Marks Jessica A, Biermann Christiane H, Eanes Walter F, Kryvi Harald
Department of Biology, University of Bergen, N-5007 Bergen, Norway.
Biol Bull. 2008 Oct;215(2):115-25. doi: 10.2307/25470692.
The rapid evolution of traits related to fertilization such as sperm morphology may be pivotal in the evolution of reproductive barriers and speciation. The sea urchin Strongylocentrotus droebachiensis has a circumarctic distribution and shows substantial genetic subdivision between northeastern Atlantic populations and northwestern Atlantic and Pacific populations. Using transmission electron microscopy, we show here that sperm shape, size, and ultrastructure differ markedly among populations of S. droebachiensis from different oceans and reflect patterns of genetic divergence. Sperm nuclei from northwestern Atlantic and Pacific populations were longer and narrower than those from the northeastern Atlantic. We additionally demonstrate population-level differences in the amount and location of filamentous actin (F-actin) prior to the occurrence of the acrosome reaction. Sperm from Pacific and northwest Atlantic populations differed from that of all other echinoids examined in that intact sperm contains a partly preformed acrosomal process, a structure more closely resembling the acrosomal rod seen in some molluscs. Immunofluorescent studies using anti-bindin antibodies and the F-actin-specific stain phalloidin confirmed these findings. Divergence of reproductive traits such as sperm morphology may be related to divergence in gamete compatibility and genetic divergence, and could represent the first stages of speciation in free-spawning marine invertebrates.
与受精相关的性状（如精子形态）的快速进化可能在生殖隔离和物种形成的进化过程中起关键作用。海胆强壮球海胆分布于环北极地区，在东北大西洋种群与西北大西洋和太平洋种群之间表现出显著的遗传分化。通过透射电子显微镜，我们在此表明，来自不同海洋的强壮球海胆种群的精子形状、大小和超微结构存在明显差异，并且反映了遗传分化模式。来自西北大西洋和太平洋种群的精子细胞核比来自东北大西洋的精子细胞核更长更窄。我们还证明了在顶体反应发生之前，丝状肌动蛋白（F-肌动蛋白）的数量和位置存在种群水平的差异。太平洋和西北大西洋种群的精子与所有其他已检测的棘皮动物的精子不同，因为完整的精子含有部分预先形成的顶体突起，这一结构更类似于在一些软体动物中看到的顶体棒。使用抗结合素抗体和F-肌动蛋白特异性染色剂鬼笔环肽的免疫荧光研究证实了这些发现。诸如精子形态等生殖性状的分化可能与配子兼容性的分化和遗传分化有关，并且可能代表了自由产卵海洋无脊椎动物物种形成的最初阶段。
