microCOOL: microbial endosymbiotic thermal buffer against heatwaves

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Comparative mitogenomic analyses and gene rearrangements reject the alleged polyphyly of a bivalve genus

Publication . Cunha, Regina L.; Nicastro, Katy; Zardi, Gerardo I.; Madeira, Celine; McQuaid, Christopher D.; J. Cox, Cymon; Castilho, Rita

Background: The order and orientation of genes encoded by animal mitogenomes are typically conserved, although there is increasing evidence of multiple rearrangements among mollusks. The mitogenome from a Brazilian brown mussel (hereafter named B1) classified as Perna perna Linnaeus, 1758 and assembled from Illumina short-length reads revealed an unusual gene order very different from other congeneric species. Previous mitogenomic analyses based on the Brazilian specimen and other Mytilidae suggested the polyphyly of the genus Perna. Methods: To confirm the proposed gene rearrangements, we sequenced a second Brazilian P. perna specimen using the "primer-walking" method and performed the assembly using as reference Perna canaliculus. This time-consuming sequencing method is highly effective when assessing gene order because it relies on sequentially-determined, overlapping fragments. We also sequenced the mitogenomes of eastern and southwestern South African P. perna lineages to analyze the existence of putative intraspecific gene order changes as the two lineages show overlapping distributions but do not exhibit a sister relationship. Results: The three P. perna mitogenomes sequenced in this study exhibit the same gene order as the reference. CREx, a software that heuristically determines rearrangement scenarios, identified numerous gene order changes between B1 and our P. perna mitogenomes, rejecting the previously proposed gene order for the species. Our results validate the monophyly of the genus Perna and indicate a misidentification of B1.

2022-09Journal article

Open access

Photoautotrophic Euendoliths and their complex ecological effects in marine bioengineered ecosystems

Publication . Dievart, Alexia M.; McQuaid, Christopher D.; Zardi, Gerardo I.; Nicastro, Katy; Froneman, Pierre W.

Photoautotrophic euendolithic microorganisms are ubiquitous where there are calcium carbonate substrates to bore into and sufficient light to sustain photosynthesis. The most diverse and abundant modern euendolithic communities can be found in the marine environment. Euendoliths, as microorganisms infesting inanimate substrates, were first thought to be ecologically irrelevant. Over the past three decades, numerous studies have subsequently shown that euendoliths can colonize living marine calcifying organisms, such as coral skeletons and bivalve shells, causing both sub-lethal and lethal damage. Moreover, under suitable environmental conditions, their presence can have surprising benefits for the host. Thus, infestation by photoautotrophic euendoliths has significant consequences for calcifying organisms that are of particular importance in the case of ecosystems underpinned by calcifying ecosystem engineers. In this review, we address the nature and diversity of marine euendoliths, as revealed recently through genetic techniques, their bioerosive mechanisms, how environmental conditions influence their incidence in marine ecosystems and their potential as bioindicators, how they affect live calcifiers, and the potential future of euendolithic infestation in the context of global climate change and ocean acidification

2022Journal article

Open access

Microplastic leachates inhibit small-scale self-organization in mussel beds

Publication . Zardi, Gerardo I; Nicastro, Katy R; Truong, Stéphanie Lau; Decorse, Philippe; Nozak, Sophie; Chevillot-Biraud, Alexandre; Froneman, Pierre William; Akoueson, Fleurine; Duflos, Guillaume; Seuront, Laurent

Self-organized spatial patterns are increasingly recognized for their contribution to ecosystem functioning. They can improve the ecosystem's ability to respond to perturbation and thus increase its resilience to environmental stress. Plastic pollution has now emerged as major threat to aquatic and terrestrial biota. Under laboratory conditions, we tested whether plastic leachates from pellets collected in the intertidal can impair small-scale, spatial self-organization and byssal threads production of intertidal mussels and whether the effect varied depending on where the pellets come from. Specifically, leachates originating from plastic pellets collected from relatively pristine and polluted areas respectively impaired and inhibited the ability of mussels to self-organize at small-scale and to produce byssal threads compared to control conditions (i.e., seawater without leaching solution). Limitations to natural self-organizing processes and threads formation may translate to a declined capacity of natural ecosystems to avoid tipping points and to a reduced restoration success of disturbed ecosystems.

2024-03Journal article

Restricted access

Parasitism by endolithic cyanobacteria reduces reproductive output and attachment strength of intertidal ecosystem engineers

Publication . Ndhlovu, Aldwin; McQuaid, Christopher D.; Nicastro, Katy; Zardi, Gerardo I.

Mussels are ecological engineers in intertidal communities; they afect coastal species richness by increasing habitat spatial complexity, bufering against environmental extremes, and providing protection from predators. Parasitic activities of endolithic cyanobacteria on mussels weaken their shells, requiring the expenditure of energy on shell repair, with potential indirect efects on organisms that rely on mussels as habitat providers. Given the seasonality of reproduction and the need for strong attachment during winter storms, we examined the consequences of redirecting energy for shell repair to two other energetically expensive processes: reproduction and byssal attachment. We examined seasonality in the efects of cyanobacterial infestation on reproduction and attachment strength in two intertidal mussels, the indigenous Perna perna and the invasive Mytilus galloprovincialis from the south coast of South Africa, using both qualitative and quantitative analyses. Reproductive efects were examined by measuring the weight of mussel gonads and the density of eggs within each gonad for co-occurring infested and non-infested mussels, while attachment strength was measured for mussels exhibiting diferent levels of infestation. Endolithic infestation was found to afect reproduction by reducing the mass of gonads, but not the density of eggs within them. Attachment strength was closely correlated with the degree of endolithic infestation, with very infested mussels requiring much less force to detach them from the substratum than mussels with low or no infestation. Thus, endolithic infestation afected mussel ftness directly, by increasing the probably of mortality through wave dislodgement and by reducing reproductive output.

2022Journal article

Restricted access

The relative effects of interspecific and intraspecific diversity on microplastic trapping in coastal biogenic habitats

Publication . Cozzolino, Lorenzo; Nicastro, Katy; Seuront, Laurent; McQuaid, Christopher D.; Zardi, Gerardo I.

Our understanding of how anthropogenic stressors such as climate change and plastic pollution interact with biodiver-sity is being widened to include diversity below the species level, i.e., intraspecific variation. The emerging apprecia-tion of the key ecological importance of intraspecific diversity and its potential loss in the Anthropocene, further highlights the need to assess the relative importance of intraspecific versus interspecific diversity. One such issue is whether a species responds as a homogenous whole to plastic pollution. Using manipulative field transplant experi-ments and laboratory-controlled hydrodynamic simulations, we assessed the relative effects of intraspecific and inter -specific diversity on microplastic trapping in coastal biogenic habitats dominated by two key bioengineers, the brown intertidal macroalgae Fucus vesiculosus and F. guiryi. At the individual level, northern morphotypes of F. guiryi trapped more microplastics than southern individuals, and F. vesiculosus trapped more microplastics than F. guiryi. Canopy den-sity varied among species, however, leading to reversed patterns of microplastic accumulation, with F. guiryi canopies accumulating more microplastics than those of F. vesiculosus, while no differences were observed between the canopies of F. guiryi morphotypes. We emphasize the importance of assessing the effects of intraspecific variation which, along with other crucial factors such as canopy density, flow velocity and polymer composition, modulates the extent of microplastic accumulation in coastal biogenic habitats. Our findings indicate that a realistic estimation of plastic accu-mulation in biogenic habitats requires an understanding of within-and between-species traits at both the individual and population levels.

2022Journal article

Restricted access