对蜗牛Cepaea Nemoralis多态性变异与杂合性相互关系的研究

Study of the Relation of Morphological Variation and Heterozygosity in the Snail Cepaea Nemoralis

Cepaea壳颜色与壳样式(pattern)上的多态性一直被认为与壳可见外型无关,而是由杂合优势所决定.检验这种说法的一种途径就是察看是否显性表型的变异性要比隐性表型的变异性低.研究对两组蜗牛壳进行观察,两组样本内个体数分别是1 972和5 423个,经分析,隐性表型的变异性比显性表型显著(P<0.05).在同一壳中,对壳测量所得数据进行相关分析,表性性状差异的证据未找到.如果变异的差异是真实的,那么将表明或者是可见的壳外型是不重要的,多态性由于杂合平衡决定的,或者是这种多态性平衡的进化是由壳外形的自然选择所维持的.

It has been suggested that the polymorphism for shell colour and pattern in Cepaea may be unrelated to the visible appearance of the shells,but maintained by heterosis or heterozygote advantage.A possible way to test this supposition is to examine whether phenotypic variance is lower in the morph exhibiting the dominant phenotype than in that with the recessive phenotype.This has been tested in two samples of shells involving totals of 1 792 and 5 423 individuals,respectively.Overall,there is a significantly greater variance in the recessive than the dominant class（P0.05）.Correlation between measurements on the same shell was also examined.No evidence of difference between phenotypes was found.If the difference in variance is real,it may indicate either of the followings：1.that visible appearance is not important and the polymorphism is maintained by a heterozygous balance;or 2.evolution of such a balance in a polymorphism maintained over a long time span by selection acting on visible attributes of the shells.