Dataset and R code for Bottini et al. 2025_Effects of wintering under methylmercury exposure on spring reproductive onset in song sparrows (Melospiza melodia).

This folder contains all the datasets and R code needed to reproduce the analysis of manuscript from Bottini et al. 2025 "Effects of wintering under methylmercury exposure on spring reproductive onset in song sparrows (Melospiza melodia)" published in Journal of Neuroendocrinology (freely accessible on https://doi.org/10.1111/jne.70027).

Project description:
We assessed if MeHg exposure during winter may affect the bird's reproductive onset. The experiment main hypothesis and predictions were that due to MeHg exposure energetic cost / toxicity and the onset of seasonal change caused by photostimulation, the treatments (control vs MeHg) and time (almost 7 months of captivity) will affect the quantified physiological and neurological measures. Also, we predicted a potential time per treatment interaction, either caused by
1) bird's recovery from MeHg harm after a time without exposure, or 2) because the physiological changes associated with photostimulation promoted the appearance of latent MeHg effects not detected previously.

Article Key Findings:
• Winter exposure to methylmercury does not affect male song sparrows’ spring testes mass, syrinx mass, plasma androgen concentrations, overall number of GnRH neurosecretory cells, and body condition.
• However, methylmercury exposure slightly decreased the development of cloacal protuberances after photostimulation and the number of region-specific GnRH producing cells.
• Songbird male reproductive onset appears buffered against methylmercury’s deleterious effects but some carry-over effects on secondary sexual traits that may affect birds’ breeding performance.