The impact of chromosome number changes on the diversification of angraecoids in tropical Africa (Epidendroideae: Vandeae: Angraecinae)

International audienceThe impact of the widespread occurrence of polyploidisation anddescending dysploidy on lineage diversification has never been explicitly tested, to our knowledge, in Orchidaceae. Angraecoids (Vandeae: Angraecinae) present a diverse rangeof chromosome numbers which makes them a good study system to understand karyotype evolution and its role in cladogenesis. Within Angraecinae, two major clades are recognised: one mostly confined to Madagascar, where only x= 19 is reported; and the Afroneotropical clade, which apparently presents a rare example of ascending dysploidy in the orchid family, with c. 90% of its species inferred to have x = 25. In this study, we aimed to trace the evolution of the chromosome number in the Afroneotropical cladeand to test, for the first time, the likely impact of chromosome changes on diversification in Orchidaceae. By using a near-comprehensive phylogenetic tree of angraecoids at the genus level, including 280 species, we mapped the chromosome counts of 116 species in 35 genera. Accordingly, we inferred the ancestral haploid number of most Afroneotropical angraecoid genera, starting from x = 19, and we identified a total of three first step ascending dysploid events in Conchograecum(x= 21), Dendrophylax(x = 22) and in the ‘Aerangidinae’ (x= 25); and a single first-step descending dysploidy occurrence in Calyptrochilum(x = 17). Within the Aerangidinae clade nine independent second step descending dysploid events were identified, which define new generic and suprageneric synapomorphies, namely in Ancistrorhynchusand Microcoelia(x= 24); and in the Cyrtorchis-Tridactyleclade (x= 23). Furthermore, two secondary and one tertiary dysploid events were identified in Aerangisand Summerhayesia, respectively. Finally, nine neopolyploid events were identified in eight genera. These findings have allowed us to test whether there was a significant contribution of chromosome number evolution to the radiation of angraecoids in tropical Afric

Rapid radiation of angraecoids (Orchidaceae, Angraecinae) in tropical Africa characterised by multiple karyotypic shifts under major environmental instability

International audienceAngraecoid orchids present a remarkable diversity of chromosome numbers, which makes them a highly suitable system for exploring the impact of karyotypic changes on cladogenesis, diversification and morphological differentiation. We compiled an annotated cytotaxonomic checklist for 126 species of Angraecinae, which was utilised to reconstruct chromosomal evolution using a newly-produced, near-comprehensive phylogenetic tree that includes 245 angraecoid taxa. In tandem with this improved phylogenetic framework, using combined Bayesian, maximum likelihood and parsimony approaches on ITS-1 and five plastid markers, we propose a new cladistic nomenclature for the angraecoids, and we estimate a new timeframe for angraecoid radiation based on a secondary calibration, and calculate diversification rates using a Bayesian approach. Coincident divergence dates between clades with identical geographical distributions in the angraecoids and the pantropical orchid genus Bulbophyllum suggest that the same events may have intervened in the dispersal of these two epiphytic groups between Asia, continental Africa, Madagascar and the Neotropics. The major angraecoid lineages probably began to differentiate in the Middle Miocene, and most genera and species emerged respectively around the Late Miocene-Pliocene boundary and the Pleistocene. Ancestral state reconstruction using maximum likelihood estimation revealed an eventful karyotypic history dominated by descending dysploidy. Karyotypic shifts seem to have paralleled cladogenesis in continental tropical Africa, where approximately 90% of the species have descended from at least one inferred transition from n = 17–18 to n = 25 during the Middle Miocene Climatic Transition, followed by some clade-specific descending and ascending dysploidy from the Late Miocene to the Pleistocene. Conversely, detected polyploidy is restricted to a few species lineages mostly originating during the Pleistocene. No increases in net diversification could be related to chromosome number changes, and the apparent net diversification was found to be highest in Madagascar, where karyotypic stasis predominates. Finally, shifts in chromosome number appear to have paralleled the evolution of rostellum structure, leaflessness, and conspicuous changes in floral colour

Integrating systematics and reproductive biology into African orchid conservation: a case study with the genus Cyrtorchis Schltr. (Angraecinae, Vandeae)

International audienceDeveloping conservation strategies of threatened species involves understanding their taxonomy, ecology and reproductive biology, and to integrate this knowledge into rational conservation management actions. Focusing on Cyrtorchis, we present here an approach that combine taxonomy and reproductive biology to develop the conservation of this angraecoid genus renowned for its challenging species delimitation problem. Indeed, its showy white long-spurred flowers, indicating a probable sphingophilous syndrome, constitute a suitable model for studieson reproductive biology of epiphytic orchids, a first step indispensable for their conservation. By using phylogenetic analyses, we tested the monophyly of 23 species hypotheses delimited using morphometrical analyses to clarify species delimitation. Based on this taxonomic background, we chose seven well-resolved species (C. aschersonii, C. ringens, C. cf ringens, C. chailluana, C. letouzeyi, C. monteiroae and a new species) to study, in our living collection in Yaoundé and in two natural populations, their breeding and pollination systems. A protocol involving phenological monitoring of 414 living specimens was implemented during which 330 hand-controlled pollination tests (177 self-vs 153 cross-pollinations) were conducted to assess factors affecting fruit set and seed viability. Pollination efficiency and reproductive success were assessed using fruit set and viable seeds production. Camera and insect light trapping were used for survey and identificationofpollinators. Preliminary results show that the flowering period of 13 species occurring in Cameroon occurs from February to November, with a flowering peak during the rainy season. For the first time in Central Africa, hawkmoths were confirmed as potential pollinators of three species of Cyrtorchis. Seeds produced are used to supply the African orchid seed bank housed at the University of Yaoundé I which currently includes 146 specimens representing 50% of Cyrtorchis species