Julid millipede and spirobolid millipede gonopod functional equivalents

Abstract

Not all male genitalic structures function only in sperm transfer during the time of copulation (in copula), they perform copulatory courtship through movements and interactions with the female genitalia. These structures were considered 'functional luxuries' through natural selection, mate choice and conflict of interests. The genital biomechanics of Centrobolus millipedes have examined ex copula then in copula to make actual correlations between the male and female genitalia. Two methods were employed: (1) artificial simulation of gonopod movements and (2) freeze-fixation in order to understand their functional equivalents. After copulating for approximately 10 minutes pairs were freeze-fixed by pouring liquid nitrogen (-196 °C) upon them. After one month in 70% ethanol at -10 °C, the copulatory organs were dissected from the animals under the light microscope to remove the vulva sacs and associated tissue that concealed the regions of contact. Structure-function relationships of the male accessory genitalia (gonopods) were discussed in the spirobolidan millipede genus Centrobolus and compared to julid millipedes.