Sexual Competition, Coercive Mating and Mate Assessment ... - CPRG

Sexual Selection and Size Dimorphism in the One-Sided Livebearer969Fig. 2: Relation between male relative length (male standard length/female standard length) and malemating success. Mating success was expressed as the frequency of copulatory attempts (gonopodialthrust) ending with a contact between genitalia, over the total number of attemptssame number of attacks as the larger one. The proportion of attacks carried out bythe large male was not correlated with the di€erence in length between the twomales (Pearson correlation coecient r ˆ 0.02, ns, n ˆ 19), nor with the size of thefemale (r ˆ 0.23, ns, n ˆ 19). Large males made signi®cantly more mating attemptsthan small ones (Table 1), but variance was large and in ®ve trials small malesshowed more attempts than large ones. Overall, the proportion of mating attemptsand dominance, i.e. proportion of aggressive attacks, were positively correlatedwith each other (r ˆ 0.60, p ˆ0.006, n ˆ 19).Table 1: Number of male copulatory attempts and attacks towards the other male in relationto male length (mean ‹ SD) and sex ratio. For behavioural data, median and interquartilerange are givenSex ratioNo. of attacksNo. of copulatoryattempts2 males, 1 female (n ˆ 19)Larger male (SL) (28.2 mm ‹ 2.3)Smaller male (SL) (23.0 mm ‹ 2.4)Wilcoxon signed-ranks test2 males, 2 females (n ˆ 14)Larger male (SL) (28.3 mm ‹ 3.1)Smaller male (SL) (21.3 mm ‹ 1.8)17 (6±25)1 (0±4)z ˆ 2.98, p ˆ0.00242 (23±52)15 (9±21)z ˆ 3.83, p