D'Souza T G, Schulte R D, Schulenburg H, Michiels N K
Animal Evolutionary Ecology, Zoological Institute, University of Tuebingen, Auf der Morgenstelle 28, Tuebingen D-72076, Germany.
Heredity (Edinb). 2006 Aug;97(2):97-101. doi: 10.1038/sj.hdy.6800841. Epub 2006 May 24.
Parthenogenesis usually includes clonal inheritance, which is thought to increase the risk of the clonal populations' extinction. Yet many parthenogenetic organisms appear to have survived for extended periods. A possible explanation is that parthenogens occasionally reproduce through sex-like processes. Although there is indirect evidence for occasional sex, the underlying mechanisms are currently unknown. In the present study, we examined sex-like processes in the planarian flatworm Schmidtea (Dugesia) polychroa. Parthenogenetic forms of this species are simultaneous hermaphrodites that require sperm to trigger embryogenesis, whereas paternal genetic material is usually excluded from the oocyte (sperm-dependent parthenogenesis). Based on a comparison of parents and offspring, using highly polymorphic microsatellites, we demonstrate the incorporation of paternal alleles in about 5% of the offspring. We detected two distinct processes: chromosome addition and chromosome displacement. Such rare sexual processes may explain the long-term persistence of the many purely parthenogenetic populations of S. polychroa in northern Europe.
孤雌生殖通常包含克隆遗传，而这被认为会增加克隆种群灭绝的风险。然而，许多孤雌生殖生物似乎存活了很长时间。一个可能的解释是，孤雌生殖生物偶尔会通过类似有性生殖的过程进行繁殖。尽管有间接证据表明偶尔会发生有性生殖，但目前其潜在机制尚不清楚。在本研究中，我们研究了多色剑尾涡虫（Schmidtea (Dugesia) polychroa）中类似有性生殖的过程。该物种的孤雌生殖形式为同步雌雄同体，需要精子来触发胚胎发育，而父本遗传物质通常被排除在卵母细胞之外（依赖精子的孤雌生殖）。基于对亲本和后代的比较，使用高度多态性的微卫星，我们证明了约5%的后代中存在父本等位基因的掺入。我们检测到两种不同的过程：染色体添加和染色体置换。这种罕见的有性生殖过程可能解释了北欧多色剑尾涡虫许多纯孤雌生殖种群的长期存续。
