Australian Centre for Evolutionary Biology and Biodiversity, The University of Adelaide, Darling Building, Adelaide SA 5005, Australia.
BMC Evol Biol. 2010 Dec 15;10:386. doi: 10.1186/1471-2148-10-386.
Molecular studies have revealed that many putative 'species' are actually complexes of multiple morphologically conservative, but genetically divergent 'cryptic species'. In extreme cases processes such as non-adaptive diversification (speciation without divergent selection) could mask the existence of ancient lineages as divergent as ecologically and morphologically diverse radiations recognised as genera or even families in related groups. The identification of such ancient, but cryptic, lineages has important ramifications for conservation, biogeography and evolutionary biology. Herein, we use an integrated multilocus genetic dataset (allozymes, mtDNA and nuclear DNA) to test whether disjunct populations of the widespread nominal Australian gecko species Crenadactylus ocellatus include distinct evolutionary lineages (species), and to examine the timing of diversification among these populations.
We identify at least 10 deeply divergent lineages within the single recognised species Crenadactylus ocellatus, including a radiation of five endemic to the Kimberley region of north-west Australia, and at least four known from areas of less than 100 km2. Lineages restricted to geographically isolated ranges and semi-arid areas across central and western Australia are estimated to have began to diversify in the late Oligocene/early Miocence (~20-30 mya), concurrent with, or even pre-dating, radiations of many iconic, broadly sympatric and much more species-rich Australian vertebrate families (e.g. venomous snakes, dragon lizards and kangaroos).
Instead of a single species, Crenadactylus is a surprisingly speciose and ancient vertebrate radiation. Based on their deep divergence and no evidence of recent gene flow, we recognise each of the 10 main lineages as candidate species. Molecular dating indicates that the genus includes some of the oldest vertebrate lineages confounded within a single species yet identified by molecular assessments of diversity. Highly divergent allopatric lineages are restricted to putative refugia across arid and semi-arid Australia, and provide important evidence towards understanding the history and spread of the Australian arid zone, suggesting at a minimum that semi-arid conditions were present by the early Miocene, and that severe aridity was widespread by the mid to late Miocene. In addition to documenting a remarkable instance of underestimation of vertebrate species diversity in a developed country, these results suggest that increasing integration of molecular dating techniques into cryptic species delimitation will reveal further instances where taxonomic conservatism has led to profound underestimation of not only species numbers, but also highly significant phylogenetic diversity and evolutionary history.
分子研究表明，许多所谓的“种”实际上是多个形态保守但遗传上有差异的“隐种”复合体。在极端情况下，非适应性多样化（无分歧选择的物种形成）等过程可能会掩盖与相关群中被视为属甚至科的生态和形态上多样化的辐射一样具有分歧的古老谱系的存在。这些古老但隐生的谱系的鉴定对保护、生物地理学和进化生物学具有重要意义。在此，我们使用综合的多点遗传数据集（同工酶、mtDNA 和核 DNA）来检验广泛分布的澳大利亚壁虎种 Crenadactylus ocellatus 的离散种群是否包含独特的进化谱系（种），并研究这些种群之间的多样化时间。
我们在单一识别物种 Crenadactylus ocellatus 中鉴定出至少 10 个深度分歧的谱系，包括分布于澳大利亚西北部金伯利地区的五个特有辐射种，以及至少四个已知的分布范围小于 100 公里的种。估计分布于澳大利亚中部和西部地理隔离范围和半干旱地区的谱系起源于渐新世/中新世晚期（约 20-30 百万年前），与许多标志性、广泛同域和物种更丰富的澳大利亚脊椎动物科（如毒蛇、蜥蜴和袋鼠）的辐射同时发生，甚至早于其辐射。
Crenadactylus 不是一个单一的物种，而是一个令人惊讶的多样化和古老的脊椎动物辐射。基于它们的深度分歧和没有最近基因流的证据，我们将这 10 个主要谱系中的每一个都视为候选种。分子定年表明，该属包括一些在单一物种中识别出的最古老的脊椎动物谱系，但通过对多样性的分子评估确定。高度分歧的异域谱系局限于澳大利亚干旱和半干旱地区的假定避难所，为理解澳大利亚干旱区的历史和传播提供了重要证据，表明至少在中新世早期就存在半干旱条件，并且中到晚中新世期间广泛存在严重干旱。除了记录在一个发达国家中对脊椎动物物种多样性的惊人低估之外，这些结果表明，将分子定年技术越来越多地整合到隐种界限中，将揭示更多由于分类保守性而导致的不仅是物种数量，而且还有高度显著的系统发育多样性和进化历史的深刻低估的实例。
