Data from: The effect of inbreeding rate on fitness, inbreeding depression and heterosis over a range of inbreeding coefficients

Understanding the effects of inbreeding and genetic drift within populations and hybridization between genetically differentiated populations is important for many basic and applied questions in ecology and evolutionary biology. The magnitudes and even the directions of these effects can be influenced by various factors, especially by the current and historical population size (i.e., inbreeding rate). Using Drosophila littoralis as a model species, we studied the effect of inbreeding rate over a range of inbreeding levels on 1) mean fitness of a population (relative to that of an outbred control population), 2) within-population inbreeding depression (reduction in fitness of offspring from inbred vs. random mating within a population), and 3) heterosis (increase in fitness of offspring from inter-population vs. within-population random mating). Inbreeding rate was manipulated by using three population sizes (2, 10, and 40), and fitness was measured as offspring survival and fecundity. Fast inbreeding (smaller effective population size) resulted in greater reduction in population mean fitness than slow inbreeding, when populations were compared over similar inbreeding coefficients. Correspondingly, populations with faster inbreeding expressed more heterosis upon inter-population hybridization. Inbreeding depression within the populations did not have a clear relationship with either the rate or the level of inbreeding.

厘清种群内近交（inbreeding）与遗传漂变（genetic drift）的效应，以及遗传分化种群间的杂交（hybridization）效应，对于生态学与进化生物学领域的诸多基础与应用研究问题均具有重要意义。上述效应的强度乃至方向均可受多种因素调控，其中尤以种群当前与历史种群大小（即近交速率）的影响最为突出。本研究以海滨果蝇（Drosophila littoralis）为模式物种，探究了一系列近交水平下，近交速率对以下三类指标的影响：1）种群平均适合度（fitness，相对于远交对照种群的适合度）；2）种群内近交衰退（inbreeding depression，即种群内近交交配子代相较于随机交配子代的适合度下降幅度）；3）杂种优势（heterosis，即种群间随机交配子代相较于种群内随机交配子代的适合度提升幅度）。本研究通过设置三种种群大小（2、10与40）来调控近交速率，并以子代存活率与繁殖力作为适合度的衡量指标。当在相近近交系数（inbreeding coefficient）下对种群进行比较时，快速近交（即更小的有效种群大小（effective population size））相较于慢速近交，会导致种群平均适合度出现更为显著的下降。相应地，快速近交的种群在进行种群间杂交时，会表现出更强的杂种优势。种群内的近交衰退则与近交速率或近交水平均无明确关联。