Adaptive evolution via a major gene effect: paedomorphosis in the Mexican axolotl

Abstract

Although adaptive evolution is thought to depend primarily on mutations of small effect, major gene effects may underlie many of the important differences observed among species in nature. The Mexican axolotl (Ambystoma mexicanum) has a derived mode of development that is characterized by metamorphic failure (paedomorphosis), an adaptation for an entirely aquatic life cycle. By using an interspecific crossing design and genetic linkage analysis, a major quantitative trait locus for expression of metamorphosis was identified in a local map of amplified fragment length polymorphisms. These data are consistent with a major gene hypothesis for the evolution of paedomorphosis in A. mexicanum.

Figure 1

LOD score profiles between AFLP34.5 and AFLP32.17 and between AFLP32.17 and AFLP11.7.

Figure 2

Plots of probability of metamorphosis as a function of map position. The values of p₀ (probability of metamorphosis given met/met genotype) and p₁ (probability of metamorphosis given MET/met genotype) for a given maximization of L₁ are estimates of the penetrance of the QTL at that position. p₀ = broken line; p₁ = solid line.