A test of the evolution of increased competitive ability in two invaded regions

The evolution of thermal performance in native and invasive populations of Mimulus guttatus

The rise of globalization has spread organisms beyond their natural range, allowing further opportunity for species to adapt to novel environments and potentially become invaders. Yet, the role of thermal niche evolution in promoting the success of invasive species remains poorly understood. Here, we use thermal performance curves (TPCs) to test hypotheses about thermal adaptation during the invasion process. First, we tested the hypothesis that if species largely conserve their thermal niche in the introduced range, invasive populations may not evolve distinct TPCs relative to native populations, against the alternative hypothesis that thermal niche and therefore TPC evolution has occurred in the invasive range. Second, we tested the hypothesis that clines of TPC parameters are shallower or absent in the invasive range, against the alternative hypothesis that with sufficient time, standing genetic variation, and temperature‐mediated selection, invasive populations would re‐establish clines found in the native range in response to temperature gradients. To test these hypotheses, we built TPCs for 18 native (United States) and 13 invasive (United Kingdom) populations of the yellow monkeyflower, Mimulus guttatus. We grew clones of multiple genotypes per population at six temperature regimes in growth chambers. We found that invasive populations have not evolved different thermal optima or performance breadths, providing evidence for evolutionary stasis of thermal performance between the native and invasive ranges after over 200 years post introduction. Thermal optimum increased with mean annual temperature in the native range, indicating some adaptive differentiation among native populations that was absent in the invasive range. Further, native and invasive populations did not exhibit adaptive clines in thermal performance breadth with latitude or temperature seasonality. These findings suggest that TPCs remained unaltered post invasion, and that invasion may proceed via broad thermal tolerance and establishment in already climatically suitable areas rather than rapid evolution upon introduction.

Evolutionary history and ecology shape the diversity and abundance of phytochemical arsenals across monkeyflowers

We examine the extent to which phylogenetic effects and ecology are associated with macroevolutionary patterns of phytochemical defence production across the Mimulus phylogeny. We grew plants from 21 species representing the five major sections of the Mimulus phylogeny in a common garden to assess how the arsenals (NMDS groupings) and abundances (concentrations) of a phytochemical defence, phenylpropanoid glycosides (PPGs), vary across the phylogeny. Very few PPGs are widespread across the genus, but many are common to multiple sections of the genus. Phytochemical arsenals cluster among sections in an NMDS and are not associated with total concentration of PPGs. There is a strong phylogenetic signal for phytochemical arsenal composition across the Mimulus genus, whereas ecological variables such as growing season length, latitude, and elevation do not significantly influence arsenal. In contrast, there is little phylogenetic signal for total PPG concentration, and this trait is significantly influenced by several ecological factors. Phytochemical arsenals and abundances are influenced by plant life history form. Both phylogenetic effects and ecology are related to phytochemical patterns across species, albeit in different ways. The independence of phytochemical defence concentrations from arsenal compositions indicates that these aspects of defence may continue to evolve independently of one another.

Evolution of growth traits in invasive Pereskia aculeata (Cactaceae): testing the EICA hypothesis using its specialist herbivore, Catorhintha schaffneri (Coreidae)

BACKGROUND

Species introduced into new habitats are fitter than their native populations, as hypothesized by the 'evolution of increased competitive ability' (EICA). Here, Pereskia aculeata Miller was used as a model to test EICA and explore how 'enemy release' may have influenced the invasion success of its 400-year-old introduced populations (genotypes) compared with native populations. Plant growth traits (height and shoot length) of 15 genotypes [four from the introduced range (South Africa) and 11 from the native range (Brazil and Argentina, Venezuela and The Dominican Republic)] were assessed. Damage and impact of a shoot-feeding, sap-sucking specialist Catorhintha schaffneri Brailovsky & Garcia on ten genotypes were also compared.

RESULTS

All but one of the invasive genotypes were significantly taller than native genotypes. Although the invasive genotypes were relatively more damaged by herbivory than some of the native genotypes, the observed differences were not explained completely by their origins. Nonetheless, the findings partially supported the predictions of the EICA hypothesis because invasive genotypes were generally taller than native genotypes, but did not fully support the hypothesis because they were not always more damaged than the native genotypes by C. schaffneri.

CONCLUSION

Invasive genotypes had an advantage in the introduced range as they can climb neighbouring vegetation more quickly than native genotypes, but the damage incurred by the invasive genotypes relative to the native genotypes suggests only that C. schaffneri would be as damaging in South Africa, where it serves as a biocontrol agent, as it is in its native distribution in Brazil. © 2020 Society of Chemical Industry.

The Genetic Architecture of Plant Defense Trade-offs in a Common Monkeyflower

Determining how adaptive combinations of traits arose requires understanding the prevalence and scope of genetic constraints. Frequently observed phenotypic correlations between plant growth, defenses, and/or reproductive timing have led researchers to suggest that pleiotropy or strong genetic linkage between variants affecting independent traits is pervasive. Alternatively, these correlations could arise via independent mutations in different genes for each trait and extensive correlational selection. Here we evaluate these alternatives by conducting a quantitative trait loci (QTL) mapping experiment involving a cross between 2 populations of common monkeyflower (Mimulus guttatus) that differ in growth rate as well as total concentration and arsenal composition of plant defense compounds, phenylpropanoid glycosides (PPGs). We find no evidence that pleiotropy underlies correlations between defense and growth rate. However, there is a strong genetic correlation between levels of total PPGs and flowering time that is largely attributable to a single shared QTL. While this result suggests a role for pleiotropy/close linkage, several other QTLs also contribute to variation in total PPGs. Additionally, divergent PPG arsenals are influenced by a number of smaller-effect QTLs that each underlie variation in 1 or 2 PPGs. This result indicates that chemical defense arsenals can be finely adapted to biotic environments despite sharing a common biochemical precursor. Together, our results show correlations between defense and life-history traits are influenced by pleiotropy or genetic linkage, but genetic constraints may have limited impact on future evolutionary responses, as a substantial proportion of variation in each trait is controlled by independent loci.