Ecological speciation in palms on an oceanic island

物种多样性的起源已经挑战了生物学家两个多世纪。查尔斯达尔文认识到，异地分布，即地理隔离导致的物种分化，是物种形成的驱动力，但他也认为，在没有地理隔离的情况下，种群可以分化成不同的物种，这种机制现在被称为同域物种形成。在过去的十年中，数学模型表明同域物种形成在理论上是可能的，但在自然界中记录的例子非常少。今年早些时候，Savolainen和他的同事们（也是这项提议的申请人）在一项关于两种棕榈树的案例研究中，为同域物种形成提供了完整的证据。belmoreana，偏远的豪勋爵岛（LHI）特有（“海洋岛屿上棕榈树的同域物种形成”，自然441：210-213，2006）。在这里，我们建议把我们的研究带到更深的层次。我们的目标是记录的基因组结构和遗传基础的物种分歧在我们的案例研究的棕榈树，从而带来了新类型的数据来测试的替代品，以分歧同域和解开生态物种形成的机制，必须在这个独特的LHI系统。LHI是一个亚热带小岛，面积不到12平方公里，距离澳大利亚东海岸580公里。它的植物群包括241种维管植物，其中105种是特有的。地理隔离在LHI上实际上是不可能的，因此它是测试同域物种形成的四个标准的理想场所：1）物种同域，2）姐妹关系，3）生殖隔离，以及4）早期的异域阶段是极不可能的。许多植物属，如棕榈树，在岛上有一个以上的特有物种，这很可能是同域物种形成的产物。在我们以前的实验中的Howea棕榈，我们发现，物种分歧的遗传特征表明，只有四个位点的差异更强烈的两个物种之间比预期的中性和这些是最有可能被链接到基因的分歧选择在同域物种形成。为了在这个独特的岛屿系统中研究Howea生态物种形成的基因组和遗传结构，我们将开展六项活动：a）使用更全面的AFLP基因组扫描，在Howea中鉴定最趋异的标记基因座，从而鉴定可能处于选择下的基因组区域B）使用这些趋异的基因座作为BAC文库上的探针，肯蒂亚棕榈基因组中可能含有与物种分化有关的基因的部分（测试Gavrilets关于只有少数基因座参与Howea物种形成的预测）c）使用肯蒂亚棕榈的BAC序列作为模板，鉴定卷曲棕榈基因组中的同源序列和开放阅读框（ORF），d）确定趋异基因组区段在两种棕榈物种的基因组中是集中还是广泛分布（测试Felsenstein的经典预测物种形成是由低重组促进）。e）使用聚结模型和多位点，评估基因流是否被中断/并估计中断的程度/在Howea物种分化期间。f）与油棕EST文库相比，提供在选择下发现的任何ORF的可能功能。

The origin of species diversity has challenged biologists for over two centuries. Charles Darwin recognised that allopatry, species divergence resulting from geographical isolation, is a driving force in speciation, but he also thought that populations could diverge into separate species in the absence of geographical isolation, a mechanism now called sympatric speciation. During the last decade, mathematical models have shown that sympatric speciation is theoretically possible, but extremely few examples have been documented in nature. Early this year, Savolainen and colleagues (some of the applicants of this proposal) provided complete evidence for sympatric speciation in a case study of two species of palm, Howea forsteriana and H. belmoreana, endemic of the remote Lord Howe Island (LHI) ('sympatric speciation in palms on an oceanic island', Nature 441: 210-213, 2006). Here we propose to take our research to a much deeper level. Our goal is to document the genomic architecture and genetic basis for species divergence in our case study of palms, thus bringing new types of data to test alternatives to divergence in sympatry and disentangle the mechanisms of ecological speciation that must have operated in this unique LHI system. LHI is a minute subtropical island of less than 12 km2, situated 580 km off the eastern coast of Australia. Its flora comprises 241 vascular plant species of which 105 are endemic. Geographic isolation is not realistically possible on LHI and thus it is an ideal site on which to test the four criteria for sympatric speciation: 1) species sympatry, 2) sister relationships, 3) reproductive isolation, and 4) that an earlier allopatric phase is highly unlikely. Numerous plant genera, like the palms Howea, are represented by more than one endemic species on the island, which may well be products of sympatric speciation. In our previous experiments of the Howea palms, we found that the genetic signature of species divergence indicated that only four loci differ more strongly between the two species than expected under neutrality and these are those most likely to be linked to genes subject to divergent selection during sympatric speciation. To characterise the genomic and genetic architecture underlying the ecological speciation of Howea in this unique island system, we will conduct six activities: a) Using a more comprehensive AFLP genome scan, identify in Howea the most divergent marker loci and so regions of the genome that may be under selection b) Using these divergent loci as probes on a BAC library, characterise portions of the kentia palm's genome that may contain genes involved in species divergence (testing Gavrilets' prediction of only a few loci being involved in speciation in Howea) c) Using the BACs sequences of the kentia palm as template, identify in the curly palm's genome homologous sequences and open reading frames (ORFs), which may contain the signature of positive selection d) Determine whether the divergent genomic segments are concentrated versus widely distributed in the genomes of the two palm species (testing Felsenstein's classic prediction of speciation being facilitated by low recombination). e) Using coalescence models and multiple loci, evaluate whether gene flow has been interrupted / and estimate the extent of disruption / during species divergence in Howea. f) In comparison with an EST library for the oil palm, provide possible functions for any ORFs found under selection.