Li Pui-Sze, Thomas Daniel C, Saunders Richard M K
School of Biological Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong, China.
, Current address: Singapore Botanic Gardens, 1 Cluny Road, Singapore, 259569, Singapore.
BMC Evol Biol. 2017 Aug 14;17(1):188. doi: 10.1186/s12862-017-1038-4.
The Asimina-Disepalum clade (Annonaceae subfam. Annonoideae tribe Annoneae) includes a major Neotropical-Asian biogeographical disjunction. We evaluate whether this disjunction can be explained by the Eocene boreotropics hypothesis, which relies on the existence of extensive boreotropical forests during the Late Palaeocene-Early Eocene thermal maximum (52-50 Ma), followed by disruption of boreotropical vegetation during post-Eocene cooling. Molecular dating using an uncorrelated relaxed molecular clock (UCLD) model with two fossil calibrations, ancestral range estimation, and ecological niche modelling across evolutionary time were performed. Our focus was the geographical origin of Disepalum and general biogeographic patterns within this genus. Comparison of ecological tolerance among extant species and niche reconstructions at ancestral nodes within the clade enabled insights in likely migration routes of lineages, as well as evaluating the role of bioclimatic ecological differentiation in the diversification of Disepalum within Southeast Asia.
The inferred vicariance event associated with the Asimina-Disepalum disjunction is estimated to have originated ca. 40 Mya [95% highest posterior density (HPD): 44.3-35.5 Mya]. The Disepalum crown lineage is estimated to have originated ca. 9 Mya (95% HPD: 10.6-7.6), either in western Malesia and continental Southeast Asia, or exclusively in western Malesia. Ecological niche modelling shows that seasonality of temperature and precipitation are major contributors determining the geographical range of species. Ancestral niche modelling furthermore indicates that the ancestor of the Asimina-Disepalum clade likely had bioclimatic preferences close to conditions found in current tropical and subtropical climates across Asia, whereas the ancestors of the Asimina and Disepalum crown groups are projected onto the more subtropical and tropical regions, respectively.
The vicariance event associated with the Neotropical-Asian disjunction within the Asimina-Disepalum clade likely coincided with climatic deterioration at the Eocene-Oligocene boundary. Although detrended component analyses (DCA) indicate that altitude and seasonality of temperature and precipitation have the greatest influence in determining the geographical range of species, isolation due to palaeogeographic and palaeoclimatic events appears to be of greater significance than climate niche differentiation in driving diversification in Disepalum.
番荔枝科番荔枝亚科番荔枝族中的北美番荔枝-双瓣番荔枝分支包含一个主要的新热带-亚洲生物地理间断分布。我们评估这种间断分布是否可以用始新世泛北极植物区系假说解释，该假说依赖于古新世晚期-始新世早期热极大期（5200-5000万年前）期间广泛存在的泛北极森林，随后在始新世之后的降温过程中泛北极植被遭到破坏。我们使用具有两个化石校准点的不相关宽松分子钟（UCLD）模型进行分子年代测定、祖先分布区估计，并在进化时间内进行生态位建模。我们关注的是双瓣番荔枝的地理起源以及该属内的一般生物地理模式。比较现存物种之间的生态耐受性以及该分支内祖先节点处的生态位重建，有助于深入了解谱系可能的迁移路线，以及评估生物气候生态分化在东南亚双瓣番荔枝多样化过程中的作用。
与北美番荔枝-双瓣番荔枝间断分布相关的推断的隔离事件估计约在4000万年前发生[95%最高后验密度（HPD）：4430-3550万年前]。双瓣番荔枝的冠群谱系估计约在900万年前起源（95% HPD：1060-760万年前），要么在马来群岛西部和东南亚大陆，要么仅在马来群岛西部。生态位建模表明，温度和降水的季节性是决定物种地理分布范围的主要因素。祖先生态位建模进一步表明，北美番荔枝-双瓣番荔枝分支的祖先可能具有与当前亚洲热带和亚热带气候条件相近的生物气候偏好，而北美番荔枝和双瓣番荔枝冠群的祖先分别分布在更亚热带和热带地区。
与北美番荔枝-双瓣番荔枝分支内新热带-亚洲间断分布相关的隔离事件可能与始新世-渐新世边界的气候恶化同时发生。尽管去趋势成分分析（DCA）表明海拔以及温度和降水的季节性对决定物种地理分布范围的影响最大，但在驱动双瓣番荔枝多样化方面，古地理和古气候事件导致的隔离似乎比气候生态位分化更为重要。
