Abstract
Geographic
isolation of sister taxa in the African and Asian tropics
(palaeotropical intercontinental disjunction; PID) is a major
biogeographic pattern explained by four competing hypotheses: rafting on
the Indian tectonic plate (‘Gondwanan vicariance hypothesis’);
migration facilitated by a northern mid-latitude corridor of frost-free
climates during the Eocene (‘boreotropical migration hypothesis’);
overland dispersal across Arabia associated with the Miocene Climatic
Optimum; and transoceanic dispersal. The explanatory challenges posed by
PIDs are addressed here using the pantropical flowering plant family
Annonaceae as a study system. Molecular dating and ancestral area
reconstructions were undertaken using plastid DNA sequence data (ca.
6 kb) derived from an extensive taxon sampling, incorporating ca. 75% of
all genera, with phylogenetically informed sampling of species within
genera that are distributed across the African and Asian tropics.
Statistical dispersal-vicariance analysis and likelihood reconstructions
indicated 12 intercontinental dispersal events between Africa and Asia.
All but one of these dispersals were from Africa to Asia. Between 10
and 12 vicariance events were inferred, ranging from the late Palaeocene
to the late Miocene, with mean divergence times of seven events in the
Miocene. Although migration through the Eocene boreotropics has
previously been highlighted as the predominant process underlying
intercontinental disjunctions in Annonaceae, our results indicate that
post-boreotropical processes have also had a major impact on shaping
PIDs. Palaeogeographic reconstructions and the fossil record from the
Arabian Peninsula support the plausibility of a hypothesized window of
overland dispersal opportunity for lowland tropical forest taxa prior to
climate deterioration commencing in the late Middle Miocene, providing
an alternative to transoceanic dispersal. The patterns observed
underscore the hypothesis that intercontinental floristic exchange,
facilitated by both the Eocene boreotropics and the erosion of oceanic
and climatic biogeographic barriers between Africa and Asia in the
Miocene, had a substantial impact on the assembly of palaeotropical
forest floras.
Keywords
- Boreotropics;
- Geodispersal;
- Gondwanan vicariance;
- Molecular dating;
- Palaeotropics;
- Tropical intercontinental disjunction
Copyright © 2014 Geobotanisches Institut ETH, Stiftung Ruebel. Published by Elsevier GmbH All rights reserved.
