Centre for Ecological Sciences, Indian Institute of Science, Bangalore, India.
PLoS One. 2013 Aug 1;8(8):e71573. doi: 10.1371/journal.pone.0071573. Print 2013.
High elevation montane areas are called "sky islands" when they occur as a series of high mountains separated by lowland valleys. Different climatic conditions at high elevations makes sky islands a specialized type of habitat, rendering them naturally fragmented compared to more continuous habitat at lower elevations. Species in sky islands face unsuitable climate in the intervening valleys when moving from one montane area to another. The high elevation shola-grassland mosaic in the Western Ghats of southern India form one such sky island complex. The fragmented patches make this area ideal to study the effect of the spatial orientation of suitable habitat patches on population genetic structure of species found in these areas. Past studies have suggested that sky islands tend to have genetically structured populations, possibly due to reduced gene flow between montane areas. To test this hypothesis, we adopted the comparative approach. Using Amplified Fragment Length Polymorphisms, we compared population genetic structures of two closely related, similar sized butterfly species: Heteropsis oculus, a high elevation shola-grassland specialist restricted to the southern Western Ghats, and Mycalesis patnia, found more continuously distributed in lower elevations. In all analyses, as per expectation the sky island specialist H. oculus exhibited a greater degree of population genetic structure than M. patnia, implying a difference in geneflow. This difference in geneflow in turn appears to be due to the natural fragmentation of the sky island complexes. Detailed analysis of a subset of H. oculus samples from one sky island complex (the Anamalais) showed a surprising genetic break. A possible reason for this break could be unsuitable conditions of higher temperature and lower rainfall in the intervening valley region. Thus, sky island species are not only restricted by lack of habitat continuity between montane areas, but also by the nature of the intervening habitat.
高海拔山区在一系列高山之间形成，如果这些高山被低地山谷隔开，就被称为“天空岛屿”。高海拔地区的不同气候条件使得天空岛屿成为一种特殊类型的栖息地，与低海拔地区更连续的栖息地相比，天空岛屿自然更加破碎化。当物种从一个山地地区移动到另一个山地地区时，它们会在中间的山谷中面临不适宜的气候。印度南部西高止山脉的高海拔 shola-草原镶嵌体就是这样一个天空岛屿复合体。破碎的斑块使该地区成为研究适宜栖息地斑块的空间方向对这些地区物种的种群遗传结构影响的理想场所。过去的研究表明，天空岛屿的种群可能存在遗传结构，这可能是由于山地地区之间的基因流减少所致。为了验证这一假设，我们采用了比较方法。使用扩增片段长度多态性（AFLP），我们比较了两种密切相关、体型相似的蝴蝶物种的种群遗传结构：Heteropsis oculus，一种仅限于南部西高止山脉高海拔 shola-草原的特有物种，和 Mycalesis patnia，分布范围更广，分布在较低海拔。在所有分析中，正如预期的那样，天空岛屿专家 H. oculus 表现出更大程度的种群遗传结构，这表明基因流的差异。这种基因流的差异似乎是由于天空岛屿复合体的自然破碎化造成的。对来自一个天空岛屿复合体（Anamalais）的 H. oculus 样本子集的详细分析显示出了一个令人惊讶的遗传断裂。这种断裂的一个可能原因是中间山谷地区的高温和低降雨量的不适宜条件。因此，天空岛屿物种不仅受到山地地区之间栖息地连续性的限制，还受到中间栖息地性质的限制。
