The diversification of Pterocarpus (Leguminosae: Papilionoideae) was influenced by biome-switching and infrequent long-distance dispersal

Aim: Phenotypes which evolved for dispersal over ecological timescales may lead to significant macroevolutionary consequences, such as infrequent long-distance dispersal and diversification in novel environments. We aimed to reconstruct the phylogenetic history of Pterocarpus (Leguminosae/ Fabaceae) to assess whether seed dispersal phenotypes help to explain the current biogeographical patterns of this group. Location: Pantropical. Taxon: The Pterocarpus clade, particularly Pterocarpus (Leguminosae/Fabaceae). Methods: We sequenced ~300 nuclear loci captured using Angiosperms-353, a genomic 'bait set' for flowering plants, from which we generated a time-calibrated phylogenomic tree. To corroborate this, we also generated a time-calibrated phylogenetic tree from data-mined Sanger-sequencing data. We then collated distribution data and fruit dispersal morphology traits to compare trait-dependent and trait-independent biogeographical models, allowing us to assess whether dispersal traits influenced the spatio-temporal evolution of Pterocarpus. Finally, using the results of these model tests, we estimated the ancestral ranges and biomes of Pterocarpus species to better understand their biogeographical history. Results: We recovered well-supported phylogenetic relationships within Pterocarpus, within which there were two subclades - one Neotropical and the other Palaeotropical. Our divergence date estimates suggested that Pterocarpus largely diversified from around 12 Ma, during the Miocene. Trait-dependent biogeographical models were rejected for both range and biome evolution within Pterocarpus, but models parameterising dispersal were supported. Pterocarpus largely diversified in the Neotropics, followed by dispersal and diversification into Africa and Asia, with later dispersal into Australasia/Oceania. The neotropical subclade of Pterocarpus underwent multiple biome switches between moist forest and dry forest, while in palaeotropical Pterocarpus we reconstructed multiple switches between moist forest and grassland. Main conclusions: Overall, our analyses suggest that Pterocarpus underwent infrequent cross-continental dispersal and adaptation to novel biomes. While this was minimally impacted by fruit dispersal syndromes, shifts between moist and arid environments precipitated by long-distance dispersal and environmental change have played an important role in diversification within Pterocarpus since the Miocene.

Simarouba versicolor (Simaroubaceae) Dispersal by the Leaf-Cutter Ant Atta sexdens

The importance of Simarouba versicolor St. Hil. fruit dispersal by the leaf-cutting ant Atta sexdens (L.) was studied in the Cerrado, Tocantins, Brazil. The trees and nests were located between a forest area and a Brachiaria decumbens Stapf pasture. Seeds were collected in October 2015 along foraging trails and on the anthill of an A. sexdens colony. Germination of three groups of seeds was tested: (1) seeds with the tegument removed by the ants; (2) seeds without tegument, cleaned manually, and (3) seeds with tegument. The germination rates for the three treatments were similar; however, it was verified that the seeds cleaned by ants germinated faster. In addition, it was verified that the ants dispersed the seeds by at least 20 meters in the study area. Simarouba versicolor is a plant studied for its insecticidal properties, and this is the first study to our knowledge reporting its dispersal by ants.

Fruit dispersal dynamics of the cold desert shrub Zygophyllum xanthoxylon

The pattern of seed dispersal in time and space can affect plant fitness and the soil seed bank, and thus information is needed on this aspect of the seed biology of a species before it is selected for use in habitat restoration projects. Zygophyllum xanthoxylon is a super-xerophilous shrub that is a potential pioneer species for use in revegetating highly disturbed areas of the cold deserts of northwest China. We studied fruit release and soil seed banks of Z. xanthoxylon for 3 years in two cold desert habitats characterized by different degrees of drought and wind velocity. In our study, fruit (a three-winged capsule) release began in summer (June 2010, August 2011, July 2012) and extended for 9–10 months, but plants can be found in the population with previous- and current-year fruits attached to them. More than 50% of the fruits were released in the first 3–4 months after maturity, while the others were released gradually over a 7–8 month period. The temporal pattern of fruit dispersal varied with habitat but not with amount of precipitation during summer. The pattern of fruit deposition on the soil surface was affected by neighbouring plants, wind velocity, wind direction and topography. In both habitats, >90% of the fruits were deposited beside large and small clusters of plants, mainly Ephedra przewalskii. To facilitate plant community development, we suggest that E. przewalskii should be planted (as a wind break) together with Z. xanthoxylon when native pioneer species are used for restoration of cold desert shrublands.

Effects of relative emergence time and water deficit on the timing of fruit dispersal in Raphanus raphanistrum L.

Seed dispersal is both a spatial and a temporal phenomenon, although most studies focus on spatial aspects. Seed initiation on the maternal plant may occur over a considerable period, especially in indeterminately flowering species, and thus seeds may be exposed to a wide range of environmental conditions during their development. The result is variation in the timing of seed development, the anatomy of structures related to the dispersal process, and the behaviour and fate of seeds post-dispersal. A key resource during the growth and development of summer-maturing species in most areas, and one that is thus likely to modify these processes, is water. Two experiments were therefore undertaken to describe (i) the development of Raphanus raphanistrum fruits and the timing of fruit dispersal, and (ii) the effects of water availability on the timing of fruit dispersal. Fewer seeds were produced and subsequently dispersed by later emerging plants. The duration of fruit dispersal became shorter when the plants emerged progressively later than the crop, and the time of maximum dispersal was later. For cohorts of fruits initiated at the same time, those that developed under mild and severe water deficit reached their final length sooner, and were dispersed sooner, than those receiving a plentiful supply of water. Thus, the phenology of the maternal plant and the nature of its environment can modify the timing of propagule maturity and consequently dispersal. Such information may provide an opportunity for managers to reduce weed seed return to their field or, conversely, to regulate the amount of contaminated grain or reduce dispersal to other locations.