Maternal provisioning is structured by species’ competitive neighborhoods

Transgenerational effects of parent plant competition on offspring development in contrasting conditions

Conditions during a parent's lifetime can induce phenotypic changes in offspring, providing a potentially important source of variation in natural populations. Yet, to date, biotic factors have seldom been tested as sources of transgenerational effects in plants. In a greenhouse experiment with the generalist annual Polygonum persicaria, we tested for effects of parental competition on offspring by growing isogenic parent plants either individually or in competitive arrays and comparing their seedling progeny in contrasting growth environments. Offspring of competing vs. non-competing parents showed significantly altered development, resulting in greater biomass and total leaf area, but only when growing in neighbor or simulated canopy shade, rather than sunny dry conditions. A follow-up experiment in which parent plants instead competed in dry soil found that offspring in dry soil had slightly reduced growth, both with and without competitors. In neither experiment were effects of parental competition explained by changes in seed provisioning, suggesting a more complex mode of regulatory inheritance. We hypothesize that parental competition in moist soil (i.e., primarily for light) confers specific developmental effects that are beneficial for light-limited offspring, while parental competition in dry soil (i.e., primarily for belowground resources) produces offspring of slightly lower overall quality. Together, these results indicate that competitive conditions during the parental generation can contribute significantly to offspring variation, but these transgenerational effects will depend on the abiotic resources available to both parents and progeny.

Maternal effects and the outcome of interspecific competition

Maternal environmental effects create lagged population responses to past environments. Although they are ubiquitous and vary in expression across taxa, it remains unclear if and how their presence alters competitive interactions in ecological communities.Here, we use a discrete-time competition model to simulate how maternal effects alter competitive dynamics in fluctuating and constant environments. Further, we explore how omitting maternal effects alter estimates of known model parameters from observational time series data.Our simulations demonstrate that (i) maternal effects change competitive outcomes, regardless of whether competitors otherwise interact neutrally or exhibit non-neutral competitive differences, (ii) the consequences of maternal effects for competitive outcomes are mediated by the temporal structure of environmental variation, (iii) even in constant conditions, competitive outcomes are influenced by species' maternal effects strategies, and (iv) in observational time series data, omitting maternal effects reduces variation explained by models and biases parameter estimates, including competition coefficients.Our findings demonstrate that the ecological consequences of maternal effects hinge on the competitive environment. Evolutionary biologists have long recognized that maternal effects can be an important but often overlooked strategy buffering populations from environmental change. We suggest that maternal effects are similarly critical to ecology and call for research into maternal effects as drivers of dynamics in populations and communities.

Competition-induced transgenerational plasticity influences competitive interactions and leaf decomposition of offspring

Phenotypic plasticity, within and across generations (transgenerational plasticity), allows organisms and their progeny to adapt to the environment without modification of the underlying DNA. Recent findings suggest that epigenetic modifications are important mediators of such plasticity. However, empirical studies have, so far, mainly focused on plasticity in response to abiotic factors, overlooking the response to competition. We tested for within-generation and transgenerational phenotypic plasticity triggered by plant-plant competition intensity, and we tested whether it was mediated via DNA methylation, using the perennial, apomictic herb Taraxacum brevicorniculatum in four coordinated experiments. We then tested the consequences of transgenerational plasticity affecting competitive interactions of the offspring and ecosystem processes, such as decomposition. We found that, by promoting differences in DNA methylation, offspring of plants under stronger competition developed faster and presented more resource-conservative phenotypes. Further, these adjustments associated with less degradable leaves, which have the potential to reduce nutrient turnover and might, in turn, favour plants with more conservative traits. Greater parental competition enhanced competitive abilities of the offspring, by triggering adaptive phenotypic plasticity, and decreased offspring leaf decomposability. Our results suggest that competition-induced transgenerational effects could promote rapid adaptations and species coexistence and feed back on biodiversity assembly and nutrient cycling.