Biology subjects

Stoy, K. S.

Publications and source records attributed to Stoy, K. S..

4 recordsLinked to original sources

bioRxiv2025

Partner fidelity and coevolution: Useful but not required for rapidly increased mutualistic benefits

Evolutionary theory predicts that specialization between mutualistic partners is beneficial, limiting conflict and increasing the opportunity to evolve cooperative benefits through sustained reciprocal selection. However, specialized mutualisms are relatively rare in nature. Few empirical studies have directly examined how multi-partner interactions affect mutualistic evolution, largely because tracking partner dynamics over evolutionary timescales is challenging in natural systems. We circumvent this constraint via experimental evolution with an engineered resource sharing mutualism in Bakers yeast (Saccharomyces cerevisiae), which allows precise control of partner fidelity across generations. We compared high partner fidelity (consistent pairings) with low partner fidelity (temporally rotating partners) across 54 rounds of selection. High partner fidelity produced the strongest mutualistic benefits (7.2% increased growth over controls), while low partner fidelity yielded only modest benefits (2.2% increase). Time-shift experiments confirmed that while coevolution enhanced benefit evolution, it was not strictly necessary: benefits also evolved through one-sided adaptation. Genomic analyses revealed parallel evolution in amino acid metabolism and starvation response genes, with the slower-growing genotype driving most evolutionary change. Surprisingly, high-fidelity lineages evolved as generalists rather than specialists, cooperating equally well with all partners tested. Overall, these results demonstrate that partner fidelity facilitates the rapid evolution of mutualistic benefits but is not strictly required for mutualistic evolution.

evolutionary biology↗

bioRxiv2025

Multiple pathways to the evolution of positive assortment in aggregative multicellularity

The evolutionary transition to multicellularity requires shifting the primary unit of selection from cells to multicellular collectives. How this occurs in aggregative organisms remains poorly understood. Clonal development provides a direct path to multicellular adaptation through genetic identity between cells, but aggregative organisms face a constraint: selection on collective-level traits cannot drive adaptation without positive genetic assortment. We leveraged experimental evolution of flocculating Saccharomyces cerevisiae to examine the evolution and role of genetic assortment in multicellular adaptation. After 840 generations of selection for rapid settling, 13 of 19 lineages evolved increased positive assortment relative to their ancestor. However, assortment provided no competitive advantage during settling selection, suggesting it arose as an indirect effect of selection on cell-level traits rather than through direct selection on collective-level properties. Genetic reconstruction experiments and protein structure modeling revealed two distinct pathways to assortment: kin recognition mediated by mutations in the FLO1 adhesion gene and generally enhanced cellular adhesion that improved flocculation efficiency independent of partner genotype. The evolution of assortment without immediate adaptive benefit suggests that key innovations enabling multicellular adaptation may arise indirectly through cell-level selection. Our results demonstrate fundamental constraints on aggregative multicellularity and help explain why aggregative lineages have remained simple.

evolutionary biology↗

bioRxiv2021

Evaluating the role of coevolution in a horizontally transmitted mutualism

Mutualism depends on the alignment of host and symbiont fitness. Horizontal transmission can readily decouple fitness interests, yet horizontally transmitted mutualisms are common in nature. We hypothesized that pairwise coevolution and specialization in host-symbiont interactions underlies the maintenance of cooperation in a horizontally transmitted mutualism. Alternatively, we predicted selection by multiple host species may select for cooperative traits in a generalist symbiont through diffuse coevolution. We tested for signatures of pairwise coevolutionary change between the squash bug Anasa tristis and its horizontally acquired bacterial symbiont Caballeronia spp. by measuring local adaptation. We found no evidence for local adaptation between sympatric combinations of A. tristis squash bugs and Caballeronia spp. across their native geographic range. To test for diffuse coevolution, we performed reciprocal inoculations to test for specialization between three Anasa host species and Caballeronia spp. symbionts isolated from conspecific hosts. We observed no evidence of specialization across host species. Our results demonstrate generalist dynamics underlie the interaction between Anasa insect hosts and their Caballeronia spp. symbionts. Specifically, diffuse coevolution between multiple host species with a shared generalist symbiont may maintain cooperative traits despite horizontal transmission.

evolutionary biology↗

bioRxiv2021

The importance of environmentally-acquired bacterial symbionts for the squash bug (Anasa tristis), a significant agricultural pest

Most insects maintain associations with microbes that shape their ecology and evolution. Such symbioses have important applied implications when the associated insects are pests or vectors of disease. The squash bug, Anasa tristis (Coreoidea: Coreidae), is a significant pest of human agriculture in its own right and also causes damage to crops due to its capacity to transmit a bacterial plant pathogen. Here, we demonstrate that complete understanding of these insects requires consideration of their association with bacterial symbionts in the family Burkholderiaceae. Isolation and sequencing of bacteria housed in midgut crypts in these insects indicates that these bacteria are consistent and dominant members of the crypt-associated bacterial communities. These symbionts are closely related to Caballeronia spp. associated other true bugs in the superfamiles Lygaeoidea and Coreoidea. Fitness assays with representative Burkholderiaceae strains indicate that the association can significantly increase survival and decrease development time, though strains do vary in the benefits that they confer to their hosts, with Caballeronia spp. providing the greatest benefit. Experiments designed to assess transmission mode indicate that unlike many other beneficial insect symbionts, the bacteria are not acquired from parents before or after hatching but are instead acquired from the environment after molting to a later development stage. The bacteria do, however, have the capacity to escape adults to be transmitted to later generations, leaving the possibility for a combination of indirect vertical and horizontal transmission.

ecology↗