Klaas Vrieling

The complete chloroplast genome of 17 individuals of pest species Jacobaea vulgaris: SNPs, microsatellites and barcoding markers for population and phylogenetic studies.

Invasive individuals from the pest species Jacobaea vulgaris show different allocation patterns in defence and growth compared with native individuals. To examine if these changes are caused by fast evolution, it is necessary to identify native source populations and compare these with invasive populations. For this purpose, we are in need of intraspecific polymorphic markers. We therefore sequenced the complete chloroplast genomes of 12 native and 5 invasive individuals of J. vulgaris with next generation sequencing and discovered single-nucleotide polymorphisms (SNPs) and microsatellites. This is the first study in which the chloroplast genome of that many individuals within a single species was sequenced. Thirty-two SNPs and 34 microsatellite regions were found. For none of the individuals, differences were found between the inverted repeats. Furthermore, being the first chloroplast genome sequenced in the Senecioneae clade, we compared it with four other members of the Asteraceae family to identify new regions for phylogentic inference within this clade and also within the Asteraceae family. Five markers (ndhC-trnV, ndhC-atpE, rps18-rpl20, clpP and psbM-trnD) contained parsimony-informative characters higher than 2%. Finally, we compared two procedures of preparing chloroplast DNA for next generation sequencing.

Palatability to a generalist herbivore, defence and growth of invasive and native Senecio species: testing the evolution of increased competitive ability hypothesis

This paper tests the prediction that introduced plants may become successful invaders because they experience evolutionary changes in growth and defence in their new range [evolution of increased competitive ability hypothesis (EICA)]. Interspecific and intraspecific binary feeding choices were offered to the snail Helix aspersa. The choices were between: (1) plants of the invasive Senecio inaequidens and Senecio pterophorus derived from populations in the introduced range (Europe) and plants of three indigenous species (Senecio jacobea, Senecio vulgaris and Senecio malacitanus) from populations in Europe; (2) plants of the invasive S.inaequidens and S. pterophorus from populations in the introduced range (Europe) and from populations in the native range (South Africa). We did not find a clear pattern of preference for indigenous or alien species of Senecio. However, we found that European invasive populations of S. inaequidens and S. pterophorus were less palatable than South African native populations. Moreover, in contrast to the predictions of the EICA hypothesis, the invasive genotypes of both species also showed a higher total concentration of pyrrolizidine alkaloids, and in the case of S. inaequidens we also found higher growth than in native genotypes. Our results are discussed with respect to the refinement of the EICA hypothesis that takes into account the difference between specialist and generalist herbivores and between qualitative and quantitative defences. We conclude that invasive populations of S. inaequidens and S. pterophorus are less palatable than native populations, suggesting that genetic differentiation associated with founding may occur and contribute to the plants’ invasion success by selecting the best-defended genotypes in the introduced range.

Genetic variation in constitutive and inducible pyrrolizidine alkaloid levels in Cynoglossum officinale L.

The constitutive pyrrolizidine alkaloid (PA) concentration of both shoots and roots differed significantly between 17 selfed families. The broad-sense heritability accounted for 33–43% of the variation in PA levels. Families also differed significantly in the amount and the direction of PA induction in both shoots and roots, 24 h after punching 15 holes in the leaves. We found a significantly negative relationship between the changes in PA content of the shoots and changes in PA content of the roots. The total PA content of the plants did not increase. We thus concluded that changes in PA distribution over the plant resulted from transport of PAs within the plant. The direction of transport differed between families: some transported PAs to the shoots, others to the roots. This makes it questionable whether PAs act as damage-induced defences. The effect of damage on the PA concentration is far less than the differences found between families in the constitutive PA concentration. This again strongly suggests that damage-induced defences inCynoglossum officinale do not play an important role. We argue that the general lack of attention that is given to genotype in induction experiments, has led to false conclusions.

Genetic analysis of the concentrations of pyrrolizidine alkaloids in Senecio jacobaea

Abstract We investigated whether the large phenotypic variation in pyrrolizidine alkaloid (PA) concentration in Senecio jacobaea has a genetic component. A diallel cross and a half-sib analysis showed that 50–100% of the total variation in total PA concentration is due to genetic differences in the laboratory. For a large number of the major individual PAs significant heritabilities (for concentration as well as composition) were found in a nutrient-stressed and drought-stressed environment in half-sib analyses. PA concentrations differed significantly between the nutrient and drought treatments.

Diversity of pyrrolizidine alkaloids in Senecio species does not affect the specialist herbivore Tyria jacobaeae

Abstract. The evolution of the diversity of related secondary metabolites in plants is still poorly understood. It is often thought that the evolution of plant secondary metabolites is driven by specialist insect herbivores and under this coevolutionary model it is expected that related compounds differ in their effects on specialist herbivores. Here we focus on the diversity of pyrrolizidine alkaloids (PAs) in Senecio species and their effects on Tyria jacobaeae, a specialist moth on Senecio jacobaea. As a first step to determine the effects of related PAs on T. jacobaeae, we studied larval performance on plants from 11 S. jacobaea populations and eight Senecio species with different PA compositions. Although the populations of S. jacobaea differed in their PA compositions, there was no difference in larval performance among the populations. Larval performance differed among the eight species but we could not show a correlation with PA composition. Oviposition choice experiments showed a strong correlation between oviposition preference and larval performance on the eight species but oviposition preference did not seem to be correlated with PAs. We found no indications that related PAs differ in effects on the specialist T. jacobaeae; therefore it seems unlikely that T. jacobaeae is a driving force behind the evolution of the diversity of PAs. Alternatively, we propose that the evolution of the diversity of PAs is driven by selection pressure from generalist herbivores or that the diversity of PAs may even be selectively neutral.

Tritrophic interactions between aphids (Aphis jacobaeae Schrank), ant species, Tyria jacobaeae L., and Senecio jacobaea L. lead to maintenance of genetic variation in pyrrolizidine alkaloid concentration

SummaryWe hypothesize that the tritrophic interaction between ants, the aphid Aphis jacobaeae, the moth Tyria jacobaeae, and the plant Senecio jacobaea can explain the genetic variation observed in pyrrolizidine alkaloid concentration in natural populations of S. jacobaea. The ant Lasius niger effectively defends S. jacobaea plants infested with A. jacobaeae against larvae of T. jacobaeae. S. jacobaea plants with A. jacobaeae which are defended by ants escape regular defoliation by T. jacobaeae. Plants with aphids and ants have a lower pyrrolizidine alkaloid concentration than plants without aphids and ants. When these data are fitted to an existing theoretical model for temporal variation in fitness it is shown that varying herbivore pressure by T. jacobaeae in interaction with ants defending aphid-infested plants with a low pyrrolizidine alkaloid concentration can lead to a stable polymorphism in pyrrolizidine alkaloid concentration. Costs of the production and maintenance of pyrrolizidine alkaloids are not accounted for in the model.

A review of the phytochemical support for the shifting defence hypothesis

Several theories have been developed to explain why invasive species are very successful and develop into pest species in their new area. The shifting defence hypothesis (SDH) argues that invasive plant species quickly evolve towards new defence levels in the invaded area because they lack their specialist herbivores but are still under attack by local (new) generalist herbivores. The SDH predicts that plants should increase their cheap, toxic defence compounds and lower their expensive digestibility reducing compounds. As a net result resources are saved that can be allocated to growth and reproduction giving these plants a competitive edge over the local plant species. We conducted a literature study to test whether toxic defence compounds in general are increased in the invaded area and if digestibility reducing compounds are lowered. We specifically studied the levels of pyrrolizidine alkaloids, a toxin which is known for its beneficial and detrimental impact against specialists and generalists, respectively. Digestibility reducers did not show a clear trend which might be due to the small number of studies and traits measured. The meta analysis showed that toxic compounds in general and pyrrolizidine alkaloid levels specifically, increased significantly in the invaded area, supporting the predictions of the SDH that a fast evolution takes place in the allocation towards defence.

Pyrrolizidine Alkaloids as Oviposition Stimulants for the Cinnabar Moth, Tyria jacobaeae

In choice experiments with artificial leaves, we tested related pyrrolizidine alkaloids (PAs) for their stimulatory effects on the oviposition of the cinnabar moth, a specialist on the PA-containing plant Senecio jacobaea. The PAs from S. jacobaea that we tested stimulated oviposition. Monocrotaline also stimulated oviposition although this PA is not found in plants of the genus Senecio. The moths preferred ovipositing on filter paper with a PA mixture extracted from S. jacobaea to ovipositing on filter paper with single PAs. Senkirkine, heliotrine, and retrorsine did not stimulate oviposition. The nonactive retrorsine differs only in one OH group to the active senecionine, indicating that small structural differences alter the stimulatory activity of PAs. However, a PA mixture extracted from a nonhost plant, Senecio inaequidens, that consisted of 81% of the nonactive retrorsine did stimulate oviposition. Oviposition preferences between Senecio species seem to be determined by chemical compounds other than PAs.

Natural hybridization between Senecio jacobaea and Senecio aquaticus: molecular and chemical evidence

Hybridization is known to be involved in a number of evolutionary processes, including species formation, and the generation of novel defence characteristics in plants. The genus Senecio of the Asteraceae family is highly speciose and has historically demonstrated significant levels of interspecific hybridization. The evolution of novel chemical defence characteristics may have contributed to the success of Senecio hybrids. Chemical defence against pathogens and herbivores has been studied extensively in the model species Senecio jacobaea, which is thought to hybridize in nature with Senecio aquaticus. Here, we use amplified fragment length polymorphisms (AFLPs) and pyrrolizidine alkaloid (PA) composition to confirm that natural hybridization occurs between S. jacobaea and the closely related species S. aquaticus. AFLPs are also used to estimate the ancestry of hybrids. We also demonstrate that even highly back‐crossed hybrids can possess a unique mixture of defence chemicals specific to each of the parental species. This hybrid system may therefore prove to be useful in further studies of the role of hybridization in the evolution of plant defence and resistance.

Pyrrolizidine alkaloid variation in shoots and roots of segregating hybrids between Jacobaea vulgaris and Jacobaea aquatica

Hybridization can lead to novel qualitative or quantitative variation of secondary metabolite (SM) expression that can have ecological and evolutionary consequences. We measured pyrrolizidine alkaloid (PA) expression in the shoots and roots of a family including one Jacobaea vulgaris genotype and one Jacobaea aquatica genotype (parental genotypes), two F(1) hybrid genotypes, and 102 F(2) hybrid genotypes using liquid chromatography-tandem mass spectrometry (LC-MS/MS). We detected 37 PAs in the roots and shoots of J. vulgaris, J. aquatica and the hybrids. PA concentrations and compositions differed between genotypes, and between roots and shoots. Three otosenine-like PAs that only occurred in the shoots of parental genotypes were present in the roots of F(2) hybrids; PA compositions were sometimes novel in F(2) hybrids compared with parental genotypes, and in some cases transgressive PA expression occurred. We also found that PAs from within structural groups covaried both in the roots and in the shoots, and that PA expression was correlated between shoots and roots. Considerable and novel variation present among F(2) hybrids indicates that hybridization has a potential role in the evolution of PA diversity in the genus Jacobaea, and this hybrid system is useful for studying the genetic control of PA expression.