Energetic costs of size and sexual signalling in a wolf spider

Abstract

A prerequisite for honest handicaps is that there are signi¢cant condition-dependent costs in the expression of sexual traits. In the wolf spider Hygrolycosa rubrofasciata (Ohlert), sexual signalling (drumming) is costly in terms of increased mortality. Here we investigated whether this mortality may be caused by increased energy expenditure. During sexual signalling, metabolic rate was 22 times higher than at rest and four times higher than when males were actively moving. Metabolic rate per unit mass was positively related to absolute body mass during sexual signalling but not during other activities. This positive relationship is novel to any studies of metabolic rates. Indeed, it seems that the largest males can drum only 12 times per minute before reaching the maximum sustainable metabolic rate, whereas the smallest males may drum up to 39 times per minute. However, there is no relationship between body mass and drumming rate, indicating that larger males are able to compensate for the higher cost of drumming. There was a quadratic relationship between relative abdomen mass and overall body mass, which may provide a partial explanation for the increased energy expenditure of largest males while drumming. Altogether, our results indicate that sexual signalling is highly energetically demanding, which may be the main reason for the honesty of signalling in this species. In addition, the energetic costs are surprisingly strongly size dependent, which may compensate any disadvantage of small male size.

Temporal patterns of nutrition dependence in secondary sexual traits and their varying impacts on male mating success

“…This is despite the fact that courtship behavior is metabolically costly (Kotiaho et al, 1998) and that the intensity of the display (at least across species) is correlated with the degree of metabolic rate increase (Cady, Delaney, & Uetz, 2011). This pattern, although not intuitive, is well established in several other wolf spider species Rosenthal & Hebets, 2012).…”

“…For example, a shift in prey intake by males during development may affect the female's ability to accurately assess their display. Courtship is an energetically costly behavior (Kotiaho et al, 1998), and a male's ability to sustain rapid courtship may be a signal of his vigor (e.g. motor performance; Byers, Hebets, & Podos, 2010).…”

“…motor performance; Byers, Hebets, & Podos, 2010). Because the energetic costs of courtship vary with male body size (Kotiaho et al, 1998), females may need to assess courtship rate in the context of a male's size in order to accurately gauge his degree of effort. It is possible that the variable diet produces a male phenotype that prevents females from being able to accurately assess a male's size, or leads to inaccurate assessments.…”

Enigmatic ornamentation eases male reliance on courtship performance for mating success

“…Thus, our findings that female choice depends upon courtship rate and that higher courtship rates result in faster copulations in S. stridulans were not unexpected. Courtship behavior is costly for wolf spiders, as it is in other taxonomic groups (great snipe: Hoglund et al 1992 (Kotiaho et al 1998b), and increased drumming results in higher mortality and significant weight loss (Mappes et al 1996). Furthermore, courtship rate in numerous wolf spiders is condition dependent (Mappes et al, 1996;Kotiaho, 2000;Lomborg and Toft, 2009), increases predation risk (Kotiaho et al, 1998a;Lindstrom et al, 2006;Hoefler, 2008), and carries significant immunological costs (Ahtiainen et al, 2004(Ahtiainen et al, , 2005.…”

Female mate choice based upon male motor performance

“…Mature male Hygrolycosa rubrofasciata court females by striking their abdomens against the substrate (typically dry leaves) in an action termed "drumming." Drumming increases an individual's metabolic rate 22-fold over resting metabolic rate (Kotiaho et al 1998b), and is condition dependent (Mappes et al 1996). Males with high drumming rates survive better in both laboratory and field conditions (Mappes et al, 1996;Kotiaho et al, 1999), and have superior mobility and the ability to evade predators (Lindström et al 2006).…”