyika was not a gradual
process, but rather occurred in three discrete pulse-like stages of
rapid morphological evolution.

"Each of these stages was characterized by specialization to a different
aspect of the habitat provided by the lake," says lead author Dr. Fabrizia Ronco. The first pulse involved diversification in body shape followed
by a pulse in mouth morphology and a final pulse in pharyngeal jaw
shape. Especially the pharyngeal jaw has played a key role in the
radiation, since its rapid morphological evolution coincided with a high
number of speciation events.

Insight into the evolution of organismal diversity Through the analysis
of the roughly 600 newly sequenced genomes, the Basel researchers showed
that the most species-rich and ecologically and morphologically diverse lineages of Tanganyikan cichlids contain species that are genetically more diverse. "Whether an elevated level of genetic diversity is a general
feature of highly diverse lineages, or if this pattern is unique to
cichlids of Lake Tanganyika, is still unknown," says Salzburger.

By studying exceptionally species-rich adaptive radiations, like the
African cichlids, scientist can learn more about how biodiversity
arises and what factors are associated with it. The present findings
of the zoologists from the University of Basel offer new routes to
these questions.


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


========================================================================== Journal Reference:
1. Fabrizia Ronco, Michael Matschiner, Astrid Bo"hne, Anna Boila,
Heinz H.

Bu"scher, Athimed El Taher, Adrian Indermaur, Milan Malinsky,
Virginie Ricci, Ansgar Kahmen, Sissel Jentoft, Walter
Salzburger. Drivers and dynamics of a massive adaptive radiation
in cichlid fishes. Nature, 2020; DOI: 10.1038/s41586-020-2930-4 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/11/201118141831.htm

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