Wu Z, Hopper K R, Ode P J, Fuester R W, Tuda M, Heimpel G E
Department of Entomology, University of Minnesota, St Paul, MN 55108, USA.
Heredity (Edinb). 2005 Sep;95(3):228-34. doi: 10.1038/sj.hdy.6800720.
In the haplodiploid Hymenoptera, haploid males arise from unfertilized eggs, receiving a single set of maternal chromosomes while diploid females arise from fertilized eggs and receive both maternal and paternal chromosomes. Under single-locus complementary sex determination (sl-CSD), sex is determined by multiple alleles at a single locus. Sex locus heterozygotes develop as females, while hemizygous and homozygous eggs develop as haploid and diploid males, respectively. Diploid males, which are inviable or sterile in almost all cases studied, are therefore produced in high frequency under inbreeding or in populations with low sex allele diversity. CSD is considered to be the ancestral form of sex determination within the Hymenoptera because members of the most basal taxa have CSD while some of the more derived groups have other mechanisms of sex determination that produce the haplo-diploid pattern without penalizing inbreeding. In this study, we investigated sex determination in Heterospilus prosopidis Viereck, a parasitoid from a relatively primitive subfamily of the Braconidae, a hymenopteran family having species with and without CSD. By comparing sex ratio and mortality patterns produced by inbred and outbred females, we were able to rule out sl-CSD as a sex determination mechanism in this species. The absence of sl-CSD in H. prosopidis was unexpected given its basal phylogenetic position in the Braconidae. This and other recent studies suggest that sex determination systems in the Hymenoptera may be evolutionary labile.
在单倍二倍体膜翅目昆虫中，单倍体雄虫由未受精的卵发育而来，仅继承一套母本染色体，而二倍体雌虫由受精卵发育而来，同时继承母本和父本染色体。在单基因座互补性性别决定（sl-CSD）中，性别由单个基因座上的多个等位基因决定。性别基因座杂合子发育为雌虫，而半合子和纯合子卵分别发育为单倍体雄虫和二倍体雄虫。在几乎所有已研究的案例中，二倍体雄虫都是不可存活或不育的，因此在近亲繁殖或性别等位基因多样性较低的种群中，二倍体雄虫的产生频率较高。CSD被认为是膜翅目昆虫性别决定的原始形式，因为最基部类群的成员具有CSD，而一些进化程度更高的类群具有其他性别决定机制，这些机制能产生单倍二倍体模式且不会对近亲繁殖造成不利影响。在本研究中，我们调查了Prosopidis异距茧蜂（Heterospilus prosopidis Viereck）的性别决定情况，该蜂是茧蜂科一个相对原始亚科的寄生蜂，茧蜂科是一个膜翅目科，其物种有的具有CSD，有的则没有。通过比较近亲繁殖和非近亲繁殖雌虫产生的性别比例和死亡率模式，我们能够排除sl-CSD作为该物种性别决定机制的可能性。鉴于Prosopidis异距茧蜂在茧蜂科中的基部系统发育位置，其不存在sl-CSD是出乎意料的。本研究及其他近期研究表明，膜翅目昆虫的性别决定系统可能在进化上不稳定。
