Irestedt Martin, Jønsson Knud A, Fjeldså Jon, Christidis Les, Ericson Per G P
Molecular Systematics Laboratory, Swedish Museum of Natural History, PO Box 50007, SE-104 05 Stockholm, Sweden.
BMC Evol Biol. 2009 Sep 16;9:235. doi: 10.1186/1471-2148-9-235.
The birds-of-paradise (Paradisaeidae) form one of the most prominent avian examples of sexual selection and show a complex biogeographical distribution. The family has accordingly been used as a case-study in several significant evolutionary and biogeographical syntheses. As a robust phylogeny of the birds-of-paradise has been lacking, these hypotheses have been tentative and difficult to assess. Here we present a well supported species phylogeny with divergence time estimates of the birds-of-paradise. We use this to assess if the rates of the evolution of sexually selected traits and speciation have been excessively high within the birds-of-paradise, as well as to re-interpret biogeographical patterns in the group.
The phylogenetic results confirm some traditionally recognized relationships but also suggest novel ones. Furthermore, we find that species pairs are geographically more closely linked than previously assumed. The divergence time estimates suggest that speciation within the birds-of-paradise mainly took place during the Miocene and the Pliocene, and that several polygynous and morphologically homogeneous genera are several million years old. Diversification rates further suggest that the speciation rate within birds-of-paradise is comparable to that of the enitre core Corvoidea.
The estimated ages of morphologically homogeneous and polygynous genera within the birds-of-paradise suggest that there is no need to postulate a particularly rapid evolution of sexually selected morphological traits. The calculated divergence rates further suggest that the speciation rate in birds-of-paradise has not been excessively high. Thus the idea that sexual selection could generate high speciation rates and rapid changes in sexual ornamentations is not supported by our birds-of-paradise data. Potentially, hybridization and long generation times in polygynous male birds-of-paradise have constrained morphological diversification and speciation, but external ecological factors on New Guinea may also have allowed the birds-of-paradise to develop and maintain magnificent male plumages. We further propose that the restricted but geographically complex distributions of birds-of-paradise species may be a consequence of the promiscuous breeding system.
极乐鸟科（Paradisaeidae）是性选择最为显著的鸟类范例之一，呈现出复杂的生物地理分布。因此，该科在多个重要的进化和生物地理综合研究中被用作案例分析。由于一直缺乏可靠的极乐鸟系统发育树，这些假说具有一定的试探性且难以评估。在此，我们给出了一个得到充分支持的极乐鸟物种系统发育树以及分歧时间估计。我们用此来评估极乐鸟中性选择特征的进化速率和物种形成速率是否过高，同时重新解读该类群的生物地理模式。
系统发育结果证实了一些传统上认可的关系，但也提出了新的关系。此外，我们发现物种对在地理上的联系比之前认为的更为紧密。分歧时间估计表明，极乐鸟的物种形成主要发生在中新世和上新世，并且几个一夫多妻且形态同质化的属已有数百万年历史。多样化速率进一步表明，极乐鸟的物种形成速率与整个核心鸦总科相当。
极乐鸟中形态同质化和一夫多妻属的估计年龄表明，无需假定性选择形态特征有特别快速的进化。计算出的分歧速率进一步表明，极乐鸟的物种形成速率并非过高。因此，我们关于极乐鸟的数据并不支持性选择会导致高物种形成速率和性装饰快速变化这一观点。可能是一夫多妻的雄性极乐鸟的杂交和较长世代时间限制了形态多样化和物种形成，但新几内亚的外部生态因素也可能促使极乐鸟发展并维持其华丽的雄性羽毛。我们还提出，极乐鸟物种有限但地理分布复杂的情况可能是其混杂繁殖系统的结果。
