[Sperm transfer from Glomeris (Diplopoda)]

Indirect sperm transfer in arthropods: behavioral and evolutionary trends

Arachnids, myriapods, and wingless hexapods exhibit a fascinating diversity of sperm transfer behaviors. Modes of sperm transfer can be categorized by the degree of contact between male and female during transfer, with direct transfer (copulation) involving the greatest contact, paired-indirect transfer an intermediate degree, and dissociated transfer the least. Internal fertilization, spermatophores, and copulation are sometimes assumed to have evolved after invasion of land, but all have evolved many times in the marine habitat. Behaviors associated with indirect sperm transfer include those having close parallels with direct transfer (provision of nuptial gifts) as well as unique phenomena (spermatophore trampling by rival males). The morphology and physiology of indirectly transferred spermatophores have been shaped by environmental factors (e.g. humidity) as well as biological ones (e.g. clutch size of females), and they may provide useful phylogenetic characters. Unanswered questions about indirect transfer include the following: Are females of dissociated species able to choose their partners? What determines size and number of spermatophores? Do speciation rates differ between taxa with direct versus indirect transfer?

Mating behaviour and spermatophore morphology: a comparative test of the female-choice hypothesis

Complex, species-specific morphology of genitalia or "paragenitalia" such as spermatophores is traditionally considered an adaptation to prevent heterospecific matings. Eberhard argued against this lock-and-key hypothesis and suggested that elaborate male genitalia evolve through female preference for increased tactile stimulation. He found support for this argument in a cross-taxon comparison of spermatophore complexity among species with different degrees of contact between the sexes during spermatophore transfer. After expanding Eberhard's list of species, we tested the female-choice hypothesis with appropriate controls for phylogeny and using naive human subjects to rank spermatophore complexity. Our results uphold Eberhard's conclusion that the lock-and-key hypothesis does not explain the distribution of spermatophore complexity among taxa; however, they do not clearly support female choice as an alternative explanation. Other factors that may influence spermatophore complexity include environmental stress and whether spermatophores are deposited on a substrate. Because we seldom know what parts of a spermatophore are touched by females, or whether there are spermatophore-associated pheromones, human visual assessment may not always allow accurate judgement of realized spermatophore complexity.

Fine structure of postgonopodial glands of a myriapod Glomeris marginata (Villers)

The postgonopodial gland of the myriapod Glomeris marginata (Villers), which produces a pheromone, is an integumentary gland comprising numerous functional secretory units. Each secretory unit consists of two proximal secretory cells, an intermediary cells lacking secretory characteristics and a canal cell surrounding the canal, which is secretory in nature. Secretory proximal cells exhibit a zone of small channels originating from invaginations of the plasma membrane and through which secreted material is released. Apposing each invagination of these cells is a corresponding invagination of the intermediary cell: the two units in the centre of the intermediary cell join another which communicates with the canal. Secretion produced by the latter passes through the canal wall and bends with secretion of the two proximal cells. The most striking feature of all these cells is the abundance of tubules and fibrils in the small canal zone in the proximal cells, which also exhibits a centriole; in the intermediary cell around cytoplasmic membrane invaginations where a diplosome is present, and in almost the entire canal cell.