Inner Workings: A microscopic mystery at the heart of mass-coral bleaching

Polystyrene nanoplastics impair the photosynthetic capacities of Symbiodiniaceae and promote coral bleaching

Reef-building corals are increasingly threatened by global and regional stresses, which affect the stability of the coral-Symbiodiniaceae association. Among them, plastic pollution has been an ongoing and growing concern. Whereas several studies have highlighted the detrimental impact of microplastics (0.1 μm-5 mm) on corals and their symbiotic dinoflagellate algae, the physiological changes induced by nanoplastic (NP, <0.1 μm) pollution are still poorly known. Long-term experiments (4 weeks) were conducted to investigate the effects of ecologically relevant NP concentrations (0 to 0.5 mg/L of 20 nm polystyrene NPs) on two Symbiodiniaceae in culture [CCMP2467 or Clade A1 and pd44b or Clade F1]. The effects of 0.5 mg/L NPs were also evaluated on Clade A1 living in symbiosis with the coral Stylophora pistillata, to assess the in hospite effects of NPs on coral symbionts. The photosynthetic efficiency of photosystem II, the oxidative status of the Symbiodiniaceae and the coral host, as well as the host-symbiont stability were evaluated at the end of the experiment. Symbiodiniaceae in culture exhibited a significant decrease in the maximal electron transport rate (ETR_max) at NP concentrations as low as 0.005 mg/L, highlighting an impairment of the photosynthetic capacities of the dinoflagellates in presence of nanoplastics. Also, Clade A1 exhibited a significant decrease in its Total Antioxidant Capacity (TAC) and an increase in Lipid Peroxidation (LPO), which evidence oxidative stress and cellular damage. Interestingly, Clade A1 in hospite did not show any signs of oxidative stress, however, the coral host exhibited increased TAC and LPO. Additionally, exposure of S. pistillata to 0.5 mg/L NPs induced significant bleaching (loss of symbionts and photosynthetic pigments). Overall, NPs were detrimental for both the Symbiodiniaceae in culture and the host-symbiont association. In the future, the persistence of reef corals may be severely impacted by the cumulative effects of nanoplastic pollution along with global warming.

Evolutionary developmental biology and sustainability: A biology of resilience

Evolutionary developmental biology, and especially ecological developmental biology, is essential for discussions of sustainability and the responses to global climate change. First, this paper explores examples of animals that have successfully altered their development to accommodate human-made changes to their environments. We next document the ability of global warming to disrupt the development of those organisms with temperature-dependent sex-determination or with phenologies coordinating that organism's development with those of other species. The thermotolerance of Homo sapiens is also related to key developmental factors concerning brain development and maintenance, and the development of corals, the keystone organisms of tropical reefs, is discussed in relation to global warming as well as to other anthropogenic changes. While teratogenic and endocrine-disrupting compounds are not discussed in this essay, the ability of glyphosate herbicides to block insect development is highlighted. Last, the paper discusses the need to creatively integrate developmental biology with ecological, political, religious, and economic perspectives, as the flourishing of contemporary species may require altering the ways that Western science has considered the categories of nature, culture, and self.

Toward a Symbiotic Perspective on Public Health: Recognizing the Ambivalence of Microbes in the Anthropocene

Microbes evolve in complex environments that are often fashioned, in part, by human desires. In a global perspective, public health has played major roles in structuring how microbes are perceived, cultivated, and destroyed. The germ theory of disease cast microbes as enemies of the body and the body politic. Antibiotics have altered microbial development by providing stringent natural selection on bacterial species, and this has led to the formation of antibiotic-resistant bacterial strains. Public health perspectives such as "Precision Public Health" and "One Health" have recently been proposed to further manage microbial populations. However, neither of these take into account the symbiotic relationships that exist between bacterial species and between bacteria, viruses, and their eukaryotic hosts. We propose a perspective on public health that recognizes microbial evolution through symbiotic associations (the hologenome theory) and through lateral gene transfer. This perspective has the advantage of including both the pathogenic and beneficial interactions of humans with bacteria, as well as combining the outlook of the "One Health" model with the genomic methodologies utilized in the "Precision Public Health" model. In the Anthropocene, the conditions for microbial evolution have been altered by human interventions, and public health initiatives must recognize both the beneficial (indeed, necessary) interactions of microbes with their hosts as well as their pathogenic interactions.