Extrafloral nectar increases seed removal by ants inTurnera ulmifolia

Genetic architecture of multiple mutualisms and mating system in Turnera ulmifolia

Plants often associate with multiple arthropod mutualists. These partners provide important services to their hosts, but multiple interactions can constrain a plant's ability to respond to complex, multivariate selection. Here, we quantified patterns of genetic variance and covariance among rewards for pollination, biotic defence and seed dispersal mutualisms in multiple populations of Turnera ulmifolia to better understand how the genetic architecture of multiple mutualisms might influence their evolution. We phenotyped plants cultivated from 17 Jamaican populations for several mutualism and mating system-related traits. We then fit genetic variance-covariance (G) matrices for the island metapopulation and the five largest individual populations. At the metapopulation level, we observed significant positive genetic correlations among stigma-anther separation, floral nectar production and extrafloral nectar production. These correlations have the potential to significantly constrain or facilitate the evolution of multiple mutualisms in T. ulmifolia and suggest that pollination, seed dispersal and defence mutualisms do not evolve independently. In particular, we found that positive genetic correlations between floral and extrafloral nectar production may help explain their stable coexistence in the face of physiological trade-offs and negative interactions between pollinators and ant bodyguards. Locally, we found only small differences in G among our T. ulmifolia populations, suggesting that geographic variation in G may not shape the evolution of multiple mutualisms.

Extrafloral nectar as entrée and elaiosomes as main course for ant visitors to a fireprone, mediterranean‐climate shrub

Thousands of plants produce both extrafloral nectaries (EFNs) on their leaves and nutrient‐rich appendages on their diaspores (elaiosomes). Although their individual ecology is well‐known, any possible functional link between these structures has almost always been ignored. Here, we recognized their co‐presence in the shrub, Adenanthos cygnorum (Proteaceae), and studied their function and interaction. We observed that the same ants frequently visit both structures, seeds are attractive to vertebrate granivores but are released into a leafy cup from where they are harvested by ants and taken to their nests, from which seeds, lacking elaiosomes, germinate after fire. We showed that juvenile plants do not produce EFNs and are not visited by ants. We conclude that EFNs are not just an indirect adaptation to minimize herbivory via aggressive ant visitors (the role of a minority) but specifically enhance reproductive success in two ways: First, by inducing ants to visit the plant as a reliable food source throughout the year. Second, by promoting discovery of the seasonally available, elaiosome‐bearing seeds for transport to their nests (the majority of visitors), so avoiding the risk of granivory should seeds instead fall to the ground. Parasitoid wasps play a supporting role in controlling the main insect herbivore whose larvae devour the reproductive apices. Thus, the EFN‐elaiosome relationship has three components that enhance species fitness: foliage protection, seed transport, and granivore escape. A similar system has been described only once before (in an unrelated biome) and, consistent with the objectives of ecology as an integrative science, deserves wider study.

A brainstorm on the systematics of Turnera (Turneraceae, Malpighiales) caused by insights from molecular phylogenetics and morphological evolution

With 145 species, Turnera is the largest genus of Turneraceae (Malpighiales). Despite several morphotaxonomic and cytogenetic studies, our knowledge about the phylogenetic relationships in Turnera remains mainly based on morphological data. Here, we reconstruct the most comprehensive phylogeny of Turnera with molecular data to understand the morphological evolution within this group and to assess its circumscription and infrageneric classification. We analyzed two nuclear and six plastid markers and 112 taxa, including species and infraspecific taxa, 97 from Turnera, covering the 11 series of the genus. Bayesian inference, maximum parsimony and maximum likelihood analyses show that Turnera, as traditionally circumscribed, is not monophyletic. The genus is divided into two well-supported independent clades; one of them is sister to the genus Piriqueta and is here segregated as the new genus Oxossia. According to our reconstructions, Turnera probably evolved from an ancestor without extrafloral nectaries and with solitary, homostylous flowers with yellow petals. The emergences of extrafloral nectaries and distyly, both common in extant taxa, played an important role in the diversification of the genus. An updated infrageneric classification reflecting the relationships within Turnera is now possible based on morphological synapomorphies and is here designed for further studies.

From dispersal to predation: A global synthesis of ant-seed interactions

Ant-seed interactions take several forms, including dispersal, predation, and parasitism, whereby ants consume seed appendages without dispersal of seeds. We hypothesized that these interaction outcomes could be predicted by ant and plant traits and habitat, with outcomes falling along a gradient of cost and benefit to the plant. To test this hypothesis, we conducted a global literature review and classified over 6,000 pairs of ant-seed interactions from 753 studies across six continents. Linear models showed that seed and ant size, habitat, and dispersal syndrome were the most consistent predictors. Predation was less likely than parasitism and seed dispersal among myrmecochorous plants. A classification tree of the predicted outcomes from linear models revealed that dispersal and predation formed distinct categories based on habitat, ant size, and dispersal mode, with parasitism outcomes forming a distinct subgroup of predation based on seed size and shape. Multiple correspondence analysis indicated some combinations of ant genera and plant families were strongly associated with particular outcomes, whereas other ant-seed combinations were much more variable. Taken together, these results demonstrate that ant and plant traits are important overall predictors of potential seed fates in different habitat types.