The effects of urban life on animal immunity: Adaptations and constraints

Land transformation, including urbanization, is a dominant form of anthropogenic change to the global environment at the dawn of the Anthropocene epoch. More and more species are brought into direct contact with humans, being either required to develop broad-scale adaptations to urban environment or filtered out from urbanized areas. While behavioural or physiological adaptations are at the forefront of urban biology research, there is accumulating evidence for divergent pathogen pressure across urbanization gradients, requiring adjustments in host immune func-tion. At the same time, host immunity may be constrained by unfavourable components of an urban environment, such as poor-quality food resources, disturbance, or pollution. Here, I reviewed existing evidence for adaptations and con-strains in the immune system of urban animals, focusing on the recent implementation of metabarcoding, genomic, transcriptomic, and epigenomic approaches in urban biology research. I show that spatial variation in pathogen pres-sure across urban and non-urban landscapes is highly complex and may be context-dependent, but there is solid evi-dence for pathogen-driven immunostimulation in urban-dwelling animals. I also show that genes coding for molecules directly involved in interactions with pathogens are the prime candidates for immunogenetic adaptations to urban life. Evidence emerging from landscape genomics and transcriptomics show that immune adaptations to urban life may have a polygenic nature, but immune traits may not be among the key biological functions experiencing broad-scale microevolutionary changes in response to urbanization. Finally, I provided recommendations for future re-search, including i) a better integration of different 'omic' approaches to obtain a more complete picture of immune adaptations to urban life in non-model animal taxa, ii) quantification of fitness landscapes for immune phenotypes and genotypes across urbanization gradient, and iii) much broader taxonomic coverage (including invertebrates) necessary to draw more robust conclusions on how general (or taxa-specific) are immune responses of animals to urbanization.

Automated summary

Land transformation, especially urbanization, has a significant impact on the global environment. More species are facing direct contact with humans and have to adapt to urban environments or leave urbanized areas. Urban animals experience diverse immune responses to the complex pathogen pressure and environmental constraints.