Swallow John G, Wallace Lisa E, Christianson Sarah J, Johns Philip M, Wilkinson Gerald S
Department of Biology, University of South Dakota, Vermillion, SD 57069, USA.
Mol Ecol. 2005 Oct;14(12):3787-800. doi: 10.1111/j.1365-294X.2005.02691.x.
Stalk-eyed flies (Diptera: Diopsidae) possess eyes at the ends of elongated peduncles, and exhibit dramatic variation in eye span, relative to body length, among species. In some sexually dimorphic species, evidence indicates that eye span is under both intra- and intersexual selection. Theory predicts that isolated populations should evolve differences in sexually selected traits due to drift. To determine if eye span changes as a function of divergence time, 1370 flies from 10 populations of the sexually dimorphic species, Cyrtodiopsis dalmanni and Cyrtodiopsis whitei, and one population of the sexually monomorphic congener, Cyrtodiopsis quinqueguttata, were collected from Southeast Asia and measured. Genetic differentiation was used to assess divergence time by comparing mitochondrial (cytochrome oxidase II and 16S ribosomal RNA gene fragments) and nuclear (wingless gene fragment) DNA sequences for c. five individuals per population. Phylogenetic analyses indicate that most populations cluster as monophyletic units with up to 9% nucleotide substitutions between populations within a species. Analyses of molecular variance suggest a high degree of genetic structure within and among the populations; > 97% of the genetic variance occurs between populations and species while < 3% is distributed within populations, indicating that most populations have been isolated for thousands of years. Nevertheless, significant change in the allometric slope of male eye span on body length was detected for only one population of either dimorphic species. These results are not consistent with genetic drift. Rather, relative eye span appears to be under net stabilizing selection in most populations of stalk-eyed flies. Given that one population exhibited dramatic evolutionary change, selection, rather than genetic variation, appears to constrain eye span evolution.
长眼柄蝇（双翅目：长眼柄蝇科）的眼睛位于细长眼柄的末端，并且相对于体长而言，不同物种之间的眼间距存在显著差异。在一些两性异形的物种中，有证据表明眼间距受到性内选择和性间选择的双重影响。理论预测，由于遗传漂变，隔离的种群在性选择性状上应该会进化出差异。为了确定眼间距是否会随着分化时间而变化，从东南亚收集了来自两性异形物种达尔曼氏长眼柄蝇（Cyrtodiopsis dalmanni）和怀特氏长眼柄蝇（Cyrtodiopsis whitei）的10个种群以及两性单形的同属物种五点长眼柄蝇（Cyrtodiopsis quinqueguttata）的1个种群的1370只苍蝇，并对其进行了测量。通过比较每个种群约五个个体的线粒体（细胞色素氧化酶II和16S核糖体RNA基因片段）和核（无翅基因片段）DNA序列，利用遗传分化来评估分化时间。系统发育分析表明，大多数种群聚为单系类群，同一物种内不同种群之间的核苷酸替换率高达9%。分子方差分析表明种群内部和种群之间存在高度的遗传结构；超过97%的遗传方差存在于种群和物种之间，而不到3%分布在种群内部，这表明大多数种群已经隔离了数千年。然而，仅在其中一个两性异形物种的一个种群中检测到雄性眼间距与体长的异速生长斜率有显著变化。这些结果与遗传漂变不一致。相反，在大多数长眼柄蝇种群中，相对眼间距似乎受到净稳定选择的影响。鉴于有一个种群表现出显著的进化变化，选择而非遗传变异似乎限制了眼间距的进化。
