Pulse-radiolytic investigations of catechols and catecholamines II. Reactions of Tiron with oxygen radical species

Transient spectra and kinetic data of Tiron (1,2-dihydroxybenzene-3,5-disulphonic acid) are reported, obtained after pulse-radiolytic oxidation by hydroxyl radicals (°OH), superoxide anions (O₂^?) or a combination of both oxygen radicals. The rate constant with °OH radicals was determined at 1.0·10⁹ M^?1·s^?1. Contrary to a previous report (Greenstock, C.L. and Miller, R.W. (1975) Biochim. Biophys. Acta 396, 11–16), the rate constant with O₂^? of 1.0·10⁷ M^?1·s^?1 is lower by one order of magnitude; also the semiquinone absorbs at 300 nm rather than at 400 nm. The ratio of the rate constants with °OH and O₂^? of 100 again demonstrates that any oxidation reaction by the latter radical is unspecific due to the more efficient reaction of °OH radicals, leading to the same products with catechol compounds.     

Divide and conquer: Multicolonial structure,nestmate recognition,and antagonistic behaviors in dense populations of the invasive ant Brachymyrmex patagonicus

The ecological success of ants has made them abundant in most environments, yet inter‐ and intraspecific competition usually limit nest density for a given population. Most invasive ant populations circumvent this limitation through a supercolonial structure, eliminating intraspecific competition through a loss of nestmate recognition and lack of aggression toward non‐nestmates. Native to South America, Brachymyrmex patagonicus has recently invaded many locations worldwide, with invasive populations described as extremely large and dense. Yet, in contrast with most invasive ants, this species exhibits a multicolonial structure, whereby each colony occupies a single nest. Here, we investigated the interplay between genetic diversity, chemical recognition, and aggressive behaviors in an invasive population of B. patagonicus. We found that, in its invasive range, this species reaches a high nest density with individual colonies located every 2.5 m and that colony boundaries are maintained through aggression toward non‐nestmates. This recognition and antagonism toward non‐nestmates is mediated by chemical differentiation between colonies, as different colonies exhibit distinct chemical profiles. We highlighted that the level of aggression between colonies is correlated with their degree of genetic difference, but not their overall chemical differentiation. This may suggest that only a few chemical compounds influence nestmate recognition in this species or that weak chemical differences are sufficient to elicit aggression. Overall, this study demonstrates that invasive ant populations can reach high densities despite a multicolonial structure with strong aggression between colonies, raising questions about the factors underlying their ecological success and mitigating negative consequences of competitive interactions.     

Oxidation of hydroxylamine to nitrite as an assay for the combined presence of superoxide anions and hydroxyl radicals.

The pulse-radiolytic oxidation of hydroxylamine by either hydroxyl radicals (OH), superoxide anions (O₂^?), or a combination of both radicals was investigated. It was found that only OH radicals efficiently attack the substrate, while O₂^? is necessary for the subsequent formation of nitrite. Determination of the latter reaction thus allows the detection of the combined presence of both oxygen radical species.