Baylor Scientists Review Impact of Geology, Climate on Cichlid Diversification

August 15, 2012

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WACO, Texas (Aug. 15, 2012) - In East Africa, the complex interaction of geologic processes and climatic changes over the past 35 million years have shaped the extraordinary diversification of over 2,000 species of cichlid fish in Lakes Victoria, Malawi, and Tanganyika.

In a review article published in the International Journal of Evolutionary Biology, Baylor University scientists shed new light on how the highly dynamic geological and ecological history of the region led to the rapid evolutionary diversification of species over the past 10 million years.

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The cichlids of East Africa have long been recognized by scientists as an evolutionary model system in which to study divergence and speciation. Cichlids also provide researchers with an exemplary system to study the impact of geologic, paleoecological, and paleoclimatic factors on the biogeography of a lineage.

In each of these lakes, cichlids formed remarkably large species flocks in an exceedingly short length of time, according to the authors, Patrick D. Danley, Ph.D., assistant professor in the department of biology, and Daniel J. Peppe, Ph.D., assistant professor in the department of geology, in Baylor's College of Arts and Sciences.

"The cichlids of East Africa have experienced an unusually recent and rapid diversification. This diversification resulted in the world's largest living radiation of vertebrates. As such, the Great Lakes of East Africa provide scientists with a natural laboratory to understand the origin and maintenance of biodiversity," said Danley. "The cichlids in these lakes allow scientists to study the origin of species at the molecular level through to the geologic level. Very few biological groups allow such a wide-ranging scope in the study of biodiversity. "
While each lake has a unique geologic and climatic history that has influenced the growth of cichlid populations, the authors note that as a general rule found across all of the lakes, cichlid evolution is strongly influenced by lake depth, species diversification is dependent upon the size of the lake, and species hybridization is climate dependent.
"In this work, we reviewed the evolution of cichlid lineages and the climatic and geologic history of each of the East African Great Lakes," said Peppe. "Through this synthesis, we were able to see the large-scale patterns of how climate change and geologic processes have strongly influenced the evolution and diversification of cichlids across all of the lakes over the last several million years."

Lake levels fluctuated over time, and during arid periods in East Africa the lakes were greatly reduced in size and occasionally fully dried up. The reduction of lake levels reshaped the lake habitats, dividing once connected cichlid populations and, at the same time, causing the mixture of previously isolated populations. Such processes facilitated the continued diversification of species and, at least in one instance, led to the creation of new hybrid cichlid.
For example, Lake Victoria was most recently completely dried up about 14,000 years ago causing the extinction of its endemic cichlids. The lake then refilled and was recolonized by cichlids that survived through the arid interval in the extremely deep, but relatively small, nearby Lake Kivu. Following this recolonization, the invading cichlid species then rapidly diversified into the several hundred species found in the lake today.

Follow this link for more information on Daniel Peppe's research
Baylor University is a private Christian university and a nationally ranked research institution, characterized as having "high research activity" by the Carnegie Foundation for the Advancement of Teaching. The university provides a vibrant campus community for approximately 15,000 students by blending interdisciplinary research with an international reputation for educational excellence and a faculty commitment to teaching and scholarship. Chartered in 1845 by the Republic of Texas through the efforts of Baptist pioneers, Baylor is the oldest continually operating university in Texas. Located in Waco, Baylor welcomes students from all 50 states and more than 80 countries to study a broad range of degrees among its 11 nationally recognized academic divisions. Baylor sponsors 19 varsity athletic teams and is a founding member of the Big 12 Conference.

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