Abstracts - Deutsche Zoologische Gesellschaft

P EB.18 - ENLoss of sex in rotifers: mechanisms and adaptive significanceClaus-Peter StelzerInstitute for Limnology, Austrian Academy of Sciences, Mondsee, AustriaEvolutionary Biology Posters 133Even after decades of intensive research, the “paradox of sex” has remained largely unresolved. Acentral problem within this paradox is the fate of asexual lineages soon after they arise: Will theyspread or decline? Empirical estimates of the “invasive potential” of new asexual lineages can bebiased, especially if such estimates are derived from specimens collected in the field. First, asexualsand sexuals may not be comparable due to genetic differences, a problem that can arise if inferencesabout ancestry are drawn indirectly using genetic markers. Likewise, uncertainty about the exactage of an asexual lineage may be source of error: some asexuals may be old and already suffer fromsecondary effects of asexual reproduction, e.g. mutation accumulation. Here I introduce a new experimentalsystem to study the origin and evolution of obligate asexuality. The monogonont rotiferBrachionus calyciflorus normally reproduces by a mixture of sexual and asexual reproduction, yetlaboratory populations often show a transition to obligate asex (i.e., a complete and permanently inheritedloss of sexual reproduction). We have observed obligate asexuals arising among the sexuallyproduced offspring of individual females (i.e.; asexuals and sexuals were full sibs). I will presentexperiments targeted to identify the mechanisms and evolutionary dynamics of such transitions toasex. I will also discuss potential implications for long-term asexuality, which has evolved in theclosely related bdelloid rotifers.P EB.19 - ENVisual signalling in pollinator attraction in a sexual deceptive orchidMartin Streinzer, Hannes F. Paulus, Johannes SpaetheDepartment of Evolutionary Biology, University of Vienna, AustriaOrchids of the genus Ophrys are pollinated by males of solitary bees and wasps through sexualdeception. The flowers mimic the odor of a receptive female and thus attract males that seek tocopulate. The specificity of the sexual pheromones imitated by the flowers results in attraction ofsingle pollinator species which thus utilizes a private communication channel. General signals likevisually conspicuous coloration of the perigon are rather uncommon components of this pollinationsystem and have been assumed to play only a minor role in pollinator attraction. We studied therole of the bright pink and visually conspicuous perigon of Ophrys heldreichii for attraction of itsspecific pollinator, the long-horned bee Tetralonia berlandi (Apidae:Eucerini). Using dual-choiceexperiments and video recordings of male bees approaching artificial flowers we tested the role ofpresence/absence, size and color of the perigon. Our data suggest that the colored perigon servesas a close range signal in male attraction. When the perigon was removed search time significantlyincreased. Moreover, search time was also affected by the color contrast of the perigon against thefoliage background. We hypothesize that this kind of visual signal is adaptive particularly in thoseOphrys species where the targeted males patrol resource-based encounter sites and strongly rely ontheir visual system when searching for females.