2. Behavioral Biology TALKS - Deutsche Zoologische Gesellschaft

eceiving less food per individual invested approximately the same amount of energy
in reproduction as males from the better fed population, thus having less energy left
for survival. Another trade off exists between the time males spend on calling and
the time they need to find food. In the population, in which individuals got less food,
males spent more time on foraging and less time on calling. But despite of their lower
investment in calling and, additionally, their shorter life spans, the mating success of
the badly fed males was nearly as high as that of the well fed males. Here, the
operational sex ratio, which differed between the two test populations, affects
reproductive success through varying levels of intrasexual competition.
����66 Christiane Bramer
Evolution of cardenolide sequestration and resistance in lygaeid bugs
Authors: Christiane Bramer 1 , Georg Petschenka 1 , Jürgen Deckert 1 , Susanne Dobler 1
Affiliations: 1 Biozentrum Grindel und Zoologisches Museum, Hamburg
Conspicuous black and red aposematism is a pervasive feature of the hemipteran
subfamily Lygaeinae distinguishing them from other members of the mostly dull
colored family Lygaeidae. Indeed, the warning coloration is associated with chemical
defense which is often relying on sequestered host plant toxins. The best investigated
species, the large milkweed bug Oncopeltus fasciatus, obtains cardenolides from
Asclepias seeds and displays intricate adaptations to these toxins. However, usage of
cardenolides seems to be widespread within the Lygaeinae. Cardenolides are
powerful toxins which specifically inhibit the ubiquitous animal enzyme Na+K+-
ATPase. In O. fasciatus cardenolide resistance is mediated by a Na+K+-ATPase
possessing reduced sensitivity to cardenolides (target site insensitivity). To
reconstruct the evolution of cardenolide sequestration and metabolism as well as
target site insensitivity we established a molecular phylogeny comprising 18 lygaeine
species and 4 outgroups (CO I/II; 28S rRNA). Cardenolide sequestration and
metabolism were assessed by feeding studies with radioactive tracers in 7 species.
Target site insensitivity was evaluated by in vitro assays of Na+K+-ATPase and
sequence analysis. We found that sequestration of cardenolides and also target site
insensitivity are probably synapomorphic characters of the lygaeine subfamily. Our
data suggest that European members of the genus Arocatus lost black and red
aposematism as well as the ability to sequester cardenolides. Nevertheless target site
insensitivity, was retained although these species are no longer exposed to dietary
cardenolides. The extensive association of Lygaeines with apocynaceous plants and
the basal origin of adaptations to cardenolides suggest that this host plant
relationship is the original one yet dependence on cardenolides led the bugs on to
plants from many other families (Ranunculaceae, Plantaginaceae, Brassicaceae,
Asparagaceae) featuring these compounds.
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