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Kibale’s Divergent Selection (Fishy Ugandan Tales: Episode 8)

I recently visited Kibale National Park, in Uganda, where some of the other researchers in my lab conducted field work this summer. Kibale is famous for its primate diversity and density, which are amongst the highest in Africa. Thirteen different types of primates can be found in this park.

Redtail (Photo by Vincent Fugère)
Red-tail (Photo by Vincent Fugère)
L'Hoests (Photo by Vincent Fugère)
L’Hoests (Photo by Vincent Fugère)

 

Black and while colobus (Photo by Vincent Fugère)
Black and while colobus (Photo by Vincent Fugère)

 

Chimpanzee (Photo by Vincent Fugère)
Chimpanzee (Photo by Vincent Fugère)

Black and white colobus, red-tail monkeys, baboons, the rare L’Hoest’s monkey, and chimpanzees are some of the species my colleague, Vincent Fugère, came across this summer while working in the park.

Although Kibale is most famous for its primates, the park is also home to a number of interesting fish. Catherine Baltazar is another researcher in my lab, and she has spent the last few months studying one of the park’s fish. Using Barbus neumayeri as a model species, Catherine explorers the topic of divergent selection.

Barbus newmayeri (Photo by Vincent Fugère)
Barbus newmayeri (Photo by Vincent Fugère)

What exactly is ‘divergent selection’?  Consider this classic ecology story: The peppered moth, a species found in Asia, Europe and North America, has different color morphs.  In other words, some individuals of the species are dark colored, whereas others are light colored. In England, individuals usually had light colored wings which allowed them to rest on lichens and remain camouflaged from predators.  When the industrial revolution took place, the light colored peppered moths became scarce, and dark colored ones became more frequent. These changes were induced by the forces of divergent selection, which allow different populations of a same species to be better adapted to their respective local environments. In this story, pollution during the industrial revolution killed lichens and blackened trees with soot, favoring darker populations.  Naturally, different habitat types are likely to select for different traits. Most previous research suggests that this is caused either by genetic differences, differences in gene expression (phenotypic differences), or a combination of both.

One does not always have to look on different continents to observe examples of different environmental conditions. Different habitat types can also be found side by side and even be connected. This theoretically allows individuals of a same species to move between them and reproduce. If individuals are moving between habitat types and reproducing with each other, then there is no reason for there to be different populations in each habitat. Yet, in these types of situations, individuals of different populations sometimes seem to maintain both genetic and phenotypic differences. Catherine is interested in helping us understand why this is the case.

A swamp in Kibale (Photo by Vincent Fugère)
A swamp in Kibale (Photo by Vincent Fugère)

 

A stream in Kibale (Photo by Vincent Fugère)
A stream in Kibale (Photo by Vincent Fugère)

 Barbus neumayeri,  or Neumayer’s barb, is found in both swamps and streams of Kibale. Water often connects these two different habitat types, making dispersal between them possible for barbs.  Nonetheless, previous research has shown that distinct stream and swamp populations exist. Streams are highly oxygenated, whereas swamps have very little oxygen available for fish. This environmental variation is thought to drive the differences that previous research has observed between the Barbs from both habitats. For example, in swamps, barbs have larger gills, which facilitates respiration in the low-oxygen swamp environment.

Catherine is now interested in finding out if these types of adaptations are what induce swamp barbs to stay in the swamps in spite of the ‘difficult’ living conditions. Do these adaptations allow swamp barbs to have an equivalent performance to the stream barbs in their respective habitat? Is selection now acting against fish that try to move between habitats?

Catherine Baltazar, working in Kibale's swamps (Photo by Vincent Fugère)
Catherine Baltazar, working in Kibale’s swamps (Photo by Vincent Fugère)
Catherine Baltazar and Ugandan field assistants Emmanuel and Giovan working int he field (Photo by Vincent Fugère)
Catherine Baltazar and Ugandan field assistants, Emmanuel and Giovan, working at their study site in Kibale (Photo by Vincent Fugère)

 

Using a mark and recapture technique, Catherine and her field assistants are going to measure the performance of fish from both habitats over the next 6 months. Using growth rate as an indicator of performance, Catherine will determine if swamp adapted individuals perform as well as stream adapted individuals. She will also see if individuals that move between habitats are disadvantaged for venturing into a place that they are not adapted to.

To follow the progress of Catherine’s research, you can visit her supervisors’ webpage at http://biology.mcgill.ca/faculty/chapman/.

To see more of Vincent Fugère’s photography, you can visit his website at: http://biology.mcgill.ca/grad/vincent/.