Context-dependent telomere dynamics in wild fish populations under anthropogenic stress.

Anthropogenic environmental change imposes severe physiological challenges on wild populations, often leading to accelerated cellular aging. In many vertebrate models, the 'conventional expectation' is that chronic exposure to stressors triggers oxidative damage and increases turnover, resulting in accelerated telomere shortening. However, the universality of this pattern remains poorly understood, particularly in high-biodiversity regions of the Southern Hemisphere. This study explores pollution-linked telomere dynamics in Cnesterodon decemmaculatus, a native Neotropical fish, along a steep anthropogenic gradient in the Suquía River Basin (Argentina). Age-related changes in RTL differed significantly among sampling sites. Fish from the most contaminated site (IP) showed a tendency toward increasing RTL within the analyzed age range, a pattern that stands in contrast to most findings from temperate-region fish. Meanwhile, a moderately contaminated site (LC) followed the classic pattern of age-related telomere loss. We suggest that these divergent RTL patterns reflect site-specific physiological or compensatory responses, potentially involving the up-regulation of cellular maintenance or the selective persistence of tolerant phenotypes under extreme chronic stress. These results highlight the complex and context-dependent nature of telomere dynamics in the wild. Our findings indicate that while RTL is a sensitive indicator of environmental impact, its application as a robust biomarker requires a multi-proxy framework -integrating oxidative stress and telomerase assays- to accurately interpret the diverse biological responses of native species to anthropogenic change.