Evolution of sexual size dimorphism in grouse and allies (Aves: Phasianidae) in relation to mating competition, fecundity demands and resource division

Abstract

Sexual size dimorphism (SSD) is often assumed to be driven by three major selective processes: (1) sexual selection influencing male size and thus mating success, (2) fecundity selection acting on females and (3) inter‐sexual resource division favouring different size in males and females to reduce competition for resources. Sexual selection should be particularly strong in species that exhibit lek polygyny, since male mating success is highly skewed in such species. We investigated whether these three selective processes are related to SSD evolution in grouse and allies (Phasianidae). Male‐biased SSD increased with body size (Rensch’s rule) and lekking species exhibited more male‐biased SSD than nonlekking ones. Directional phylogenetic analyses indicated that lekking evolved before SSD, but conclusions were highly dependent on the body size traits and chosen model values. There was no relationship between SSD and male display agility, nor did resource division influence SSD. Although clutch mass increased with female body size it was not related to the degree of SSD. Taken together, the results are most consistent with the hypothesis that lekking behaviour led to the evolution of male‐biased SSD in Phasianidae.

Loss of sexual dimorphism is associated with loss of lekking behavior in the green manakinXenopipo holochora

“…Traditionally, sexual dimorphism has been assumed to result chiefly from directional selection on increased male ornamentation, as documented in the context of mating systems that exert strong sexual selection on males (Oakes 1992, Lislevand et al 2009). More recently, a growing body of work has made clear that changes in female plumage can also be a major factor underlying patterns of dichromatism in birds (Burns 1998, Hofman et al 2008, Friedman et al 2009, Johnson et al 2013, Price and Eaton 2014, calling into question the use of sexual dichromatism as a proxy for the intensity of sexual selection acting on males.…”

“…Yet, cases of decreased male elaboration, and consequent loss of dimorphism, associated with weakened sexual selection seem to be rare in birds, and remain poorly understood (Lislevand et al 2009). Comparative and species-level studies addressing the evolutionary and life history correlates of monomorphic species with dimorphic ancestors are a powerful yet still relatively under-utilized tool for understanding the processes underlying interspecific phenotypic variation.…”

“…Among grackles and allies (another clade in the family Icteridae), socially monogamous species are significantly less dichromatic than species with other mating systems, but other life history traits such as migratory status and breeding latitude seem to influence patterns of sexual dimorphism as well (Price and Eaton 2014). In some groups, gains or increases in sexual dimorphism have been causally associated 308 with evolutionary transitions from monogamy to lekking or non-lekking polygyny (Oakes 1992, Lislevand et al 2009). Taken together, these studies corroborate the long-held observation that when changes in mating systems increase the intensity of sexual selection, males and females tend to become more distinct in sexually-selected traits such as size or plumage color.…”

Differential sex-specific walking kinematics in leghorn chickens (Gallus gallus domesticus) selectively bred for different body size

“…Intraspecifically, the sexes may differ not only in body size (Lislevand et al, 2009;Remes and Szekely, 2010) but also in morphological proportions, which are likely to influence muscle force, work and power demands. For example, in many vertebrate species, the relative proportions of total body mass (M b ) allocated to different somatic and reproductive components are usually biased towards males and females, respectively (Shine et al, 1998;Hammond et al, 2000;Lourdais et al, 2006).…”

Neither season nor sex affects the cost of terrestrial locomotion in a circumpolar diving duck: the common eider (Somateria mollissima)

“…In species in which paternal care is minimal and males compete for females, sex differences in morphology, physiology and locomotor behaviours are common (Portugal and Guillemette 2011). For example, males often possess ornamental and colourful plumage and may be larger, compared to less conspicuous females (Dunn et al 2001;Lislevand et al 2009). Energetically costly courtship, territorial or lekking displays are exclusive to male birds giving rise to sex differences in energy budget (Unander and Steen 1985;Vehrencamp et al 1989;Barske et al 2011).…”