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Origins of lake-stream pairs of threespine stickleback (Gasterosteus aculeatus)

University of British Columbia

I examined lake-stream pairs of threespine stickleback {Gasterosteus aculeatus) using molecular techniques with special emphasis on the Misty Lake pair. Analysis of the lake-stream pair in Misty Lake (Keogh River system, northern Vancouver Island) revealed that the forms represent two separate gene pools as opposed to a single gene pool with some complex polymorphism. There were significant differences between the forms in the frequencies of both mitochondrial restriction fragment length polymorphism (RFLP) haplotypes and nuclear sequence types (the D3 region of 28S rRNA). As far as we know, lake-stream pairs only occur in two other drainages. I used the mitochondrial RFLP data to distinguish between two hypotheses that attempt to account for the distribution and origins of the pairs. The first hypothesis postulates a single origin of the pairs followed by dispersal. This hypothesis assumes that initial divergence of forms is allopatric subsequently followed by secondary contact. The second hypothesis postulates independent parallel evolution in at least two of the three drainages where lake-stream pairs occur. Under this hypothesis, divergence of forms could have been either allopatric or parapatric. The mitochondrial RFLP data supports the parallel evolution hypothesis; furthermore, divergence of at least the Misty Lake pair was allopatric. Lastly, unrooted neighbor-joining trees based on the mitochondrial RFLP haplotypes indicate the presence of two very divergent lineages; a Northern lineage and a Southern lineage. Other studies have identified this split, but they have never observed the Northern lineage in populations as far south as Vancouver Island.

Thesis/Dissertation

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2009-01-24

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http://hdl.handle.net/2429/3860

Zoology

University of British Columbia

UBCV

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