Bhat, B. A. | Search bioRxiv

bioRxiv2025

Nematode infections induce distinct chemical signatures and provoke aggression in ants

Maintaining group integrity by excluding outsiders and pathogens is a fundamental requirement and challenge of social living. In social insects, these defences rely heavily on chemical communication, with cuticular hydrocarbons (CHCs) mediating both nestmate recognition and infection-related social responses. In ants, CHCs are stored and homogenised in the pharyngeal gland, contributing to the formation of a shared colony odour that enables nestmate recognition. We investigated the behavioural and chemical responses of the clonal raider ant Ooceraea biroi to infections by the nematode Diploscapter sp., which specifically infects the pharyngeal gland. Using behavioural and chemical analyses, we show that: 1) infected ants elicit increased aggression from uninfected nestmates and non-nestmates, consistent with a social immune defence that limits parasite entry in colonies, 2) aggression is likely driven by infection-specific changes in CHC profiles, and 3) infections do not compromise nestmate recognition, which acts through distinct CHCs. Thus, while many parasitic nematodes can evade host immune recognition, Diploscapter fails to evade the social recognition system of its host. The efficient detection and exclusion of infected individuals likely reduce parasite introduction and transmission both within and between colonies.

animal behavior and cognition↗

bioRxiv2020

Shifts in mutation spectra enhance access to beneficial mutations

Biased mutation spectra are pervasive, with wide variation in the magnitude of mutational biases that influence genome evolution and adaptation. How do such diverse biases evolve? Our experiments show that changing the mutation spectrum allows populations to sample previously under-sampled mutational space, including beneficial mutations. The resulting shift in the distribution of fitness effects is advantageous: beneficial mutation supply and beneficial pleiotropy both increase, while deleterious load reduces. More broadly, simulations indicate that reducing or reversing the direction of a long-term bias is always selectively favoured. Such changes in mutation bias can occur easily via altered function of DNA repair genes. A phylogenetic analysis shows that these genes are repeatedly gained and lost in bacterial lineages, leading to frequent bias shifts in opposite directions. Thus, shifts in mutation spectra may evolve under selection, and can directly alter the outcome of adaptive evolution by facilitating access to beneficial mutations. SIGNIFICANCE STATEMENTMutations are important because they provide raw material for evolution. Some types of mutations occur more often than others, and the strength of such mutational bias varies across species. It is not clear how this variation arises. We experimentally measured the immediate effects of changing the mutation bias of E. coli, and used simulations to understand the long-term effects. Altering mutational bias is beneficial whenever the new bias increases sampling of mutational classes that were previously under-sampled. We also show that historically, bacteria have often experienced such beneficial bias switches. Our work thus demonstrates the importance of mutational biases in evolution. By allowing exploration of new mutational space, altered mutation biases could drive rapid adaptation.

evolutionary biology↗