Oxidation of amines by yeasts grown on 1-aminoalkanes or putrescine as the sole source of carbon,nitrogen and energy

The maximum growth rate of Trichosporon cutaneum CBS 8111 in chemostat cultures was 0.185 h^-1 on ethylamine and 0.21 h^-1 on butylamine, that of Candida famata CBS 8109 was 0.32 h^-1 on putrescine.The amine oxidation pattern of the ascomycetous strains studied, viz. Candida famata CBS 8109, Stephanoascus ciferrii CBS 4856 and Trichosporon adeninovorans CBS 8244 was independent of the amine that had been used as the growth substrate. It resembled that of benzylamine/putrescine oxidase found in other ascomycetous yeasts. However, differences in pH optimum and substrate specificity were observed between the amine-oxidizing systems of these three species.The amine oxidation pattern of cell-free extracts of Trichosporon cutaneum CBS 8111 varied with the amine that was used as growth substrate. The enzyme system produced by Cryptococcus laurentii CBS 7140 failed to oxidize isobutylamine and benzylamine, and showed a high pH optimum.The synthesis of amine oxidase in the four yeast strains studied was not repressed by ammonium chloride and was weakly repressed by glucose but was strongly repressed if both compounds were present in the growth medium.     

Floral specialization for different pollinators and divergent use of the same pollinator among co‐occurring Impatiens species (Balsaminaceae) from Southeast Asia

Floral variation among closely related species is thought to often reflect differences in pollination systems. Flowers of the large genus Impatiens are characterized by extensive variation in colour, shape and size and in anther and stigma positioning, but studies of their pollination ecology are scarce and most lack a comparative context. Consequently, the function of floral diversity in Impatiens remains enigmatic. This study documents floral variation and pollination of seven co‐occurring Impatiens spp. in the Southeast Asian diversity hotspot. To assess whether floral trait variation reflects specialization for different pollination systems, we tested whether species depend on pollinators for reproduction, identified animals that visit flowers, determined whether these visitors play a role in pollination and quantified and compared key floral traits, including floral dimensions and nectar characteristics. Experimental exclusion of insects decreased fruit and seed set significantly for all species except I. muscicola, which also received almost no visits from animals. Most species received visits from several animals, including bees, birds, butterflies and hawkmoths, only a subset of which were effective pollinators. Impatiens psittacina, I. kerriae, I. racemosa and I. daraneenae were pollinated by bees, primarily Bombus haemorrhoidalis. Impatiens chiangdaoensis and I. santisukii had bimodal pollination systems which combined bee and lepidopteran pollination. Floral traits differed significantly among species with different pollination systems. Autogamous flowers were small and spurless, and did not produce nectar; bee‐pollinated flowers had short spurs and large floral chambers with a wide entrance; and bimodally bee‐ and lepidopteran‐pollinated species had long spurs and a small floral chamber with a narrow entrance. Nectar‐producing species with different pollination systems did not differ in nectar volume and sugar concentration. Despite the high frequency of bee pollination in co‐occurring species, individuals with a morphology suggestive of hybrid origin were rare. Variation in floral architecture, including various forms of corolla asymmetry, facilitates distinct, species‐specific pollen‐placement on visiting bees. Our results show that floral morphological diversity among Impatiens spp. is associated with both differences in functional pollinator groups and divergent use of the same pollinator. Non‐homologous mechanisms of floral asymmetry are consistent with repeated independent evolution, suggesting that competitive interactions among species with the same pollination system have been an important driver of floral variation among Impatiens spp.     

Little interspecific pollen transfer despite overlap in pollinators between sympatric Aeonium (Crassulaceae) species pairs

It is still unknown what exact role interspecific gene flow and reticulate patterns of gene transfer may play in adaptive radiations. To contribute to a better understanding of gene flow in a morphologically diverse and species-rich lineage, we investigated pollen transfer in the adaptively radiated Macaronesian Crassulaceae-Sempervivoideae. We aimed at comparing pollinator spectra and pollen transfer rates among sympatric species of Aeonium. Field studies were conducted on Tenerife (Canary Islands) including pollinator observations and estimations of pollen transfer using fluorescent dye powder as pollen analogue. Our results indicate an overlap in visiting insects among four sympatric species pairs of Aeonium. However, our dye experiments indicate that on an average about 95% of the detected pollen transfer was infraspecific. Only a small proportion of interspecific pollen transfer could be recorded. We explain these outcomes by specific pollinator behaviour such as floral preference and constancy during a foraging bout. This may be linked to different reward regimes of the studied Aeonium species.     

Tribal and intergeneric relationships of Mesechiteae (Apocynoideae, Apocynaceae): evidence from three noncoding plastid DNA regions and morphology

The Neotropical tribe Mesechiteae (Apocynaceae) is currently considered to include nine genera: Allomarkgrafia, Galactophora, Macrosiphonia, Mandevilla, Mesechites, Quiotania, Secondatia, Telosiphonia, and Tintinnabularia. Tribal and intergeneric relationships, however, are in dispute. To test the monophyly of the tribe and evaluate intratribal relationships, a maximum parsimony analysis was conducted based on DNA sequences from the plastid rpl16 intron, rps16 intron, and trnS-G intergenic spacer region as well as morphological data for 23 taxa of Mesechiteae and 11 taxa from other tribes of Apocynoideae. Mesechiteae, as currently circumscribed, was found to be polyphyletic. Only removal of Secondatia and Galactophora and inclusion of Forsteronia rendered the tribe monophyletic. Thus defined, Mesechiteae forms a strongly supported clade including seven genera in three subclades: the Mesechites subclade (comprising Tintinnabularia, Allomarkgrafia, and Mesechites), the Forsteronia subclade (containing only Forsteronia) and the Mandevilla subclade (comprising Macrosiphonia, Mandevilla, and Telosiphonia). Allomarkgrafia is nested in Mesechites. Macrosiphonia and Telosiphonia form two distinct monophyletic clades. Both, however, are nested in Mandevilla. Results suggest upholding the following genera in Mesechiteae: Allomarkgrafia, Forsteronia, Mandevilla, Mesechites, and Tintinnabularia. The status of Quiotania could not be evaluated.     

From dusk till dawn: camera traps reveal the diel patterns of flower feeding by hawkmoths

1. Diel rhythms of foraging activity by animal flower visitors can reflect niche partitioning and are considered an important component of selection on floral traits. However, it has been notoriously difficult to obtain objective information on the patterns of flower visitation by crepuscular and nocturnal insects. 2. Motion-activated cameras were used for field-based studies of hawkmoth foraging behaviour on six African plant species. 3. The results showed that short-tongued hawkmoth species forage mainly around dusk and then sporadically throughout the night, whereas long-tongued hawkmoth species feed consistently throughout the night, with a peak shortly before midnight. 4. These results provide the first quantitative estimates of diel patterns of interactions between multiple hawkmoth and plant species and, when combined with qualitative reports from other studies, suggest that differences in diel activity between the two main hawkmoth functional groups (short- and long-tongued) are consistent across the Old and New Worlds.     

Phylogenetic evidence for pollinator-driven diversification of angiosperms

Since Darwin, the diversity of flowers has been attributed to selection by pollinators. Although pollinators commonly act as selective agents on floral traits, determining the extent to which they have influenced angiosperm diversification requires a historical perspective. Here we review recent studies that combine species-level phylogenies with pollinator data and show that pollinator shifts are common, being associated with at least a quarter of documented divergence events. However, shift frequency and directionality vary extensively, owing to variation in intrinsic factors such as floral features and phylogenetic history, as well as extrinsic factors such as interactions with local pollinator assemblages. Despite technical advances, phylogenies remain limited in their power to distinguish among various pollinator-driven evolutionary processes.     

Pollinator-driven ecological speciation in plants: new evidence and future perspectives

Background

The hypothesis that pollinators have been important drivers of angiosperm diversity dates back to Darwin, and remains an important research topic today. Mounting evidence indicates that pollinators have the potential to drive diversification at several different stages of the evolutionary process. Microevolutionary studies have provided evidence for pollinator-mediated floral adaptation, while macroevolutionary evidence supports a general pattern of pollinator-driven diversification of angiosperms. However, the overarching issue of whether, and how, shifts in pollination system drive plant speciation represents a critical gap in knowledge. Bridging this gap is crucial to fully understand whether pollinator-driven microevolution accounts for the observed macroevolutionary patterns. Testable predictions about pollinator-driven speciation can be derived from the theory of ecological speciation, according to which adaptation (microevolution) and speciation (macroevolution) are directly linked. This theory is a particularly suitable framework for evaluating evidence for the processes underlying shifts in pollination systems and their potential consequences for the evolution of reproductive isolation and speciation.

Scope

This Viewpoint paper focuses on evidence for the four components of ecological speciation in the context of plant-pollinator interactions, namely (1) the role of pollinators as selective agents, (2) floral trait divergence, including the evolution of ‘pollination ecotypes‘, (3) the geographical context of selection on floral traits, and (4) the role of pollinators in the evolution of reproductive isolation. This Viewpoint also serves as the introduction to a Special Issue on Pollinator-Driven Speciation in Plants. The 13 papers in this Special Issue range from microevolutionary studies of ecotypes to macroevolutionary studies of historical ecological shifts, and span a wide range of geographical areas and plant families. These studies further illustrate innovative experimental approaches, and they employ modern tools in genetics and floral trait quantification. Future advances to the field require better quantification of selection through male fitness and pollinator isolation, for instance by exploiting next-generation sequencing technologies. By combining these new tools with strategically chosen study systems, and smart experimental design, we predict that examples of pollinator-driven speciation will be among the most widespread and compelling of all cases of ecological speciation.     

Origin and diversification of the Greater Cape flora: ancient species repository, hot-bed of recent radiation, or both?

Like island-endemic taxa, whose origins are expected to postdate the appearance of the islands on which they occur, biome-endemic taxa should be younger than the biomes to which they are endemic. Accordingly, the ages of biome-endemic lineages may offer insights into biome history. In this study, we used the ages of multiple lineages to explore the origin and diversification of two southern African biomes whose remarkable floristic richness and endemism has identified them as global biodiversity hotspots (succulent karoo and fynbos). We used parsimony optimization to identify succulent karoo- and fynbos-endemic lineages across 17 groups of plants, for which dated phylogenies had been inferred using a relaxed Bayesian (BEAST) approach. All succulent karoo-endemic lineages were less than 17.5 My old, the majority being younger than 10 My. This is largely consistent with suggestions that this biome is the product of recent radiation, probably triggered by climatic deterioration since the late Miocene. In contrast, fynbos-endemic lineages showed a broader age distribution, with some lineages originating in the Oligocene, but most being more recent. Also, in groups having both succulent karoo- and fynbos-endemic lineages, there was a tendency for the latter to be older. These patterns reflect the greater antiquity of fynbos, but also indicate considerable recent speciation, probably through a combination of climatically-induced refugium fragmentation and adaptive radiation.     

Pollinators,floral morphology and scent chemistry in the southern African orchid genus Schizochilus

Floral evolution often involves suites of traits, including morphology, colour and scent, but these traits are seldom analysed together in comparative studies. We investigated the associations between floral traits and pollination systems in Schizochilus, a southern African orchid genus with small nectar-producing flowers that has not been studied previously with respect to pollination biology. Field observations indicated the presence of distinct pollination systems in the four species which occur in the Drakensberg, including pollination by muscid flies in Schizochilus angustifolius, tachinid flies in Schizochilus zeyheri, various small flies in Schizochilus bulbinella and bees and wasps in Schizochilus flexuosus. Pollination success and pollen transfer efficiency clearly differed among the four species but were not correlated with the quantity of nectar rewards. Multivariate analysis of floral morphology and floral scent chemistry based on GC-MS data revealed significant differences among species as well as populations within species. The floral scent of S. angustifolius was dominated by the benzenoid compounds benzaldehyde and phenylacetaldehyde. Samples of one population of S. bulbinella were relatively similar to S. angustifolius but samples of another population were very distinct due to the occurrence of the nitrogen-containing compounds 3-methyl-butyl aldoxime (syn/anti) and the higher amounts of aliphatic esters, alcohols and acids. In contrast, the floral scent of S. flexuosus and S. zeyheri was characterized by high relative amounts of methyl benzoate. We conclude that Schizochilus has distinct, specialized pollination systems associated with subtle but significant variation in floral morphology and scent chemistry. We also caution that sampling of several populations may be required to characterize floral scent composition at the species-level in plants.