AP Biology 7.10: Speciation

Existing isolated brook trout populations in Newfoundland, Canada, were once part of a larger population that was fragmented at the end of the most recent glaciation period about 10,000 to 12,000 years ago. Researchers investigated 14 naturally separated stream populations of brook trout. They found that the populations are all genetically distinct and show differences in morphology.

Twenty million years ago the Caribbean Sea and Pacific Ocean were connected, and water

flowed freely between the two bodies of water. Many of the same marine species were found

in both areas. Over millions of years, the land referred to as the Isthmus of Panama formed,

eventually closing off the connection between the Caribbean Sea and Pacific Ocean and creating

two separate bodies of water. The ecology of these two marine habitats was dramatically altered

by this land formation. The warmer Caribbean water could no longer flow west, so the Pacific

water cooled and became more nutrient-rich, while the Caribbean water became warmer.

Explain how the isolation of marine species by the formation of a land barrier can lead to

divergent evolution of those species.

The formation of the Isthmus of Panama connected two continents, North America and South

America. Many North American land animal species migrated to South America after the

formation of the isthmus and occupied similar niches as South American species.

Researchers study mechanisms that enable or prevent speciation.

Describe a post-zygotic mechanism that prevents gene flow and thus enables speciation.

New genes can evolve from noncoding regions of DNA. It is not until certain regulatory elements are present in the DNA that a noncoding region becomes a new, functional gene that encodes a protein. These regulatory elements include a promoter, a 5' untranslated region (UTR) followed by a start codon, and a 3' UTR following a codon (Figure 1).

Researchers studied the evolution of the family of antifreeze-glycoprotein (AG) encoding genes in Gadidae, a family of marine fish known as cods. When present in the fish, these glycoproteins reduce the freezing temperature of the fish. The researchers compared genomic sequences in nine cod species and one non-cod fish species, B. brosme. They recorded the presence or absence of the elements of functional ag genes as well as ag-like sequences that are similar to a functional gene but have undergone mutation and do not contain all the elements required to enable protein production (Figure 2).