Function‐related Drivers of Skull Morphometric Variation and Sexual Size Dimorphism in a Subterranean Rodent, Plateau Zokor (Eospalax baileyi)

• Published in: Ecology and evolution Vol. 8; no. 9; pp. 4631 - 4643
• Main Authors: Su, Junhu, Hegab, Ibrahim M., Ji, Weihong, Nan, Zhibiao
• Format: Journal Article
• Language: English
• Published: England John Wiley & Sons, Inc 01.05.2018; John Wiley and Sons Inc
• Subjects: Animal behavior; Body length; Body size; Body weight; Eospalax baileyi; Females; Growth rate; Investigations; Males; natural selection; Original Research; plateau zokor; Regression analysis; Rensch's rule; Sex; Sex differences; Sexes; Sexual dimorphism; sexual size dimorphism; Skull; Species; subterranean rodents; Rensch's rule; natural selection; subterranean rodents; sexual size dimorphism; plateau zokor
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.3986

Sexual dimorphism is prevalent in most living organisms. The difference in size between sexes of a given species is generally known as sexual size dimorphism (SSD). The magnitude of the SSD is determined by Rensch's rule where size dimorphism increases with increasing body size when the male is the larger sex and decreases with increasing average body size when the female is the larger sex. The unique underground environment that zokors (Eospalax baileyi) live under in the severe habitat of the Qinghai‐Tibetan Plateau (QTP) could create SSD selection pressures that may or may not be supported by Rensch's rule, making this scientific question worthy of investigation. In this study, we investigated the individual variation between sexes in body size and SSD of plateau zokors using measurements of 19 morphological traits. We also investigated the evolutionary mechanisms underlying SSD in plateau zokors. Moreover, we applied Rensch's rule to all extant zokor species. Our results showed male‐biased SSD in plateau zokors: The body‐ and head‐related measurements were greater in males than in females. Linear regression analysis between body length, body weight, and carcass weight showed significant relationships with some traits such as skull length, lower incisor length, and tympanic bulla width, which might support our prediction that males have faster growth rates than females. Further, the SSD pattern corroborated the assumption of Rensch's rule in plateau zokors but not in the other zokor species. Our findings suggest that the natural underground habitat and behavioral differences between sexes can generate selection pressures on male traits and contribute to the evolution of SSD in plateau zokors. Male‐biased sexual size dimorphism is evident in Plateau zokors. Sexual size dimorphism conformed to Rensch's rule in the extant zokor species. Sexual size dimorphism showed age‐dependent traits in Plateau zokors. Behavioral differences between genders generate selection pressures on sexual size dimorphism in plateau zokors.