Out of Africa: Linked continents, overland migration and differential survival explain abundance of Proteaceae in Australia

Abstract

The centres of diversification of the iconic family Proteaceae are in South Africa and southern Australia. Since the ancestors of the family can be traced to NW Africa our task was to explain how all subfamilies (Proteoideae, Grevilleoideae, Persoonioideae) managed to reach Australia and we propose the pathway: (Africa (N South America (S South America (Antarctica (Australia))))). Our dated molecular phylogeny shows that the family arose 132 million years ago (Ma), and by 125 Ma had separated into the three subfamilies that remain dominant today. The age and location of records for 420 fossil pollen with Proteaceae affinities were collated per continent and submitted to curve-fitting analysis. This showed spread of early Proteaceae into N South America from ∼121 Ma that was able to continue for another 20–25 My. These three subfamilies (plus Carnarvonia) travelled south through South America and Antarctica, crossing the Weddellian Isthmus from ∼110 Ma, to reach southern Australia by ∼104 Ma. The history of Proteaceae in South America mimics that of Africa, where Grevilleoideae diversified instead of Proteoideae that died out. Entry to Australia via Antarctica was possible until ∼70 Ma at its SW corner and 45 Ma at its SE (Tasmanian) corner enabling the three subfamilies (and Carnarvonia) restricted entry into Australia over 35–60 million years. The SW Australian sclerophyll flora became the centre of diversification and emigration at the species level of all but the rainforest (mesophyll) Grevilleoid/Proteoid clades within Australia. Close genetic links between clades in South Africa (the centre of diversification of the sclerophyll flora in Africa) and SW Australia are the product of disparate migratory histories from their common ancestor in NW Africa, differential survival among subfamilies and parallel evolution in matched environments. SE Australia became the centre of diversification at the subtribe level. Close genetic links between clades in South America and SE Australia are the product of long-distance dispersal from their common ancestor in N South America, genetic stability in matched environments and eventual vicariance.