Seed source regions drive fitness differences in invasive macrophytes

International audiencePremise Worldwide, ecosystems are threatened by global changes, including biological invasions. Invasive species arriving in novel environments experience new climatic conditions that can affect their successful establishment. Determining the response of functional traits and fitness components of invasive populations from contrasting environments can provide a useful framework to assess species responses to climate change and the variability of these responses among source populations. Much research on macrophytes has focused on establishment from clonal fragments; however, colonization from sexual propagules has rarely been studied. Our objective was to compare trait responses of plants generated from sexual propagules sourced from three climatic regions but grown under common environmental conditions, using L. peploides subsp. montevidensis as a model taxon. Methods We grew seedlings to reproductive stage in experimental mesocosms under a mediterranean California (MCA) climate from seeds collected in oceanic France (OFR), mediterranean France (MFR), and MCA. Results Seed source region was a major factor influencing differences among invasive plants recruiting from sexual propagules of L. peploides subsp. montevidensis. Trait responses of young individual recruits from MCA and OFR, sourced from geographically distant and climatically distinct source regions, were the most different. The MCA individuals accumulated more biomass, flowered earlier, and had higher leaf N concentrations than the OFR plants. Those from MFR had intermediate profiles. Conclusions By showing that the closer a seedling is from its parental climate, the better it performs, this study provides new insights to the understanding of colonization of invasive plant species and informs its management under novel and changing environmental conditions

Germination timing and chilling exposure create contingency in life history and influence fitness in the native wildflower Streptanthus tortuosus

The timing of life history events, such as germination and reproduction, influences ecological and selective environments throughout the life cycle. Many organisms evolve responses to seasonal environmental cues to synchronize these key events with favourable conditions. Often the fitness consequences of each life history transition depend on previous and subsequent events in the life cycle. If so, shifts in environmental cues can create cascading effects throughout the life cycle, which can influence fitness, selection on life history traits, and population viability. We examined variation in cue responses for contingent life history expression and fitness in a California native wildflower, Streptanthus tortuosus, by manipulating seasonal germination timing in a common garden experiment. We also manipulated chilling exposure to test the role of vernalization cues for seasonal life history contingency. Plants germinating early in the growing season in autumn were more likely to flower in the first year and less likely to perennate than later germinants in spring. First-year reproduction and overall fitness was the highest for autumn cohorts. Sensitivity analyses showed that optimal germination date depended on survival beyond the first year and fruit production in later years. Experimental chilling exposure induced first-year flowering in spring germinants, demonstrating that seasonal life history contingency is mediated by a vernalization requirement. This requirement reduced fitness of spring germinants without increasing survival or later fecundity and may be maladaptive. Such mismatches between cues and fitness may become more pervasive as predicted climate change reduces exposure to chilling, shortens growing seasons, and increases severity of summer drought. Synthesis. Shifts in germination timing in seasonal environments can cause cascading effects on trait expression and fitness that extend beyond the first year of the life cycle. Climate change is likely to shift seasonal conditions, influencing such life history contingency, with significant impacts on trait expression, fitness, and population persistence. These shifts may cause strong natural selection on cue sensitivity and life history expression, but it is an open question whether populations have the potential for rapid adaptation in response to this selection

Host evolutionary relationships explain tree mortality caused by a generalist pest–pathogen complex

The phylogenetic signal of transmissibility (competence) and attack severity among hosts of generalist pests is poorly understood. In this study, we examined the phylogenetic effects on hosts differentially affected by an emergent generalist beetle-pathogen complex in California and South Africa. Host types (non-competent, competent and killed-competent) are based on nested types of outcomes of interactions between host plants, the beetles and the fungal pathogens. Phylogenetic dispersion analysis of each host type revealed that the phylogenetic preferences of beetle attack and fungal growth were a nonrandom subset of all available tree and shrub species. Competent hosts were phylogenetically narrower by 62 Myr than the set of all potential hosts, and those with devastating impacts were the most constrained by 107 Myr. Our results show a strong phylogenetic signal in the relative effects of a generalist pest-pathogen complex on host species, demonstrating that the strength of multi-host pest impacts in plants can be predicted by host evolutionary relationships. This study presents a unifying theoretical approach to identifying likely disease outcomes across multiple host-pest combinations