Sexual behaviour and morphological variation in the millipede Megaphyllum bosniense (Verhoeff, 1897)

Sexual selection can be a major driving force that favours morphological evolution at the intraspecific level. According to the sexual selection theory, morphological variation may accompany non-random mating or fertilization. Here both variation of linear measurements and variation in the shape of certain structures can significantly influence mate choice in different organisms. In the present work, we quantified sexual behaviour of the millipede Megaphyllum bosniense (Verhoeff, 1897) as characterized by several sequences. These are: mating latency, duration of copulation, contact to copulation time, duration of contact without copulation, time from entrance (time-point when individuals were placed in boxes in which tests occurred) to contact with copulation, and time from entrance to contact without copulation. Further, we analysed the influence of morphological variation (both variation of linear measurements and variation in the shape of several structures) on mating success. Variation of body length, antennal length, length of the walking legs, trunk width, and trunk height was analysed by traditional morphometrics, while variation in size and shape of the antennae, walking legs, head, and gonopods (promeres, opisthomeres) was analysed using geometric morphometrics. More than half of all physical contacts detected among the millipedes resulted in copulation. Based on the value of sexual selection coefficients, preferences toward the previous partner were found to be prevalent in both female and male choice tests. Individuals with different mating status significantly differed in some morphological traits (body mass, head centroid size, head shape, and promere shape). Our study yielded new information about the sexual behaviour of millipedes and variation of morphological traits as a potential basis for mate preferences.