p127

知的能力は何のために進化したのか?

ここで，世界と言っているのは何も物理的環境世界だけを言っているのではない．社会的な関係を処理するということや，他の個体から学ぶこと(social learning) が重要であったに違いない．たとえば，S. M. Reader and K. N. Laland, Proc. Nat. Acad. Sci.  99 , 4436 (2002) など参照．あるいは，言語の習得過程においては，社会的接触がきわめて重要だという実験もある．たとえば，P. K. Kuhl, F.-M. Tsao, and H.-M. Liu, “Foreign-language experience in infancy: Effects of short-term exposure and social interaction on phonetic learning,” Proc. Nat. Acad. Sci., 100, 9096 (2003). しかし，社会的認識能力は複雑な社会関係に対応するために進化したと考えるのは単純にすぎる．K. Zuberbuler and R. W. Byrne, “Social cognition,” Curr. Biol.  16 , R786 (2006) 参照．( 未完 )

積極的退化

Mexican blind cavefish  Astyanax mexicanus については

Price et al. Why cavefish are blind

BE 27, 235 (2005)

Hyperactive midline signaling by Shh in Astyanax mexicanus reduced pax6, but may have enhanced sense of tastes, advantageous for cave-dwelling fish.

Eye regression is not by drift.

Protas et al.,Regressive Evolution in the Mexican Cave Tetra, Astyanax mexicanus

CB 17 452 (2007)

＊Cave alleles at every eye or lens QTL we detected caused size reductions, consistent with evolution by natural selection but not with drift.

＊The energetic cost of their maintenance is sufficiently high for eyes to be detrimental in the cave environment.

Pleiotropic basis of rapidly evolved syndromes

Protas et al., Multi-trait evolution in a cave fish, Astyanax mexicanus

ED 10 196 (2008)

＊Mexican cave tetra and its surface conspecific. 

＊The traits were a representative set, including eye size, pigment cell numbers, chemical sensitivity, body and skull morphology, standard length, and metabolism. 

＊QTL effects of these traits were significantly clustered in the genome. 

＊Given the relatively short time available to construct clusters from unlinked genes through genomic rearrangement, and the counterintuitive polarities of some of the substitution effects, we argue that at least some of the clusters must have a pleiotropic basis.

＊p265 is a good summary of ED use of Astyanax.

以上についての総説の決定版は

William R. Jeffery  Regressive Evolution in Astyanax Cavefish

Annual Rev. Genetics,  43 25 (2009).

バクテリアを使った実験は

HALL et al.,  Decay of unused characters by selection and drift

JEB 21 610 (2008)

＊We outline a simple framework where the relative importance of selective and neutral processes varies with environmental factors, because of variation in the fitness costs associated with unused traits. 

＊We tested our hypotheses using experimental evolution of the bacterium Pseudomonas fluorescence in spatially uniform environments. Results show that an unused character, swimming motility, decayed over evolutionary time and the rate of this decay varied among selection environments with different levels of resource availability.

＊Selection against an unused character was most effective in environments where the fitness cost was the greatest. This suggests that the same character can decay by different mechanisms depending upon environmental factors.