Biology subjects

Larsen, T.

Publications and source records attributed to Larsen, T..

4 recordsLinked to original sources

bioRxiv2023

Reduced social function in experimentally evolved Dictyostelium discoideum implies selection for social conflict in nature

Many microbes interact with one another, but the difficulty of directly observing these interactions in nature makes interpreting their adaptive value complicated. The social amoeba Dictyostelium discoideum forms aggregates wherein some cells are sacrificed for the benefit of others. Within chimeric aggregates containing multiple unrelated lineages, cheaters can gain an advantage by undercontributing, but the extent to which wild D. discoideum has adapted to cheat is not fully clear. In this study, we experimentally evolved D. discoideum in an environment where there were no selective pressures to cheat or resist cheating in chimeras. D. discoideum lines grown in this environment evolved reduced competitiveness within chimeric aggregates and reduced ability to migrate during the slug stage. By contrast, we did not observe a reduction in cell number, a trait for which selection was not relaxed. The observed loss of traits that our laboratory conditions had made irrelevant suggests that these traits were adaptations driven and maintained by selective pressures D. discoideum faces in its natural environment. Our results suggest that D. discoideum faces social conflict in nature, and illustrate a general approach that could be applied to searching for social or non-social adaptations in other microbes. SIGNIFICANCE STATEMENTMicrobes interact in diverse and important ways, but the difficulty of directly observing microbes in nature can make it challenging to understand the adaptive significance of these interactions. In this study, we present an experimental evolution approach to infer the selective pressures behind an apparently social trait in the microbe Dictyostelium discoideum. We take advantage of the observation that organisms use it or lose it - when selective pressures are relaxed, adaptations that evolved in response to those pressures tend to be lost. Our work helps resolve debate over the importance of cheating in D. discoideum, and demonstrates a general approach that could be applied to the study of other microbial traits that are difficult to observe in nature.

evolutionary biology↗

bioRxiv2023

In the social amoeba D. discoideum, shortened stalks limit obligate cheater success even when exploitable partners are available.

Cooperation is widespread across life, but its existence can be threatened by exploitation. The rise of obligate social cheaters that are incapable of contributing to a necessary cooperative function can lead to the loss of that function and to the extinction of populations. In the social amoeba Dictyostelium discoideum, obligate social cheaters cannot form dead stalk cells and in chimeras instead form living spore cells. This gives them a competitive advantage within chimeras. However, obligate cheaters of this kind are not found in nature, probably because they are often enough in clonal populations that they need to retain the ability to produce stalks. In this study we discovered an additional cost to obligate cheaters. Even when there are wild-type cells to parasitize, the chimeric fruiting bodies that result have shorter stalks and these are disadvantaged in spore dispersal. The inability of obligate cheaters to form fruiting bodies when they are on their own combined with the lower functionality of fruiting bodies when they are not represent limits on obligate social cheating as a strategy.

evolutionary biology↗

bioRxiv2022

Dynamic subcellular localization of sodium-bicarbonate cotransporter NBCn1/SLC4A7 to plasma membrane, centrosomes, spindle, and primary cilia

Finely tuned regulation of transport protein localization is vital for epithelial function. Sodium-bicarbonate co-transporter NBCn1 (SLC4A7) is a key contributor to epithelial pH homeostasis, yet the regulation of its subcellular localization is not understood. Here, we show that a predicted N-terminal {beta}-sheet and short C-terminal -helical motif are essential for NBCn1 plasma membrane localization in epithelial cells. This localization was abolished by cell-cell contact disruption, and co-immunoprecipitation (co-IP) and proximity ligation (PLA) revealed NBCn1 interaction with E-cadherin and DLG1, linking the transporter to adherens junctions and the Scribble complex. NBCn1 also interacted with RhoA and localized to lamellipodia and filopodia in migrating cells. Finally, analysis of localization of native and GFP-tagged NBCn1, subcellular fractionation, co-IP of NBCn1 with Arl13B and CEP164, and PLA of NBCn1 and tubulin in mitotic spindles led to the surprising conclusion that NBCn1 additionally localizes to the centrosome and primary cilium in non-dividing, polarized epithelial cells, and to spindle, centrosome and midbodies during mitosis. We propose that NBCn1 traffics between lateral junctions, leading edge, and cell division machinery in Rab11 endosomes, adding new insight to the role of NBCn1 in cell cycle progression. Summary statementWe unravel molecular determinants of plasma membrane localization of the Na+,HCO3- cotransporter NBCn1 and discover that NBCn1 also localizes to centrosomes, spindle, midbody and primary cilia, likely cycling between these compartments.

cell biology↗

bioRxiv2020

Foraging strategies under extreme events: Contrasting adaptations by benthic macrofauna to drastic biogeochemical disturbance

Extreme events caused by global change are increasingly affecting the oceans biogeochemical cycling and ecosystem functioning, but it is challenging to observe how food webs respond to rapid habitat disturbances. Benthic communities are particularly vulnerable because their habitats are easily affected by extreme events. Here, we examined how benthic macrofauna responded to a "near shutdown" of shallow marine hydrothermal vents, triggered by M5.8 earthquake and C5 typhoon events. Despite reduced vent fluxes, we shows that the endemic vent crab Xenograpsus testudinatus continued to rely on chemosynthetic sulfur bacteria rather than photosynthetic sources. We posit this obligate nutritional dependence caused a population decline of vent crabs. In contrast, the non-endemic mollusks exhibited much greater dietary plasticity with no detectable impact on the population. Our study based on naturally occurring extreme events exemplifies how specialist species in marine system are particularly vulnerable to the unprecedented evolutionary and environmental pressures exerted by human activities worldwide.

ecology↗