Interaction between chloride ions mediated by carbon nanotubes: a chemical attraction

The interaction between two Cl− ions separated by the wall of a narrow carbon nanotube has been investigated by density functional theory (DFT) and by DFT-based tight binding (DFTB+). The direct Coulomb interaction between the ions is screened by the nanotube, no matter if the latter is conducting or semiconducting. The presence of the ions induces changes in the electronic density of states of the nanotube, which results in an effective attraction between the ions of the order of 0.2–0.3 eV. The interaction of the outside ions with the tube has a covalent component, when the two ions are near there is even a direct chemical attraction between the ions. In contrast to the effective attraction between two Li+ ions reported before (Juarez et al., Phys Chem Chem Phys 22:10,603, 2020), the effect cannot be explained in terms of physical concepts alone. DFTB+ performs well when compared with DFT, and lends itself to fast calculations for large systems.

Experimental evidence of chemical attraction in the mutualistic zebra mussel-killer shrimp system

Invasion facilitation, whereby one species has a positive effect on the establishment of another species, could help explain the rapid colonisation shown by some freshwater invasive species, but the underlying mechanisms remain unclear. We employed two-choice test arenas to test whether the presence of zebra mussel (Dreissena polymorpha) could facilitate the establishment of the killer shrimp (Dikerogammarus villosus). Killer shrimp preferred to settle on mats of zebra mussel, but this was unrelated to mat size, and was not different from attraction shown to artificial grass, suggesting that zebra mussel primarily provides substrate and refuge to the killer shrimp. Killer shrimp were strongly attracted to water scented by zebra mussel, but not to water scented by fish. Chemical attraction to the zebra mussel’s scent did not differ between sympatric and allopatric populations of killer shrimp, suggesting that chemical attraction is not an acquired or learned trait. Our study shows, for the first time, chemical attraction between two highly invasive freshwater species, thereby providing a plausible mechanism for invasion facilitation. This has implications for managing the spread of killer shrimp, and perhaps other freshwater invasive species, because chemical attraction could significantly increase establishment success in mutualistic systems. Failure to consider invasion facilitation may underestimate the risk of establishment, and likely also the impact of some aquatic invaders.

Collective behaviour in 480-million-year-old trilobite arthropods from Morocco

Interactions and coordination between conspecific individuals have produced a remarkable variety of collective behaviours. This co-operation occurs in vertebrate and invertebrate animals and is well expressed in the group flight of birds, fish shoals and highly organized activities of social insects. How individuals interact and why they co-operate to constitute group-level patterns has been extensively studied in extant animals through a variety mechanistic, functional and theoretical approaches. Although collective and social behaviour evolved through natural selection over millions of years, its origin and early history has remained largely unknown. In-situ monospecific linear clusters of trilobite arthropods from the lower Ordovician (ca 480 Ma) of Morocco are interpreted here as resulting either from a collective behaviour triggered by hydrodynamic cues in which mechanical stimulation detected by motion and touch sensors may have played a major role, or from a possible seasonal reproduction behaviour leading to the migration of sexually mature conspecifics to spawning grounds, possibly driven by chemical attraction (e.g. pheromones). This study confirms that collective behaviour has a very ancient origin and probably developed throughout the Cambrian-Ordovician interval, at the same time as the first animal radiation events.

Experimental evidence of invasion facilitation in the zebra mussel-killer shrimp system

Invasion facilitation, whereby one species has a positive effect on the establishment of another species, could help explain the rapid colonisation shown by some freshwater invasive species, but the underlying mechanisms remain unclear. We employed two-choice test arenas to test whether the presence of zebra mussel (Dreissena polymorpha) could facilitate the establishment of the killer shrimp (Dikerogammarus villosus). Killer shrimp preferred to settle on mats of zebra mussel, but this was unrelated to mat size, and was not different from attraction shown to artificial grass, suggesting that zebra mussel primarily provides substrate and refuge to the killer shrimp. Killer shrimp were strongly attracted to water scented by zebra mussel, but not to water scented by fish. Chemical attraction to the zebra mussel’s scent did not differ between sympatric and allopatric populations of killer shrimp, suggesting that chemical facilitation is not an acquired or learned trait. Our results have implications for managing the spread of killer shrimp, and perhaps other freshwater invasive species, because invasion facilitation could significantly increase establishment success. Failure to consider invasion facilitation may underestimate the risk of establishment and likely impact of some aquatic invaders.

Settlement and early survival of southern rock lobster, Jasus edwardsii, under climate-driven decline of kelp habitats

Kelp habitats provide food, refuge, and enhance the recruitment of commercially important marine invertebrates. The southern rock lobster, Jasus edwardsii, supports valuable fisheries in southern Australia and New Zealand. Kelp habitats once covered large areas of inshore reef around Tasmania, Australia, but coverage has reduced over the last few decades due to climate change, especially off the eastern coast of the island. We investigated whether the kelp influences the settlement of lobster post-larvae to artificial collectors and how the presence of kelp affected the overnight predation on the early benthic phase (EBP). Settlement of lobster was tracked over 6 months using crevice collectors that had either natural or artificial giant kelp, Macrocystis pyrifera attached, or nothing attached (control). Collectors with natural kelp had higher catches than those with artificial kelp or controls (p = 0.003), which suggested enhanced settlement through chemical attraction. Additionally, we measured overnight predation of the EBP in barren and kelp habitats individually tethered to artificial shelters. The kelp habitat was dominated by brown macroalgal species of Ecklonia radiata, Phyllospora comosa, and M. pyrifera, while the barren was devoid of macroalgae. Survival of the EBP was higher (∼40%) in the kelp habitat than in the barren habitat (∼10%) due to differences in predation (p = 0.016). These results suggest that the kelp habitat improves the recruitment of J. edwardsii and that decline in this habitat may affect local lobster productivity along the east coast of Tasmania.