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Facultative parasites as evolutionary stepping-stones towards parasitic lifestyles.

ABSTRACT: Parasites and parasitic lifestyles have evolved from free-living organisms multiple times. How such a key evolutionary transition occurred remains puzzling. Facultative parasites represent potential transitional states between free-living and fully parasitic lifestyles because they can be either free-living or parasitic depending on environmental conditions. We suggest that facultative parasites with phenotypically plastic life-history strategies may serve as evolutionary stepping-stones towards obligate parasitism. Pre-adaptations provide a starting point for the transition towards opportunistic or facultative parasitism, but what evolutionary mechanism underlies the transition from facultative to obligate parasitism? In this Opinion Piece, we outline how facultative parasites could evolve towards obligate parasites via genetic assimilation, either alone or in combination with the Baldwin effect. We further describe the key predictions stemming from each of these evolutionary pathways. The importance of genetic assimilation in evolution has been hotly debated. Studies on facultative parasites may not only provide key insights regarding the evolution of parasitism, but also provide ideal systems in which to test evolutionary theory on genetic accommodation.

SUBMITTER: Luong LT

PROVIDER: S-EPMC6501370 | biostudies-literature | 2019 Apr

REPOSITORIES: biostudies-literature

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Facultative parasites as evolutionary stepping-stones towards parasitic lifestyles.

Luong Lien T LT Mathot Kimberley J KJ

Biology letters 20190401 4

Parasites and parasitic lifestyles have evolved from free-living organisms multiple times. How such a key evolutionary transition occurred remains puzzling. Facultative parasites represent potential transitional states between free-living and fully parasitic lifestyles because they can be either free-living or parasitic depending on environmental conditions. We suggest that facultative parasites with phenotypically plastic life-history strategies may serve as evolutionary stepping-stones towards ...[more]

PMID: 30991912

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Project description:BackgroundNematodes are a widespread and diverse group comprising free-living and parasitic species, some of which have major detrimental effects on crops, animals, and human health. Genomic comparisons of nematodes may help reveal the genetic bases for the evolution of parasitic lifestyles. Fatty acid and retinol-binding proteins (FARs) are thought to be unique to nematodes and play essential roles in their development, reproduction, infection, and possibly parasitism through promoting the uptake, transport, and distribution of lipid and retinol. However, the evolution of FAR family proteins across the phylum Nematoda remains elusive.ResultsWe report here the evolutionary relationship of the FAR gene family across nematodes. No FAR was found in Trichocephalida species and Romanomermis culicivorax from Clade I, and FAR could be found in species from Clades III, IV, and V. FAR proteins are conserved in Clade III species and separated into three clusters. Tandem duplications and high divergence events lead to variable richness and low homology of FARs in Steinernema of Clade IVa, Strongyloides of Clade IVb, and intestinal parasitic nematodes from Clades Vc and Ve. Moreover, different richness and sequence variations of FARs in pine wood, root-knot, stem, and cyst nematodes might be determined by reproduction mode or parasitism. However, murine lungworm Angiostrongylus and bovine lungworm Dictyocaulus viviparus from Clade Vd have only 3-4 orthologs of FAR. RNA-seq data showed that far genes, especially far-1 and far-2, were highly expressed in most nematodes. Angiostrongylus cantonensis FAR-1 and FAR-3 have low sequence homology and distinct ligand-binding properties, leading to differences in the cavity volume of proteins. These data indicate that FAR proteins diverged early and experienced low selective pressure to form genus-level diversity. The far genes are present in endophyte or root-colonized bacteria of Streptomyces, Kitasatospora sp., Bacillus subtilis, and Lysobacter, suggesting that bacterial far genes might be derived from plant-parasitic nematodes by horizontal gene transfer.ConclusionsData from these comparative analyses have provided insights into genus-level diversity of FAR proteins in the phylum Nematoda. FAR diversification provides a glimpse into the complicated evolution history across free-living and parasitic nematodes.

Project description:UNLABELLED:As they mature, many capsids undergo massive conformational changes that transform their stability, reactivity, and capacity for DNA. In some cases, maturation proceeds via one or more intermediate states. These structures represent local minima in a rich energy landscape that combines contributions from subunit folding, association of subunits into capsomers, and intercapsomer interactions. We have used scanning calorimetry and cryo-electron microscopy to explore the range of capsid conformations accessible to bacteriophage HK97. To separate conformational effects from those associated with covalent cross-linking (a stabilization mechanism of HK97), a cross-link-incompetent mutant was used. The mature capsid Head I undergoes an endothermic phase transition at 60°C in which it shrinks by 7%, primarily through changes in its hexamer conformation. The transition is reversible, with a half-life of ~3 min; however, >50% of reverted capsids are severely distorted or ruptured. This observation implies that such damage is a potential hazard of large-scale structural changes such as those involved in maturation. Assuming that the risk is lower for smaller changes, this suggests a rationalization for the existence of metastable intermediates: that they serve as stepping stones that preserve capsid integrity as it switches between the radically different conformations of its precursor and mature states. IMPORTANCE:Large-scale conformational changes are widespread in virus maturation and infection processes. These changes are accompanied by the release of conformational free energy as the virion (or fusogenic glycoprotein) switches from a precursor state to its mature state. Each state corresponds to a local minimum in an energy landscape. The conformational changes in capsid maturation are so radical that the question arises of how maturing capsids avoid being torn apart. Offering proof of principle, severe damage is inflicted when a bacteriophage HK97 capsid reverts from the (nonphysiological) state that it enters when heated past 60 °C. We suggest that capsid proteins have been selected in part by the criterion of being able to avoid sustaining collateral damage as they mature. One way of achieving this---as with the HK97 capsid-involves breaking the overall transition down into several smaller steps in which the risk of damage is reduced.

Project description:In the marine environment, understanding the biophysical mechanisms that drive variability in larval dispersal and population connectivity is essential for estimating the potential impacts of climate change on the resilience and genetic structure of populations. Species whose populations are small, isolated and discontinuous in distribution will differ fundamentally in their response and resilience to environmental stress, compared with species that are broadly distributed, abundant and frequently exchange conspecifics. Here, we use an individual-based modelling approach, combined with a population genetics projection model, to consider the impacts of a warming climate on the population connectivity of two contrasting Antarctic fish species, Notothenia rossii and Champsocephalus gunnari. Focussing on the Scotia Sea region, sea surface temperatures are predicted to increase significantly by the end of the 21st century, resulting in reduced planktonic duration and increased egg and larval mortality. With shorter planktonic durations, the results of our study predict reduced dispersal of both species across the Scotia Sea, from Antarctic Peninsula sites to islands in the north and east, and increased dispersal among neighbouring sites, such as around the Antarctic Peninsula. Increased mortality modified the magnitude of population connectivity but had little effect on the overall patterns. Whilst the predicted changes in connectivity had little impact on the projected regional population genetic structure of N. rossii, which remained broadly genetically homogeneous within distances of ~1,500 km, the genetic isolation of C. gunnari populations in the northern Scotia Sea was predicted to increase with rising sea temperatures. Our study highlights the potential for increased isolation of island populations in a warming world, with implications for the resilience of populations and their ability to adapt to ongoing environmental change, a matter of high relevance to fisheries and ecosystem-level management.

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Facultative parasites as evolutionary stepping-stones towards parasitic lifestyles.

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Facultative parasites as evolutionary stepping-stones towards parasitic lifestyles.

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