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.

本文件夹包含复现Bottini等人2025年发表于《Journal of Neuroendocrinology》（可通过https://doi.org/10.1111/jne.70027免费获取）的论文《越冬甲基汞暴露对歌带鹀（Melospiza melodia）春季繁殖启动的影响》的分析所需的全部数据集与R代码。

项目概况：
本研究旨在评估冬季甲基汞（methylmercury, MeHg）暴露是否会影响鸟类的繁殖启动。本实验的核心假设与预测为：鉴于甲基汞暴露会带来能量成本与毒性，且光刺激可引发季节性变化，因此处理组（对照组vs甲基汞暴露组）与饲养时长（近7个月的圈养期）会对量化得到的生理与神经学指标产生影响。此外，我们还预测存在处理×时间的潜在交互效应，其成因可能为以下二者之一：1）鸟类在无暴露时段内从甲基汞损伤中恢复；或2）与光刺激相关的生理变化，促使了此前未被检测到的潜在甲基汞效应显现。

论文核心发现：
• 冬季甲基汞暴露不会影响雄性歌带鹀的春季睾丸质量、鸣管质量、血浆雄激素浓度、促性腺激素释放激素（GnRH）神经分泌细胞总数以及身体状况。
• 但甲基汞暴露会略微降低光刺激后泄殖腔突的发育程度，以及区域特异性促性腺激素释放激素分泌细胞的数量。
• 鸣禽雄性的繁殖启动似乎可抵御甲基汞的有害影响，但部分残留效应会作用于第二性征，进而可能影响鸟类的繁殖表现。