Rensch’s rule inverted – female‐driven gigantism in nine‐spined stickleback Pungitius pungitius

Abstract

Summary1. Allometric scaling of sexual size dimorphism (SSD) with body size is a commonplace occurrence in intraspecific or interspecific comparisons. Typically, SSD increases with body size when males, and decreases when females are the larger sex -a pattern known as Rensch's rule. Intraspecific studies of Rensch's rule in vertebrates are extremely scarce. 2. In an allometric SSD-body size relationship, the sex with the larger body size variation is the driver of size divergence whereas the other sex is following it owing to correlational selection. Hence, one can test which sex is responsible for the observed body size divergence within this framework. 3. Nine-spined stickleback (Pungitius pungitius) provides an excellent model to study intraspecific variation in SSD owing to the large interpopulation variation in mean body size. Using data on body size variation in 11 nine-spined stickleback populations covering the full known size range of the species, we investigated: (i) whether variation in SSD scales allometrically with mean body size across the populations; (ii) which sex is driving the allometric relationship and (iii) whether the observed pattern is likely to have a genetic component. In addition, we analysed the size dependency of female reproductive output. 4. We found strong support for an inverse of Rensch's rule: level of female-biased SSD increased with increasing mean size while females were the more variable sex. Results from a common garden experiment supported the pattern found in the wild. Females from giant populations had 2-3 times larger reproductive output than normal-sized females. 5. The fact that females were the more variable sex indicates that the evolution of gigantism in nine-spined sticklebacks is driven by females, and the 2-3 times larger reproductive output per clutch of giant vs. normal-sized females suggests fecundity selection to have an important role in it. Our results oppose the commonly held view that males drive the evolution of SSD as a result of sexual selection favouring larger males.

Re-assessment of rensch’s rule in Centrobolus

“…The regression of SSD on body size (Figure 1) of the data for SSD and body size (Table 1) indicates a positive regression to reject Rensch's rule in Centrobolus. Although the null hypothesis is accepted and the rule rejected the inverse relationship is true [26][27][28][29][30][31][32] . This was seen in the SSD increases with body size.…”

Body size and the number of vertebrae in the nine-spined stickleback (Pungitius pungitius)

“…In other words, the profound differences in mean body size among populations and sexes (Herczeg et al, 2010a) cannot be explained by corresponding differences in vertebral numbers. Similarly, the results do not lend much support for Jordan's rule; a phenomenon referring to a positive association between vertebral numbers and latitude (McDowall, 2008).…”

“…Several lines of evidence, including comparisons of body armour (Herczeg, Turtiainen & Merilä, 2010b), behaviour (Herczeg, Gonda & Merilä, 2009b, c) and brain architecture (Gonda, Herczeg & Merilä, 2009a, b), suggest that the observed differentiation is driven by selection for delayed maturation at large body size in pond populations that are lacking predatory fish and subject to a high degree of intraspecific competition. These studies have also revealed that female nine-spined sticklebacks are considerably larger than males, especially in ponds (Herczeg et al, 2010a). Hence, if vertebral number is an important determinant of body size variation, one would expect to find that females and pond fish have more vertebra than males and fish from marine or lake habitats.…”

“…Recent studies of intraspecific variation in body size of nine-spined sticklebacks (Pungitius pungitius Linnaeus, 1758) have revealed that fish from pond populations typically reach a mean body size that is two-to three-fold larger than their lake and sea conspecifics , 2010a. Several lines of evidence, including comparisons of body armour (Herczeg, Turtiainen & Merilä, 2010b), behaviour (Herczeg, Gonda & Merilä, 2009b, c) and brain architecture (Gonda, Herczeg & Merilä, 2009a, b), suggest that the observed differentiation is driven by selection for delayed maturation at large body size in pond populations that are lacking predatory fish and subject to a high degree of intraspecific competition.…”

Sex-specific variation in morphology and performance in the Asian house gecko

“…However, there still remains limited empirical evidence to support these hypotheses and the generality of this rule has been questioned, as it is unlikely that any single mechanism is responsible for the scaling of Rensch's rule across all taxa (Fairbairn, 1997(Fairbairn, , 2005. For this reason more recent studies have taken a microevolutionary approach, primarily with the aim of investigating the putative mechanisms causing Rensch's rule, through intraspecific comparisons of geographically dispersed populations (Fairbairn and Preziosi, 1994;Emlen and Allen, 2003;Fairbairn, 2005;Emlen, 2008;Herczeg et al, 2010;Kelly et al, 2013).…”