Genetic structure and bio-climatic modeling support allopatric over parapatric speciation along a latitudinal gradient
<p>Abstract</p> <p>Background</p> <p>Four of the five species of <it>Telopea</it> (Proteaceae) are distributed in a latitudinal replacement pattern on the south-eastern Australian mainland. In similar circumstances, a simple allopatric speciation model that...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
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BMC
2012-08-01
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| Series: | BMC Evolutionary Biology |
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| Online Access: | http://www.biomedcentral.com/1471-2148/12/149 |
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| author | Rossetto Maurizio Allen Chris B Thurlby Katie AG Weston Peter H Milner Melita L |
| author_facet | Rossetto Maurizio Allen Chris B Thurlby Katie AG Weston Peter H Milner Melita L |
| author_sort | Rossetto Maurizio |
| collection | DOAJ |
| description | <p>Abstract</p> <p>Background</p> <p>Four of the five species of <it>Telopea</it> (Proteaceae) are distributed in a latitudinal replacement pattern on the south-eastern Australian mainland. In similar circumstances, a simple allopatric speciation model that identifies the origins of genetic isolation within temporal geographic separation is considered as the default model. However, secondary contact between differentiated lineages can result in similar distributional patterns to those arising from a process of parapatric speciation (where gene flow between lineages remains uninterrupted during differentiation). Our aim was to use the characteristic distributional patterns in <it>Telopea</it> to test whether it reflected the evolutionary models of allopatric or parapatric speciation. Using a combination of genetic evidence and environmental niche modelling, we focused on three main questions: do currently described geographic borders coincide with genetic and environmental boundaries; are there hybrid zones in areas of secondary contact between closely related species; did species distributions contract during the last glacial maximum resulting in distributional gaps even where overlap and hybridisation currently occur?</p> <p>Results</p> <p>Total genomic DNA was extracted from 619 individuals sampled from 36 populations representing the four species. Seven nuclear microsatellites (nSSR) and six chloroplast microsatellites (cpSSR) were amplified across all populations. Genetic structure and the signature of admixture in overlap zones was described using the Bayesian clustering methods implemented in STUCTURE and NewHybrids respectively. Relationships between chlorotypes were reconstructed as a median-joining network. Environmental niche models were produced for all species using environmental parameters from both the present day and the last glacial maximum (LGM).</p> <p>The nSSR loci amplified a total of 154 alleles, while data for the cpSSR loci produced a network of six chlorotypes. STRUCTURE revealed an optimum number of five clusters corresponding to the four recognised species with the additional division of <it>T. speciosissima</it> into populations north and south of the Shoalhaven River valley. Unexpectedly, the northern disjunct population of <it>T. oreades</it> grouped with <it>T. mongaensis</it> and was identified as a hybrid swarm by the Bayesian assignment test implemented in NewHybrids. Present day and LGM environmental niche models differed dramatically, suggesting that distributions of all species had repeatedly expanded and contracted in response to Pleistocene climatic oscillations and confirming strongly marked historical distributional gaps among taxes.</p> <p>Conclusions</p> <p>Genetic structure and bio-climatic modeling results are more consistent with a history of allopatric speciation followed by repeated episodes of secondary contact and localised hybridisation, rather than with parapatric speciation. This study on <it>Telopea</it> shows that the evidence for temporal exclusion of gene flow can be found even outside obvious geographical contexts, and that it is possible to make significant progress towards excluding parapatric speciation as a contributing evolutionary process.</p> |
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| spelling | doaj.art-37fdc05845d041239cd6aced8bfde00e2022-12-21T21:04:15ZengBMCBMC Evolutionary Biology1471-21482012-08-0112114910.1186/1471-2148-12-149Genetic structure and bio-climatic modeling support allopatric over parapatric speciation along a latitudinal gradientRossetto MaurizioAllen Chris BThurlby Katie AGWeston Peter HMilner Melita L<p>Abstract</p> <p>Background</p> <p>Four of the five species of <it>Telopea</it> (Proteaceae) are distributed in a latitudinal replacement pattern on the south-eastern Australian mainland. In similar circumstances, a simple allopatric speciation model that identifies the origins of genetic isolation within temporal geographic separation is considered as the default model. However, secondary contact between differentiated lineages can result in similar distributional patterns to those arising from a process of parapatric speciation (where gene flow between lineages remains uninterrupted during differentiation). Our aim was to use the characteristic distributional patterns in <it>Telopea</it> to test whether it reflected the evolutionary models of allopatric or parapatric speciation. Using a combination of genetic evidence and environmental niche modelling, we focused on three main questions: do currently described geographic borders coincide with genetic and environmental boundaries; are there hybrid zones in areas of secondary contact between closely related species; did species distributions contract during the last glacial maximum resulting in distributional gaps even where overlap and hybridisation currently occur?</p> <p>Results</p> <p>Total genomic DNA was extracted from 619 individuals sampled from 36 populations representing the four species. Seven nuclear microsatellites (nSSR) and six chloroplast microsatellites (cpSSR) were amplified across all populations. Genetic structure and the signature of admixture in overlap zones was described using the Bayesian clustering methods implemented in STUCTURE and NewHybrids respectively. Relationships between chlorotypes were reconstructed as a median-joining network. Environmental niche models were produced for all species using environmental parameters from both the present day and the last glacial maximum (LGM).</p> <p>The nSSR loci amplified a total of 154 alleles, while data for the cpSSR loci produced a network of six chlorotypes. STRUCTURE revealed an optimum number of five clusters corresponding to the four recognised species with the additional division of <it>T. speciosissima</it> into populations north and south of the Shoalhaven River valley. Unexpectedly, the northern disjunct population of <it>T. oreades</it> grouped with <it>T. mongaensis</it> and was identified as a hybrid swarm by the Bayesian assignment test implemented in NewHybrids. Present day and LGM environmental niche models differed dramatically, suggesting that distributions of all species had repeatedly expanded and contracted in response to Pleistocene climatic oscillations and confirming strongly marked historical distributional gaps among taxes.</p> <p>Conclusions</p> <p>Genetic structure and bio-climatic modeling results are more consistent with a history of allopatric speciation followed by repeated episodes of secondary contact and localised hybridisation, rather than with parapatric speciation. This study on <it>Telopea</it> shows that the evidence for temporal exclusion of gene flow can be found even outside obvious geographical contexts, and that it is possible to make significant progress towards excluding parapatric speciation as a contributing evolutionary process.</p>http://www.biomedcentral.com/1471-2148/12/149AllopatryEnvironmental niche modelsParapatrySecondary hybridisationSpeciationProteaceae<it>Telopea</it>waratah |
| spellingShingle | Rossetto Maurizio Allen Chris B Thurlby Katie AG Weston Peter H Milner Melita L Genetic structure and bio-climatic modeling support allopatric over parapatric speciation along a latitudinal gradient BMC Evolutionary Biology Allopatry Environmental niche models Parapatry Secondary hybridisation Speciation Proteaceae <it>Telopea</it> waratah |
| title | Genetic structure and bio-climatic modeling support allopatric over parapatric speciation along a latitudinal gradient |
| title_full | Genetic structure and bio-climatic modeling support allopatric over parapatric speciation along a latitudinal gradient |
| title_fullStr | Genetic structure and bio-climatic modeling support allopatric over parapatric speciation along a latitudinal gradient |
| title_full_unstemmed | Genetic structure and bio-climatic modeling support allopatric over parapatric speciation along a latitudinal gradient |
| title_short | Genetic structure and bio-climatic modeling support allopatric over parapatric speciation along a latitudinal gradient |
| title_sort | genetic structure and bio climatic modeling support allopatric over parapatric speciation along a latitudinal gradient |
| topic | Allopatry Environmental niche models Parapatry Secondary hybridisation Speciation Proteaceae <it>Telopea</it> waratah |
| url | http://www.biomedcentral.com/1471-2148/12/149 |
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