A Test of Rensch’s Rule in Greater Horseshoe Bat (Rhinolophus ferrumequinum) with Female-Biased Sexual Size Dimorphism

Abstract

Sexual size dimorphism (SSD) is widespread within the animal kingdom. Rensch’s rule describes a relationship between SSD and body size: SSD increases with body size when males are the larger sex, and decreases with body size when females are the larger sex. Rensch’s rule is well supported for taxa that exhibit male-biased SSD but patterns of allometry among taxa with female-biased size dimorphism are mixed, there is evidence both for and against the rule. Furthermore, most studies have investigated Rensch’s rule across a variety of taxa; but among-population studies supporting Rensch’s rule are lacking, especially in taxa that display only slight SSD. Here, we tested whether patterns of intraspecific variation in SSD in greater horseshoe bats conform to Rensch’s rule, and evaluated the contribution of latitude to Rensch’s rule. Our results showed SSD was consistently female-biased in greater horseshoe bats, although female body size was only slightly larger than male body size. The slope of major axis regression of log10 (male) on log10 (female) was significantly different from 1. Forearm length for both sexes of greater horseshoe bats was significantly negatively correlated with latitude, and males displayed a slightly but nonsignificant steeper latitudinal cline in body size than females. We suggest that variation in patterns of SSD among greater horseshoe bat populations is consistent with Rensch’s rule indicating that males were the more variable sex. Males did not have a steeper body size–latitude relationship than females suggesting that sex-specific latitudinal variation in body size may not be an important contributing factor to Rensch’s rule. Future research on greater horseshoe bats might best focus on more comprehensive mechanisms driving the pattern of female-biased SSD variation.

A re-assessment of Rensch's rule in tuco-tucos (Rodentia: Ctenomyidae: Ctenomys) using a phylogenetic approach

“…Although Rensch (1950) formulated his pattern as a seemingly interspecific trend, it is interesting that it has been often verified at the intraspecific level in groups where higher taxonomic units are not consistent with the rule. This was observed in the Greater Horseshoe bat (Rhinolophus ferrumequinum) (Wu et al, 2014), Panthera tigris subspecies (Martinez et al, 2014), domestic dog, cattle, and chicken (Polák and Frynta, 2010;Remeš and Székely, 2010;Frynta et al, 2012), and a melanopline grasshopper (Bidau and Martí, 2008a,b). As shown here and in Bidau and Medina (2013) at least one tuco-tuco species follows Rensch's rule intraspecifically although the other one tested (C. talarum), does not at least for the analysed trait.…”

Intraspecific variation in body size and sexual size dimorphism, and a test of Rensch's rule in bats

“…And finally, according to Wu et al (2014), skeletal measurements, such as forearm length as a proxy for body size, were more reliable than using body mass. First, we found that most studies dealing with variation in sexual size dimorphism in mammals used data collected from literature.…”

“…Males and females may respond differently to changes in temperature, and the degree of SSD can change substantially (Blanckenhorn and Demont 2004;Clauss et al 2013). Blanckenhorn and Demont 2004;Clauss et al 2013), studies investigating intraspecific variation in SSD trends are lacking Wu et al 2014). More recently, variations in SSD among populations within species were described (Kraushaar and Blanckenhorn 2002;Teder and Tammaru 2005), and in these cases, intraspecific changes in SSD may also occur due to sex differences in body size plasticity (Fairbairn 2005;.…”

“…In other taxa, neither Rensch's rule nor the converse of Rensch's rule is followed (Tubaro and Bertelli 2003;Liao et al 2013). Although Rensch's rule was originally proposed for interspecific comparisons, recent studies have also tested this hypothesis within species (Wu et al 2014). Although Rensch's rule was originally proposed for interspecific comparisons, recent studies have also tested this hypothesis within species (Wu et al 2014).…”

“…Despite this female-biased SSD pattern, studies addressing SSD variation are still too scarce for bats (Welbergen 2010), especially for comparisons among populations within species (Bornholdt et al 2008). Rensch's rule has rarely been tested for bats (Wu et al 2014), which leaves a gap in the research to be filled. As many bats are slightly size dimorphic towards females, the contribution of this taxa to Rensch's rule has not been thoroughly elucidated.…”