Local adaptation of a parasite to solar radiation impacts disease transmission potential, spore yield, and host fecundity*

Environmentally transmitted parasites spend time in the abiotic environment, where they are subjected to a variety of stressors. Learning how they face this challenge is essential if we are to understand how host–parasite interactions may vary across environmental gradients. We used a zooplankton–bacteria host–parasite system where availability of sunlight (solar radiation) influences disease dynamics to look for evidence of parasite local adaptation to sunlight exposure. We also examined how variation in sunlight tolerance among parasite strains impacted host reproduction. Parasite strains collected from clearer lakes (with greater sunlight penetration) were most tolerant of the negative impacts of sunlight exposure, suggesting local adaptation to sunlight conditions. This adaptation came with both a cost and a benefit for parasites: parasite strains from clearer lakes produced relatively fewer transmission stages (spores) but these strains were more infective. After experimental sunlight exposure, the most sunlight‐tolerant parasite strains reduced host fecundity just as much as spores that were never exposed to sunlight. Sunlight availability varies greatly among lakes around the world. Our results suggest that the selective pressure sunlight exposure exerts on parasites may impact both parasite and host fitness, potentially driving variation in disease epidemics and host population dynamics across sunlight availability gradients.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/156433/3/evo13940.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156433/2/evo13940-sup-0001-SuppMat.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156433/1/evo13940_am.pd

Daphniid zooplankton assemblage shifts in response to eutrophication and metal contamination during the Anthropocene

Additional results from the principal component analyses conducted on eutrophication and metals data, as well as daphniid assemblages, and species richness rarefaction

Ecological and evolutionary responses of zooplankton communities to changes in lake chemical environments

One of the consequences of the development of landscapes for human uses is the release and accumulation of chemicals in the environment. The long-term effects of multigenerational exposure to this chemical pollution in wild populations are poorly understood. Both ecological and rapid evolutionary responses are likely, as both species and populations are known to vary in sensitivity to toxicant exposure. While we have observed frequent rapid evolutionary changes in wild populations, particularly in response to human impacts, we are only beginning to understand how important rapid evolution might be in shaping long-term ecological and evolutionary responses to environmental stressors such as chemical pollution. My dissertation uses freshwater zooplankton as a model to contribute to this knowledge gap, examining both ecological and evolutionary consequences of exposure to pollution stress across a variety of spatial and temporal scales. In chapter one I surveyed 51 small lakes in Connecticut, US to evaluate the relative importance of the lake physicochemical environment, habitat connectivity and broader spatial properties in shaping pelagic crustacean zooplankton communities. I found that the chemical environment, particularly dissolved ions, was far more important than space and connectivity in predicting zooplankton species distributions. This evidence suggests that for the most part in this system zooplankton dispersal is not limited and environmental filtering is playing a key role in the distribution of zooplankton species across the landscape. Chapters 2 through 4 examined long-term ecological and evolutionary changes in daphniid zooplankton taxa in four Connecticut lakes that have experienced differing degrees of pollution over the past century. Using paleolimnological techniques I reconstructed changes in eutrophication and heavy metal contamination in these lakes over time. Examination of daphniid diapausing egg banks deposited in sediments of these lakes uncovered evidence of taxonomic homogenization of the daphniid species over time in the three eutrophied lakes. I also found that eutrophication may have been more influential than metals in shaping species compositional patterns (chapter 2). Chapters 3 and 4 investigated phenotypic responses of Daphnia ambigua populations to heavy metal contamination. I found that Daphnia diapausing eggs from time periods when metal contamination was elevated were less likely to hatch and that those animals that did hatch had a higher rate of juvenile mortality (chapter 3). Daphnia hatched and successfully cultured from high copper and high cadmium time periods were more sensitive to exposure of these metals (chapter 4), a pattern consistent with rapid maladaptation to metals over multi-decadal timescales. Overall, my dissertation research uncovers widespread long-term effects of changes in lake chemical environments on both ecological and evolutionary trajectories of lake zooplankton communities. Future research into the drivers and consequences of these trends, particularly those observed in chapters 3 and 4, is warranted. It is important to understand, both for basic scientific and conservation purposes, whether exposure to widely distributed toxicants such as heavy metals is disrupting the evolutionary capacity of lake zooplankton, an important component to lake communities worldwide

Data from: Maladaptation to acute metal exposure in resurrected Daphnia ambigua clones after decades of increasing contamination

Human environmental impacts have driven some of the strongest and fastest phenotypic changes recorded in wild animal populations. Across populations, this variation is often adaptive, as populations evolve fitness advantages in response to human-modified environments. Yet some populations fail to adapt to changing environments. Evidenced by declines in relative fitness, such seemingly maladaptive outcomes are less common, but may be more likely in human modified contexts. Further, our ability to investigate the dynamics of these adaptive and maladaptive responses over time is typically limited in natural systems. I combined resurrection ecology and paleolimnology approaches to examine evolutionary responses of the freshwater zooplankter Daphnia to exposure to heavy metal contamination over the past 50-75 years using animals hatched from diapausing egg banks. In contrast to the predicted trend of adaptation to metal exposure over time, I observed an increase in sensitivity to both copper and cadmium exposure associated with increasing historic contamination. This potentially maladaptive trend occurred in Daphnia populations in three lakes. Given that the release of toxicants such as heavy metals is widespread and other researchers have observed local maladaptation to toxicant exposure, it is important to understand the drivers and implications of this pattern

Rogalski_AmNat_2016_Daphnia_Toxicity_Trials

Acute toxicity responses (48 hour LC50s) to metal exposure for Daphnia ambigua clones hatched from lake sediment egg banks. Mortality responses were measured for 1-5 replicates per clone on one or more test dates

Positive Effects of Nonnative Invasive <em>Phragmites australis</em> on Larval Bullfrogs

<div><h3>Background</h3><p>Nonnative <em>Phragmites australis</em> (common reed) is one of the most intensively researched and managed invasive plant species in the United States, yet as with many invasive species, our ability to predict, control or understand the consequences of invasions is limited. Rapid spread of dense <em>Phragmites</em> monocultures has prompted efforts to limit its expansion and remove existing stands. Motivation for large-scale <em>Phragmites</em> eradication programs includes purported negative impacts on native wildlife, a view based primarily on observational results. We took an experimental approach to test this assumption, estimating the effects of nonnative <em>Phragmites australis</em> on a native amphibian.</p> <h3>Methodology/Principal Findings</h3><p>Concurrent common garden and reciprocal transplant field experiments revealed consistently strong positive influences of <em>Phragmites</em> on <em>Rana catesbeiana</em> (North American bullfrog) larval performance. Decomposing <em>Phragmites</em> litter appears to contribute to the effect.</p> <h3>Conclusions/Significance</h3><p>Positive effects of <em>Phragmites</em> merit further research, particularly in regions where both <em>Phragmites</em> and <em>R. catesbeiana</em> are invasive. More broadly, the findings of this study reinforce the importance of experimental evaluations of the effects of biological invasion to make informed conservation and restoration decisions.</p> </div

Multivariate and univariate Analyses of Variance results for the field experiment (n = 68 enclosures) showing effects of origin (<i>Phragmites</i> or control), vegetation treatment (<i>Phragmites</i> or native deciduous leaf litter control), and the interaction between origin and treatment on the growth (final mass), survival rate, and final developmental stage of larval <i>Rana catesbeiana</i>.

<p>Multivariate and univariate Analyses of Variance results for the field experiment (n = 68 enclosures) showing effects of origin (<i>Phragmites</i> or control), vegetation treatment (<i>Phragmites</i> or native deciduous leaf litter control), and the interaction between origin and treatment on the growth (final mass), survival rate, and final developmental stage of larval <i>Rana catesbeiana</i>.</p

Multivariate and univariate Analyses of Variance results showing effects of vegetation treatment (<i>Phragmites</i> or native leaf litter control) on: dissolved oxygen, pH and temperature in the common garden experiment; and dissolved oxygen, conductivity, pH and temperature in the field. ^a.

a<p>Temperature was not included in the MANOVA in the field experiment for reasons explained in the <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0044420#s4" target="_blank">methods</a>.</p