Florivory defence: are phenolic compounds distributed non-randomly within perianths?

Plants might allocate chemical defences unequally within attractive units of flowers including petals, sepals, and bracts because of variations in the probability of florivory. Based on optimal defence theory, which predicts that plants allocate higher chemical defences to tissues with higher probabilities of herbivore attack, we predicted that distal parts and sepals would have higher chemical defence allocations than proximal parts and petals. To test this prediction, we compared total phenolics and condensed tannins concentrations as well as presence of florivory within attractive units of ten angiosperm species. In agreement with the prediction, the overall results showed that the distal parts had higher total phenolics and condensed tannins than the proximal parts. On the other hand, contrary to the prediction, petals and sepals showed no tissue-specific variations. Florivory was more severe on the distal parts than the proximal parts, although statistical support for the variation was slightly weak, while the variations in presence of florivory between petals and sepals differed between the distal and proximal parts. These results may support the prediction of the optimal defence theory because distal parts of attractive units had higher presence of florivory and concentration of chemical defences.

Floral scent in Iris planifolia (Iridaceae) suggests food reward

Iris species can adopt different pollination strategies to attract their pollinators, generalized shelter-mimicking, specialized deceptive sexual-mimicking or food-rewarding. As attractive stimuli, Iris flowers may use their colours, large-size, symmetry, and volatile organic compounds (VOCs). However, relatively few studies investigated Iris floral olfactory cues in the context of plant-visitor/pollinator interactions. In the present study we combined the identification of the floral volatiles of the nectariferous I. planifolia with insects visiting its flowers to gather data on its biology. Floral volatiles were collected in the natural environment by dynamic headspace and analysed by gas chromatography-mass spectrometry (GC-MS). Insect visitors/pollinators were also recorded. The volatile bouquet was aromatic-dominated with 1,4 dimethoxybenzene as major compound. Among the insects visiting its flowers, bumble and honey bees were the most abundant followed by hover flies. Overall, our results suggest that I. planifolia advertises its food reward by an aromatic dominated volatile composition.

Intraflower variation in nectar secretion: Secretion patterns and pollinator behavior in male- and female-phase flowers

PREMISE OF THE STUDY

Plants that secrete abundant nectar attract many pollinator visits, potentially leading to a high frequency of geitonogamous pollination. However, intraflower variation in nectar volume might enhance early departure from the flower or inflorescence, reducing geitonogamy. To examine the adaptive significance of multiple nectar-producing spurs within flowers, we related intraflower variation in nectar characteristics to pollinator foraging behavior and plant reproductive success in protandrous Aquilegia buergeriana var. oxysepala.

METHODS

We investigated if nectar volume and sugar mass relate to spur length and if intraflower variation in nectar characteristics differ between male- and female-phase flowers. Because male function requires more pollinator visits than female function, male-phase flowers are expected to have greater nectar volume and lower intraflower variation in nectar volume than female-phase flowers. We used intraflower variation in spur length as an indicator of variation in nectar characteristics and investigated how spur length variation affects pollinator behavior, pollen removal, and seed production.

KEY RESULTS

Male-phase flowers had greater nectar volume and lower intraflower variation in nectar volume than female-phase flowers. Intraflower variation in spur length reduced the duration of bumblebee visits. Short visits reduced seed production, but increased pollen removal.

CONCLUSIONS

Our results suggest that high intraflower variation in nectar production rate can reduce geitonogamy and potentially increase the genetic diversity of pollen received. Such pattern of nectar secretion within and among flowers may allow flowers to ensure effective pollen transfer or high seed production.

Mechanisms for the evolution of complex and diversely elaborated sepals in Iris identified by comparative analysis of developmental sequences

PREMISE OF THE STUDY

Crested sepals, which have evolved at least five times in Iris, are adaxially elaborated with a sinuous and/or uneven median structure (crest) along the proximal-distal axis and sometimes with various lateral structures (ridges, crests, and linear protuberances) flanking the median crest. These structural elaborations are complex yet diverse in form, providing a good opportunity to investigate developmental mechanisms for the diversification of reproductive lateral organs.

METHODS

Morphologies of the median and lateral structures at different developmental stages from selected crested sepals representing the major types of structural elaborations were recorded using scanning electron microscopy and light microscopy. Developmental (morphogenetic) events that contribute to changes in shape (e.g., sinuousness, unevenness) between consecutive stages were recorded. Developmental sequences-trajectories that consist of a series of developmental events-were compared in a phylogenetic context.

KEY RESULTS

Three developmental events (development of outgrowths, greater expansion of the upper zone, and greater expansion of the lower zone), are shared across lineages, occur in the same developmental sequences, and are responsible for the changes in shape during the development of diverse structural elaborations. In addition, two novel developmental events and the development of trichomes on elaborate structures were observed within the core-crested clade.

CONCLUSIONS

Developmental sequences are conserved across independently evolved crested lineages. Heterochronic and heterotopic shifts of developmental events play the major role in the diversification of elaborations of crested sepals in Iris. The evolution of novel developmental events and the development of trichomes also contribute to the diversity.