Mutualistic Strategies Research Articles

Improved Remora Optimization Algorithm with Mutualistic Strategy for Solving Constrained Engineering Optimization Problems

Recently, a new swarm intelligence optimization algorithm called the remora optimization algorithm (ROA) was proposed. ROA simulates the remora’s behavior of the adsorption host and uses some formulas of the sailfish optimization (SFO) algorithm and whale optimization algorithm (WOA) to update the solutions. However, the performance of ROA is still unsatisfactory. When solving complex problems, ROA’s convergence ability requires further improvement. Moreover, it is easy to fall into local optimization. Since the remora depends on the host to obtain food and optimize ROA performance, this paper introduces the mutualistic strategy to strengthen the symbiotic relationship between the remora and the host. Meanwhile, chaotic tent mapping and roulette wheel selection are added to further improve the algorithm’s performance. By incorporating the above improvements, this paper proposes an improved remora optimization algorithm with a mutualistic strategy (IROA) and uses 23 benchmark functions in different dimensions and CEC2020 functions to validate the performance of the proposed IROA. Experimental studies on six classical engineering problems demonstrate that the proposed IROA has excellent advantages in solving practical optimization problems.

New evidence of a fish–bird interspecific feeding association between the European seabass and the European shag in the Mediterranean Sea

Although they have received little attention, interspecific feeding associations are a particular predation behavior in which two or more different species temporary feed simultaneously on the same food sources to obtain greater success in predation. These collaborations can be either mutualistic, commensalistic, or parasitic. One of the best-known examples is the seabird–cetacean associations. Prey herding is the foraging tactic most used in these associations and consists of swimming around and under prey balls to trap them in the water column. Here we reported some new evidence of a fish–bird interspecific feeding association between the European seabass, Dicentrarchus labrax (Linnaeus, 1758) and the European shag, Gulosus aristotelis (Linnaeus, 1761). We analyzed this association through the photograph and video documentation provided by “citizen scientists” in the Mediterranean Sea. We collected reliable proofs of this behavior, at least, in three instances from observations made by recreational fishermen in the Kvarner bay (Croatia, North Adriatic Sea). From the photographs and videos made available, we attempted to reconstruct a predation strategy adopted by these associated species to better understand the advantage this provides during hunting. Although it is not yet clear whether this association is an opportunistic behavior of the European seabass or a mutualistic strategy used by both species to improve their catching success, this feeding association seems to increase the chances to defeat prey defense strategies. Notably, some behavioral imitation of hunting strategies may be put in place by seabasses, which often feed in association with dolphins and other birds using similar prey herding strategies.

Molecular causes of an evolutionary shift along the parasitism–mutualism continuum in a bacterial symbiont

Symbiosis with microbes is a ubiquitous phenomenon with a massive impact on all living organisms, shaping the world around us today. Theoretical and experimental studies show that vertical transmission of symbionts leads to the evolution of mutualistic traits, whereas horizontal transmission facilitates the emergence of parasitic features. However, these studies focused on phenotypic data, and we know little about underlying molecular changes at the genomic level. Here, we combined an experimental evolution approach with infection assays, genome resequencing, and global gene expression analysis to study the effect of transmission mode on an obligate intracellular bacterial symbiont. We show that a dramatic shift in the frequency of genetic variants, coupled with major changes in gene expression, allow the symbiont to alter its position in the parasitism-mutualism continuum depending on the mode of between-host transmission. We found that increased parasitism in horizontally transmitted chlamydiae residing in amoebae was a result of processes occurring at the infectious stage of the symbiont's developmental cycle. Specifically, genes involved in energy production required for extracellular survival and the type III secretion system-the symbiont's primary virulence mechanism-were significantly up-regulated. Our results identify the genomic and transcriptional dynamics sufficient to favor parasitic or mutualistic strategies.

Host-transposon interactions: conflict, cooperation, and cooption.

Transposable elements (TEs) are mobile DNA sequences that colonize genomes and threaten genome integrity. As a result, several mechanisms appear to have emerged during eukaryotic evolution to suppress TE activity. However, TEs are ubiquitous and account for a prominent fraction of most eukaryotic genomes. We argue that the evolutionary success of TEs cannot be explained solely by evasion from host control mechanisms. Rather, some TEs have evolved commensal and even mutualistic strategies that mitigate the cost of their propagation. These coevolutionary processes promote the emergence of complex cellular activities, which in turn pave the way for cooption of TE sequences for organismal function.

Shifts along the parasite-mutualist continuum are opposed by fundamental trade-offs.

Theory suggests that symbionts can readily evolve more parasitic or mutualistic strategies with respect to hosts. However, many symbionts have stable interactions with hosts that improve nutrient assimilation or confer protection from pathogens. We explored the potential for evolution of increased parasitism or decreased parasitism and mutualism in a natural gut symbiosis between larvae of Plutella xylostella and the microbe Enterobacter cloacae. We focused on interactions with the pathogen, Bacillus thuringiensis: selecting for parasitism in terms of facilitating pathogen infection, or increased mutualism in terms of host protection. Selection for parasitism led to symbionts increasing pathogen-induced mortality but reduced their competitive ability with pathogens and their in vitro growth rates. Symbionts did not evolve to confer protection from pathogens. However, several lineages evolved reduced parasitism, primarily in terms of moderating impacts on host growth, potentially because prudence pays dividends through increased host size. Overall, the evolution of increased parasitism was achievable but was opposed by trade-offs likely to reduce fitness. The evolution of protection may not have occurred because suppressing growth of B. thuringiensis in the gut might provide only weak protection or because evolution towards protective interactions was opposed by the loss of competitive fitness in symbionts.

Differential expression of a prophage-encoded glycocin and its immunity protein suggests a mutualistic strategy of a phage and its host

Sublancin 168 is a highly potent and stable antimicrobial peptide secreted by the Gram-positive bacterium Bacillus subtilis. Production of sublancin gives B. subtilis a major competitive growth advantage over a range of other bacteria thriving in the same ecological niches, the soil and plant rhizosphere. B. subtilis protects itself against sublancin by producing the cognate immunity protein SunI. Previous studies have shown that both the sunA gene for sublancin and the sunI immunity gene are encoded by the prophage SPβ. The sunA gene is under control of several transcriptional regulators. Here we describe the mechanisms by which sunA is heterogeneously expressed within a population, while the sunI gene encoding the immunity protein is homogeneously expressed. The key determinants in heterogeneous sunA expression are the transcriptional regulators Spo0A, AbrB and Rok. Interestingly, these regulators have only a minor influence on sunI expression and they have no effect on the homogeneous expression of sunI within a population of growing cells. Altogether, our findings imply that the homogeneous expression of sunI allows even cells that are not producing sublancin to protect themselves at all times from the active sublancin produced at high levels by their isogenic neighbors. This suggests a mutualistic evolutionary strategy entertained by the SPβ prophage and its Bacillus host, ensuring both stable prophage maintenance and a maximal competitive advantage for the host at minimal costs.

The effect of the dispersion of rewarding and rewardless flowers on visitation and constancy by bumblebees (<i>Bombus impatiens</i>)

Deceptive pollination strategies, in which plants rely on animal pollinators but provide no benefits to their pollinators, have evolved many times in angiosperms. However, the conditions that favour deceptive pollination strategies over mutualistic strategies are poorly understood. One factor that may be important for the success of deceptive strategies is the plants’ dispersion in relation to co-flowering, rewarding species. We compared pollinator behaviour across two artificial environments, one in which a rewardless species was mixed with a rewarding species and one in which the two species occurred in contiguous patches. Bumblebees both encountered and visited rewardless flowers more often when they were mixed with rewarding species. However, the rate of switching was also higher under those conditions, which could result in higher rates of interspecific pollen transfer. The environmental conditions most favourable to deceptive pollination strategies may vary depending on the vulnerability of the plant species to interspecific pollen transfer.

Lignin degradation: microorganisms, enzymes involved, genomes analysis and evolution.

Extensive research efforts have been dedicated to describing degradation of wood, which is a complex process; hence, microorganisms have evolved different enzymatic and non-enzymatic strategies to utilize this plentiful plant material. This review describes a number of fungal and bacterial organisms which have developed both competitive and mutualistic strategies for the decomposition of wood and to thrive in different ecological niches. Through the analysis of the enzymatic machinery engaged in wood degradation, it was possible to elucidate different strategies of wood decomposition which often depend on ecological niches inhabited by given organism. Moreover, a detailed description of low molecular weight compounds is presented, which gives these organisms not only an advantage in wood degradation processes, but seems rather to be a new evolutionatory alternative to enzymatic combustion. Through analysis of genomics and secretomic data, it was possible to underline the probable importance of certain wood-degrading enzymes produced by different fungal organisms, potentially giving them advantage in their ecological niches. The paper highlights different fungal strategies of wood degradation, which possibly correlates to the number of genes coding for secretory enzymes. Furthermore, investigation of the evolution of wood-degrading organisms has been described.

Mutualistic strategies minimize coextinction in plant-disperser networks.

The global decline of mutualists such as pollinators and seed dispersers may cause negative direct and indirect impacts on biodiversity. Mutualistic network models used to understand the stability of mutualistic systems indicate that species with low partner diversity are most vulnerable to coextinction following mutualism disruption. However, existing models have not considered how species vary in their dependence on mutualistic interactions for reproduction or survival, overlooking the potential influence of this variation on species' coextinction vulnerability and on network stability. Using global databases and field experiments focused on the seed dispersal mutualism, we found that plants and animals that depend heavily on mutualistic interactions have higher partner diversity. Under simulated network disruption, this empirical relationship strongly reduced coextinction because the species most likely to lose mutualists depend least on their mutualists. The pattern also reduced the importance of network structure for stability; nested network structure had little effect on coextinction after simulations incorporated the empirically derived relationship between partner diversity and mutualistic dependence. Our results highlight a previously unknown source of stability in mutualistic networks and suggest that differences among species in their mutualistic strategy, rather than network structure, primarily accounts for stability in mutualistic communities.

Partner abundance controls mutualism stability and the pace of morphological change over geologic time

Mutualisms that involve symbioses among specialized partners may be more stable than mutualisms among generalists, and theoretical models predict that in many mutualisms, partners exert reciprocal stabilizing selection on traits directly involved in the interaction. A corollary is that mutualism breakdown should increase morphological rates of evolution. We here use the largest ant-plant clade (Hydnophytinae), with different levels of specialization for mutualistic ant symbionts, to study the ecological context of mutualism breakdown and the response of a key symbiosis-related trait, domatium entrance hole size, which filters symbionts by size. Our analyses support three predictions from mutualism theory. First, all 12 losses apparently only occur from a generalist symbiotic state. Second, mutualism losses occurred where symbionts are scarce, in our system at high altitudes. Third, domatium entrance hole size barely changes in specialized symbiotic species, but evolves rapidly once symbiosis with ants has broken down, with a "morphorate map" revealing that hotspots of entrance hole evolution are clustered in high-altitude areas. Our study reveals that mutualistic strategy profoundly affects the pace of morphological change in traits involved in the interaction and suggests that shifts in partners' relative abundances may frequently drive reversions of generalist mutualisms to autonomy.

Weathering, secondary mineral genesis, and soil formation caused by lichens and mosses growing on granitic gneiss in a boreal forest environment

Lichens and mosses growing on granitic gneiss in a boreal forest environment caused intense chemical weathering of the rock, producing exclusively biogenic secondary minerals and soils and accumulating solubilised rock-forming elements (Si and metals), but weathering in the absence of these organisms was relatively ineffective. Apart from primary biotite, the only phyllosilicates in the rock were sericite and chlorite formed by hydrothermal metamorphism or abiotic weathering, or both, but the biogenic soils contained expandable clay minerals and, in several cases, kaolinite and calcite, together with illite and chlorite. Lichens were especially effective in altering feldspars to clay, but mosses generally produced a greater abundance of expandable clay minerals, and kaolinite was produced only by certain species of moss — specifically the ones whose rock-derived element concentrations and Mg/Ca ratios were highest. Rock-derived element concentrations were usually highest in mosses, and element enrichment increased with the charge/radius ratio of the cation of the element, suggesting carrier-mediated transport across cell membranes. Furthermore, lichens and mosses produced different assemblages of expandable clay minerals, and most mosses (but none of the lichens) produced authigenic amphiboles and pyroxenes. Biological weathering is attributable to solubilisation of rock-forming elements by chelating agents and H2CO3, bioaccumulation of the elements, and nucleation of secondary silicates by chelate complexes functioning as templates for epitaxial growth of specific crystal structures. The different weathering and soil-forming processes of lichens and mosses suggest a mutualistic strategy for maximising the release of inorganic nutrients from rocks and retaining them in bioavailable forms in the soil.

Sustainable agriculture: possible trajectories from mutualistic symbiosis and plant neodomestication

Food demand will increase concomitantly with human population. Food production therefore needs to be high enough and, at the same time, minimize damage to the environment. This equation cannot be solved with current strategies. Based on recent findings, new trajectories for agriculture and plant breeding which take into account the belowground compartment and evolution of mutualistic strategy, are proposed in this opinion article. In this context, we argue that plant breeders have the opportunity to make use of native arbuscular mycorrhizal (AM) symbiosis in an innovative ecologically intensive agriculture.

Bet hedging based cooperation can limit kin selection and form a basis for mutualism

Mutualism is a mechanism of cooperation in which partners that differ help each other. As such, mutualism opposes mechanisms of kin selection and tag-based selection (for example the green beard mechanism), which are based on giving exclusive help to partners that are related or carry the same tag. In contrast to kin selection, which is a basis for parochialism and intergroup warfare, mutualism can therefore be regarded as a mechanism that drives peaceful coexistence between different groups and individuals. Here the competition between mutualism and kin (tag) selection is studied. In a model where kin selection and tag-based selection are dominant, mutualism is promoted by introducing environmental fluctuations. These fluctuations cause reduction in reproductive success by the mechanism of variance discount. The best strategy to counter variance discount is to share with agents who experience the most anticorrelated fluctuations, a strategy called bet hedging. In this way, bet hedging stimulates cooperation with the most unrelated partners, which is a basis for mutualism. Analytic results and simulations reveal that, if this effect is large enough, mutualistic strategies can dominate kin selective strategies. In addition, mutants of these mutualistic strategies that experience fluctuations that are more anticorrelated to their partner, can outcompete wild type, which can lead to the evolution of specialization. In this way, the evolutionary success of mutualistic strategies can be explained by bet hedging-based cooperation.