Biology subjects

Malusare, S.

Publications and source records attributed to Malusare, S..

3 recordsLinked to original sources

bioRxiv2023

Population size shapes trade-off dilution and adaptation to a marginal niche unconstrained by sympatric habitual conditions

Niche expansion remains significantly understudied in sympatric scenarios where marginal and habitual niches are simultaneously available. Devoid of spatial constraints, such conditions impose selection to maintain fitness in habitual (high-productivity) niches while adapting to marginal (low-productivity) niches. Hence, habitual niche composition should constrain adaptation to marginal niches. This remains untested. Similarly, it is unknown if larger populations expand their niches better. We tested these hypotheses using experimental evolution with Escherichia coli and found that larger populations consistently adapted better to both marginal and habitual niches. Whereas the habitual niche composition (constant versus fluctuating environments; environmental fluctuations varying in both predictability and speed) significantly shaped fitness in habitual niches, surprisingly, it failed to constrain adaptation to the marginal niche. Curiously, two negatively correlated habitual niches can still each be positively correlated with the marginal niche. This allows the marginal niche to dilute trade-offs between habitual niches, thereby enabling costless niche expansion.

evolutionary biology↗

bioRxiv2020

An interplay of population size and environmental heterogeneity explains why fitness costs are rare

Theoretical models of ecological specialization commonly assume that adaptation to one environment leads to fitness reductions (costs) in others. However, empirical studies often fail to detect such costs. We addressed this conundrum using experimental evolution with Escherichia coli in several homogeneous and heterogeneous environments at multiple population sizes. We found that in heterogeneous environments, smaller populations paid significant costs, but larger ones avoided them altogether. Contrastingly, in homogeneous environments, larger populations paid more costs than the smaller ones. Overall, large population sizes and heterogeneous environments led to cost avoidance when present together but not on their own. Whole-genome whole-population sequencing revealed that the enrichment of multiple mutations within the same lineage (and not subdivision into multiple distinct specialist subpopulations) was the mechanism of cost avoidance. Since the conditions revealed by our study for avoiding costs are widespread, it explains why the costs expected in theory are rarely detected in experiments.

evolutionary biology↗

bioRxiv2020

Larger bacterial populations evolve heavier fitness trade-offs and undergo greater ecological specialization

Evolutionary studies over the last several decades have invoked fitness trade-offs to explain why species prefer some environments to others. However, the effects of population size on trade-offs and ecological specialization remain largely unknown. To complicate matters, trade-offs themselves have been visualized in multiple ways in the literature. Thus, it is not clear how population size can affect the various aspects of trade-offs. To address these issues, we conducted experimental evolution with Escherichia coli populations of two different sizes in two nutritionally limited environments and studied fitness trade-offs from three different perspectives. We found that larger populations evolved greater fitness trade-offs, regardless of how trade-offs are conceptualized. Moreover, although larger populations adapted more to their selection conditions, they also became more maladapted to other environments, ultimately paying heavier costs of adaptation. To enhance the generalizability of our results, we further investigated the evolution of ecological specialization across six different environmental pairs and found that larger populations specialized more frequently and evolved consistently steeper reaction norms of fitness. This is the first study to demonstrate a relationship between population size and fitness trade-offs and the results are important in understanding the population genetics of ecological specialization and vulnerability to environmental changes.

evolutionary biology↗