Meeting Abstract

89.3  Wednesday, Jan. 7  The cost of bearing a sword: an examination of the locomotor costs associated with a sexually selected trait in Xiphophorus. OUFIERO, Christopher E.*; GARLAND, JR., Theodore; Univ. of California, Riverside coufi001@student.ucr.edu

An underlying assumption of sexual selection theory is that while the secondary traits that arise increase reproductive fitness, they also impose costs of various types. One potential cost is a reduction in locomotor abilities caused by elaborate morphologies that arise through sexual selection (e.g., enlarged fish fins). These costs can be studied in various ways, including comparison of males, comparison of males with females, or by experimentally reducing the trait. Another way to examine locomotor costs is through a phylogenetic comparative approach with a group in which the species vary in their expression of the trait. The purpose of this study is to examine the locomotor costs and potential compensatory mechanisms of the sexually selected "sword" exhibited by males in species of Xiphophorus (swordtails and platyfish). This genus of fish is unique in that some species exhibit full expression of the trait (e.g., X. helleri), some have a reduced expression of the trait (e.g., X. pygmaeus), and some lack the trait completely (e.g. X. variatus). Therefore, through a phylogenetic comparative approach we can determine some of the evolutionary costs of the trait. To do this, we have been measuring the critical swimming speed, sprint speed, and c-start velocity of males and females of species within the genus. We have also been examining traits that may evolve to offset the cost, such as organ masses, enzyme activities, and maximum oxygen consumption. Here, we present preliminary findings on the potential cost of the sword on critical swimming speed and sprint speed from ~10 species. Supported by NSF DDIG IOS-0709788 to T.G. and C.E.O.