Allometry of Sexual Size Dimorphism in Dioecious Plants: Do Plants Obey Rensch’s Rule?

Abstract

Rensch's rule refers to a pattern in sexual size dimorphism (SSD) in which SSD decreases with body size when females are the larger sex and increases with body size when males are the larger sex. Many animal taxa conform to Rensch's rule, but it has yet to be investigated in plants. Using herbarium collections from New Zealand, we characterized the size of leaves and stems of 297 individuals from 38 dioecious plant species belonging to three distantly related phylogenetic lineages. Statistical comparisons of leaf sizes between males and females showed evidence for Rensch's rule in two of the three lineages, indicating SSD decreases with leaf size when females produce larger leaves and increases with leaf size when males produce larger leaves. A similar pattern in SSD was observed for stem sizes. However, in this instance, females of small-stemmed species produced much larger stems than did males, but as stem sizes increased, SSD often disappeared. We hypothesize that sexual dimorphism in stem sizes results from selection for larger stems in females, which must provide mechanical support for seeds, fruits, and dispersal vectors, and that scaling relationships in leaf sizes result from correlated evolution with stem sizes. The overall results suggest that selection for larger female stem sizes to support the weight of offspring can give rise to Rensch's rule in dioecious plants.

Patterns of sexual size dimorphism in Chelonia

“…If true, the slope of a logarithmic plot of female size on male size will be less than 1.0 (Abouheif & Fairbairn, 1997;Fairbairn, 1997). Patterns of allometric scaling consistent with Rensch's rule have been reported within clades of a surprising diversity of taxa, including arthropods (Blanckenhorn, Meier & Teder, 2007;Serrano-Meneses et al, 2008), bony fish (Young, 2005), reptiles (Cox, Butler & John-Alder, 2007;Stuart-Fox, 2009;Frydlova & Frynta, 2010), birds (Székely et al, 2004;Raihani et al, 2006;Dale et al, 2007), mammals (Lindenfors, Gittleman & Jones, 2007), and even dioecious flowering plants (Kavanagh et al, 2011); Rensch's rule indeed appears to be valid among breeds of some domestic animals (Polak & Frynta, 2009). Patterns of allometric scaling consistent with Rensch's rule have been reported within clades of a surprising diversity of taxa, including arthropods (Blanckenhorn, Meier & Teder, 2007;Serrano-Meneses et al, 2008), bony fish (Young, 2005), reptiles (Cox, Butler & John-Alder, 2007;Stuart-Fox, 2009;Frydlova & Frynta, 2010), birds (Székely et al, 2004;Raihani et al, 2006;Dale et al, 2007), mammals (Lindenfors, Gittleman & Jones, 2007), and even dioecious flowering plants (Kavanagh et al, 2011); Rensch's rule indeed appears to be valid among breeds of some domestic animals (Polak & Frynta, 2009).…”

The unrealized potential of herbaria for global change biology

“…) and have documented selection on species traits through changes in plant morphology (Kavanagh et al. , Burns et al. ).…”

Does ‘gliding while gravid’ explain Rensch's rule in flying lizards?

“…Sexual selection on males typically explains the former pattern, whereas a myriad of alternative hypothesized selection pressures may explain the latter, including female fecundity selection, sexual selection for larger females, or sexual selection for small males, among others (Colwell, ; Székely, Freckleton & Reynolds, ; Dale et al ., ; Stuart‐Fox, ; Pincheira‐Donoso & Tregenza, ). Rensch's rule has been documented in a wide variety of distantly related taxa, ranging from insects (Blanckenhorn et al ., ; Serrano‐Meneses et al ., ) to birds (Székely et al ., ; Székely, Lislevand & Figuerola, ) and mammals (Lindenfors, Gittleman & Jones, ; Sibly et al ., ), and even to plants (Kavanagh et al ., ), but the ‘rule’ is conspicuously and surprisingly absent in others, including some groups of insects (Blanckenhorn, Meier & Teder, ; Bidau, Martí & Castillo, ) and spiders (Foellmer & Moya‐Laraño, ).…”