# Histological and Proteomic Approaches to Assessing the Adrenal Stress Response in Common Dolphins (Delphinus delphis)

## TL;DR

This study explores how chronic stress affects adrenal glands in common dolphins using histology and protein analysis, revealing potential biomarkers for stress in wild populations.

## Contribution

The study introduces a novel combination of histological and proteomic methods to assess chronic stress in wild dolphin populations.

## Key findings

- Chronic stress in dolphins is associated with larger adrenal cortices and higher cortex-to-medulla ratios.
- Proteomic analysis of archived tissues is feasible and can reveal stress-related proteins.
- Archived dolphin tissues can provide insights into stress physiology and biomarker discovery.

## Abstract

Dolphins, like humans, rely on their adrenal glands to produce hormones that regulate stress. Yet, little is known about how these glands respond to long-term stress in wild populations. In this study, we examined adrenal glands from common dolphins (Delphinus delphis) stranded along the Irish coast. Animals that died suddenly from causes such as bycatch were compared with those that succumbed to infectious disease, representing chronic stress. Dolphins that experienced chronic stress had significantly larger adrenal cortices and higher cortex-to-medulla ratios, consistent with prolonged hormone production. We also tested a pilot method for extracting proteins from formalin-fixed, paraffin-embedded tissues and identified several stress-related proteins, some associated with the type of stress experienced. These findings demonstrate that combining tissue structure and protein analysis can reveal markers of chronic stress in dolphins and highlight the potential of archived material for improving conservation health assessments.

The adrenal glands are central to the stress response in cetaceans, yet their morphological and molecular changes under chronic stress remain poorly described. We investigated adrenal histology and protein composition in stranded common dolphins (Delphinus delphis) to assess whether post-mortem material can provide insights into stress physiology. Adrenal glands from 58 dolphins recovered along the Irish coast during a period of reported nutritional stress in the species were analyzed for adrenal mass, cortex-to-medulla (C:M) ratios, and cortical cell density. Additionally, two archival formalin-fixed, paraffin-embedded (FFPE) tissues were included in a pilot trial to assess the feasibility of protein extraction and mass spectrometry analysis. While adrenal mass did not differ significantly between stress types, chronically stressed dolphins exhibited significantly higher C:M ratios and cortical mass, consistent with cortical hypertrophy. Protein extraction from FFPE tissues was feasible, with the in-gel digestion method yielding more proteins (136) than the filter-aided sample preparation method (22). These findings demonstrate that histological and proteomic approaches can detect stress-related signatures in dolphins and highlight the potential of archival tissues for retrospective biomarker discovery.