New insights into the phylogeny and evolution of Podocarpaceae inferred from transcriptomic data

Phylogenies of an increasing number of taxa have been resolved with the development of phylogenomics. However, the intergeneric relationships of Podocarpaceae, the second largest family of conifers comprising 19 genera and approximately 187 species mainly distributed in the Southern Hemisphere, have not been well disentangled in previous studies, even when genome-scale data sets were used. Here we used 993 nuclear orthologous groups (OGs) and 54 chloroplast OGs (genes), which were generated from 47 transcriptomes of Podocarpaceae and its sister group Araucariaceae, to reconstruct the phylogeny of Podocarpaceae. Our study completely resolved the intergeneric relationships of Podocarpaceae represented by all extant genera and revealed that topological conflicts among phylogenetic trees could be attributed to synonymous substitutions. Moreover, we found that two morphological traits, fleshy seed cones and flattened leaves, might be important for Podocarpaceae to adapt to angiosperm-dominated forests and thus could have promoted its species diversification. In addition, our results indicate that Podocarpaceae originated in Gondwana in the late Triassic and both vicariance and dispersal have contributed to its current biogeographic patterns. Our study provides the first robust transcriptome-based phylogeny of Podocarpaceae, an evolutionary framework important for future studies of this family.

What causes size coupling in fruit--frugivore interaction webs?

The simplest and arguably the most ubiquitous pattern in seed dispersal mutualisms is size coupling: large frugivores tend to consume larger fruits and small frugivores tend to consume smaller fruits. Despite the simplicity of this pattern, the potential mechanisms responsible for fruit--frugivore size coupling are mechanistically divergent and poorly resolved. Size coupling could arise deterministically, if large frugivores actively seek out larger fruits to maximize their foraging efficiency. Alternatively, size coupling could also arise passively, if frugivores forage randomly, but are able to consume only those fruit species that are smaller than their gape width. I observed birds forage for fruits in a New Zealand forest reserve at approximately five-day intervals for six years to test for fruit--frugivore size coupling. I then derived a suite of network analyses to establish whether fruit--frugivore size coupling was best explained by active or passive foraging by frugivores. Results showed a strikingly strong pattern in size coupling; the average size of fruits consumed by each frugivore species increased with their maximum gape width. Simulation analyses revealed that over 70% of variation in interaction frequencies in the observed fruit-frugivore web could be explained by a size-constrained, passive, foraging model. Foraging models in which birds foraged actively for different-sized fruits to improve their foraging efficiency performed more poorly. Results were therefore consistent with the hypothesis that apparently nonrandom patterns in seed dispersal mutualisms can sometimes arise from simple stochastic processes.