Department Biologie II, Evolutionsökologie, Ludwig-Maximilians-Universität, Großhaderner Str, 2, 82152 Planegg-Martinsried, Germany.
BMC Evol Biol. 2014 Apr 12;14:80. doi: 10.1186/1471-2148-14-80.
In natural communities of cyclical parthenogens, rapid response to environmental change is enabled by switching between two reproduction modes. While long periods of asexual reproduction allow some clones to outcompete others, and may result in "clonal erosion", sexual reproduction restores genetic variation in such systems. Moreover, sexual reproduction may result in the formation of interspecific hybrids. These hybrids can then reach high abundances, through asexual clonal reproduction. In the present study, we explored genetic variation in water fleas of the genus Daphnia. The focus was on the short-term dynamics within several clonal assemblages from the hybridizing Daphnia longispina complex and the impact of gene flow at small spatial scales.
Daphnia individuals belonged either to the parental species D. galeata and D. longispina, or to different hybrid classes, as identified by 15 microsatellite markers. The distribution and genotypic structure of parental species, but not hybrids, corresponded well with the geographical positions of the lakes. Within parental species, the genetic distance among populations of D. galeata was lower than among populations of D. longispina. Moreover, D. galeata dominance was associated with higher phosphorous load. Finally, there was no evidence for clonal erosion.
Our results suggest that the contemporary structure of hybridizing Daphnia communities from ten nearby lakes is influenced by colonization events from neighbouring habitats as well as by environmental factors. Unlike the parental species, however, there was little evidence for successful dispersal of hybrids, which seem to be produced locally. Finally, in contrast to temporary Daphnia populations, in which a decrease in clonal diversity was sometimes detectable over a single growing season, the high clonal diversity and lack of clonal erosion observed here might result from repeated hatching of sexually produced offspring. Overall, our study provides insights into spatio-temporal dynamics in a hybridizing Daphnia species complex in a recently established lake system, and relates genetic similarities of populations to a scenario of secondary invasion enhanced by environmental factors.
在周期性孤雌生殖的自然群落中，通过在两种繁殖模式之间切换，可以快速应对环境变化。虽然长时间的无性繁殖使一些克隆体能够胜过其他克隆体，并可能导致“克隆侵蚀”，但有性繁殖可以恢复此类系统中的遗传变异。此外，有性繁殖可能导致形成种间杂种。这些杂种可以通过无性克隆繁殖达到高丰度。在本研究中，我们探索了水蚤属的遗传变异。重点是杂交 Daphnia longispina 复合体中的几个克隆组合体的短期动态以及小空间尺度上基因流的影响。
Daphnia 个体要么属于亲代物种 D. galeata 和 D. longispina，要么属于通过 15 个微卫星标记识别的不同杂种类。亲代物种的分布和基因型结构，但杂种除外，与湖泊的地理位置非常吻合。在亲代物种中，D. galeata 种群之间的遗传距离低于 D. longispina 种群之间的遗传距离。此外，D. galeata 优势与较高的磷负荷有关。最后，没有证据表明存在克隆侵蚀。
我们的研究结果表明，来自十个附近湖泊的杂交 Daphnia 群落的当代结构受来自相邻栖息地的殖民事件以及环境因素的影响。然而，与亲代物种不同的是，杂种成功传播的证据很少，这些杂种似乎是在当地产生的。最后，与单一生长季节内有时可检测到的暂时 Daphnia 种群中克隆多样性减少相反，这里观察到的高克隆多样性和缺乏克隆侵蚀可能是由于有性繁殖产生的后代的反复孵化所致。总体而言，本研究提供了对新近建立的湖泊系统中杂交 Daphnia 物种复合体的时空动态的见解，并将种群的遗传相似性与受环境因素增强的二次入侵情景联系起来。
