A highly resolved nuclear phylogeny uncovers strong phylogenetic conservatism and correlated evolution of fruit color and size in Solanum L.

Mutualisms between plants and fruit-eating animals were key to the radiation of angiosperms. Still, phylogenetic uncertainties limit our understanding of fleshy-fruit evolution, as in the case of Solanum, a genus with remarkable fleshy-fruit diversity, but with unresolved phylogenetic relationships. We used 1786 nuclear genes from 247 species, including 122 newly generated transcriptomes/genomes, to reconstruct the Solanum phylogeny and examine the tempo and mode of the evolution of fruit color and size. Our analysis resolved the backbone phylogeny of Solanum, providing high support for its clades. Our results pushed back the origin of Solanum to 53.1 million years ago (Ma), with most major clades diverging between 35 and 27 Ma. Evolution of Solanum fruit color and size revealed high levels of trait conservatism, where medium-sized berries that remain green when ripe are the likely ancestral form. Our analyses revealed that fruit size and color are evolutionary correlated, where dull-colored fruits are two times larger than black/purple and red fruits. We conclude that the strong phylogenetic conservatism shown in the color and size of Solanum fruits could limit the influences of fruit-eating animals on fleshy-fruit evolution. Our findings highlight the importance of phylogenetic constraints on the diversification of fleshy-fruit functional traits.

Seabird guano inputs increase impacts from introduced mammals on the native plants and animals of an oceanic island.

Seabirds create fluxes of nutrients from marine to terrestrial ecosystems that influence the food webs of small islands. We investigated how guano inputs shape terrestrial food webs by comparing species of selected plant and animal species in a red-footed booby colony in Mona Island (Puerto Rico, Caribbean Sea), to sites of the island lacking guano inputs. We quantified guano deposition and its relationship to plant biomass production, fecundity and density, as well as the activity of native and introduced animal species. In general, guano inputs increased the gross primary plant productivity, size, and fecundity by twofold. Guano inputs were also associated with twofold increases in density of Anole lizards, but also to increases in the activity of introduced pigs (> 500%), goats (> 30%), and cats (> 500%), which negatively impact native species. In particular, elevated pig and cat activity within the booby colony was correlated with lower activity of endemic ground lizards and of introduced rats. Our results also suggest that severe droughts associated with climate change exacerbate the negative effects that introduced species have on vegetation and reduce the positive effects of seabird guano inputs. Our findings underscore the importance of allochthonous guano inputs in subsidizing plant productivity and native and endemic species in small oceanic islands, but also in increasing the negative impacts of introduced mammals. Management and conservation efforts should focus on the exclusion (or eradication) of introduced mammals, particularly pigs and goats, from remnant seabird colonies in Mona Island.

Negative density dependence characterizes mutualistic interactions between birds and fruiting plants across latitudes.

Negative density dependence (NDD) in biotic interactions of interference such as plant-plant competition, granivory and herbivory are well-documented mechanisms that promote species' coexistence in diverse plant communities worldwide. Here, we investigated the generality of a novel type of NDD mechanism that operates through the mutualistic interactions of frugivory and seed dispersal among fruit-eating birds and plants. By sampling community-wide frugivory interactions at high spatial and temporal resolution in Pennsylvania, Puerto Rico, Peru, Brazil and Argentina, we evaluated whether interaction frequencies between birds and fruit resources occurred more often (selection), as expected, or below expectations (under-utilization) set by the relative fruit abundance of the fruit resources of each plant species. Our models considered the influence of temporal scales of fruit availability and bird phylogeny and diets, revealing that NDD characterizes frugivory across communities. Irrespective of taxa or dietary guild, birds tended to select fruits of plant species that were proportionally rare in their communities, or that became rare following phenological fluctuations, while they mostly under-utilized abundant fruit resources. Our results demonstrate that negative density-dependence in frugivore-plant interactions provides a strong equalizing mechanism for the dispersal processes of fleshy-fruited plant species in temperate and tropical communities, likely contributing to building and sustaining plant diversity. This article is part of the theme issue 'Diversitydependence of dispersal: interspecific interactions determine spatial dynamics'.