Transcriptome analysis of ageing in a long-lived seabird reveals sex-specific differences across age classes in immune and DNA repair pathways.

Abstract

Introduction: Sex differences in ageing rate and longevity are widespread across animals, but their molecular bases remain poorly understood. Ageing involves multiple hallmarks of functional decline, and experimental studies suggest sex-specific differences in gene expression, particularly in immune, metabolic, and mitochondrial pathways. Yet, transcriptional variation associated with sex and age in natural populations remains largely unexplored.

Methods: Here, we present the first RNA-seq study of a free-living bird, the Scopoli's shearwater (Calonectris diomedea), aimed at investigating sex differences in gene expression across age classes, comparing younger and older individuals of both sexes (16 males and 16 females).

Results: We identified a sex-linked transcriptional signature involving genes associated with immune function, stress response, energetics, and development. Age-related reductions in energy metabolism were more pronounced in females, whereas the strongest sex-related differences were detected in immune function and genome stability pathways. Across age classes, males showed higher expression of genes involved in DNA repair and genome maintenance, while females displayed a shift from immune-related processes in early adulthood to stress-response pathways in late adulthood.

Discussion: Together, these findings reveal pronounced sex-biased transcriptional regulation across age classes, which we hypothesise is driven by the differentiation of sex-specific reproductive strategies during the egg-laying phase. Furthermore, our results indicate sustained investment in somatic maintenance into late adulthood, consistent with patterns typically observed in long-lived species.