Howard Daniel J, Waring Gwendolyn L, Tibbets C Alana, Gregory Pamela G
Department of Biology, New Mexico State University, Las Cruces, New Mexico, 88003.
Department of Biology, Museum of Northern Arizona, Flagstaff, Arizona, 86001.
Evolution. 1993 Jun;47(3):789-800. doi: 10.1111/j.1558-5646.1993.tb01234.x.
The ground crickets Allonemobius fasciatus and A. socius meet in a mosaic hybrid zone that stretches from New Jersey at least as far west as Illinois. Within mixed populations from the contact zone, "pure" species individuals predominate. To determine whether hybrids are less viable than pure-species individuals, and to assess whether the high proportion of pure-species individuals in mixed populations results from hybrid inviability, we performed a cohort analysis. In this study, five mixed populations from the hybrid zone were each sampled three to five times from the fall of 1986 to the spring of 1988. Individuals were assigned to one of three categories based on their genotypes: A. socius (individuals harboring only alleles unique to A. socius), hybrid (individuals with alleles unique to both species), and A. fasciatus (individuals harboring only alleles unique to A. fasciatus). This sampling and measurement scheme permitted monitoring of the proportion of hybrid individuals in a population over time. The results were fairly consistent. The relative survival of A. socius was greater than the relative survival of members of the other two groups in four of the five populations. The relative viability of A. fasciatus was greater than that of hybrids in one population, approximately equal to that of hybrids in two populations, and less than that of hybrids in two populations. These results not only shed light on an important component of fitness, viability from hatching to adulthood, but they demonstrate that loss of hybrid individuals during the course of the field season will not explain deviations from random mating expectations present in mixed populations in late summer. The deviations must be due to assortative mating or to a reproductive barrier operating prior to egg hatch.
地栖蟋蟀Allonemobius fasciatus和A. socius在一个镶嵌杂交带相遇，该杂交带从新泽西州一直延伸到至少以西的伊利诺伊州。在接触区的混合种群中，“纯”物种个体占主导地位。为了确定杂种是否比纯物种个体的生存能力更低，并评估混合种群中纯物种个体的高比例是否源于杂种的生存能力不足，我们进行了一项队列分析。在这项研究中，从1986年秋季到1988年春季，对杂交带的五个混合种群分别进行了三到五次采样。根据个体的基因型，将其分为三类：A. socius（仅携带A. socius特有的等位基因的个体）、杂种（具有两个物种特有的等位基因的个体）和A. fasciatus（仅携带A. fasciatus特有的等位基因的个体）。这种采样和测量方案允许监测种群中杂种个体比例随时间的变化。结果相当一致。在五个种群中的四个种群中，A. socius的相对存活率高于其他两组成员的相对存活率。在一个种群中，A. fasciatus的相对生存能力高于杂种，在两个种群中大致等于杂种，在两个种群中低于杂种。这些结果不仅揭示了适应性的一个重要组成部分，即从孵化到成年的生存能力，而且表明在野外季节期间杂种个体的损失并不能解释夏末混合种群中与随机交配预期的偏差。这些偏差一定是由于选型交配或在卵孵化之前起作用的生殖障碍。
