Fidler Andrew E, Bacq-Labreuil Aurelie, Rachmilovitz Elad, Rinkevich Baruch
Institute of Marine Science, University of Auckland, Auckland, New Zealand.
École Supérieure de Biotechnologie Strasbourg, Strasbourg, France.
PeerJ. 2018 Jun 13;6:e5006. doi: 10.7717/peerj.5006. eCollection 2018.
Over the past three decades the colonial ascidian has been expanding its global range, significantly impacting marine habitats and aquaculture facilities. What biological features make so highly invasive? Here, we show that juxtaposed allogeneic colony fragments ('ramets') may, initially, form chimeric entities. Subsequently, zooids of the differing genotypes within such chimeras coordinately retreat away from fusion zones. A few days following such post-fusion retreat movements there is further ramet fission and the formation of zooid-depauperate tunic zones. Using polymorphic microsatellite loci to distinguish between genotypes, we found that they were sectorial at the fusion zones and the subsequent ramet movements resulted in further spatial separation of the paired-genotypes indicating that the fusion events observed did not lead to formation of long-term, stable chimeras. Thus, movements of colony ramets from initial fusion zones lead to progressive segregation of genotypes probably minimizing potential somatic/germ-cell competition/parasitism. We speculate that relatively fast (≤10 mm/day) movement of colonies on substrates along with frequent, and perhaps unrestrained, transient allogeneic fusions play significant roles in this species' striking invasiveness and capacity to colonize new substrates.
在过去三十年里，殖民海鞘一直在扩大其全球分布范围，对海洋栖息地和水产养殖设施造成了重大影响。是什么生物学特征使其具有如此高的入侵性？在这里，我们表明并置的同种异体群体片段（“分株”）最初可能形成嵌合实体。随后，此类嵌合体中不同基因型的游动孢子会协调地从融合区撤离。融合后这种撤离运动发生几天后，会有进一步的分株裂变以及游动孢子贫乏的被囊区形成。利用多态微卫星位点来区分基因型，我们发现它们在融合区呈扇形分布，随后的分株运动导致配对基因型进一步在空间上分离，这表明观察到的融合事件并未导致形成长期稳定的嵌合体。因此，群体分株从初始融合区的移动导致基因型逐渐分离，这可能最大限度地减少了潜在的体细胞/生殖细胞竞争/寄生现象。我们推测，该物种的群体在基质上相对较快（≤10毫米/天）的移动，以及频繁且可能不受限制的短暂同种异体融合，在其显著的入侵性和定殖新基质的能力中发挥了重要作用。
