Pegoraro L, Cafasso D, Rinaldi R, Cozzolino S, Scopece G
Department of Biology, University of Padua, Padua, Italy.
Department of Biology, University Federico II of Naples, Naples, Italy.
J Evol Biol. 2016 Oct;29(10):2070-2082. doi: 10.1111/jeb.12930. Epub 2016 Jul 27.
Tetraploid lineages are typically reproductively isolated from their diploid ancestors by post-zygotic isolation via triploid sterility. Nevertheless, polyploids often also exhibit ecological divergence that could contribute to reproductive isolation from diploid ancestors. In this study, we disentangled the contribution of different forms of reproductive isolation between sympatric diploid and autotetraploid individuals of the food-deceptive orchid Anacamptis pyramidalis by quantifying the strength of seven reproductive barriers: three prepollination, one post-pollination prezygotic and three post-zygotic. The overall reproductive isolation between the two cytotypes was found very high, with a preponderant contribution of two prepollination barriers, that is phenological and microhabitat differences. Although the contribution of post-zygotic isolation (triploid sterility) is confirmed in our study, these results highlight that prepollination isolation, not necessarily involving pollinator preference, can represent a strong component of reproductive isolation between different cytotypes. Thus, in the context of polyploidy as quantum speciation, that generates reproductive isolation via triploid sterility, ecological divergence can strengthen the reproductive isolation between cytotypes, reducing the waste of gametes in low fitness interploidy crosses and thus favouring the initial establishment of the polyploid lineage. Under this light, speciation by polyploidy involves ecological processes and should not be strictly considered as a nonecological form of speciation.
四倍体谱系通常通过三倍体不育导致的合子后隔离与它们的二倍体祖先生殖隔离。然而，多倍体通常也表现出生态分化，这可能有助于与二倍体祖先生殖隔离。在本研究中，我们通过量化七个生殖障碍的强度，厘清了食源性欺骗性兰花金字塔兰同域分布的二倍体和同源四倍体个体之间不同形式生殖隔离的贡献：三个授粉前障碍、一个授粉后合子前障碍和三个合子后障碍。发现这两种细胞型之间的总体生殖隔离非常高，其中两个授粉前障碍，即物候和微生境差异，起了主要作用。虽然在我们的研究中证实了合子后隔离（三倍体不育）的作用，但这些结果突出表明，授粉前隔离不一定涉及传粉者偏好，可能是不同细胞型之间生殖隔离的一个重要组成部分。因此，在多倍体作为量子物种形成的背景下，即通过三倍体不育产生生殖隔离，生态分化可以加强细胞型之间的生殖隔离，减少低适合度倍间杂交中配子的浪费，从而有利于多倍体谱系的初始建立。据此，多倍体物种形成涉及生态过程，不应被严格视为一种非生态的物种形成形式。
