![](img028.GIF) |
Rieseberg (1997) suggested that hybrid fitness
can be studied comparing the responses of hybrid and parental populations in
selection experiments that incorporate the ideas of Stebbins (1959) and
Lewontin & Birch (1966). Contained in that framework is the idea that
hybrids by high heterozygosity are well prepared to meet new environments.
Nonetheless, this is not seen in mesquites that mutate in the new niche.
What is seen is that as heat load increases, leaves become smaller which is
perhaps Lamarckian. The necessary and sufficient proof of backcrossing to
spread the mutant is commonly called introgression in mesquites, but they
are clinal races not species. The spread of superior private genes that
swamp parents seems axiomatic.
|