Next steps for understanding the selective relevance of female-female competition

Title: Next steps for understanding the selective relevance of female-female competition Short title: Selective relevance of female-female competition Authors: Kristal E. Cain1 and Kimberly A. Rosvall2 1 Evolution, Ecology & Genetics Research School of Biology Australian National University Acton, ACT 0200 kristalcain@gmail.com kecain.weebly.com 2 Department of Biology Indiana University 1001 E 3rd ST Bloomington, IN 47405 www.indiana.edu/~krosvlab/ Words (body, references, and figures): ~1994 1. Introduction After decades of neglect, recent empirical research on exaggerated female traits (e.g. ornaments, armaments, aggression, acoustic signals, etc.) has revived interest in this widespread but poorly understood phenomenon, and shown that these traits often function in the context of female-female competition (West-Eberhard 1983; Amundsen 2000; Clutton-Brock 2009; Stockley & Bro-J？rgensen 2011; Rosvall 2011a; Rubenstein 2012 [Theme issue]; Stockley & Campbell 2013 [Theme issue]). However, recent reviews have emphasized the applicability of sexual vs. social selection, rather than rigorously examining the role of different ecological contexts in shaping the evolution of traits used in competitive contexts (hereafter, ‘competitive traits’) in females. Thus, we still lack a solid understanding of the ecological and evolutionary mechanisms driving the evolution of female trait expression, in particular whether, how, and why these mechanisms vary among species, and between the sexes. It is our opinion that two critical issues impede our understanding the evolution of competitive traits in females. (1) The field has yet to investigate the ecological and evolutionary mechanisms that underlie interspecific and intersexual variation in the expression of these traits. This is perhaps due to a perceived ‘apples and oranges’ problem stemming from the observation that animals compete over a wide variety of resources that vary by species or sex. However, by focusing on fitness currencies in addition to the nature of the resources over which animals compete, we can empirically compare the strength and direction of selection across species and sexes. (2) To date, research has primarily focused on the fitness costs or benefits of female competitive traits. As with many questions in behavioral and evolutionary ecology, quantifying how costs and benefits interact is essential to furthering our understanding of the evolution of competitive traits. Here, our goal is to draw attention to these solutions in order to spur more efficient and transformative progress. 2. Apples