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A Case of Stress Related Heterozygote Superiority in Nature

abstract1 (full description below): Evolution, Vol. 37, No. 3. (May, 1983), pp. 646-649.
Heterozygote Superiority. PDF/Acrobat file     SoulĂ©, M. E. and P. Samallow

Exerpt: Evidence of the superior growth and survival of relatively heterozygous individuals has slowly been accumulating, especially during the past decade (see reviews listed). These studies, in general, provide convincing support for the concept of heterozygote advantage, but fail to discriminate between processes of constant superior survival and ones of transient or episodic superiority, as may be associated with particular seasons or life history stages (but see Redfield, 1974). Both constant and episodic heterozygote advantage can lead to increased proportions of heterozygous genotypes even though they result from distinct patterns of selective mortality. Genotype-related differences in survival have been reported for pre-reproductive stages of the western toad, Bufo boreas (Samollow, 1980), but evidence of heterozygote advantage was scant when considering the larval, metamorphic, and post-metamorphic stages collectively. Recently we re-examined these data with regard to shorter time spans, and discovered a striking case of superior heterozygote survivorship among immature toads during the winter.