Since the time of Darwin, evolutionary biologists have been fascinated by the spectacular adaptations to insect pollination exhibited by orchids. However, despite being the most diverse plant family on Earth, the Orchidaceae lack a definitive fossil record and thus many aspects of their evolutionary history remain obscure. Here we report an exquisitely preserved orchid pollinarium (of Meliorchis caribea gen. et sp. nov.) attached to the mesoscutellum of an extinct stingless bee, Proplebeia dominicana, recovered from Miocene amber in the Dominican Republic, that is 15-20 million years (Myr) old. This discovery constitutes both the first unambiguous fossil of Orchidaceae and an unprecedented direct fossil observation of a plant-pollinator interaction. By applying cladistic methods to a morphological character matrix, we resolve the phylogenetic position of M. caribea within the extant subtribe Goodyerinae (subfamily Orchidoideae). We use the ages of other fossil monocots and M. caribea to calibrate a molecular phylogenetic tree of the Orchidaceae. Our results indicate that the most recent common ancestor of extant orchids lived in the Late Cretaceous (76-84 Myr ago), and also suggest that the dramatic radiation of orchids began shortly after the mass extinctions at the K/T boundary. These results further support the hypothesis of an ancient origin for Orchidaceae.

Most flowering plants establish mutualistic associations with insect pollinators to facilitate sexual reproduction. However, the evolutionary processes that gave rise to these associations remain poorly understood. We reconstructed the times of divergence, diversification patterns, and interaction networks of a diverse group of specialized orchids and their bee pollinators. In contrast to a scenario of coevolution by race formation, we show that fragrance-producing orchids originated at least three times independently after their fragrance-collecting bee mutualists. Whereas orchid diversification has apparently tracked the diversification of orchids' bee pollinators, bees appear to have depended on the diverse chemical environment of neotropical forests. We corroborated this apparent asymmetrical dependency by simulating co-extinction cascades in real interaction networks that lacked reciprocal specialization. These results suggest that the diversification of insect-pollinated angiosperms may have been facilitated by the exploitation of preexisting sensory biases of insect pollinators.

The orchid bees constitute a clade of prominent insect pollinators distributed throughout the Neotropical region. Males of all species collect fragrances from natural sources, including flowers, decaying vegetation and fungi, and store them in specialized leg pockets to later expose during courtship display. In addition, orchid bees provide pollination services to a diverse array of Neotropical angiosperms when foraging for food and nesting materials. However, despite their ecological importance, little is known about the evolutionary history of orchid bees. Here, we present a comprehensive molecular phylogenetic analysis based on~4.0 kb of DNA from four loci [cytochrome oxidase (CO1), elongation factor 1-a (EF1-a), arginine kinase (ArgK) and RNA polymerase II (Pol-II)] across the entire tribe Euglossini, including all five genera, eight subgenera and 126 of the approximately 200 known species. We investigated lineage diversification using fossil-calibrated molecular clocks and the evolution of morphological traits using disparity-through-time plots. In addition, we inferred past biogeographical events by implementing model-based likelihood methods. Our dataset supports a new view on generic relationships and indicates that the cleptoparasitic genus Exaerete is sister to the remaining orchid bee genera. Our divergence time estimates indicate that extant orchid bee lineages shared a most recent common ancestor at 27-42 Mya. In addition, our analysis of morphology shows that tongue length and body size experienced rapid disparity bursts that coincide with the origin of diverse genera (Euglossa and Eufriesea). Finally, our analysis of historical biogeography indicates that early diversification episodes shared a history on both sides of Mesoamerica, where orchid bees dispersed across the Caribbean, and through a Panamanian connection, thus reinforcing the hypothesis that recent geological events (e.g. the formation of the isthmus of Panama) contributed to the diversification of the rich Neotropical biota.

SummaryVolatile communication between sagebrush (Artemisia tridentata) individuals has been found previously to reduce herbivory and to be more effective between individuals that are genetically identical or related relative to between strangers. The chemical nature of the cues involved in volatile communication remains unknown for this and other systems.We collected headspace volatiles from sagebrush plants in the field and analyzed these using GC-MS.Volatile profiles were highly variable among individuals, but most individuals could be characterized as belonging to one of two chemotypes, dominated by either thujone or camphor. Analyses of parents and offspring revealed that chemotypes were highly heritable.The ecological significance of chemotypes and the genetic mechanisms that control them remain poorly understood. However, we found that individuals of the same chemotype communicated more effectively and experienced less herbivory than individuals of differing chemotypes. Plants may use chemotypes to distinguish relatives from strangers.