Data from: Vascularization underlies differences in sexually selected skin coloration in a wild primate

Male reproductive competition can select for condition-dependent,
conspicuous traits that signal some aspect of fighting ability and
facilitate assessment of potential rivals. However, the underlying
mechanisms that link the signal to a male’s current condition are
difficult to investigate in wild populations. In this study, we used
digital photographs and chest skin samples to investigate mechanisms of a
visual signal used in male competition in a wild primate, the red chest
patch in geladas (Theropithecus gelada) in the Simien Mountains National
Park, Ethiopia. We analyzed photographs collected during natural and
anesthetized conditions to understand variability in male and female chest
redness, and we used chest skin biopsies to explore sex differences in
gene expression. Male and female geladas showed similar average redness,
but males exhibited a wider within-individual range in redness under
natural conditions. These sex differences were reflected at the molecular
level, with 10.5% of genes exhibiting significant sex differences in
expression. Subadult males exhibited intermediate expression patterns
between adult males and females, pointing to mechanisms underlying the
development of the red chest patch. We found that genes more highly
expressed in males were associated with blood vessel development and
maintenance but not with androgen or estrogen activity. Together, our
results suggest male gelada redness variability is driven by increased
blood vessel branching in the chest skin, providing a potential link
between male chest redness and current condition as increased blood
circulation to exposed skin could lead to heat loss in the cold,
high-altitude environment of geladas.

雄性生殖竞争可筛选出依赖个体状态、且具显著表型的性状，这类性状能够传递雄性战斗能力的相关信息，并辅助其评估潜在竞争对手。然而，在野生种群中，解析该信号与雄性当前个体状态间关联的潜在机制颇具挑战。本研究以埃塞俄比亚塞米恩山国家公园内的野生灵长类——狮尾狒（gelada，*Theropithecus gelada*）为研究对象，利用数码照片与胸部皮肤样本，解析其雄性竞争中使用的视觉信号（红色胸部斑块）的相关机制。我们分析了自然状态与麻醉状态下采集的照片，以探究雌雄个体胸部红色程度的变异情况；同时通过胸部皮肤活检样本，分析基因表达的性别差异。狮尾狒雌雄个体的平均胸部红色程度无显著差异，但在自然状态下，雄性个体胸部红色程度的个体内波动范围更广。这种性别差异在分子层面也有所体现：10.5%的基因存在显著的性别表达差异。亚成年雄性的基因表达模式介于成年雄性与雌性之间，为红色胸部斑块的发育机制提供了线索。研究发现，雄性中高表达的基因与血管发育及维持相关，而非雄激素或雌激素的信号通路活动。综合以上结果，我们认为狮尾狒雄性胸部红色程度的变异源于胸部皮肤血管分支的增多；这一发现为雄性胸部红色程度与当前个体状态间的潜在关联提供了依据——在狮尾狒栖息的寒冷高海拔环境中，裸露皮肤的血液循环增强可能会导致热量散失。