Phylogeny of Paullinia L. (Paullinieae: Sapindaceae), a diverse genus of lianas with rapid fruit evolution

Paullinia L. is a genus of c. 220 mostly Neotropical forest-dwelling lianas that displays a wide diversity of fruit morphologies. Paullinia resembles other members of the Paullinieae in being a climber with stipulate compound leaves and paired inflorescence tendrils. However, it is distinct in having capsular fruits with woody, coriaceous, or crustaceous pericarps. While consistent in this basic plan, the pericarps of Paullinia fruits are otherwise highly variable—in some species they are winged, whereas in others they are without wings or covered with spines. With the exception of the water-dispersed indehiscent spiny fruits of some members of Paullinia sect. Castanella, all species are dehiscent, opening their capsules while they are still attached to the branch, to reveal arillate animal-dispersed seeds. Here we present a molecular phylogeny of Paullinia derived from 11 molecular markers, including nine novel single-copy nuclear markers amplified by microfluidics PCR. This is the first broadly sampled molecular phylogeny for the genus. Paullinia is supported as monophyletic and is sister to Cardiospermum L., which together are sister to Serjania Mill + Urvillea Kunth. We apply this novel phylogenetic hypothesis to test previous infrageneric classifications and to infer that unwinged fruits represent the ancestral condition, from which there were repeated evolutionary transitions and reversals. However, because the seeds of both winged and unwinged fruits are all dispersed by animals, we conclude that the repeated transitions in fruit morphology may relate to visual display strategies to attract animal dispersers, and do not represent transitions to wind dispersal.

Explaining the distribution of breeding and dispersal syndromes in conifers

The evolution of plants exhibiting different sexes, or dioecy, is correlated with a number of ecological and life-history traits such as woody growth form and animal-dispersed seeds, but the underlying causes of these associations are unclear. Previous work in seed plants has suggested that the evolution of fleshy cones or seeds may favour dioecy. In this study, we use a well-sampled molecular phylogeny of conifers to show that although dioecy and fleshiness strongly co-occur at the species level, this relationship has not resulted from numerous separate origins of this trait combination or from differential rates of diversification. Instead, we suggest that two character combinations—the ancestral dry-monoecious condition and the derived fleshy-dioecious condition—have persisted in conifers longer than other combinations over evolutionary time. The persistence of these trait combinations appears to reflect differences in the rate of successful transition into and out of these character states over time, as well as the geographical restriction of species with rare combinations and their consequent vulnerability to extinction. In general, we argue that such persistence explanations should be considered alongside ‘key innovation’ hypotheses in explaining the phylogenetic distribution of traits.

Seed rain under the canopies of female and male Myrsine coriacea, a pioneer tree from the Brazilian Atlantic forest

Isolated pioneer trees have been shown to increase the deposition of animal-dispersed seeds. The effect of gender on seed rain has not yet been investigated, and this study aimed to evaluate whether female and male plants of a pioneer dioecious zoochoric tree differ with respect to the seed rain under their canopies. Seed rain was evaluated for 13 mo, from October 2009 to October 2010, in secondary vegetation of the Atlantic forest in southern Brazil. We used 60 seed traps (0.5 m2): 40 traps under the crowns of 40 Myrsine coriacea (Primulaceae) trees (20 male and 20 female individuals) and 20 at sites without trees. We found 365071 diaspores belonging to 115 morphospecies from 37 families, and 38.3% of the morphospecies were trees, most of them zoochoric. The female trees accumulated a greater number of diaspores and species richness than male trees. The male trees accumulated a higher number of seeds and species than areas without trees. This study shows that sites containing female and male trees of M. coriacea and sites without trees differed significantly in terms of seed rain, and there is a gender effect in this dioecious, pioneer tree species because female plants promote an increase in the richness and abundance of diaspores.

Effects of remnant trees in fallows on diversity and structure of forest regrowth in a slash-and-burn agricultural system in southern Cameroon

Remnant trees in fields may facilitate regeneration in fallows by attracting seed dispersers and creating favourable sites for plant establishment. Ntumu shifting cultivators in Cameroon clearing rain forest spare some trees to provide shade for crops. This study examines their effects on regeneration by comparing vegetation in quadrats beneath and away from their crowns, in fallows of varying age (3-20 y). For fallows of all age classes, plant diversity was not significantly different between positions. Trees accounted for larger proportions of species and stems beneath remnant trees. Herbs, principally large monocots, accounted for larger proportions away from trees. Basal area was much higher in quadrats beneath trees. In all quadrats, the majority of individuals belonged to species with animal-dispersed seeds. These accounted for a larger proportion of individuals beneath trees (75%) than away (64%). Wind-dispersed species accounted for a larger proportion of stems away from trees (23.6%) than beneath (11.7%). These data suggest that enhanced seed rain by attraction of perching animals, demonstrated in a companion study, nfluenced regeneration patterns. Effects on regeneration were similar beneath trees of an animal-dispersed (Pycnanthus angolensis, Myristicaceae) and a wind-dispersed (Triplochiton scleroxylon, Sterculiaceae) species. Remnant trees in fallows may facilitate succession by nucleation, resulting in more rapid restoration of forest and conservation of nutrients in plant biomass.

Evolutionary ecology of seed dormancy and seed size

The theoretical ideas underpinning the evolution of seed dormancy and seed mass are briefly reviewed. Comparative tests of these theoretical ideas are then presented; all tests use modern comparative methods to allow accurate, meaningful comparisons across species. The comparative analyses of seed dormancy demonstrate that species that average the environment across time, by having long-lived adults or space as a result of clonal growth, typically have less dormant seeds. Amongst species with seeds unspecialized for spatial dispersal, seed mass is not related to dormancy. However, in species with wind- or animal dispersed seeds those with heavy seeds typically have less dormancy. This is consistent with heavy seeds having better establishment success and /or suffering higher levels of herbivory. The relationships between seed mass and plant height, lateral spread and adult longevity are explored using the Sheffield dataset. The complex pattern of relationships between these variables is interpreted in terms of dispersal limitation, escape from competition with clonal ramets and differences in establishment conditions. Some of the problems that are frequently encountered in the interpretation of comparative data are briefly discussed.