Saccheri Ilik J, Brakefield Paul M, Nichols Richard A
Research Group in Evolutionary Biology, Institute of Evolutionary and Ecological Sciences, University of Leiden, Schelpenkade 14a, 2313 ZT, Leiden, The Netherlands.
Conservation Genetics Group, Institute of Zoology, The Zoological Society of London, Regent's Park, London, NW1 4RY, UK.
Evolution. 1996 Oct;50(5):2000-2013. doi: 10.1111/j.1558-5646.1996.tb03587.x.
We established inbred laboratory lines of the satyrid Bicyclus anynana with one, three and 10 pairs of butterflies, which were subsequently allowed to increase freely to a maximum size of 300 butterflies. Minimally inbred control lines were established with 300 randomly selected virgin butterflies of equal sex ratio. We measured fecundity, egg weight, egg hatching, adult emergence, adult size, and the proportion of crippled adults in generations F , F , F , and F (the latter two for the one pair bottleneck lines only). The most striking result was an unexpectedly large decrease in egg hatching with increase in inbreeding (25% per 10% increase in inbreeding). Such a level of inbreeding depression has not been reported previously for any insect. The distribution of egg hatching rate for individual clutches within inbred lines was markedly skewed, with a large fraction of clutches producing no eggs at all. This is interpreted as a relatively lower ratio of detrimental to lethal (or sterile) mutation loads than is found in Drosophila, the only insects for which mutation loads have been well characterized. Possible explanations for this severe inbreeding depression include a relatively high rate of mutation to recessive alleles with substantial damaging effects and infrequent episodes of inbreeding in nature. In the experiments, average egg hatching rate recovered rapidly between F and F in three of the six one-pair lines. We discuss the implications of these results for survival of populations through extreme bottlenecks in nature and in captivity.
我们用1对、3对和10对蝴蝶建立了眼蝶科物种小环蛱蝶（Bicyclus anynana）的近交实验室品系，随后任其自由繁殖，最大规模达到300只蝴蝶。用300只随机挑选的、性别比例均等的未交配蝴蝶建立了最低限度近交的对照品系。我们测量了F1、F2、F3和F4代（后两代仅针对单对瓶颈品系）的繁殖力、卵重、卵孵化率、成虫羽化率、成虫大小以及残翅成虫比例。最显著的结果是，随着近亲繁殖的增加，卵孵化率意外大幅下降（近亲繁殖每增加10%，卵孵化率下降25%）。此前尚未有任何昆虫报道过如此程度的近亲繁殖衰退。近交品系内单个卵块的卵孵化率分布明显偏斜，很大一部分卵块根本不产卵。这被解释为与果蝇相比，有害突变负荷与致死（或不育）突变负荷的比例相对较低，果蝇是唯一突变负荷得到充分表征的昆虫。这种严重近亲繁殖衰退的可能解释包括隐性等位基因的突变率相对较高，且具有重大破坏作用，以及在自然环境中近亲繁殖事件较少。在实验中，六个单对品系中的三个品系，其平均卵孵化率在F1和F2代之间迅速恢复。我们讨论了这些结果对于自然界和圈养环境中种群通过极端瓶颈期生存的意义。
