Data_Sheet_1_Morphological and osteological characterization of indigenous domestic chickens (Gallus gallus domesticus): validation of Rensch’s, Bergmann’s and Allen’s rules.docx

Ecogeographical habitat heterogeneity in wild endotherm species results in morphological variability associated with physiological mechanisms for maintaining their body temperature at a thermoneutral state in different environments. This habitat-induced morphological variation has led to the proposal of three main ecogeographical and biological rules (Rensch, Bergmann, and Allen). Whether or not domesticated animal species, under the care and management of humans, follow the same rules has not yet been investigated in detail. In this study, we randomly sampled 333 adult indigenous chickens (Gallus gallus domesticus) from three habitats representing the highland, midland and lowland agro-ecologies in the Tigray Region (Ethiopia). We aimed to assess the importance of Rensch’s, Bergmann’s, and Allen’s rules in shaping their morphology and osteology. For Bergmann’s and Allen’s rules, we analyzed the morphological characteristics of 297 (208 female, 89 male) and the osteological characteristics of 36 (19 female, 17 male) indigenous chickens. For the morphological validation of Rensch’s rule, we used 89 male chickens and randomly selected 89 female chickens, while for the osteological validation, 17 male and female chickens were analyzed. Chickens from the lowland agro-ecology (warm climate) had a smaller body mass index (BMI) and larger appendages, while chickens from the highland agro-ecology (cold climate) had a larger BMI and smaller appendages (Bergmann’s and Allen’s rules). Morphological and osteological sexual dimorphism were observed, with the male chickens being larger than the female chickens and with size differences proportional to the body size (Rensch’s rule). In both sexes, regression analysis showed a relationship between BMI and altitude as well as temperature. Shank length, wingspan, and the length and surface area (earlobe, wattle, and beak) of the appendages were significantly associated with climatic variables. Moreover, our regression model revealed that wingspan and shank length could be predicted from the greatest length of the humerus and tarsometatarsus. Our findings support the idea that indigenous chickens’ adaptation mechanisms to environmental challenges largely agree with the expectation of Rensch’s, Bergmann’s, and Allen’s biogeographical rules across the different altitudinal habitats of the Tigray Region.

野生恒温物种的生态地理生境异质性会引发形态变异，该变异与不同环境下维持体温处于热中性状态的生理机制密切相关。由生境诱导产生的形态变异催生了三大核心生态地理与生物学法则——伦施法则（Rensch）、伯格曼法则（Bergmann）与艾伦法则（Allen）。目前，针对受人类照料与管理的家养动物是否遵循这些通用法则，尚未有详尽的研究。本研究从埃塞俄比亚提格雷地区的高地、中地与低地农业生态区三类生境中，随机抽样了333只成年本土家鸡（Gallus gallus domesticus），旨在评估伦施、伯格曼与艾伦法则在塑造其形态学与骨骼学特征中的重要性。针对伯格曼与艾伦法则，我们分析了297只（雌208只、雄89只）本土家鸡的形态学特征，以及36只（雌19只、雄17只）的骨骼学特征；针对伦施法则的形态学验证，我们使用了89只雄性家鸡并随机选取89只雌性家鸡，而骨骼学验证则分析了17只雌雄家鸡样本。来自低地农业生态区（温暖气候）的家鸡体重指数（Body Mass Index，BMI）更低、附肢更长，而来自高地农业生态区（寒冷气候）的家鸡体重指数更高、附肢更短，这符合伯格曼与艾伦法则的预测。研究观察到形态学与骨骼学层面的性二态性：雄性家鸡体型大于雌性，且体型差异与身体大小呈正比，符合伦施法则。在两性个体中，回归分析均显示体重指数与海拔及温度存在关联；胫长、翼展以及附肢（耳垂、肉垂与喙）的长度与表面积均与气候变量显著相关。此外，本研究的回归模型显示，可通过肱骨与跗跖骨的最大长度预测翼展与胫长。本研究结果证实，本土家鸡应对环境挑战的适应机制，在提格雷地区不同海拔梯度的生境中，基本契合伦施、伯格曼与艾伦生物地理学法则的预期。