Genomic evidence for the parallel evolution of coastal forms in the <i>Senecio lautus</i> complex

Roda, Federico; Ambrose, Luke; Walter, Greg M.; Liu, Huanle L.; Schaul, Andrea; Lowe, Andrew J.; Pelser, Pieter B.; Prentis, Peter J.; Rieseberg, Loren H.; Ortiz‐Barrientos, Daniel

doi:10.1111/mec.12311

Cited by 117 publications

(183 citation statements)

References 81 publications

(166 reference statements)

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“…The study of adaptive divergence between ecotypes may, thus, be an important contribution for understanding the process of speciation. Instances of parallel ecotypic divergence where adaptation to similar conditions repeatedly cause similar phenotypic changes in closely related organisms are especially useful for disentangling the respective roles of drift and natural selection in shaping genomic divergence among genomes and for studying the genes underlying local adaptation 7 . The ecological variation found among populations of the autotetraploid Cochlearia officinalis in northern Norway potentially represents a highly valuable system to explore parallel ecotypic differentiation in plants.…”

Section: Introductionmentioning

confidence: 99%

RADseq provides evidence for parallel ecotypic divergence in the autotetraploid Cochlearia officinalis in Northern Norway

Brandrud

Paun

Lorenzo

et al. 2017

Sci Rep

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Speciation encompasses a continuum over time from freely interbreeding populations to reproductively isolated species. Along this process, ecotypes – the result of local adaptation – may be on the road to new species. We investigated whether three autotetraploid Cochlearia officinalis ecotypes, adapted to different habitats (beach, estuary, spring), are genetically differentiated and result from parallel ecotypic divergence in two distinct geographical regions. We obtained genetic data from thousands of single nucleotide polymorphisms (SNPs) from restriction-site associated DNA sequencing (RADseq) and from six microsatellite markers for 12 populations to assess genetic divergence at ecotypic, geographic and population level. The genetic patterns support differentiation among ecotypes as suggested by morphology and ecology. The data fit a scenario where the ancestral beach ecotype has recurrently and polytopically given rise to the estuary and spring ecotypes. Several ecologically-relevant loci with consistent non-random segregating patterns are identified across the recurrent origins, in particular around genes related to salt stress. Despite being ecologically distinct, the Cochlearia ecotypes still represent an early stage in the process of speciation, as reproductive isolation has not (yet) developed. A sequenced annotated genome is needed to specifically target candidate genes underlying local adaptation.

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Section: Introductionmentioning

confidence: 99%

RADseq provides evidence for parallel ecotypic divergence in the autotetraploid Cochlearia officinalis in Northern Norway

Brandrud

Paun

Lorenzo

et al. 2017

Sci Rep

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“…Secondly, it must be considered that the genetic values obtained here may reflect common aspects of the biology of Asteraceae. To determine this, values obtained here were compared to document genetic values for the wide spread Asteraceae Senecio lautus (Roda, et al 2013). FST value for T. retroflexa were significantly higher than those documented for S. lautus.…”

Section: Discussionmentioning

confidence: 99%

Evaluating the rarity and genetic structure of populations of the endangered Australian endemic plant Trioncinia retroflexa (Asteraceae): potential consequences for management and conservation

Haller¹

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Trioncinia retroflexa is an endangered endemic plant species found in the Bluegrass grasslands of central Queensland Australia. The recent degradation and fragmentation of this ecosystem is commonly assumed to have driven this species to become rare and persist only in isolated populations. Despite a lack of empirical evidence supporting this assumption (and equivocal anecdotal evidence), conservation and restoration plans for this species are generally based on it. Using microsatellites, the genetic diversity, structure and differentiation of all known populations of these species were examined to determine if there is evidence for recent isolation of remaining populations. Populations had high genetic differentiation, with little heterozygosity, minimal gene flow and few migrants, reflecting long-term population isolation well beyond the scope of modern fragmentation. High genetic differentiation also suggests that all known populations of this species maintain a similar proportion of the species' total genetic diversity, despite varying extensively in the number of individuals they support. As such, the loss of any population may drastically reduce the species' adaptive potential in the future. In the context of longterm population isolation, seed and germination traits related to species dispersal and establishment were examined among these long isolated populations. Though some significant differences in traits among populations were found, there was not strong evidence of trait divergence. Given the findings of this study, this species has likely persisted in isolated populations for at least the last 158 years (time since identification) and may have been rare prior to this time. A large restoration experiment completed in association with this project failed to establish a new population over a two-year period.The difficulty of establishing new populations of T. retroflexa highlights the lack of information we have about this species' environmental requirements and the importance of maintaining the remaining natural populations of this species.ii

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“…This species complex consists of multiple divergent varieties associated with different environmental conditions . There is evidence within the system of parallel divergence to parapatric coastal environments (Roda et al 2013). There is also evidence of ecologically dependent reproductive isolation in multiple parapatric populations (Chapter 4 -this thesis), and evidence that immigrant inviability is a major contributor to reproductive isolation (Chapter 3 -this thesis).…”

Section: Study Systemmentioning

confidence: 99%

Response to natural selection in Senecio lautus

Richards¹

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Natural selection is the established force driving evolutionary change in populations, however the link between selection and the formation of new species is much less concrete. There is a growing body of evidence that differences in ecological conditions within a species range can lead to adaptive changes in both appearance and underlying genetic background that can lead to the formation of discrete and divergent populations. When these differences accumulate to a degree that prevents genetic exchange, these populations may satisfy many of the categories defining distinct species. In the works described in this thesis, I examine the mechanisms of natural selection driving evolutionary divergence between three adjacent populations of Senecio lautus, a native Australian plant. First, I describe the phenotypic differences that have accumulated between the three populations and use empirical experiments to show that these changes are most likely the result of adaptation to divergent ecological conditions. In the second chapter I examine whether this adaptation to local conditions can influence the rate of gene exchange between populations by quantifying a range of potential ecological and genetic mechanisms that may influence the ability of populations to breed with one another. Results from this experiment suggest that intrinsic genetic differences between populations do not affect gene exchange and that the main barrier to gene flow between populations is associated with different patterns of adaptation preventing immigrant plants from establishing. These findings are consistent with the theories of ecological speciation, where speciation occurs primarily as a result of environmental factors, and I specifically test this hypothesis in chapter IV. The prediction of ecologically dependent hybrid fitness is a unique prediction of ecological speciation, and I use field based reciprocal transplant experiments to determine whether this pattern is observed between S. lautus ecotypes. Together, these chapters provide evidence that natural selection based on ecological variation drives phenotypic divergence between populations, is the major factor preventing gene exchange between populations, and leads to patterns of hybrid fitness that are consistent with the theoretical predictions of ecological speciation.3

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Genomic evidence for the parallel evolution of coastal forms in the Senecio lautus complex

Cited by 117 publications

References 81 publications

RADseq provides evidence for parallel ecotypic divergence in the autotetraploid Cochlearia officinalis in Northern Norway

RADseq provides evidence for parallel ecotypic divergence in the autotetraploid Cochlearia officinalis in Northern Norway

Evaluating the rarity and genetic structure of populations of the endangered Australian endemic plant Trioncinia retroflexa (Asteraceae): potential consequences for management and conservation

Response to natural selection in Senecio lautus

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