Relative effects of genetic variation sensu lato and sexual dimorphism on plant traits and associated arthropod communities

Constructing ecological indices for urban environments using species distribution models

In an increasingly urbanized world, there is a need to study urban areas as their own class of ecosystems as well as assess the impacts of anthropogenic impacts on biodiversity. However, collecting a sufficient number of species observations to estimate patterns of biodiversity in a city can be costly. Here we investigated the use of community science-based data on species occurrences, combined with species distribution models (SDMs), built using MaxEnt and remotely-sensed measures of the environment, to predict the distribution of a number of species across the urban environment of Los Angeles. By selecting species with the most accurate SDMs, and then summarizing these by class, we were able to produce two species richness models (SRMs) to predict biodiversity patterns for species in the class Aves and Magnoliopsida and how they respond to a variety of natural and anthropogenic environmental gradients.

We found that species considered native to Los Angeles tend to have significantly more accurate SDMs than their non-native counterparts. For all species considered in this study we found environmental variables describing anthropogenic activities, such as housing density and alterations to land cover, tend to be more influential than natural factors, such as terrain and proximity to freshwater, in shaping SDMs. Using a random forest model we found our SRMs could account for approximately 54% and 62% of the predicted variation in species richness for species in the classes Aves and Magnoliopsida respectively. Using community science-based species occurrences, SRMs can be used to model patterns of urban biodiversity and assess the roles of environmental factors in shaping them.

Plant volatiles as cues and signals in plant communication

Volatile organic compounds are important mediators of mutualistic interactions between plants and their physical and biological surroundings. Volatiles rapidly indicate competition or potential threat before these can take place, and they regulate and coordinate adaptation responses in neighbouring plants, fine-tuning them to match the exact stress encountered. Ecological specificity and context-dependency of plant-plant communication mediated by volatiles represent important factors that determine plant performance in specific environments. In this review, we synthesise the recent progress made in understanding the role of plant volatiles as mediators of plant interactions at the individual and community levels, highlighting the complexity of the plant receiver response to diverse volatile cues and signals and addressing how specific responses shape plant growth and survival. Finally, we outline the knowledge gaps and provide directions for future research. The complex dialogue between the emitter and receiver based on either volatile cues or signals determines the outcome of information exchange, which shapes the communication pattern between individuals at the community level and determines their ecological implications at other trophic levels.

Consistent community genetic effects in the context of strong environmental and temporal variation in Eucalyptus

Provenance translocations of tree species are promoted in forestry, conservation, and restoration in response to global climate change. While this option is driven by adaptive considerations, less is known of the effects translocations can have on dependent communities. We investigated the relative importance and consistency of extended genetic effects in Eucalyptus using two species-E. globulus and E. pauciflora. In E. globulus, the dependent arthropod and pathogen canopy communities were quantified based on the abundance of 49 symptoms from 722 progeny from 13 geographic sub-races across 2 common gardens. For E. pauciflora, 6 symptoms were quantified over 2 years from 238 progeny from 16 provenances across 2 common gardens. Genetic effects significantly influenced communities in both species. However, site and year effects outweighed genetic effects with site explaining approximately 3 times the variation in community traits in E. globulus and site and year explaining approximately 6 times the variation in E. pauciflora. While the genetic effect interaction terms were significant in some community traits, broad trends in community traits associated with variation in home-site latitude for E. globulus and home-site altitude for E. pauciflora were evident. These broad-scale trends were consistent with patterns of adaptive differentiation within each species, suggesting there may be extended consequences of local adaptation. While small in comparison to site and year, the consistency of genetic effects highlights the importance of provenance choice in tree species, such as Eucalyptus, as adaptive divergence among provenances may have significant long-term effects on biotic communities.

Sexual and genotypic variation in terpene quantitative and qualitative profiles in the dioecious shrub Baccharis salicifolia

Terpenoids are secondary metabolites produced in most plant tissues and are often considered toxic or repellent to plant enemies. Previous work has typically reported on intra-specific variation in terpene profiles, but the effects of plant sex, an important axis of genetic variation, have been less studied for chemical defences in general, and terpenes in particular. In a prior study, we found strong genetic variation (but not sexual dimorphism) in terpene amounts in leaves of the dioecious shrub Baccharis salicifolia. Here we build on these findings and provide a more in-depth analysis of terpene chemistry on these same plants from an experiment consisting of a common garden with male (N = 19) and female (N = 20) genotypes sourced from a single population. Our goal in the present study was to investigate quantitative and qualitative differences in terpene profiles associated with plant sex and genotypic variation. For this, we quantified leaf mono- and sesquiterpene amount, richness, and diversity (quantitative profile), as well as the composition of compounds (qualitative profile). We found no evidence of sexual dimorphism in monoterpene or sesquiterpene profiles. We did, however, find significant genotypic variation in amount, diversity, and composition of monoterpenes, but no effects on sesquiterpenes. These findings indicated that genotypic variation in terpene profiles largely surpassed variation due to sexual dimorphism for the studied population of this species.

Specificity of plant-plant communication for Baccharis salicifolia sexes but not genotypes

Plants are able to adjust their anti-herbivore defenses in response to the volatile organic compounds (VOCs) emitted by herbivore-damaged neighbors, and some of these changes increase resistance against subsequent herbivory. This phenomenon of plant-plant communication is thought to be widespread, but recent investigations have cautioned that it can be context dependent, including variation in the strength of communication based on the identity of plants and their associated herbivores. Here, we performed three greenhouse experiments using multiple male and female genotypes of the dioecious woody shrub Baccharis salicifolia and its specialist aphid Uroleucon macolai to test for specificity of plant-plant communication with respect to plant sex and genotype. Moreover, we evaluated plant sexual dimorphism and genotypic variation in VOC emissions (i.e., the "speaking" side of the interaction) and response of plants to VOC exposure (i.e., the "listening" side of the interaction) in order to identify the chemical mechanisms underlying such specificity. We did not find genotypic specificity of communication; emitter plants damaged by U. macolai significantly reduced subsequent U. macolai performance on receivers, but these effects were indistinguishable for communication within vs. among genotypes. In contrast, we found sex specificity of communication; male emitter plants reduced subsequent U. macolai performance on male and female receiver plants equally, while female emitter plants only did so for female receivers. We found sexual (but not genotypic) dimorphism in speaking but not listening; of the seven compounds induced by U. macolai feeding (speaking), pinocarvone was approximately fivefold greater in female than in male plants, while exposure of plants to pinocarvone emissions (listening) reduced U. macolai performance equally in both male and female plants. Together, our study demonstrates novel evidence for sexually dimorphic specificity of plant-plant communication and the chemical mechanism underlying this effect.

The community and ecosystem consequences of intraspecific diversity: a meta-analysis

Understanding the relationships between biodiversity and ecosystem functioning has major implications. Biodiversity-ecosystem functioning relationships are generally investigated at the interspecific level, although intraspecific diversity (i.e. within-species diversity) is increasingly perceived as an important ecological facet of biodiversity. Here, we provide a quantitative and integrative synthesis testing, across diverse plant and animal species, whether intraspecific diversity is a major driver of community dynamics and ecosystem functioning. We specifically tested (i) whether the number of genotypes/phenotypes (i.e. intraspecific richness) or the specific identity of genotypes/phenotypes (i.e. intraspecific variation) in populations modulate the structure of communities and the functioning of ecosystems, (ii) whether the ecological effects of intraspecific richness and variation are strong in magnitude, and (iii) whether these effects vary among taxonomic groups and ecological responses. We found a non-linear relationship between intraspecific richness and community and ecosystem dynamics that follows a saturating curve shape, as observed for biodiversity-function relationships measured at the interspecific level. Importantly, intraspecific richness modulated ecological dynamics with a magnitude that was equal to that previously reported for interspecific richness. Our results further confirm, based on a database containing more than 50 species, that intraspecific variation also has substantial effects on ecological dynamics. We demonstrated that the effects of intraspecific variation are twice as high as expected by chance, and that they might have been underestimated previously. Finally, we found that the ecological effects of intraspecific variation are not homogeneous and are actually stronger when intraspecific variation is manipulated in primary producers than in consumer species, and when they are measured at the ecosystem rather than at the community level. Overall, we demonstrated that the two facets of intraspecific diversity (richness and variation) can both strongly affect community and ecosystem dynamics, which reveals the pivotal role of within-species biodiversity for understanding ecological dynamics.

Genotypic variation in plant traits shapes herbivorous insect and ant communities on a foundation tree species

Community genetics aims to understand the effects of intraspecific genetic variation on community composition and diversity, thereby connecting community ecology with evolutionary biology. Multiple studies have shown that different plant genotypes harbor different communities of associated organisms, such as insects. Yet, the mechanistic links that tie insect community composition to plant genetics are still not well understood. To shed light on these relationships, we explored variation in both plant traits (e.g., growth, phenology, defense) and herbivorous insect and ant communities on 328 replicated aspen (Populus tremuloides) genets grown in a common garden. We measured traits and visually surveyed insect communities annually in 2014 and 2015. We found that insect communities overall exhibited low heritability and were shaped primarily by relationships among key insects (i.e., aphids, ants, and free-feeders). Several tree traits affected insect communities and the presence/absence of species and functional groups. Of these traits, tree size and foliar phenology were the most important. Larger trees had denser (i.e., number of insects per unit tree size) and more diverse insect communities, while timing of bud break and bud set differentially influenced particular species and insect groups, especially leaf modifying insects. These findings will inform future research directed toward identification of plant genes and genetic regions that underlie the structure of associated insect communities.