Aline C. Martins

Changes in wild bee fauna of a grassland in Brazil reveal negative effects associated with growing urbanization during the last 40 years

Bee fauna and associated flora from a grassland site in Brazil, surveyed 40 and 20 years ago, were newly surveyed with comparable methodology to evaluate changes in the bee fauna of this site, considering that human population and urbanization has exponentially increased in the last 40 years. In general, bee species richness has declined in 22%, as well as their abundance. Some of the previously abundant species are now absent, including Bombus bellicosus Smith, 1879, Gaesischia fulgurans (Holmberg, 1903) and Thectochlora basiatra (Strand, 1910). No particular trend of differential decrease among either taxonomic or functional groups was observed, except for a minor increase in the proportion of oligolectic species and a 50% reduction in the number of large species. The first two surveys were more similar to each other in species richness per bee genus, while the two most recent grouped together based on measures of anthropogenic impact. Furthermore, the number of plant species visited by bees increased, with a pronounced increase in ruderal and exotic species. Crop cultivation, competition with honeybees and climate changes may all be related to bee decline. Nevertheless, the effects of urbanization, in particular intense land occupation and few preserved natural areas can be pointed as the main causes of species decline. Due to continuing increase in human population, increased erosion in diversity is expected. Habitat protection is an additional challenge to bee conservation in the region, with no local conservation units set aside for grasslands. State and municipal agencies should urgently consider the establishment of reserves for the few remaining patches of natural grasslands.

The New World oil‐collecting bees Centris and Epicharis (Hymenoptera, Apidae): molecular phylogeny and biogeographic history

We present a first comprehensive time‐calibrated phylogeny for two Neotropical genera of bees, Centris and Epicharis, whose females collect floral oil together with pollen for larval provisioning, and that traditionally have been grouped in the tribe Centridini. Our analyses rely on a matrix of 167 taxa and 4228 aligned nucleotides for the subfamily Apinae, with denser sample of Centris and Epicharis. Centris and Epicharis are strongly supported monophyletic groups, but Centridini is paraphyletic in relation to the corbiculate bees. The inner phylogenetic relationships of Epicharis agree with the current taxonomic classification. In Centris, three main clades were recovered, namely the Centris, Trachina and Melacentris groups. Inner relationships in Centris suggest the reinstatement of some subgenera and proposition of new ones. Early diversification of Centris and Epicharis took place at the tropical regions of South America. Epicharis and the Melacentris group in Centris mostly diversified in that region, expanding over Central America and tropical North America only recently in the last 3 My. The groups Trachina and Centris present a complex biogeographic history, with expansions to the Nearctic region, the Antilles, and temperate regions of South America in the late Oligocene and Miocene.

Multiple Geographical Origins of Environmental Sex Determination enhanced the diversification of Darwin’s Favourite Orchids

Environmental sex determination (ESD) − a change in sexual function during an individual life span driven by environmental cues − is an exceedingly rare sexual system among angiosperms. Because ESD can directly affect reproduction success, it could influence diversification rate as compared with lineages that have alternative reproductive systems. Here we test this hypothesis using a solid phylogenetic framework of Neotropical Catasetinae, the angiosperm lineage richest in taxa with ESD. We assess whether gains of ESD are associated with higher diversification rates compared to lineages with alternative systems while considering additional traits known to positively affect diversification rates in orchids. We found that ESD has evolved asynchronously three times during the last ~5 Myr. Lineages with ESD have consistently higher diversification rates than related lineages with other sexual systems. Habitat fragmentation due to mega-wetlands extinction, and climate instability are suggested as the driving forces for ESD evolution.

From tree tops to the ground: Reversals to terrestrial habit in Galeandra orchids (Epidendroideae: Catasetinae)

The colonization of the epiphytic niche of Neotropical forest canopies played an important role in orchids extraordinary diversification, with rare reversions to the terrestrial habit. To understand the evolutionary context of those reversals, we investigated the diversification of Galeandra, a Neotropical orchid genus which includes epiphytic and terrestrial species. We hypothesized that reversion to the terrestrial habit accompanied the expansion of savannas. To test this hypothesis we generated a comprehensive time-calibrated phylogeny and employed comparative methods. We found that Galeandra originated towards the end of the Miocene in Amazonia. The terrestrial clade originated synchronously with the rise of dry vegetation biomes in the last 5 million years, suggesting that aridification dramatically impacted plant diversification and habits in the Neotropics. Shifts in habit impacted floral spur lengths and geographic range size, but not climatic niche. The longer spurs and narrower ranges characterize epiphytic species, which probably adapted to specialized long-tongued Euglossini bee pollinators inhabiting forested habits. The terrestrial species present variable floral spurs and wider distribution ranges, with evidence of self-pollination, suggesting the loss of specialized pollination system and concomitant range expansion. Our study highlights how climate change impacted habit evolution and associated traits such as mutualistic interactions with pollinators.

HISTORICAL APPROACHES IN THE STUDY OF PLANT-POLLINATOR INTERACTIONS

Interactions between plants and pollinating animals are well-known examples of interspecific mutualism, which involves reciprocal adaptations and can lead to coevolution. In plant-pollinator interaction the concept of coevolution is frequently inappropriate since the majority of interactions is non-obligate and makes conflicting patterns of association between species. Due to the diffuse nature of this kind of interaction, there is an attempt to divide the interactions in classes of specialization, such as the floral syndromes. Ecological approaches could be applied in the study of those interactions (for example, the floral visitor records and behavior and pollinator efficiency, among others), not necessarily based in the historical or evolutionary view of the interaction. In the present review two approaches in the historical view of the plant-pollinator interaction are presented according to their main methods and some examples. The first approach is regarding to the fossil record of interaction, which is rare and could be indirect, when a fossil animal presents morphological characters previously known for a particular kind of interaction; or direct, when the process of fossilization have occurred in the exact moment of the interaction, preserving together animals and plants (or parts of plants). The second part of the revision is regarding to phylogenetic hypothesis and is divided in four different approaches: (1) mapping characters in phylogeny; (2) estimating the age of interactions; (3) co-phylogenies and (4) association between phylogenetic and biogeographical hypothesis. Parsimony and/or model-based method are present in all revised papers and their efficacy is also discussed. The use of phylogenetic hypothesis is suggested as the most important approach in the study of evolution of those interactions and, within this line of thought, the ancestral state character reconstruction and mapping them in the phylogeny is the base of a main part of our knowledge about the evolution of plant-pollinator interactions. However all those approaches require the availability of good collected ecological data, which is a major challenge for the understanding of those interactions in the Neotropical biota.

Floral uniformity through evolutionary time in a species-rich tree lineage

Changes in floral morphology are expected across evolutionary time and are often promoted as important drivers in angiosperm diversification. Such a statement, however, is in contrast to empirical observations of species-rich lineages that show apparent conservative floral morphologies even under strong selective pressure to change from their environments. Here, we provide quantitative evidence for prolific speciation despite uniform floral morphology in a tropical species-rich tree lineage. We analyse floral disparity in the environmental and phylogenetic context of Myrcia (Myrtaceae), one of the most diverse and abundant tree genera in Neotropical biomes. Variation in floral morphology among Myrcia clades is exceptionally low, even among distantly related species. Discrete floral specialisations do occur, but these are few, present low phylogenetic signal, have no strong correlation with abiotic factors, and do not affect overall macroevolutionary dynamics in the lineage. Results show that floral form and function may be conserved over large evolutionary time scales even in environments full of opportunities for ecological interactions and niche specialisation. Species accumulation in diverse lineages with uniform flowers apparently does not result from shifts in pollination strategies, but from speciation mechanisms that involve other, nonfloral plant traits.

Paleocene origin of the Neotropical lineage of cleptoparasitc bees Ericrocidini-Rhathymini (Hymenoptera, Apidae)

Cleptoparasitic bees abandoned the pollen collecting for their offspring and lay their eggs on other bees’ provisioned nests. Also known as cuckoo bees they belong to several lineages, especially diverse in Apinae. We focused on a lineage of Apinae cleptoparasitic bees, the clade Ericrocidini+Rhathymini, which attack nests of the oil-collecting bees. We sequenced five genes for a broad sampling in this clade plus a large outgroup and reconstruct phylogeny and divergence times. We confirmed the monophyly of the clade Ericrocidini+Rhathymini and its position inside the ericrocidine line, together with the tribes Protepeolini, Isepeolini and Coelioxoidini. Our results corroborate the current taxonomic classification. Ericrocis is the basal most lineage in Ericrocidini and the position of Acanthopus and the most diverse genus Mesoplia were inconclusive. Ericrocidini+Rhathymini diverged from Parepeolus aterrimus 74 mya in the Cretaceous. Considering the robust molecular evidence of their sister relationships, the striking differences on the first instar larvae morphology of the two groups are probably adaptations to the distinct nesting biology of their hosts. As other parasites in the ericrocidine line, both groups possess larvae adapted to kill the immature host and to feed on floral oil provisioned by the host female. The evolution of host specialization in the line Ericrocidini+Rhathymini retroced to the Eocene when they arose synchronously with their hosts, Centris and Epicharis.