Ecology Section, School of Molecular and Life Sciences, Curtin University, Perth, WA 6845, Australia.
College of Science, Health, Engineering and Education, Murdoch University, Murdoch, WA, Australia.
Ann Bot. 2024 May 10;133(5-6):649-658. doi: 10.1093/aob/mcad055.
The prevailing view from the areocladogenesis of molecular phylogenies is that the iconic South African Cape Proteaceae (subfamily Proteoideae) arrived from Australia across the Indian Ocean during the Late Cretaceous (100-65 million years ago, Ma). Since fossil pollen indicates that the family probably arose in North-West Africa during the Early Cretaceous, an alternative view is that it migrated to the Cape from North-West-Central Africa. The plan therefore was to collate fossil pollen records throughout Africa to determine if they are consistent with an African (para-autochthonous) origin for the Cape Proteaceae, and to seek further support from other palaeo-disciplines.
We used palynology (identity, date and location of records), molecular phylogeny and chronogram preparation, biogeography of plate tectonics, and palaeo-atmospheric and ocean circulation models.
Our collation of the rich assemblage of Proteaceae palynomorphs stretching back to 107 Ma (Triorites africaensis) in North-West Africa showed its progressive overland migration to the Cape by 75-65 Ma. No key palynomorphs recorded in Australia-Antarctica have morphological affinities with African fossils but specific clade assignment of the pre-Miocene records is not currently possible. The Cape Proteaceae encompass three molecular-based clades (tribes) whose most recent apparent ancestors are sisters to those in Australia. However, our chronogram shows that the major Adenanthos/Leucadendron-related clade, originating 54-34 Ma, would have 'arrived' too late as species with Proteaceae affinities were already present ~20 million years earlier. The Franklandia/Protea-related clade arose 118-81 Ma so its distinctive pollen should have been the foundation for the scores of palynomorphs recorded at 100-80 Ma, but it was not. Also, the prevailing winds and ocean currents trended away from South Africa rather than towards, as the 'out-of-Australia' hypothesis requires. Based on the evidence assembled here, we list three points favouring an Australian origin and nine against; four points favouring an Antarctic origin and seven against; and nine points favouring a North-West-Central African origin and three against.
We conclude that a gradual migration of the Proteaceae from North-West-Central Africa southeast→south→southwest to the Cape and its surroundings occurred via adaptation and speciation during the period 95-70 Ma. We caution that incorrect conclusions may be drawn from literal interpretations of molecular phylogenies that neglect the fossil record and do not recognize the possible confounding effects of selection under matched environments leading to parallel evolution and extinction of bona fide sister clades.
从分子系统发生学的观点来看，南非开普半岛的标志性的山龙眼科（Proteoideae 亚科）是在白垩纪晚期（1 亿至 6500 万年前）从澳大利亚穿越印度洋到达这里的。由于化石花粉表明该科可能在早白垩世起源于西北非，因此另一种观点认为它是从西北中非迁徙到开普半岛的。因此，我们计划整理整个非洲的化石花粉记录，以确定它们是否与山龙眼科起源于非洲（准原地）的观点一致，并从其他古生物学领域寻求进一步的支持。
我们使用孢粉学（记录的身份、日期和地点）、分子系统发生和时间序列准备、板块构造的生物地理学、古大气和海洋环流模型。
我们对西北非早至 1.07 亿年前（三叶木贼属 Africaensis）的山龙眼科孢粉化石进行了整理，结果表明，该科在 7500 万至 6500 万年前逐渐从陆地迁移到开普半岛。在澳大利亚-南极洲没有记录到与非洲化石有形态相似的关键孢粉，但目前还不能对早于上新世的记录进行特定的分支分配。山龙眼科包含三个基于分子的分支（部落），其最近的明显祖先与澳大利亚的姐妹分支相同。然而，我们的时间序列显示，主要的 Adenanthos/Leucadendron 相关分支起源于 54-34 百万年前，它出现得太晚了，因为与山龙眼科有亲缘关系的物种早在 2000 万年前就已经存在了。Franklandia/Protea 相关分支起源于 1.18 亿至 8100 万年前，因此它特有的花粉应该是 1 亿至 8000 万年前记录的数十种孢粉的基础，但实际上并非如此。此外，盛行风和海流的趋势是远离南非，而不是朝向南非，这与“来自澳大利亚”的假说相悖。基于这里收集的证据，我们列出了三个支持澳大利亚起源的观点和九个反对的观点；四个支持南极起源的观点和七个反对的观点；九个支持西北中非起源的观点和三个反对的观点。
我们得出结论，山龙眼科是通过适应和物种形成，从西北中非向东南→南→西南方向逐渐迁移到开普半岛及其周围地区的，这一过程发生在 9500 万至 7000 万年前。我们警告说，从分子系统发生学的字面解释中可能得出错误的结论，这些解释忽视了化石记录，并且没有认识到在匹配环境下选择可能产生的混淆影响，这会导致真正的姐妹分支平行进化和灭绝。
