One of the most fascinating stories in biology
The partnership between insects and flowers in pollination is among the most fascinating stories in biology. It is a show case of organismic diversity and the working of evolution. Apart from attracting our intrinsic intellectual interest and fascination, it is of prime ecological significance and has an enormous economic impact as well. Research into this partnership, which is an opportunistic business trading food against pollination, is not new at all, but started more than 200 years ago (Sprengel 1793). Accordingly, a large number of cases of fine-tuned adaptedness to this business at all levels of organismic organization have come to light already. This applies to both the flower and the pollinator side, which both are subject to selection pressures working in favor of survival and reproductive success. Considering the staggering diversity of angiosperms and even more so that of insects, the spectrum of specializations is enormous, sometimes just beautiful for us like the colors of an alpine meadow at summertime, sometimes bizarre and hard to believe, like the stories about fraud and robbery. To reach a well-founded understanding of adaptedness and the selective pressures that have shaped it research approaches need to be both reductionist and holistic. What we see today largely is the product of some 100 million years of co-evolution. In this sense, the summer meadow to a considerable extent is to be valued as a reflection of the pollinating insects and vice versa. This is seen in countless intimate dependencies resulting from reciprocal selection. In this special issue of the Journal of Comparative Physiology A some recent research will be highlighted dealing with such different subjects as evolutionary fundamentals, functional morphology, floral signals, and insect senses and cognition. To start, Hannes Paulus in his review ‘General questions and sexually deceptive orchids’ raises some basic questions regarding evolutionary mechanisms, which are crucial for an understanding of the partnership between insects and flowers and the meaning of biodiversity. How can the reciprocal selection generating a particular pollination syndrome be reliably proven? The European orchids of the sexual deceptive genus Ophrys are taken as an example. Their flowers do not offer any food and have developed fascinating ways of manipulating their pollinators. They demonstrate the complexity and refinement in the relationship between flower signals attracting male bees and wasps and the visitors’ responses, even making use of the pollinator’s ability to memorize and learn an individual flower’s characteristics. The flower fools its highly species-specific insect visitor when attracting him by visual, chemical and tactile signals, which he expects to stem from a receptive conspecific female. However, the male insect remembers and avoids a flower already visited, associating it with an unreceptive female. These findings point to the relevance of the striking variability of both the visual and olfactory signals emanating from the flowers. In the end, the flowers’ variability supports cross-pollination and helps to avoid self pollination. The pollinator’s innate preference is overruled by learning. Clearly, this story also underlines the value and necessity of combining simple observations and manipulative experiments in the field with work in the laboratory, learning from analyses made possible by modern technology. Such technology has proven crucial with regard to the detailed analyses of many floral scents and the chemosensory capabilities of the corresponding insect visitors. ‘Floral scent, nectar and chemoreception’ is the headline for the following four contributions. Annemarie Heiduk et al. present another very specialized pollination system where floral scents are a crucial element in the communication between the partners. Ceropegia stenantha * Friedrich G. Barth friedrich.g.barth@univie.ac.at