Complexity and Diversity

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Science  23 Apr 2010:
Vol. 328, Issue 5977, pp. 494-497
DOI: 10.1126/science.1187468

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A Little Selection for a Lot of Rarity

Studies on how selection works have tended to focus on the effect of a single trait. This necessarily means that rare alleles that can be acted on by selection appear to experience high levels of frequency-dependence selection. However, selection may act on multiple traits at any one time. Doebeli and Ispolatov (p. 494) present a theoretical framework examining how multiple rare traits can persist and potentially drive speciation. The s show that only low levels of frequency-dependent selection are needed to explain the observed high levels of allelic diversity in nature.


The mechanisms for the origin and maintenance of biological diversity are not fully understood. It is known that frequency-dependent selection, generating advantages for rare types, can maintain genetic variation and lead to speciation, but in models with simple phenotypes (that is, low-dimensional phenotype spaces), frequency dependence needs to be strong to generate diversity. However, we show that if the ecological properties of an organism are determined by multiple traits with complex interactions, the conditions needed for frequency-dependent selection to generate diversity are relaxed to the point where they are easily satisfied in high-dimensional phenotype spaces. Mathematically, this phenomenon is reflected in properties of eigenvalues of quadratic forms. Because all living organisms have at least hundreds of phenotypes, this casts the potential importance of frequency dependence for the origin and maintenance of diversity in a new light.

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