Dr. Zoe Panchen The blossoming of the Arctic: Natural history records as a resource to study plant responses to climate change The Arctic is experiencing some of the most dramatic changes in climate with temperatures rising at treble the rate of the global average. Phenology, the timing of natures seasonal events, is often related to temperature and, as the climate warms, Arctic flowering and fruiting times are generally shifting earlier. Natural History records of pressed plants (herbarium specimens) are often collected in flower or fruit and offer a snap shot of flowering and fruiting times over the past century or more. Herbarium specimens are thus an excellent resource for predicting how plants will respond to climate change. In this talk, I will discuss how Arctic plants are responding to climate change, focusing on findings from my Nunavut plant phenology research using herbarium specimens and long-term phenology monitoring. I will conclude my presentation by describing my current research on evolutionary and life history trait patterns in Arctic plant phenological responses to climate change.
Investigating pollen capture, production, and size strategies in wind-pollinated flowering plants The flowering plants (angiosperms) have evolved a wide diversity of pollination strategies, from complex interactions with specialized animal pollinators to strategies that are entirely abiotic, relying on fluid currents like wind or water to transport pollen from stamen to stigma. Compared to animal pollination, abiotic strategies like wind pollination have long been considered inefficient, evolving when animal pollination becomes unreliable. Traits commonly associated with wind-pollinated plants are thought to reflect this apparent inefficiency and low probability of successful pollen transfer. Compared to animal-pollinated species, which tend to have large showy flowers design to attract animal pollinators, wind-pollinated plants tend to make many small, inconspicuous flowers that produce large volumes of pollen and often have just one ovule. These traits may represent a strategy to mitigate inevitable pollen losses – or they may represent innovative adaptations to maximize pollen capture in a unique pollination system. For example, packaging just one ovule per flower might not be because the probability of multiple grains landing on a given stigma is unusually low. Instead, having many small, relatively inexpensive flowers may allow wind-pollinated plants to maximize their pollen capture by maximizing the area they sample in space, at minimal floral costs. Similarly, pollen production strategies in wind pollinated plants may not simply reflect low probability of pollen capture by stigmas. Instead, these may be the result of a complex balance of selection on pollen size and number imposed by transport through wind and subsequent competition between pollen grains for limited ovules. In my research, I’m broadly interested in understanding the strategies wind-pollinated plants use to facilitate successful pollination from both male and female fitness perspectives, despite the inherent stochasticity in wind pollination.
Effects of turbidity and nutrients on zooplankton community structure: a mesocosm study Freshwater ecosystems make significant contributions to biodiversity and provide ecosystem services of value to humans. However, freshwater habitats are among the most threatened globally. Among the many ways that humans are altering freshwater ecosystems, elevated turbidity from suspended clay-sized sediments remains relatively under-explored, with much research limited to controlled single-species laboratory studies or community-level studies in oligotrophic environments. Sediments can adsorb nutrients and simultaneously deliver nutrients to freshwater systems, resulting in turbidity and nutrients simultaneously acting as stressors in lakes. Zooplankton play an important role in aquatic ecosystems, transferring energy from lower to higher trophic levels, and are excellent indicators of freshwater ecosystems. With the objective of exploring the causal relationships between turbidity and nutrients on zooplankton communities, I conducted a mesocosm experiment at the Queen’s University Biological Station. Using 60 mesocosms, I established two 30-increment turbidity gradients, one at ambient (mesotrophic-eutrophic) and one at high (eutrophic-hypereutrophic) nutrient levels. I stocked the mesocosms with a diverse zooplankton community and measured community-level responses (abundance, biomass, and diversity) after 6 weeks. I found no change in total zooplankton abundance or biomass, and no interaction between turbidity and nutrients. Rotifer abundance and biomass declined with turbidity, which correlated with a decline in the concentration of cryptophytes, a preferred food source for rotifers. Cladocera abundance increased with turbidity and there was no change in biomass, indicating compensatory responses within the cladocera community. Changes in the abundance of specific cladocera species further support the presence of compensatory dynamics in response to turbidity. In contrast with my findings, past laboratory studies and oligotrophic community studies found that turbidity had no impact on rotifer abundance and caused a decline in Cladocera abundance. In drawing different conclusions from previous studies, my research provides insights to how a highly diverse zooplankton community in nutrient-rich conditions respond to turbidity, and the potential for nutrients to alter the effects of turbidity on zooplankton communities.
Dr. Liana Burghardt Assistant Professor, Plant Sciences Department Pennsylvania State University Evolving together, evolving apart: Measuring the fitness of rhizobial bacteria in and out of symbiosis with leguminous plants The nitrogen-fixing symbiosis between legumes and rhizobia represents fertile ground to study the evolution and ecology of beneficial plant-microbe interactions. In facultative relationships where both partners can live independently, soil selection patterns can influence the process of host adaptation and vice versa. This talk will describe a twist on an ‘evolve and resequence’ methodology we developed to measure the relative success of scores of co-existing rhizobia isolates in host and nonhost environments. Our team of researchers has measured Sinorhizobium strain fitness in nodules of Medicago legume hosts and as free-living saprophytes in the soil. By synthesizing results from multiple experiments, we examine patterns of rhizobial fitness correlations within and between host and non-host environments. We found 1) only between host species do we observe negative fitness correlations (evolutionary constraint), 2) that in soil mesocosms, temperature and salinity influence isolate-level selection more strongly than other soil characteristics, and 3) that adaptation to nonhost soil environments is unlikely to constrain or undermine rhizobial adaptation to host environments. Our results suggest it may be possible to leverage host genetic variation to manipulate rhizobial communities and optimize rhizobial fitness without undermining the soil survival of rhizobia and that co-occurring Medicago species may function to maintain rhizobial diversity in soils.
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