Maintenacne of Parent-Species Reservoirs in a Complex Hybrid Zone

HILBISH 9708074 PIS一直在对欧洲共域的两种海洋贻贝--紫贻贝和紫贻贝--之间的杂交区域进行详细分析。PI研究表明，1)在杂交种内发生了强烈的定向选择，消除了紫贻贝和类似紫贻贝的杂交种；2)从紫贻贝纯种群的迁入抵消了定向选择；3)扩散和选择之间的平衡目前是稳定的；4)杂交是这些物种进化史上的一个重要特征。这些研究将未来的研究集中在一个新的方向：了解这个杂交区的动态的首要问题是确定如何维持美味分枝杆菌的纯种群。维持紫贻贝的纯种群是维持和形成这一杂交区的扩散选择和定向选择之间动态平衡的重要因素。PI将建议测试这样一种假设，即蓝藻在其食物中具有处理泥沙的优越生理能力，并且该物种的纯种群被选择性地维持在泥沙浓度较高的河口环境中。这一假设是由观察到的纯种群与泥沙负荷高的河口有关，以及来自单独研究的初步结果表明，当接触含有高浓度泥沙的饲料时，水母可能有更大的吸收效率。PI还将提出实验室和现场实验相结合的方法来验证这一假设。实验室实验将测试美味分枝杆菌和高氏分枝杆菌之间提出的生理差异，而田间实验是必要的，以证明这些差异在自然界中具有重大后果。

Hilbish 9708074 The PIs have been conducting a detailed analysis of a hybrid zone between two species of marine mussels, Mytilus edulis and M. galloprovincialis that are sympatric in Europe. The PIs' have shown that 1) strong directional selection occurs within hybrid populations that eliminates Mytilus edulis and M. edulis-like hybrids, 2) directional selection is offset by immigration from pure populations of M. edulis, 3) the balance between dispersal and selection is presently stable, and 4) hybridization has been an important feature in the evolutionary history of these species. These studies focus future research in a new direction: the primary issue in understanding the dynamics of this hybrid zone is to determine how pure populations of M. edulis are maintained. The maintenance of pure populations of Mytilus edulis is an essential element of the dynamic equilibrium between dispersal and directional selection that maintains and shapes this hybrid zone. The PI will propose to test the hypothesis that M. edulis has a superior physiological capacity to cope with silt in its diet and that pure populations of this species are selectively maintained in estuarine environments where silt concentrations are high. This hypothesis was suggested by the observation that pure populations of M. edulis are associated with estuaries that have high silt loads and preliminary results from separate studies that indicate that M. edulis may have a much greater absorption efficiencies when exposed to diet containing high concentrations of silt. The PI will also propose a combination of laboratory and field experiments to test this hypothesis. Laboratory experiments will test for the proposed physiological differences between M. edulis and M. galloprovincialis while the field experiments are necessary to demonstrate that these differ ences have significant consequences in nature.