The Cost of the Sword: Escape Performance in Male Swordtails

Abstract

The handicap theory of sexual selection posits that male display traits that are favored in mate choice come at a significant cost to performance. We tested one facet of this hypothesis in the green swordtail (Xiphophorus helleri). In this species, the lower ray of male caudal fin is extended into a ‘sword’, which serves to attract potential mates. However, bearing a long sword may increase drag and thus compromise a male's ability to swim effectively. We tested escape performance in this species by eliciting C-start escape responses, an instinctive escape behavior, in males with various sword lengths. We then removed males' swords and retested escape performance. We found no relationship between escape performance and sword length and no effect of sword removal on escape performance. While having a large sword may attract a predator's attention, our results suggest that sword size does not compromise a male's escape performance.

As the Sword Grows: Individual Variation and Ontogenetic Effects of a Sexually Selected Trait on Locomotor Performance inXiphophorus hellerii

“…1A), and sword size increased for approximately eight of those weeks ( fig. 1B), reaching sizes consistent with previous studies with the same species (Baumgartner et al 2011). All else being equal, body size and sword size, as developmental traits, should have positive and negative effects on locomotor performance, respectively.…”

“…The two most common ways to asses whether a putatively sexually selected trait is costly are to (1) experimentally manipulate the structure (Clark and Dudley 2009) and (2) compare individuals with naturally varying expressions of the trait (Wilson et al 2010). Both approaches have led to conflicting results even within a single genus, such as Xiphophorus fish (Ryan 1988;Basolo and Alcaraz 2003;Royle et al 2006;Kruesi and Alcaraz 2007;Baumgartner et al 2011).…”

“…Because the sword is physically linked to the thrust-producing system, several previous studies have sought to determine the energetic and locomotor costs associated with the trait. For example, completely removing the sexually selected sword through experimental manipulation in adult male Xiphophorus montezumae (the species with the longest sword) has suggested costs with respect to routine oxygen consumption and critical swimming speed (a measure of endurance; Basolo and Alcaraz 2003;Kruesi and Alcaraz 2007) but not for burst speed during a Cstart in Xiphophorus hellerii (Baumgartner et al 2011). Correlational studies of natural variation in sword length (SW) suggest no cost to endurance in Xiphophorus nigrensis (Ryan 1988) and that it may even be beneficial to burst speed during a C-start in X. hellerii (Royle et al 2006).…”

“…Several studies have assessed the repeatability of swimming performance in fish (Kolok 1992(Kolok , 1999Kolok et al 1998;Reidy et al 2000;Claireaux et al 2007;Oufiero and Garland 2009;Handelsman et al 2010;Marras et al 2010Marras et al , 2011 and of sexual signals in various taxa (Kotiaho et al 1996;Jang et al 1997). Other studies have examined the effect of sexual ornaments on swimming performance in fish (Nicoletto 1991;Basolo and Alcaraz 2003;Langerhans et al 2005;Kruesi and Alcaraz 2007;Wilson et al 2010;Baumgartner et al 2011). However, no studies to date have examined the consistency of individual performance in relation to a sexually selected trait.…”

Repeatability of locomotor performance and of morphology – locomotor performance relationships

“…The effect of sex on repeatability of U crit Although several studies have considered the effects of intra-sex variation on fish locomotion, for example, investigating the effects of sexual signalling in males (Basolo and Alcaraz, 2003;Karino et al, 2006;Baumgartner et al, 2011;Trappett et al, 2013;Oufiero et al, 2014) or reproduction (pregnancy or gravidity) in females (Plaut, 2002;Ghalambor et al, 2004;Svendsen et al, 2009;Belk and Tuckfield, 2010), surprisingly little attention has been paid to intersex differences of locomotor performance (Conradsen and McGuigan, 2015). Sexual dimorphism could have an impact on conclusions about repeatability in two ways.…”