How the temperate world was colonised by bindweeds: biogeography of the Convolvuleae (Convolvulaceae).

Thomas C Mitchell,David J Harris,Robert W Scotland,John R I Wood,Bethany R M Williams,Mark A Carine

doi:10.1186/s12862-016-0591-6

Abstract

BackgroundAt a global scale, the temperate zone is highly fragmented both between and within hemispheres. This paper aims to investigate how the world’s disjunct temperate zones have been colonised by the pan-temperate plant group Convolvuleae, sampling 148 of the c. 225 known species. We specifically determine the number and timing of amphitropical and transoceanic disjunctions, investigate the extent to which disjunctions in Convolvuleae are spatio-temporally congruent with those in other temperate plant groups and determine the impact of long-distance dispersal events on diversification rates.ResultsEight major disjunctions are observed in Convolvuleae: two Northern Hemisphere, two Southern Hemisphere and four amphitropical. Diversity in the Southern Hemisphere is largely the result of a single colonisation of Africa 3.1–6.4 Ma, and subsequent dispersals from Africa to both Australasia and South America. Speciation rates within this monophyletic, largely Southern Hemisphere group (1.38 species Myr−1) are found to be over twice those of the tribe as a whole (0.64 species Myr-1). Increased speciation rates are also observed in Calystegia (1.65 species Myr−1).ConclusionsThe Convolvuleae has colonised every continent of the world with a temperate biome in c. 18 Myr and eight major range disjunctions underlie this broad distribution. In keeping with other temperate lineages exhibiting disjunct distributions, long-distance dispersal is inferred as the main process explaining the patterns observed although for one American-Eurasian disjunction we cannot exclude vicariance. The colonisation of the temperate zones of the three southern continents within the last c. 4 Myr is likely to have stimulated high rates of diversification recovered in this group, with lineage accumulation rates comparable to those reported for adaptive radiations.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0591-6) contains supplementary material, which is available to authorized users.

Highlights

At a global scale, the temperate zone is highly fragmented both between and within hemispheres
One of the patterns documented by Thorne [9] was the ‘North–South Temperate disjunction’ which describes groups that are widespread in the northern temperate region and that occur in one or more of the southern temperate zones
Escudero et al [22] invoked longdistance dispersal (LDD) to explain this disjunction the timing is coincident with the mid-Miocene Climatic Optimum 15–17 Ma, which saw the expansion of tropical forests, an event that is thought to have facilitated the dispersal of tropical plant and animal groups between Africa and Asia [24]

Summary

Introduction

The temperate zone is highly fragmented both between and within hemispheres. One of the patterns documented by Thorne [9] was the ‘North–South Temperate disjunction’ which describes groups that are widespread in the northern temperate region and that occur in one or more of the southern temperate zones (i.e., those located in South America, Africa and Australasia). The Convolvuleae comprises three genera namely Convolvulus L., Calystegia R.Br. and Polymeria R.Br. Convolvulus is the largest, comprising 190 species [14]. Convolvulus is the largest, comprising 190 species [14] It has a main centre of diversity in the Mediterranean and western Asia, with further centres of diversity in eastern Asia and in temperate South America, southern and eastern Africa and Australasia; i.e., the three temperate zones of the southern hemisphere. Molecular analyses place it as sister group to the remainder of Convolvuleae [13, 15, 16]

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