Data from: The Red Queen unveils the sexual and mating strategies of flowers

The Red Queen Hypothesis states that sex evolved as an adaptation of hosts
against their parasites, allowing them to produce offspring protected by
rare combinations of defence-genes. It has been hypothesized that plant
species under higher pressure by short-lived natural enemies should invest
more heavily in outcrossing. Here, we test the interspecific prediction
that plant species associated with a higher richness of insect herbivores
– used as a proxy for a higher, more diverse and consistent herbivory
pressure over geographic space and evolutionary time – should exhibit
sexual and mating traits leading to outcrossing. We predict that plant
species associated with a richer insect fauna will have a higher
probability to be auto-incompatible, dichogamous, heterostylous,
dimorphic, dioecious, and allogamous. Furthermore, they are predicted to
exhibit a higher pollen-ovule ratio, to be more dependent on pollinators
or wind for cross-fertilization, and to rely mostly on sexually-generated
seeds for reproduction rather than on asexual means of reproduction. In
order to perform such comparative tests, we assembled published
insect-plant interaction records and information on key reproductive
floral traits linked to the inbreeding-outcrossing gradient for 1884
native angiosperm species from Germany. The analyses were performed with
generalized linear models and phylogenetic models using species richness
of insect herbivores as the single explanatory variable, but also with
plant geographic range size and plant height as covariates. We showed that
plant species consumed by a higher species richness of insect herbivores
have a higher probability to be auto-incompatible, dichogamous, dimorphic,
dioecious, and allogamous. In addition, they had a higher pollen-ovule
ratio, were more dependent on pollinators or wind for cross-fertilization,
and relied mostly on sexually-generated seeds for reproduction rather than
also use asexual reproduction. Model fitting improved considerably after
taking into consideration the phylogenetic structure of the data and the
results remained relatively consistent after controlling for geographic
range size and plant height. Synthesis. Although the conventional wisdom
is that floral traits of plants evolved in concert with their mutualistic
pollinators, here we showed that several key sexual and mating traits of
plants, which modulate their outcrossing strategy, evolved in response to
the pressure exerted by their antagonistic insect herbivores. The Red
Queen Hypothesis emerges as a unifying theory which helps to explain the
sexual diversity of angiosperms, with consequences for genetic and
phylogenetic diversity, animal-plant network structures, and plant-based
ecosystem services.