Biology subjects

Yammine, A.

Publications and source records attributed to Yammine, A..

4 recordsLinked to original sources

bioRxiv2021

Temperature and nutrients drive complex eco-phenotypic dynamics in a microbial food web

Anthropogenic increases in temperature and nutrient loads will likely impact food web structure and stability. Although their independent effects have been reasonably well studied, their joint effects--particularly on coupled ecological and phenotypic dynamics--remain poorly understood. Here we experimentally manipulated temperature and nutrient levels in microbial food webs and used time-series analysis to quantify the strength of reciprocal effects between ecological and phenotypic dynamics across trophic levels. We found that i) joint -often interactive- effects of temperature and nutrients on ecological dynamics are more common at higher trophic levels, ii) temperature and nutrients interact to shift the relative strength of top-down vs. bottom-up control, and iii) rapid phenotypic change mediates observed ecological responses to changes in temperature and nutrients. Our results uncover how feedbacks between ecological and phenotypic dynamics mediate food web responses to environmental change. This suggests important but previously unknown ways that temperature and nutrients might jointly control the rapid eco-phenotypic feedbacks that determine food web dynamics in a changing world.

ecology↗

bioRxiv2021

Rapid plastic shifts in body size precede and determine population growth

O_LIBody size is a fundamental trait linked to many ecological processes--from individuals to ecosystems. Although the effects of body size on metabolism are well-known, the potential reciprocal effects of body size and density are less clear. Specifically, 1) whether changes in body size or density more strongly influence the other and 2) whether coupled rapid changes in body size and density are due to plasticity, rapid evolutionary change, or a combination of both. C_LIO_LIHere, we address these two issues by experimentally tracking population density and mean body size in the protist Tetrahymena pyriformis as it grows from low density to carrying capacity. We then use Convergent Cross Mapping time series analyses to infer the direction, magnitude, and causality of the link between body size and ecological dynamics. We confirm the results of our analysis by experimentally manipulating body size and density while keeping the other constant. Last, we fit mathematical models to our experimental time series that account for purely plastic change in body size, rapid evolution in size, or a combination of both, to gain insight into the processes that most likely explain the observed dynamics. C_LIO_LIOur results indicate that changes in body size more strongly influence changes in density than the other way around, but also show that there is reciprocity in this effect (i.e., a feedback). We show that a model that only accounts for purely plastic change in size most parsimoniously explains observed, coupled phenotypic and ecological dynamics. C_LIO_LITogether, these results suggest 1) that body size can shift dramatically through plasticity, well within ecological timescales, 2) that rapid changes in body size may have a larger effect on ecological dynamics than the reverse, but 3) phenotypic and ecological dynamics influence each as populations grow. Overall, we show that rapid plastic changes in functional traits like body size may play a fundamental -but currently unrecognized- role in familiar ecological processes such as logistic population growth. C_LI

ecology↗

bioRxiv2021

Increasing temperature weakens the positive effect of genetic diversity on population growth

Genetic diversity and temperature increases associated with global climate change, are known to independently influence population growth and extinction risk. Whether increasing temperature may influence the effect of genetic diversity on population growth, however, is not known. We address this issue in the model protist system Tetrahymena thermophila. We test the hypothesis that at temperatures closer to the species thermal optimum (i.e., the temperature at which population growth is maximal), genetic diversity should have a weaker effect on population growth compared to temperatures away from the thermal optimum. To do so, we grew populations of T. thermophila with varying levels of genetic diversity at increasingly warmer temperatures and quantified their intrinsic population growth rate, r. We found that genetic diversity increases population growth at cooler temperatures, but that as temperature increases, this effect almost completely disappears. We also show that a combination of changes in the amount of expressed genetic diversity (G), plastic changes in population growth across temperatures (E), and strong GxE interactions, underlie this temperature effect. Our results uncover important but largely overlooked temperature effects that have implications for the management of small populations with depauperate genetic stocks in an increasingly warming world.

ecology↗

bioRxiv2021

Predation by protists influences the temperature response of microbial communities

Temperature strongly influences microbial community structure and function, which in turn contributes to the global carbon cycle that can fuel further warming. Recent studies suggest that biotic interactions amongst microbes may play an important role in determining the temperature responses of these communities. However, how microbial predation regulates these communities under future climates is still poorly understood. Here we assess whether predation by one of the most important bacterial consumers globally - protists - influences the temperature response of a freshwater microbial community structure and function. To do so, we exposed these microbial communities to two cosmopolitan species of protists at two different temperatures, in a month-long microcosm experiment. While microbial biomass and respiration increased with temperature due to shifts in microbial community structure, these responses changed over time and in the presence of protist predators. Protists influenced microbial biomass and function through effects on community structure, and predation actually reduced microbial respiration rate at elevated temperature. Indicator species and threshold indicator taxa analyses showed that these predation effects were mostly determined by phylum-specific bacterial responses to protist density and cell size. Our study supports previous findings that temperature is an important driver of microbial communities, but also demonstrates that predation can mediate these responses to warming, with important consequences for the global carbon cycle and future warming.

ecology↗