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. 2018 Apr 15;8(9):4631-4643.
doi: 10.1002/ece3.3986. eCollection 2018 May.

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

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Free PMC article

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

Junhu Su et al. Ecol Evol. .
Free PMC article

Abstract

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.

Keywords: Rensch's rule; natural selection; plateau zokor; sexual size dimorphism; subterranean rodents.

Figures

Figure 1
Figure 1
Plateau Zokor (Eospalax baileyi)
Figure 2
Figure 2
Linear regression between mean male and female body weight (g) with different traits
Figure 3
Figure 3
Linear regression between mean male and female carcass weight (g) with different traits
Figure 4
Figure 4
Linear regression between mean male and female body length (cm) with different traits
Figure 5
Figure 5
Linear regression between log (male body size) on log (female body size) in plateau zokors (a) and that of plateau zokors with eight other zokor species (b)
Figure 6
Figure 6
Linear regression between log (litter size) on log (female body size) in females (a) and distribution of testicle size to body size in males (b) plateau zokors

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