Beetles, berries, bumble bees and Bittersweet: Do frequency-dependent
selection processes contribute to the maintenance of steroidal glycoside
diversity in Solanum dulcamara?
Abstract
Intraspecific chemodiversity is common among plant species.
Frequency-dependent selection (FDS), combined with chemotype-specific
costs and benefits may be drivers maintaining chemodiversity. Here, we
tested the effect of heritable steroidal glycoside (SG) chemotypes on
herbivory, plant performance and pollinator visits. We manipulated
plot-level SG chemodiversity using a replacement series of two
Solanum dulcamara chemotypes accumulating predominantly saturated
(S) or unsaturated (U) SGs, creating homogeneous
(4S+4U), heterogeneous (3S+U,
3U+S) and balanced (2U+2S) plots. Herbivory,
and reproductive output were interactively affected by SG chemodiversity
and chemotype, with the highest fruit counts in 2U+2S
plots. U-chemotype plants had longer stems, more and faster
ripening berries, received more visits from Bombus lapidarius,
but were more damaged by leaf-chewers and produced fewer seeds with
higher germination rates. Our results indicate that the level of plot
chemodiversity differentially affects reproductive output of the two
chemotypes, suggesting that FDS may contribute to the maintenance of
heritable chemical polymorphisms.