Mating system, sexual dimorphism, and the opportunity for sexual selection in a territorial ungulate

Bateman gradients in a promiscuous mating system

“…Therefore, limited reproductive success in males combined with benefits of multimale mating for females in this species may have provided the ideal context to observe equal sex-specific Bateman gradients. Interestingly, the levels of I and Is found in our system reached those usually reported for males of sexually dimorphic species (Vanpé et al 2008), and thus suggest that both sexes have the opportunity to be strongly selected to increase their MS. Females had I and Is of 2.27 and 2.05, respectively, which is much higher than values previously reported for females of other promiscuous species where all I and Is were lower than 1 (e.g., Jones et al 2002;Schulte-Hostedde et al 2004;Jones 2009;Barreto and Avise 2010;Munroe and Koprowski 2011).…”

The mismeasurement of sexual selection

“…3a,b,e,f) and that it is not scientifically sound to make inferences as if the difference between actual and maximum strength of selection was analogous to a randomly distributed (and thus uninteresting) noise term when fitting models to data. This is disconcerting given that I s has been used to characterize mating systems (Krakauer, 2008;Vanpé et al, 2008), 'solve' the bigsperm paradox (Bjork & Pitnick, 2006), assess the relative effect of extra-pair or parasitic copulations on the strength of sexual selection (Albrecht et al, 2006;Kleven et al, 2006;Singer et al, 2006;Dolan et al, 2007) and draw conclusions regarding the effects of temporal variability (Weatherhead, 2005;Reichard et al, 2008), humaninduced environmental change (Jä rvenpä ä & Lindströ m, 2004;Perlut et al, 2008) and local climatic variability (Twiss et al, 2007) on the strength of sexual selection. Unfortunately, it is impossible to know if and when I s has led to spurious results and unfounded conclusions.…”

“…In practice though, both empiricists and theoreticians show a consistent tendency to interpret opportunities as if they reflect actual sexual selection (Shuster & Wade, 2003;Bjork & Pitnick, 2006;Sword & Simpson, 2008;Duval & Kempenaers, 2008;Vanpé et al, 2008;Box 2). Merely acknowledging the limitations of a metric does not justify its continued usage.…”

“…In practice, I s and the actual strength of sexual selection are regularly assumed to be strongly positively correlated and used interchangeably (Shuster & Wade, 2003;Bjork & Pitnick, 2006;Duval & Kempenaers, 2008;Vanpé et al, 2008;Sword & Simpson, 2008;Box 2).…”

“…Furthermore, there was no significant relationship between I s or I male and sperm investment across several species. Duval & Kempenaers (2008) claim that ''The potential for evolutionary change can more generally be quantified via the opportunity for selection, I, which is the variance in relative fitness… In polygynous mating systems, the opportunity for sexual selection is usually calculated as I male … This measure quantifies the potential for selection to operate, separate from the evolutionary response to selective pressure and without requiring precise knowledge of the mechanism by which selection occurs…' ' Vanpé et al (2008) state that ''Measuring the opportunity for sexual selection is crucial for addressing many questions in behavioural ecology (such as the evolution of sexual size dimorphism, conspicuous male traits, alternative mating tactics, and sexbiased parental investment, Andersson, 1994) and population dynamics…'' Box 1: The measurement of sexual selection (2004)(2005)(2006)(2007)(2008) Sexual selection has been quantified using numerous measures (Arnold and Wade, 1984a,b;Arnold & Duvall, 1994;Andersson, 1994;Ruzzante et al, 1996;Kokko et al, 1999;Mills et al, 2007;Jones, 2009). We present and define six of the most frequently used measures in Table 1.…”