Biology subjects

Geber, M. A.

Publications and source records attributed to Geber, M. A..

6 recordsLinked to original sources

bioRxiv2022

Bet hedging is not sufficient to explain intraspecific variation in germination patterns of a winter annual plant

Bet hedging consists of life history strategies that buffer against environmental variability by trading off immediate and long-term fitness. Delayed germination in annual plants is a classic example of bet hedging, and is often invoked to explain low germination fractions. We examined whether bet hedging explains low and variable germination fractions among 20 populations of the winter annual plant Clarkia xantiana ssp. xantiana that experience substantial variation in reproductive success among years. Leveraging 15 years of demographic monitoring and 3 years of field germination experiments, we assessed the fitness consequences of seed banks and compared optimal germination fractions from a density-independent bet-hedging model to observed germination fractions. We did not find consistent evidence of bet hedging or the expected trade-off between arithmetic and geometric mean fitness, though delayed germination increased long-term fitness in 7 of 20 populations. Optimal germination fractions were 2 to 5 times higher than observed germination fractions, and among-population variation in germination fractions was not correlated with risks across the life cycle. Our comprehensive test suggests that bet hedging is insufficient to explain the observed germination patterns. Understanding variation in germination strategies will likely require integrating bet hedging with complementary forces shaping the evolution of delayed germination.

ecology↗

bioRxiv2021

Interactions during growth eclipse interactions during flowering for determining plant fecundity in pollinator-sharing annual plants

Density dependent interactions are fundamental to community ecology, but studies often reduce the complex nature of species interactions. In plant ecology, interactions during vegetative growth and flowering are often considered separately, though both can affect reproductive output. Here we use communities of annual flowering plants in the genus Clarkia to ask how interactions during growth and flowering contribute to density dependence in plant seed production, and if pollinator behaviors explain apparent patterns in plant interactions during flowering. We measure seed set (seed number per ovule) and total fecundity (whole-plant seed production) of Clarkia focal plants in experimental interaction plots with the effect of pollinators experimentally removed through supplemental pollination or retained. We also observe pollinator behaviors in the plots and experimental arrays to document pollinator preference, constancy and joint attraction. During flowering, pollinators significantly changed the density dependent effects of Clarkia interactions on seed set in 31% of species interactions, and these changes corresponded to pollinator behaviors. Total fecundity, however, did not depend on interactions between Clarkia; instead, earlier-flowering, non-Clarkia forbs limited total fecundity. Our study shows that interactions during vegetative growth can preclude the effect of pollinator- mediated interactions on fecundity by limiting potential reproductive output. Simultaneously studying different types of species interactions allows for understanding the contingency of ecological outcomes.

ecology↗

bioRxiv2020

Selection favors adaptive plasticity in a long-term reciprocal transplant experiment

Spatial and temporal environmental variation can favor the evolution of adaptive phenotypic plasticity, such that genotypes alter their phenotypes in response to local conditions to maintain fitness across heterogeneous landscapes. When individuals show greater fitness in one habitat than another, asymmetric migration can restrict adaptive responses to selection in the lower quality environment. In these cases, selection is predicted to favor traits that enhance fitness in the higher-quality source habitat at the expense of fitness in the marginal habitat, resulting in specialization to the high-quality environment. Here, we test whether plasticity is adaptive in a system regulated by demographic source-sink dynamics. Vaccinium elliottii (Ericaceae) occurs in dry upland and flood-prone bottomland forests throughout the southeastern United States, and shows patterns consistent with source-sink dynamics. We conducted a multi-year field experiment to evaluate whether plasticity in foliar morphology is advantageous. Both across habitats and within the high-quality upland environment, selection favored plasticity in specific leaf area and stomatal density. Stabilizing selection acted on plasticity in these traits, suggesting that extreme levels of plasticity are disadvantageous. We conclude that even in systems driven by source-sink dynamics, temporal and spatial variation in conditions can favor the evolution of plasticity.

evolutionary biology↗

bioRxiv2020

Quantitative Amplicon Sequencing for Meta-DNA Analysis Reveals Patterns inPollen Use by Bees

Determining how pollinators visit plants versus how they carry and transfer pollen is an ongoing project in pollination ecology. The differences between how pollinators visit flowers versus how they carry pollen can be appreciable, but the current tools for identifying the pollens that bees carry have different strengths and weaknesses when used for ecological inference. In this study we use three methods to better understand a system of congeneric, co-flowering plants in the genus Clarkia and their bee pollinators: observations of plant-pollinator contact in the field, and two different molecular methods to estimate the relative abundance of each Clarkia pollen in samples collected from pollinators. We use these methods to investigate if observations of plant-pollinator contact in the field correspond to the pollen bees carry; if individual bees carry Clarkia pollens in predictable ways, based on previous knowledge of their foraging behaviors; and how the three approaches differ for understanding plant-pollinator interactions. We find that observations of plant-pollinator contact are generally predictive of the pollens that bees carry while foraging, and network topologies using the three different methods are statistically indistinguishable from each other. Results from molecular pollen analysis also show that while bees can carry multiple species of Clarkia at the same time, they often carry one species of pollen. Our work contributes to the growing body of literature aimed at resolving how pollinators use floral resources. We suggest our novel relative amplicon quantification method as another tool in the developing molecular ecology and pollination biology toolbox.

ecology↗

bioRxiv2020

Emission rates of species-specific volatiles vary across communities of Clarkia species: Evidence for character displacement in floral scent.

A current frontier of character displacement research is to determine if displacement occurs via multiple phenotypic pathways and varies across communities with different species compositions. Here, we conducted the first test for context-dependent character displacement in multimodal floral signals by analyzing variation in floral scent in a system that exhibits character displacement in flower size, and that has multiple types of sympatric communities. In a greenhouse common garden experiment, we measured quantitative variation in volatile emission rates of the progeny of two species of Clarkia from replicated communities that contain one, two, or four Clarkia species. The first two axes of a constrained correspondence analysis, which explained 24 percent of the total variation in floral scent, separated the species and community types, respectively. Of the 23 compounds that were significantly correlated with these axes, nine showed patterns consistent with character displacement. Two compounds produced primarily by C. unguiculata and two compounds produced primarily by C. cylindrica were emitted in higher amounts in sympatry. Character displacement in some volatiles varied across sympatric communities and occurred in parallel with displacement in flower size, demonstrating that this evolutionary process can be context-dependent and may occur through multiple pathways.

evolutionary biology↗

bioRxiv2018

Biotic interactions limit the geographic range of an annual plant: herbivory and phenology mediate fitness beyond a range margin

Species range limits offer powerful opportunities to study environmental factors regulating distributions and probe the limits of adaptation. However, we rarely know what aspects of the environment are actually constraining range expansion, much less which traits are mediating the organisms response to these environmental gradients. Though most studies focus on climatic limits to species distributions, biotic interactions may be just as important. We used field experiments and simulations to estimate contributions of mammal herbivory to a range boundary in the annual plant Clarkia xantiana ssp. xantiana. A steep gradient of increasing probability of herbivory occurs across the boundary, and herbivory drives several-fold declines in lifetime fitness at and beyond the boundary. By including in our analyses data from a sister taxon with more rapid phenology, we show that delayed phenology drives C. xantiana ssp. xantianas susceptibility to herbivory and low fitness beyond its border.

ecology↗