翠斑草蜥個體遺傳多樣性與體外寄生蟲及形質對稱性的相關性

Abstract

一個多倍體生物體內其各套染色體彼此間基因的異同，稱之為個體的遺傳多樣性（individual genetic diversity），而個體的遺傳多樣性與其適存度（fitness）之間的關係一直都是遺傳學家感興趣的議題。目前為止在遺傳多樣性的研究中一般會以個體的異型合子歧異度（heterozygosity）做為遺傳多樣性的指標，而所謂異型合子優勢假說（heterozygote advantage hypothesis），即指異型合子的個體相較於同型合子（homozygous）的個體會有較高的適存度。我的研究是利用一整批同時同地採獲的翠斑草蜥（Takydromus viridipunctatus），選用8組微衛星基因座作為異型合子歧異度的遺傳指標，而使用體外寄生蟲的數量與左右兩側的鱗片對稱性做為該個體的適存度指標，來檢測翠斑草蜥遺傳多樣性與適存值特徵之間的關係。如果符合異型合子優勢假說，我預期（1）異型合子歧異度愈高的個體，體外寄生蟲的承載量越少；（2）異型合子歧異度愈高的個體，其左右鱗片越對稱。結果顯示，雄性翠斑草蜥的異型合子歧異度與其體外寄生蟲的承載量呈現顯著的負相關，並且其頭部鱗片越對稱；而雌性則無此現象。目前針對爬行動物異型合子優勢假說的探討仍然極為有限，而本研究可能是目前所知唯一呈現統計顯著的案例。

Evolutionists have been interested in correlation between individual genetic diversity and fitness for decades. The heterozygote advantage hypothesis presumes that heterozygous individuals will have higher fitness than homozygous individuals. Previous studies on heterozygote advantage hypothesis usually focus on birds, mammals and fishes, but similar studies are relatively rare in reptiles. In this study, we attempt to test this hypothesis in the green spotted grass lizard (Takydromus viridipunctatus) endemic to Taiwan. I evaluate individual heterozygosity of 140 grass lizards collected at the same time from one single location by using 8 microsatellite loci, and investigate the correlations between mean d2 and (1) ectoparasite load, and (2) individual asymmetry. My results demonstrated that heterozygosity is negatively correlated with ectoparasite loads and head asymmetry in male lizards, but the correlations in females are not significant. This phenomenon indicates that male lizards are probably facing higher risks of parasitism in summers, and individual hererozygosity might provide higher fitness in courtship success and survivorship in breeding seasons.