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- den Tex, Robert-Jan, et al.
(författare)
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A molecular phylogeny of Asian barbets : Speciation and extinction in the tropics
- 2013
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Ingår i: Molecular Phylogenetics and Evolution. - : Elsevier BV. - 1055-7903 .- 1095-9513. ; 68:1, s. 1-13
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Tidskriftsartikel (refereegranskat)abstract
- We reconstruct the phylogeny of all recognized species of the tropical forest associated Asian barbets based on mitochondrial and nuclear sequence data and test for the monophyly of species and genera. Tropical regions are well known for their extraordinarily high levels of biodiversity, but we still have a poor understanding of how this richness was generated and maintained through evolutionary time. Multiple theoretical frameworks have been developed to explain this diversity, including the Pleistocene pump hypothesis and the museum hypothesis. We use our phylogeny of the Asian barbets to test these hypotheses. Our data do not find an increase in speciation in the Pleistocene as predicted by the Pleistocene pump hypothesis. We do find evidence of extinctions, which apparently contradicts the museum hypothesis. However, the extinctions are only in a part of the phylogeny that is distributed mainly across Sundaland (the Malay peninsula and the islands off southeast Asia). The theory of island biogeography predicts a higher rate of extinction on islands than on mainland areas. The data from the part of the phylogeny primarily distributed on the mainland best fit a pure birth model of speciation, and thus supports the museum hypothesis.
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| 2. |
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| 3. |
- den Tex, Robert-Jan, et al.
(författare)
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Nuclear copies of mitochondrial genes : another problem for ancient DNA
- 2010
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Ingår i: Genetica. - : Springer Science and Business Media LLC. - 0016-6707 .- 1573-6857. ; 138:9-10, s. 979-984
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Tidskriftsartikel (refereegranskat)abstract
- The application of ancient DNA techniques is subject to many problems caused primarily by low quality and by low quantity of DNA. For these reasons most studies employing ancient DNA rely on the characterization of mitochondrial DNA, which is present in many more copies per cell than nuclear DNA and hence more copies are likely to survive. We used universal and taxon specific mitochondrial primers to amplify DNA from museum specimens, and found many instances where the amplification of nuclear copies of the mitochondrial gene (numts) instead of the targeted mitochondrial fragment had occurred. Furthermore, the likelihood of amplifying numts increased dramatically when universal primers were utilized. Here we suggest that ancient DNA practitioners must consider the possibility that numts can be amplified at higher rates than previously thought. This is another complication for ancient DNA studies, but it also suggests that more extensive inclusion of nuclear markers in ancient DNA studies should be feasible.
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| 4. |
- den Tex, Robert-Jan, 1969-
(författare)
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Patterns and Processes of Evolution in Sundaland
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Biodiversity in the tropics is disproportionately high compared to other habitats, and also under disproportionate threat from human impact. It is necessary to understand how this diversity evolved and how it is partitioned across space in order to preserve it. In this thesis I construct phylogenies of tropical forest dependent vertebrates from Southeast Asia and the islands of the Sunda shelf, a region referred to as Sundaland. I focus on the tree squirrels (genus Sundasciurus) and Asian barbets (Aves: Family Megalaimidae), two taxa with similar ecological characteristics. I use these phylogenies to test hypotheses that have been put forward to explain high levels of tropical diversity including the Pleistocene pump and museum hypotheses. I also use phylogenies to elucidate phylogeographic patterns within the region. I find no evidence for an increase in speciation in the Pleistocene, but I do find within species structure that dates to this period. Common phylogeographic patterns were identified between many forest dependent vertebrates that suggest that populations on the island of Sumatra are generally more closely related to Malay Peninsula populations than to populations on Borneo. From a methodological viewpoint we propose careful usage of universal primers in ancient DNA studies because of our finding of increased risk of amplifying pseudogenes of the mtDNA.
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| 5. |
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| 7. |
- den Tex, Robert-Jan, et al.
(författare)
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Speciation dynamics in the SE Asian tropics : Putting a time perspective on the phylogeny and biogeography of Sundaland tree squirrels, Sundasciurus
- 2010
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Ingår i: Molecular Phylogenetics and Evolution. - : Elsevier BV. - 1055-7903 .- 1095-9513. ; 55:2, s. 711-720
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Tidskriftsartikel (refereegranskat)abstract
- Tropical rainforests are well known for their extraordinarily high levels of biodiversity. The origin of this species richness is still debated. For instance, the museum hypothesis states that over evolutionary time more and more species will accumulate with relatively few extinctions. In contrast, the Pleistocene diversification model argues that during the last 2 million years, climatic factors (glaciations) caused environmental changes that drove isolation and vicariant speciation events. In this study, we construct a molecular phylogeny of the Sundaland (Malay Peninsula, Sumata, Borneo, Palawan) and Greater Mindanao (Mindanao, Samar, Leyte) tree squirrels (genus Sundasciurus). Our results show that most speciation events in this forest dependent taxon occurred before the Pleistocene and that even the timing of intra-specific splits among populations from different landmasses are relatively old. Additionally, we found unexpectedly high divergence within and between highland populations of S. tenuis on Sumatra and the Malay Peninsula, highlighting the importance of Pliocene events in both speciation and within species divergences in this region. (C) 2010 Elsevier Inc. All rights reserved.
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| 8. |
- Leonard, Jennifer A., et al.
(författare)
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Phylogeography of vertebrates on the Sunda Shelf : a multi-species comparison
- 2015
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Ingår i: Journal of Biogeography. - : Wiley. - 0305-0270 .- 1365-2699. ; 42:5, s. 871-879
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Tidskriftsartikel (refereegranskat)abstract
- Aim Pleistocene environmental fluctuations had well-characterized impacts on the patterns of within-species divergences and diversity in temperate habitats. Here we examine the impact the Pleistocene had on widely distributed forest vertebrates in a tropical system where the distribution of the habitat was affected by those fluctuations. LocationSundaland, tropical Southeast Asia. Methods We conducted a comparative phylogeographical analysis of 28 non-migratory, forest-dependent vertebrates, for which we constructed rooted, intraspecifc phylogenies based on mitochondrial DNA sequences of individuals from at least the three major landmasses in the area (Borneo, Sumatra and the Malay Peninsula) and compared them to hypothetical phylogenies based on independent geological data and climate models regarding connections and relationships between the major landmasses of Sundaland. Java was included where possible. We dated the phylogenies to determine whether patterns of differentiation were concordant across species. Results In most species, populations on the Malay Peninsula and Sumatra were most closely related, and sister to those from Borneo. The dates of these divergences, however, varied extensively between species. Borneo harbours multiple deeply divergent lineages of many species compared to the diversity within those species. Javan populations of several birds were most divergent relative to those from the rest of the Sunda Shelf. Main conclusions These results suggest a dynamic history, including recurrent population extinctions and replacements and a strong priority effect for local populations. The close relationship between populations in Sumatra and the Malay Peninsula supports the existence of forest on the exposed shelf during the Pleistocene at many different times, and suggests that proximity was more important than the presence of palaeorivers for dispersal of forest taxa between landmasses.
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| 9. |
- Postma, Erik, et al.
(författare)
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Neutral markers mirror small-scale quantitative genetic differentiation in an avian island population
- 2009
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Ingår i: Biological Journal of the Linnean Society. - 0024-4066 .- 1095-8312. ; 97:4, s. 867-875
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Tidskriftsartikel (refereegranskat)abstract
- We still know remarkably little about the extent to which neutral markers can provide a biologically relevant description of population structure. In the present study, we address this question, and quantify microsatellite differentiation among a small, structured island population of great tits (Parus major), and a large mainland population 150 km away. Although only a few kilometres apart, we found small but statistically significant levels of differentiation between the eastern and the western part of the island. On the other hand, there was no differentiation between the western part of the island and the mainland population, whereas the eastern part and the mainland did differ significantly. This initially counterintuitive result provides powerful support for the hypothesis that the large genetic difference in clutch size between both parts of the island found earlier is maintained by different levels of gene flow into both parts of the island, and illustrates the capacity of microsatellites to provide a meaningful description of population structure. Importantly, because the level of microsatellite differentiation is very low, we were unable to infer any population structure without grouping individuals a priori. Hence, these low levels of differentiation in neutral markers could easily remain undetected, or incorrectly be dismissed as biologically irrelevant. Thus, although microsatellites can provide a powerful tool to study genetic structure in wild populations, they should be used in conjunction with a range of other sources of information, rather than as a replacement. (C) 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97, 867-875.
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