Institute of Environmental Sciences, Jagiellonian University, Gronostajowa 7, Krakow 30-387, Poland.
BMC Evol Biol. 2014 Feb 17;14(1):28. doi: 10.1186/1471-2148-14-28.
Geographic barriers to gene flow and divergence among populations in sexual traits are two important causes of genetic isolation which may lead to speciation. Genetic isolation may be facilitated if these two mechanisms act synergistically. The guppy from the Cumaná region (within the Cariaco drainage) of eastern Venezuela has been previously described as a case of incipient speciation driven by sexual selection, significantly differentiated in sexual colouration and body shape from the common guppy, Poecilia reticulata. The latter occurs widely in northern Venezuela, including the south-eastern side of Cordillera de la Costa, where it inhabits streams belonging to the San Juan drainage. Here, we present molecular and morphological analyses of differentiation among guppy populations in the Cariaco and San Juan drainages. Our analyses are based on a 953 bp long mtDNA fragment, a set of 15 microsatellites (519 fish from 20 populations), and four phenotypic traits.
Both microsatellite and mtDNA data showed that guppies inhabiting the two drainages are characterised by a significant genetic differentiation, but a higher proportion of the genetic variance was distributed among populations within regions. Most guppies in the Cariaco drainage had mtDNA from a distinct lineage, but we also found evidence for widespread introgression of mtDNA from the San Juan drainage into the Cariaco drainage. Phenotypically, populations in the two regions differed significantly only in the number of black crescents. Phenotypic clustering did not support existence of two distinct groupings, but indicated a degree of distinctiveness of Central Cumaná (CC) population. However, CC population showed little differentiation at the neutral markers from the proximate populations within the Cariaco drainage.
Our findings are consistent with only partial genetic isolation between the two geographic regions and indicate that the geographic barrier of Cordillera de la Costa has not played an important role in strengthening the incomplete pre-zygotic reproductive barrier between Cumaná and common guppy. Significant phenotypic differentiation between genetically similar (in terms of neutral variation) populations suggests that mate choice can maintain divergence at sexually selected traits despite gene flow. However, neither genetic nor phenotypic clustering supported delineation of two species within the region.
基因流和种群间生殖特征的分歧的地理障碍是导致遗传隔离的两个重要原因，这可能导致物种形成。如果这两种机制协同作用，遗传隔离可能会得到促进。委内瑞拉东部库马纳地区（卡里亚科流域内）的古比鱼以前被描述为一个由性选择驱动的初生物种形成的案例，其在生殖颜色和体型上与普通古比鱼，即丽鱼科的胎生丽鱼，显著不同。后者广泛分布于委内瑞拉北部，包括科迪勒拉德拉科斯塔的东南部，在那里它栖息在属于圣胡安流域的溪流中。在这里，我们展示了卡里亚科和圣胡安流域古比鱼种群之间分化的分子和形态分析。我们的分析基于一个 953bp 长的 mtDNA 片段、一组 15 个微卫星（来自 20 个种群的 519 条鱼）和四个表型特征。
微卫星和 mtDNA 数据都表明，栖息在两个流域的古比鱼具有显著的遗传分化，但遗传方差的更大比例分布在区域内的种群之间。卡里亚科流域的大多数古比鱼都有来自一个独特谱系的 mtDNA，但我们也发现了圣胡安流域的 mtDNA 广泛渗入卡里亚科流域的证据。表型上，两个地区的种群仅在黑色新月的数量上存在显著差异。表型聚类不支持存在两个明显的分组，而是表明中央库马纳（CC）种群具有一定程度的独特性。然而，CC 种群在来自卡里亚科流域内邻近种群的中性标记上显示出很少的分化。
我们的发现与两个地理区域之间只有部分遗传隔离一致，并表明科迪勒拉德拉科斯塔的地理障碍在加强库马纳和普通古比鱼之间不完全的合子前生殖隔离方面没有发挥重要作用。在遗传上相似（就中性变异而言）的种群之间存在显著的表型分化表明，尽管存在基因流，选择配偶仍可以维持在性选择特征上的分歧。然而，无论是遗传聚类还是表型聚类都不支持在该区域内划分两个物种。
