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1. Predation shifts coevolution toward higher host contact rate and parasite virulence

   https://doi.org/10.1098/rspb.2021.2800  

   Walsman, Jason C.; Cressler, Clayton E. (July 2022, Proceedings of the Royal Society B: Biological Sciences)

   Hosts can avoid parasites (and pathogens) by reducing social contact, but such isolation may carry costs, e.g. increased vulnerability to predators. Thus, many predator–host–parasite systems confront hosts with a trade-off between predation and parasitism. Parasites, meanwhile, evolve higher virulence in response to increased host sociality and consequently, increased multiple infections. How does predation shift coevolution of host behaviour and parasite virulence? What if predators are selective, i.e. predators disproportionately capture the sickest hosts? We answer these questions with an eco-coevolutionary model parametrized for a Trinidadian guppy–Gyrodactylusspp. system. Here, increased predation drives host coevolution of higher grouping, which selects for higher virulence. Additionally, higher predator selectivity drives the contact rate higher and virulence lower. Finally, we show how predation and selectivity can have very different impacts on host density and prevalence depending on whether hosts or parasites evolve, or both. For example, higher predator selectivity led to lower prevalence with no evolution or only parasite evolution but higher prevalence with host evolution or coevolution. These findings inform our understanding of diverse systems in which host behavioural responses to predation may lead to increased prevalence and virulence of parasites. 

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2. MarR Family Transcription Factors from Burkholderia Species: Hidden Clues to Control of Virulence-Associated Genes

   https://doi.org/10.1128/MMBR.00039-18  

   Gupta, Ashish; Pande, Anuja; Sabrin, Afsana; Thapa, Sudarshan S.; Gioe, Brennan W.; Grove, Anne (March 2019, Microbiology and Molecular Biology Reviews)

   SUMMARY Species within the genus Burkholderia exhibit remarkable phenotypic diversity. Genomic plasticity, including genome reduction and horizontal gene transfer, has been correlated with virulence traits in several species. However, the conservation of virulence genes in species otherwise considered to have limited potential for infection suggests that phenotypic diversity may not be explained solely on the basis of genetic diversity. Instead, differential organization and control of gene regulatory networks may underlie many phenotypic differences. In this review, we evaluate how regulation of gene expression by members of the multiple antibiotic resistance regulator (MarR) family of transcription factors may contribute to shaping the physiological diversity of Burkholderia species, with a focus on the clinically relevant human pathogens. All Burkholderia species encode a relatively large number of MarR proteins, a feature common to bacteria that must respond to environmental changes such as those associated with host invasion. However, evolution of gene regulatory networks has likely resulted in orthologous transcription factors controlling disparate sets of genes. Adaptation to, and survival in, diverse habitats, including a human or plant host, is key to the success of Burkholderia species as (opportunistic) pathogens, and recent reports suggest that control of virulence-associated genes by MarR proteins features prominently among the survival strategies employed by these species. We suggest that identification of MarR regulons will contribute significantly to clarification of virulence determinants and phenotypic diversity. 

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3. De novo origins of multicellularity in response to predation

   https://doi.org/10.1038/s41598-019-39558-8  

   Herron, Matthew_D; Borin, Joshua_M; Boswell, Jacob_C; Walker, Jillian; Chen, I-Chen_Kimberly; Knox, Charles_A; Boyd, Margrethe; Rosenzweig, Frank; Ratcliff, William_C (February 2019, Scientific Reports)

   Abstract The transition from unicellular to multicellular life was one of a few major events in the history of life that created new opportunities for more complex biological systems to evolve. Predation is hypothesized as one selective pressure that may have driven the evolution of multicellularity. Here we show thatde novoorigins of simple multicellularity can evolve in response to predation. We subjected outcrossed populations of the unicellular green algaChlamydomonas reinhardtiito selection by the filter-feeding predatorParamecium tetraurelia. Two of five experimental populations evolved multicellular structures not observed in unselected control populations within ~750 asexual generations. Considerable variation exists in the evolved multicellular life cycles, with both cell number and propagule size varying among isolates. Survival assays show that evolved multicellular traits provide effective protection against predation. These results support the hypothesis that selection imposed by predators may have played a role in some origins of multicellularity. 

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4. Conspicuous coloration of toxin‐resistant predators implicates additional trophic interactions in a predator–prey arms race

   https://doi.org/10.1111/mec.16772  

   Hague, Michael T. J.; Miller, Lauren E.; Stokes, Amber N.; Feldman, Chris R.; Brodie, Jr, Edmund D.; Brodie, III, Edmund D. (November 2022, Molecular Ecology)

   Abstract Antagonistic coevolution between natural enemies can produce highly exaggerated traits, such as prey toxins and predator resistance. This reciprocal process of adaptation and counter‐adaptation may also open doors to other evolutionary novelties not directly involved in the phenotypic interface of coevolution. We tested the hypothesis that predator–prey coevolution coincided with the evolution of conspicuous coloration on resistant predators that retain prey toxins. In western North America, common garter snakes (Thamnophis sirtalis) have evolved extreme resistance to tetrodotoxin (TTX) in the coevolutionary arms race with their deadly prey, Pacific newts (Tarichaspp.). TTX‐resistant snakes can retain large amounts of ingested TTX, which could serve as a deterrent against the snakes' own predators if TTX toxicity and resistance are coupled with a conspicuous warning signal. We evaluated whether arms race escalation covaries with bright red coloration in snake populations across the geographic mosaic of coevolution. Snake colour variation departs from the neutral expectations of population genetic structure and covaries with escalating clines of newt TTX and snake resistance at two coevolutionary hotspots. In the Pacific Northwest, bright red coloration fits an expected pattern of an aposematic warning to avian predators: TTX‐resistant snakes that consume highly toxic newts also have relatively large, reddish‐orange dorsal blotches. Snake coloration also seems to have evolved with the arms race in California, but overall patterns are less intuitively consistent with aposematism. These results suggest that interactions with additional trophic levels can generate novel traits as a cascading consequence of arms race coevolution across the geographic mosaic. 

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5. Keystone predation: trait‐based or driven by extrinsic processes? Assessment using a comparative‐experimental approach

   https://doi.org/10.1002/ecm.1436  

   Menge, Bruce A.; Foley, Melissa M.; Robart, Matthew J.; Richmond, Erin; Noble, Mae; Chan, Francis (December 2020, Ecological Monographs)

   Abstract Keystone predation can be a determinant of community structure, including species diversity, but factors underlying “keystoneness” have been minimally explored. Using the system in which the original keystone, the sea starPisaster ochraceus, was discovered, we focused on two potential (but overlapping) determinants of keystoneness: intrinsic traits or state variables of the species (e.g., size, density), and extrinsic environmental parameters (e.g., prey productivity) that may provide conditions favorable for keystone predator evolution. Using a comparative‐experimental approach, with repeated field experiments at multiple sites across a variable coastal environment, we tested predation rates, or how quickly predators consumed prey, and predation effects, or community response to predator presence or absence. We tested five hypotheses: (H₁) predation rates and effects will vary in space but not time; (H₂) per population predation rates will vary primarily with individual traits and population variables; (HJHH₃) per capita predation rates will vary only with individual traits; (H₄) predation effects will vary with traits, variables, and external drivers; and (H₅) as predicted by the keystone predation hypothesis, diversity will vary unimodally with predation pressure. As hypothesized, predation rates differed among sites but not over time (H₁), and in caging exclusion experiments, predation effect varied with both intrinsic and extrinsic factors (H₄). Unexpectedly, predation rates varied with both intrinsic and extrinsic (H₂, per population), or only with extrinsic (H₃, per capita) factors. Further, in large‐plot exclusion experiments, predation effect was most closely associated with individual traits (contraH₄). Finally, taxon diversity varied unimodally with proxies of predation pressure (sessile prey abundance) and was sensitive to extrinsic factors (mussel growth, temperature, and upwelling,H₅). Hence, keystoneness depended on predator individual traits, predator population variables, and environmental parameters. However, temporal differences in caging experiments suggested that environmental characteristics underlying prey dynamics may be preeminent. Compared to prior experiments, predation was weaker with low prey input compared to periods with high prey input. Collectively, our results suggest that keystone predator evolution depends on the coalescence of species‐specific characteristics, and environmental parameters favoring high prey productivity. Our approach may be a model for future studies exploring the generality of keystoneness. 

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