Spiders with bizarre gift-giving male head structures: morphology, biochemistry and sexual selection
Final Report Abstract
Gustatorial courtship, the transfer of male secretion to the female before or during copulation, has been documented for several arthropod species but the adaptive value and the production site and the composition of the secretions are rarely known. However, in dwarf spiders (Erigoninae, Linyphiidae), males show distinct head structures such as lateral grooves, dorsal pits and bizarre elevations. These head structures are generally connected to epidermal glands. Since females are lacking these structures they can be assumed to have evolved under sexual selection. Actually, copulation position in erigonines leads females to position their mouthparts above the male cephalic structures and gustatorial courtship is now documented for several species. We investigated dwarf spiders of the genera Diplocephalus and Oedothorax and found marked differences in the effect of the secretory head structures on male mating behavior between the genera. Gas-chromatographic and behavioural analysis of the male secretion in Oedotharox retusus demonstrated that the substance does not act as a pheromone. Histochemical analysis showed that proteins form the major part of the secretions in O. retusus, which suggests that the secretion can have a nutritive function but does not exclude the transfer of other, manipulative substances from male to female. Detailed investigation of the glandular composition using SEM and TEM techniques demonstrated that all Oedothorax species investigated possess glandular tissue irrespective of the morphology of their cephalic regions. Regarding composition, of the glandular tissue, we found marked differences between species. The glandular tissue very likely consists of two gland types in O. retusus, O. agrestis and O. gibbosus tuberosus and of only one type in O. apicatus and O. gibbosus gibbosus. Interestingly, the setae present on the head structure are multimodal sensilla and seem to function as mechano- and chemoreceptors. Molecular phylogenetic analysis suggests that sulci and morphological modifications of the male head structure are plesiomorphic and were reduced once or twice within the group of the Oedothorax species investigated. The existence of mating plugs in our focal species O. retusus impeded the rapid analysis of the adaptive value of secretory head structures but led us to explore the function of mating plugs on the species level up to a general critical evaluation of the adaptive value of mating plugs in spiders. Reports in the media BBC Wildlife: September 2009 page 44 Informationsdienst Wissenschaft: http://idw-online.de/pages/de/news198709 Vet Magazin: http://www.vet-magazin.com/wissenschaft/meldungen/Exoten- Medizin/Spinnen-Keuschheitsguertel.html Deutschlandfunk: http://www.dradio.de/dlf/sendungen/forschak/672826/
Publications
- 2008. Male head secretion triggers copulation in the dwarf spider Diplocephalus permixtus. Ethology 114:760-767
Uhl, G. & Maelfait, J.-P.
- 2009. Securing paternity in spiders? A review on occurence and effects of mating plugs and male genital mutilation. Genetica
Uhl, G.; Nessler, S.H., Schneider, J.M.
(See online at https://doi.org/10.1007/s10709-009-9388-5) - 2009. Securing paternity: mating plugs in the dwarf spider Oedothorax retusus (Araneae, Linyphiidae, Erigoninae). Biological Journal of the Linnean Society. 96:574-583
Uhl, G. & Busch, M.
