Leibniz Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 310, 12587, Berlin, Germany.
Department of Aquatic Resources, Institute of Freshwater Research, Swedish University of Agricultural Sciences, Drottningholm, Sweden.
BMC Ecol Evol. 2021 Oct 6;21(1):186. doi: 10.1186/s12862-021-01920-8.
Sympatric speciation along ecological gradients has been studied repeatedly, in particular in freshwater fishes. Rapid post-glacial ecological divergence has resulted in numerous endemic species or ecologically distinct populations in lakes of the temperate zones. Here, we focus on the Baltic cisco (Coregonus albula) complex, to study the genetic similarity among two pairs of sympatric autumn- and spring-spawning populations from post-glacial German Lakes Stechlin and Breiter Luzin. For comparison, we included a similar pair of sympatric populations from the Swedish Lake Fegen. We wanted to explore potential genetic similarities between the three sympatric cisco population pairs in the three lakes, to evaluate whether the pairs may have emerged independently in the three lakes, or whether two different species may have colonized all three lakes independently. Furthermore, we considered allopatric C. albula populations from three Polish, three Finnish, and four Swedish locations, added one Siberian population of the sister species C. sardinella and a Swedish C. maraena (whitefish) population. By genotyping nine microsatellite markers in 655 individuals from these 18 populations, we wanted to elucidate how strongly the cisco populations differ across a larger geographical area within Europe. Finally, we compared the genetic differences between the spring- and autumn-spawning populations of ciscoes in the two German lakes to infer the potentially deteriorating effect of strong anthropogenic pressure on the lakes.
Dendrogram, Principal Coordinate Analysis and admixture analysis all indicated strong correspondence between population differentiation and geographical location for most cisco populations in Europe, including the Siberian population of C. sardinella. However, populations from some Swedish lakes deviated from this general pattern, by showing a distinct genetic structure. We found evidence for independent evolution of the three sympatric population pairs, because the populations co-occurring in the same lake were always most closely related. However, genetic differentiation was weak in the two German population pairs, but strong in the Swedish Lake Fegen, indicating that the weak differentiation in the German pairs reported earlier has eroded further.
Our results suggest that the genetic differentiation at neutral genetic markers among populations of the Baltic cisco complex has evolved (and is maintained) by random genetic drift in isolated populations. However, earlier studies on the Swedish populations combining mitochondrial DNA and microsatellite data indicate that also post-glacial immigration from separate glacial refugia has shaped the present genetic population structure. The low neutral differentiation of the German sympatric pairs in contrast to the Swedish pair suggests that recent anthropogenic effects on the lakes in Germany may put the endemic spring-spawners at risk to extinction.
沿着生态梯度的同域物种形成已被反复研究，特别是在淡水鱼类中。快速的冰川后生态分歧导致温带湖泊中出现了许多特有种或具有明显生态差异的种群。在这里，我们专注于波罗的海白鲑（Coregonus albula）复合体，以研究来自冰川后德国施特林湖和布赖特吕津湖的两对同域秋季和春季产卵种群之间的遗传相似性。作为比较，我们还包括了来自瑞典法根湖的一对类似的同域种群。我们想探索这三个湖泊中的三个同域白鲑种群之间的潜在遗传相似性，以评估这两对种群是否可能在这三个湖泊中独立出现，或者两个不同的物种是否可能独立地殖民所有三个湖泊。此外，我们考虑了来自波兰的三个、芬兰的三个和瑞典的四个地点的非同域 C. albula 种群，以及一个来自姊妹种 C. sardinella 的西伯利亚种群和一个瑞典的 C. maraena（白鲑）种群。通过对来自这 18 个种群的 655 个个体的 9 个微卫星标记进行基因分型，我们希望阐明白鲑种群在欧洲更大的地理区域内的差异程度。最后，我们比较了两个德国湖中春季和秋季产卵的白鲑种群之间的遗传差异，以推断强烈的人为压力对湖泊的潜在恶化影响。
系统发育树、主坐标分析和混合分析都表明，对于欧洲的大多数白鲑种群，包括西伯利亚的 C. sardinella 种群，种群分化与地理位置之间存在很强的对应关系。然而，一些瑞典湖泊的种群偏离了这种普遍模式，表现出明显的遗传结构。我们发现这三个同域种群对的独立进化有证据，因为在同一湖中共同出现的种群总是最密切相关的。然而，在两个德国种群对中遗传分化较弱，但在瑞典法根湖中较强，这表明之前报道的德国种群对的弱分化进一步减弱了。
我们的研究结果表明，波罗的海白鲑复合体的种群之间中性遗传标记的遗传分化是通过孤立种群中的随机遗传漂变而进化（并维持）的。然而，之前结合线粒体 DNA 和微卫星数据对瑞典种群的研究表明，冰川后从单独的冰川避难所的移民也塑造了目前的遗传种群结构。与瑞典种群相比，德国同域对的低中性分化表明，德国湖泊最近的人为影响可能使地方特有的春季产卵者面临灭绝的风险。
