AUTHOR=Gebru Gebreslassie , Belay Gurja , Dessie Tadelle , Zenebe Kelkay Mulalem , Birhanie Dagnhegn Minister , Hanotte Olivier 

TITLE=Morphological and osteological characterization of indigenous domestic chickens (Gallus gallus domesticus): validation of Rensch’s, Bergmann’s and Allen’s rules

JOURNAL=Frontiers in Ecology and Evolution

VOLUME=Volume 11 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/ecology-and-evolution/articles/10.3389/fevo.2023.1032082

DOI=10.3389/fevo.2023.1032082

ISSN=2296-701X

ABSTRACT=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 morphologies and osteologies. For Bergmann’s and Allen’s rules, we analysed the morphological characteristics of 297 (208 females, 89 males) and the osteological characteristics of 36 (19 females, 17 males) indigenous chickens. For the morphological validation of Rensch’s rule, we used 89 males and randomly selected 89 females, while for the osteological validation, 17 males and females were analysed. 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 males being larger than females and with size differences proportional to 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 length and surface area (earlobe, wattle and beak) of 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.