The Speciation of Cichlid Fish in Africa

The Speciation of Cichlid Fish in Africa

Vocabulary

• Pelagic: The 'open water' region of a lake or ocean.

• Adaptive radiation: Divergent evolution events that occur relatively quickly.

Cichlids

These are a type of freshwater fish that are most commonly found in the lakes of Africa. There are approximately 1600 - 2000 known species of Cichlids, and new species are still being discovered. Due to various selection pressures, there is a great diversity of Cichlids that now exist, an example of adaptive radiation.

The African Great Lakes - home to many Cichlid species

Diversity of Cichlids

Although the lakes of Africa are geographically isolated, many Cichlid species have evolved to occupy the same feeding niches, and have very similar jaw structures (see the picture). This is a puzzling phenomenon, as the populations of Cichlids in each lake were not interacting with one another, therefore gene flow was not possible.

BMP4 Gene

• The BMP4 gene is a Master Regulatory Gene

• Stands for "Bone Morphogenetic Protein 4"

• In Cichlids, this regulates the development of cartilage and muscles during the embryonic phase

• Cichlids with high levels of BMP4 tend to have more robust, heavy jaws, whereas Cichlids with low levels of BMP4 have more slender, narrow jaws

The diversity of jaw shape/size amongst Cichlid fish

Cichlid mutations

It is hypothesised that one or several mutations has occurred in the BMP4 gene that has allowed Cichlids to develop new phenotypes for jaw shapes, which then allowed these traits to be more suited to the environment they were in (due to selection pressures i.e food) so natural selection has occurred and successful traits are passed on.

The Pharyngeal Jaw

• This is a 'secondary' jaw structure located in the pharynx of the fish (or beginning of the throat)

• DIfferent types of Cichlids have different pharyngeal jaw structures, which are adapted to different food sources

A Summary

• Cichlid fish inhabit freshwater lakes in Africa that are geographically isolated

• The fish experience the same or similar selection pressures in each environment

• Mutations to the BMP4 gene caused a variety of new phenotypes for jaw size/shape to occur

• New jaw phenotypes that gave the fish a selective advantage were more likely passed on to the next generation

• This process occurred in several ecosystems simultaneously and resulted in a rapid diversification known as adaptive radiation

Multiple Choice

The BMP4 Gene in Cichlids regulates:

• Jaw bone and cartilage development

• Jaw bone and muscle development

• Jaw cartilage and muscle development

Multiple Choice

High levels on BMP4 in Cichlid fish would suggest:

• A long, slender jaw

• A robust and heavy jaw

Multiple Choice

For adaptive radiation to occur, the fish would need to be:

• Living close together

• Separated

• About to go extinct

Multiple Select

Choose the factors that led to great diversity and speciation of Cichlids in Africa

• Mutations in the BMP4 gene

• Geographical isolation

• Food niche availability

• New jaw phenotypes providing selective advantage

Multiple Choice

What did the researchers in the video use to develop the phylogenetic tree of the Cichlids?

• Pharyngeal jaw structure

• Body shape

• DNA sequencing

• Stable isotope data

Open Ended

How could DNA sequencing allow scientists to develop an accurate timeline of evolution for the Cichlids?

Open Ended

Using information from the slides and the video, what would you expect a Cichlid fish with low level of BMP4 and high level of Nitrogen in its tissue to look and behave like? Hint: think about its jaw structure and where it might feed.