Bull J J, Millstein J, Orcutt J, Wichman H A
Institute for Cellular and Molecular Biology, Section of Integrative Biology, University of Texas, Austin, Texas 78712, USA.
Am Nat. 2006 Feb;167(2):E39-51. doi: 10.1086/499374. Epub 2005 Dec 12.
A cornerstone of evolutionary ecology is that population density affects adaptation: r and K selection is the obvious example. The reverse is also appreciated: adaptation impacts population density. Yet, empirically demonstrating a direct connection between population density and adaptation is challenging. Here, we address both evolution and ecology of population density in models of viral (bacteriophage) chemostats. Chemostats supply nutrients for host cell growth, and the hosts are prey for viral reproduction. Two different chemostat designs have profoundly different consequences for viral evolution. If host and virus are confined to the same chamber, as in a predator-prey system, viral regulation of hosts feeds back to maintain low viral density (measured as infections per cell). Viral adaptation impacts host density but has a small effect on equilibrium viral density. More interesting are chemostats that supply the viral population with hosts from a virus-free refuge. Here, a type of evolutionary succession operates: adaptation at low viral density leads to higher density, but high density then favors competitive ability. Experiments support these models with both phenotypic and molecular data. Parallels to these designs exist in many natural systems, so these experimental systems may yield insights to the evolution and regulation of natural populations.
r和K选择就是一个明显的例子。反之亦然：适应性会影响种群密度。然而，从实证角度证明种群密度与适应性之间的直接联系具有挑战性。在这里，我们在病毒（噬菌体）恒化器模型中探讨种群密度的进化与生态。恒化器为宿主细胞生长提供营养，而宿主是病毒繁殖的猎物。两种不同的恒化器设计对病毒进化有着截然不同的影响。如果宿主和病毒被限制在同一个腔室中，就像在捕食者 - 猎物系统中一样，病毒对宿主的调控会反馈以维持低病毒密度（以每个细胞的感染数来衡量）。病毒适应性会影响宿主密度，但对平衡病毒密度的影响较小。更有趣的是那些从无病毒避难所向病毒种群提供宿主的恒化器。在这里，一种进化演替在起作用：低病毒密度下的适应性会导致更高的密度，但高密度随后又有利于竞争能力。实验用表型和分子数据支持了这些模型。许多自然系统中都存在与这些设计类似的情况，所以这些实验系统可能会为自然种群的进化和调控提供见解。
