Ergänzende Informationen zu Publikationen von Fabian Cahenzli

Quantifying the relative contribution of multiple isolation barriers to gene flow between recently diverged species is essential for understanding speciation processes. In parapatric populations, local adaptation is thought to be a major contributor to the evolution of reproductive isolation. However, extrinsic postzygotic barriers assessed in reciprocal transplant experiments are often neglected in empirical assessments of multiple isolation barriers. We analyzed multiple isolation barriers between two closely related species of the plant genus Dianthus, a genus characterized by the most rapid species diversification in plants reported so far. Although D. carthusianorum L. and D. sylvestris Wulf. can easily be hybridized in crossing experiments, natural hybrids are rare. We found that in parapatry, pollinator mediated prezygotic reproductive isolation barriers are important for both D. carthusianorum (0.761) and D. sylvestris (0.468). In contrast to D. carthusianorum, high hybrid viability in D. sylvestris (-0.491) was counteracted by strong extrinsic postzygotic isolation (0.900). Our study highlights the importance of including reciprocal transplant experiments for documenting extrinsic postzygotic isolation and demonstrates clearly divergent strategies and hence asymmetric pre- and postzygotic reproductive isolation between closely related species. It also suggests that pollinator-mediated and ecological isolation could have interacted in synergistic ways, further stimulating rapid speciation in Dianthus.

Keywords: Dianthus carthusianorum - Dianthus sylvestris - extrinsic postzygotic isolation - reciprocal transplant experiments - reproductive isolation barriers - speciation

After over 30 years of research, it was recently shown that nectar amino acids increase female butterfly fecundity. However, little attention has been paid to the effect of nectar amino acids on male butterfly reproduction. Here, we show that larval food conditions (nitrogen-rich vs. nitrogen-poor host plants) and adult diet quality (nectar with or without amino acids) affected the amount of consumed nectar in Coenonympha pamphilus males. Furthermore, amino acids in the nectar diet of males increased progeny's larval hatching mass, irrespective of paternal larval reserves. Our study takes the whole reproductive cycle of male butterflies into account, and also considers the role of females in passing male nutrients to offspring, as males' realized reproduction was examined indirectly via nuptial gifts, by female performance. With this comprehensive approach, we demonstrate for the first time that nectar amino acids can improve male butterfly reproduction, supporting the old postulate that nectar amino acids generally enhance butterfly fitness.

Keywords: butterfly reproduction - larval feeding - Lepidoptera - pollination

Butterfly-pollinated flowers offer nectar with higher amino acid concentrations than most flowers pollinated by other animals, and female butterflies of some species prefer to consume amino acid-rich nectar. However, for over 30 years, there has been an ongoing discussion about whether nectar amino acids benefit butterfly fitness. A clear positive effect was only shown for the nectar-feeding Araschnia levana, and females of the fruit-feeding Bicyclus anynana also increased offspring quality when they were fed amino acids as adults. Thus, severe doubts remain about the general significance of these single positive results. We therefore tested a further species from a phylogenetically different butterfly subfamily, the small heath (Coenonympha pamphilus L., Satyrinae), taking into account feeding conditions over the whole life cycle of this species. C. pamphilus females receiving nectar amino acids as adults, irrespective of larval food quality, produced heavier larvae and also increased the hatching success of their eggs offer the oviposition period. Furthermore, females raised under nitrogen-poor larval conditions tended to use nectar amino acids to increase the number of eggs laid. Thus, C. pamphilus females used nectar amino acids primarily to increase their offspring quality, and secondly tended to increase offspring quantity, if larval resources were scarce, showing a resource allocation pattern differing from both B. anynana and A. levana. Our study supports the old postulate that nectar amino acids generally enhance butterfly fitness.

Keywords: butterfly reproduction - Coenonympha pamphilus - larval feeding - lepidoptera pollination

Nitrogen is a key nutrient for fitness in insects, but host plant defence can deter herbivores from acquiring it. Therefore, coping with host plant defence is a predominant issue for herbivores. Butterflies have the ability to compensate for a nitrogen-poor diet both as herbivorous larvae and as nectar-feeding adults. We examined whether silica (S), the main anti herbivore defence in grasses (in both fertilized nitrogen-rich (F+) and nitrogen-poor (F-) Festuca rubra host plants) affects larval development and accordingly adult feeding behaviour in the small heath butterfly, Coenonympha pamphilus. High silica levels in nitrogen-poor hostplants (F-/S+) negatively affected larval performance, and, as a consequence, female and even male butterflies preferred to consume amino acid-rich nectar. Our findings show for the first time that plant defence in larval host plants affects feeding behaviour in adult butterflies, and that even male butterflies, which have so far been thought to be indifferent to nectar amino acids, preferred to consume amino acid-rich nectar. Hence larval food quality can influence plant–pollinator dynamics.

Keywords: amino acid - Coenonympha pamphilus - Festuca rubra - larval feeding - Lepidoptera - nectar - preference - Satyrinae - silica