School of Plant Science, Private Bag 55, University of Tasmania, Hobart 7001, Tasmania, Australia.
Ann Bot. 2011 Nov;108(7):1247-56. doi: 10.1093/aob/mcr220. Epub 2011 Aug 18.
The cool temperate rainforests of Australia were much reduced in range during the cold and dry glacial periods, although genetic evidence indicates that two key rainforest species, Nothofagus cunninghamii and Tasmannia lanceolata, survived within multiple locations and underwent only local range expansions at the end of the Last Glacial. To better understand the glacial response of a co-occurring but wind-dispersed and less cold-tolerant rainforest tree species, Atherosperma moschatum, a chloroplast phylogeographic study was undertaken.
A total of 3294 bp of chloroplast DNA sequence was obtained for 155 samples collected from across the species' range.
The distribution of six haplotypes observed in A. moschatum was geographically structured with an inferred ancestral haplotype restricted to Tasmania, while three non-overlapping and endemic haplotypes were found on the mainland of south-eastern Australia. Last glacial refugia for A. moschatum are likely to have occurred in at least one location in western Tasmania and in Victoria and within at least two locations in the Great Dividing Range of New South Wales. Nucleotide diversity of A. moschatum was lower (π = 0·00021) than either N. cunninghamii (0·00101) or T. lanceolata (0·00073), and was amongst the lowest recorded for any tree species.
This study provides evidence for past bottlenecks having impacted the chloroplast diversity of A. moschatum as a result of the species narrower climatic niche during glacials. This hypothesis is supported by the star-like haplotype network and similar estimated rates of chloroplast DNA substitution for A. moschatum and the two more cold tolerant and co-occurring species that have higher chloroplast diversity, N. cunninghamii and T. lanceolata.
澳大利亚的凉爽温带雨林在寒冷和干燥的冰川时期范围大大缩小，尽管遗传证据表明，两种关键的雨林物种，即山毛榉属 Cunninghamii 和 Tasmannia lanceolata，在多个地点存活下来，并且仅在末次冰期结束时经历了局部范围的扩张。为了更好地了解共同出现但风散且耐寒性较差的雨林树种，即 Atherosperma moschatum 的冰川反应，进行了叶绿体系统地理学研究。
从该物种的整个分布范围内收集了 155 个样本，共获得了 3294 个碱基对的叶绿体 DNA 序列。
在 A. moschatum 中观察到的六个单倍型的分布具有地理结构，推断的祖单倍型仅限于塔斯马尼亚，而在澳大利亚东南部大陆发现了三个非重叠且特有单倍型。A. moschatum 的末次冰期避难所可能至少存在于塔斯马尼亚西部的一个地点、维多利亚州和新南威尔士州大分水岭的至少两个地点。A. moschatum 的核苷酸多样性较低（π=0.00021），低于山毛榉属 Cunninghamii（0.00101）或 Tasmannia lanceolata（0.00073），并且是记录的任何树种中最低的之一。
本研究为过去的瓶颈事件对 A. moschatum 的叶绿体多样性产生影响提供了证据，这是由于该物种在冰川时期具有更窄的气候生态位。这个假设得到了星形单倍型网络的支持，以及与更耐寒和共存的两种树种，即山毛榉属 Cunninghamii 和 Tasmannia lanceolata 的叶绿体 DNA 替代率相似，它们具有更高的叶绿体多样性。
