MORPHOMETRIC TRAITS AND SEXUAL SELECTION IN MEDFLY (DIPTERA: TEPHRITIDAE) UNDER FIELD CAGE CONDITIONS

The effects of male size and other morphometric traits as determinants of male mating success were evaluated under field cage conditions. Males of the laboratory Seib6-96 strain were released into field cages with males and females of a wild population from the Patagonian region. Mating pairs were classified as ‘successful’, while unmated flies were labeled as ‘unsuccessful’. Five morphometric traits were measured in a sample of 141 unsuccessful and 149 successful males: eye length (EL), head width (HW), thorax length (TL), face width (FW), and wing length (WL). An exploratory non-parametric Spearman’s rank correlation test indicated that mated males were in average larger for all traits (P < 0.01) except FW, indicating that with the exception of FW all traits are positively correlated with mating success. Step-wise multiple regression and principal component analysis + logistic regression indicated that the most likely targets of selection were TL, EL, and FW. The two former are positively correlated, while FW is negatively correlated with the fitness component analyzed here (male mating success). In previous studies where male-male interaction had been removed experimentally, EL was shown to be associated with female choice and no effect relative to mating success was detected on TL. On the basis of that study and the present results it is tempting to suggest that body size (TL) might be important in intra-sexual selection. However, size was found to be strain dependent and flies from the wild were on average bigger than laboratory ones. Size selection might then be correlated with copulatory success, as a side effect due to selection of wild males over lab males due to differential sexual activity or other causes. The potential importance of both intra-sexual selection (male-male interactions) and inter-sexual selection (mate choice) on the morphology of Ceratitis capitata is discussed on the basis of the results presented here and previous works.