Hidden genetic variation in the germline genome of <i>Tetrahymena thermophila</i>

Dimond, Kristen L.; Zufall, Rebecca A.

doi:10.1111/jeb.12868

Cited by 5 publications

(4 citation statements)

References 49 publications

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“…While others have argued that laboratory cultures should have low levels of heritable genetic variation (DeLong et al, 2014), T. pyriformis has mechanisms to maintain larger than expected levels of genetic variation (Dimond & Zufall, 2016). Because of this, and to assess whether observed changes in body size were more likely due to plasticity or rapid evolution, we fitted two possible models that track change in the abundance and average body size of a population, N , as it grows logistically towards a carrying capacity K with intrinsic growth rate r .…”

Section: Methodsmentioning

confidence: 99%

Feedbacks between size and density determine rapid eco‐phenotypic dynamics

et al. 2022

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1. Body 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, (a) whether changes in body size or density more strongly influence the other and (b) whether coupled rapid changes in body size and density are due to plasticity, rapid evolutionary change or a combination of both.2. Here, 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 population 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 insights into the processes that most likely explain the observed dynamics.3. Our 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.4. Together, these results suggest (a) that body size can shift dramatically through plasticity, well within ecological timescales, (b) that rapid changes in body size may have a larger effect on population dynamics than the reverse, but (c) phenotypic and population dynamics influence each other 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.

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Section: Methodsmentioning

confidence: 99%

Feedbacks between size and density determine rapid eco‐phenotypic dynamics

et al. 2022

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“…While others have argued that laboratory cultures should have low levels of heritable genetic variation (DeLong, Hanley & Vasseur 2014), T. pyriformis has mechanisms to maintain larger than expected levels of genetic variation (Dimond & Zufall 2016). Because of this, and to assess whether observed changes in body size were more likely due to plasticity or rapid evolution, we fitted two possible models that track change in the abundance and average body size of a population, N , as it grows logistically towards a carrying capacity K with intrinsic growth rate r .…”

Section: Methodsmentioning

confidence: 99%

Feedbacks between size and density determine rapid eco-phenotypic dynamics

Gibert

Han

Wieczynski

et al. 2021

Preprint

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1. Body 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, how body size influences, and is influenced by, population growth and density is less clear. Specifically, 1) whether body size, or population dynamics, more strongly influences the other, and, 2) whether observed changes in body size are due to plasticity or rapid evolutionary change, are not well understood. 2. Here, 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 state-of-the-art time-series analyses to infer the direction, magnitude, and causality of the link between body size and ecological dynamics. Last, we fit two alternative dynamical models to our empirical time series to assess whether plasticity or rapid evolution better explains changes in mean body size. 3. Our results clearly indicate that changes in body size precede and determine changes in population density, not the other way around. We also show that a model assuming that size changes via plasticity more parsimoniously explains these observed coupled phenotypic and ecological dynamics than one that assumes rapid evolution drives changes in size. 4. Together these results suggest that rapid, plastic phenotypic change not only occurs well within ecological timescales but may even precede -and causally influence- ecological dynamics. Furthermore, large individuals may be favored and fuel high population growth rates when population density is low, but smaller individuals may be favored once populations reach carrying capacity and resources become scarcer. Thus, rapid plastic changes in functional traits may play a fundamental and currently unrecognized role in familiar ecological processes like logistic population growth.

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“…Yet, our results very clearly indicate a strong increase in growth rates with genetic diversity that weakens at warmer temperatures (Figure 2a). One possible explanation for the observed increase in population growth with genetic diversity is the occurrence of heterosis, or outbreeding enhancement, which has not been ruled out in this particular system (Dimond & Zufall, 2016). Indeed, clonal lines from different genetic backgrounds may also belong to different mating types, which could have led to increasing levels of sexual reproduction and heterozygosity in genetically diverse combinations.…”

Section: Discussionmentioning

confidence: 92%

“…While increasing genetic diversity resulting in higher population growth is common in other systems (Frankham, 2005), it is not clear why that should be the case in this particular study system. Previous work has indicated that inbreeding depression-that is, a decrease in absolute fitness (or intrinsic growth rate) with increasing levels of inbreeding (often due to the accumulation of deleterious alleles)-is unlikely to happen in T. thermophila (Dimond & Zufall, 2016), and outbreeding depression-that is, the decrease in absolute fitness due to the arrival of maladapted alleles-is also unlikely (Dimond & Zufall, 2016). Yet, our results very clearly indicate a strong increase in growth rates with genetic diversity that weakens at warmer temperatures (Figure 2a).…”

Section: Discussionmentioning

confidence: 99%

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

Singleton

Liu

Votzke

et al. 2021

Ecology and Evolution

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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, or Topt), 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 weakens. We also show that a combination of changes in the amount of expressed genetic diversity (G) in r, plastic changes in population growth across temperatures (E), and strong G × E 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.

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Hidden genetic variation in the germline genome of Tetrahymena thermophila

Cited by 5 publications

References 49 publications

Feedbacks between size and density determine rapid eco‐phenotypic dynamics

Feedbacks between size and density determine rapid eco‐phenotypic dynamics

Feedbacks between size and density determine rapid eco-phenotypic dynamics

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

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