Metherell, C. | Search bioRxiv

bioRxiv2018

Life history evolution and phenotypic plasticity in parasitic eyebrights (Euphrasia, Orobanchaceae)

Premise of the studyParasite lifetime reproductive success is determined by both genetic variation and phenotypically plastic life history traits that respond to host quality and external environment. Here, we use the generalist parasitic plant genus Euphrasia to investigate life history trait variation, in particular whether there is a trade-off between growth and reproduction, and how life history traits are affected by host quality.\n\nMethodsWe perform a common garden experiment to evaluate life history trait differences between eleven Euphrasia taxa grown on a common host, document phenotypic plasticity when a single Euphrasia species is grown on eight different hosts, and relate our observations to trait differences recorded in the wild.\n\nKey resultsEuphrasia exhibit a range of life history strategies that differ between species that transition rapidly to flower at the expense of early season growth, and those that invest in vegetative growth and delay flowering. Many life history traits show extensive phenotypic plasticity in response to host quality and demonstrate the costs of attaching to a low-quality host.\n\nConclusionsCommon garden experiments reveal trait differences between taxonomically complex Euphrasia species that are characterised by postglacial speciation and hybridisation. Our experiments suggest life history strategies in this generalist parasitic plant genus are the product of natural selection on traits related to growth and flowering. However, host quality may be a primary determinant of lifetime reproductive success.

evolutionary biology↗

bioRxiv2017

DNA barcoding British Euphrasia reveals deeply divergent polyploids but lack of species-level resolution

Background and aimsDNA barcoding is emerging as a useful tool not only for species identification but for studying evolutionary and ecological processes. Although plant DNA barcodes do not always provide species-level resolution, the generation of large DNA barcode datasets can provide insights into the mechanisms underlying the generation of species diversity. Here, we use DNA barcoding to study evolutionary processes in taxonomically complex British Euphrasia, a group with multiple ploidy levels, frequent self- fertilization, young species divergence and widespread hybridisation.\n\nMethodsWe sequenced the core plant barcoding loci, supplemented with additional nuclear and plastid loci, in representatives of all 19 British Euphrasia species. We analyse these data in a population genetic and phylogenetic framework. We then date the divergence of haplotypes in a global Euphrasia dataset using a time-calibrated Bayesian approach implemented in BEAST.\n\nKey resultsNo Euphrasia species has a consistent diagnostic haplotype. Instead, haplotypes are either widespread across species, or are population specific. Nuclear genetic variation is strongly partitioned by ploidy levels, with diploid and tetraploid British Euphrasia possessing deeply divergent ITS haplotypes (DXY = 5.1%), with haplotype divergence corresponding to the late Miocene. In contrast, plastid data show no clear division by ploidy, and instead reveal weakly supported geographic patterns.\n\nConclusionsUsing standard DNA barcoding loci for species identification in Euphrasia will be unsuccessful. However, these loci provide key insights into the maintenance of genetic variation, with divergence of diploids and tetraploids suggesting that ploidy differences act as a barrier to gene exchange in British Euphrasia, with rampant hybridisation within ploidy levels. The scarcity of shared diploid-tetraploid ITS haplotypes supports the polyploids being allotetraploid in origin. Overall, these results show that even when lacking species-level resolution, DNA barcoding can reveal insightful evolutionary patterns in taxonomically complex genera.

evolutionary biology↗