Rapid ecological specialization despite constant population sizes
- Published
- Accepted
- Subject Areas
- Biogeography, Genetics, Zoology
- Keywords
- convergent evolution, bushbuck, species complex, stable demography, ecological adaptation
- Copyright
- © 2018 Rakotoarivelo et al.
- Licence
- This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ Preprints) and either DOI or URL of the article must be cited.
- Cite this article
- 2018. Rapid ecological specialization despite constant population sizes. PeerJ Preprints 6:e27011v2 https://doi.org/10.7287/peerj.preprints.27011v2
Abstract
Background. The bushbuck, Tragelaphus scriptus, is the most widespread and ecologically diverse ungulate species complex within the spiral-horned antelopes. This species was recently found to consist of two genetically divergent but monophyletic Scriptus and Sylvaticus lineages, which are paraphyletic at mitochondrial (mt)DNA owing to an ancient interspecific hybridization event. The Scriptus lineage inhabits the north-western half of the African continent while Sylvaticus is found in the south-eastern half. Here we test hypotheses of historical demography and adaptation in bushbuck using a higher-resolution framework, with four nuclear (MGF, PRKCI, SPTBN, and THY) and three new mitochondrial markers (cytochrome b, 12S rRNA, and 16S rRNA). Methods. Genealogies were reconstructed for the mitochondrial and nuclear data sets, with the latter dated using fossil calibration points. We also inferred the demographic history of Scriptus and Sylvaticus using coalescent-based methods. To obtain an overview of the origins and ancestral colonisation routes of ancestral bushbuck sequences across geographic space, we conducted a discrete Bayesian phylogeographic analysis on our nuclear DNA data set. Results. Both nDNA and mtDNA support previously findings of two genetically divergent Sylvaticus and Scriptus lineages, with no allele sharing despite coming into secondary contact at several geographic locations. The three mtDNA loci confirmed 15 of the previously defined ecotypes, including those with convergent phenotypes. However, the nuclear tree showed less phylogenetic resolution at the more derived parts of the genealogy, possibly due to incomplete lineage sorting of the slower evolving nuclear genome. The only exception to this was the montane ecotype meneliki (Sylvaticus) of the Ethiopian highlands, which formed a monophyletic group at three of four nDNA loci. We dated the coalescence of the two lineages to a common ancestor ∼2.54 million years ago. Both marker sets revealed similar demographic histories of constant population size over time. We show that the bushbuck likely originated in North-East Africa, with Scriptus colonising suitable habitats towards west of the rift and Sylvaticus diffusing from east of the rift into southern Africa. Discussion. Despite lower levels of genetic structure at nuclear loci, we confirmed the independent evolution of the Menelik’s bushbuck relative to the phenotypically similar montane ecotypes in East Africa, adding further weight to previous suggestions of convergent evolution within the bushbuck complex. Perhaps the most surprising result of our analysis was that both Scriptus and Sylvaticus populations remained relatively constant throughout the Pleistocene, which is remarkable given that this was a period of major climatic and tectonic change in Africa, and responsible for driving the evolution of much of the continents extant large mammal diversity.
Author Comment
This is intended to be final version to be submitted for peer review. The author Paul O’Donoghue has been added. Both Paul O’Donoghue and Michael W. Bruford commented on the manuscript and spotted quite a few errors (eg duplication of values) and typos in the text. The manuscript has been checked and corrected accordingly.