Probably most people don’t think of this, but angiosperms (flowering plants) “evolve over time” — in response a balance between how and which insects pollinate them, and herbivory (how and which animals eat them). “Pollination success” and “mating systems” are therefore the genomic responses to environmental adversity (i.e. beneficial vs detrimental insects); hence, this is the perfect gene-environment interactions topic.
Evolution and maintenance of differences in these traits have more been focused on to selective pressures imposed by pollinators, and pollen and mate limitation. Recently, the focus has changed to study the effects of antagonists — such as “grazers” and “seed predators” — on floral traits. Authors [see attached article and editorial] demonstrate that both pollinators and herbivores influence evolution of floral display and of self-pollination efficiency; moreover, these effects are not necessarily additive.
Why might the evolution of floral display and efficiency of autonomous self-pollination be affected by plant interactions with both pollinators
and herbivores? Well, a beautiful floral display might “increase attractiveness” to pollinators, but might simultaneously increase the risk of damage from herbivores eating the flowers/entire plant. So, there must be a balance between “optimal floral display” and “being not too attractive to herbivores“. Obviously, evolutionary adaptation will depend not only on the strength and direction of “survival selection“, but also on the presence of genetic variation and genetically based correlations among the traits.
Authors [see attached article] studied a rapid-cycling population of the annual plant, Brassica rapa (in the Genus of turnip, napa cabbage & bok choy), while it evolved under each of four treatment combinations: [a] hand-pollination with or [b] without herbivory, and [c] bee pollination with or [d] without herbivory. “Pollination by hand” ensured that flowers received a surplus of pollen, whereas in the other, bees determined pollination success of individual plants. As authors had hypothesized, selection by bees resulted in the evolution of plant phenotypes that were more attractive to bees. And this effect was reduced when plants evolved in the presence of both bees and leaf herbivores (caterpillars of the butterfly Pieris brassicae).
These findings are consistent with the concept that plant traits that influence attractiveness to pollinators may be subject to conflicting selection from herbivores. Furthermore, plants pollinated by bees (which are presumably “more strongly pollen-limited” than were plants pollinated by hand), tended to evolve greater ability to produce offspring through autonomous self-pollination. In other words, the evolution of most plant traits was affected by the interaction of bee pollination and herbivory — emphasizing the importance of cross-talk between both types of interactions for plant evolution.
DwN
Science 12 Apr 2o19; 364: 193-196 + editorial pp 122-123