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Biologist Susan Foster and her students study the threespine stickleback in the lab and in the field. These small fish provide big insights into evolutionary biology. |
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Publication: Nested biological variation and speciation
Foster, S.A., Scott, R.J., and W. A. Cresko. 1998. Nested biological
variation and speciation. Phil. Trans. Royal Soc. London, B.
353L207-218.
Abstract
The modes of speciation that are thought to have contributed most to
the generation of biodiversity require population differentiation as the
initial stage in the speciation process. Consequently, a complete understanding
of the mechanisms of speciation requires that the process be examined not just
after speciation is complete, or nearly so, but also much earlier. Because
reproductive isolation defines biological species, and it evolves slowly, study
of the process may require a prohibitive span of time. Even if speciation could
be observed directly, selection of populations in the process of speciation is
typically difficult or impossible, because those that will ultimately undergo
speciation cannot be distinguished from those that will differentiate but never
assume the status of new biological species. One means of circumventing this
problem is to study speciation in taxa comprising several sibling species, at
least one of which exhibits extensive population differentiation. We illustrate
this approach by exploring patterns of population variation in the post-glacial
radiation of the threespine stickleback, Gasterosteus aculeatus. We focus
on lacustrine populations and species within this complex, demonstrating parallel
axes of divergence within populations, among populations and among species.
The pattern that emerges is one of parallel relationships between phenotype and
fitness at all three hierarchical levels, a pattern that facilitates exploration
of the causes and consequences of speciation and secondary contact. A second outcome
of this exploration is the observation that speciation can be the consequence
of a cascade of effects, beginning with selection on trophic or other characteristics
that in turn force the evolution of other population characteristics that precipitate
speciation. Neither of these conclusions could have been reached without comparative
studies of wild populations at several hierarchical levels, a conclusion reinforced
by a brief survey of similar efforts to elucidate the process of speciation. We
address the issues most likely to be resolved using this approach, and suggest
that comparisons of natural variation within taxa at several hierarchical levels
may substantially increase our understanding of the speciation
process.
Complete text of this article is available online to
those with institutional access to JSTOR.
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Additional Resources
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