A framework for delineating biogeographical regions based on species distributions

Aim Biogeographical regionalizations, such as zoogeographical regions, floristic kingdoms or ecoregions, represent categorizations central to many basic and applied questions in biogeography, ecology, evolution and conservation. Traditionally established by experts based on qualitative evidence, the lack of transparency and quantitative support has set constraints on their utility. The recent availability of global species range maps, novel multivariate techniques and enhanced computational power now enable a quantitative scrutiny and extension of biogeographical regionalizations that will facilitate new and more rigorous uses. In this paper we develop and illustrate a methodological roadmap for species‐level biogeographical regionalizations at the global scale and apply it to mammals. Location Global. Methods We explore the relative usefulness of ordination and clustering methods and validation techniques. The performance of nine different clustering algorithms is tested at different taxonomic levels. The grain of regionalization (i.e. the number of clusters) will usually be driven by the purpose of the study, but we present several approaches that provide guidance. Results Non‐metric multidimensional scaling offers a valuable first step in identifying and illustrating biogeographical transition zones. For the clustering of regions, the nine different hierarchical clustering methods varied greatly in utility, with UPGMA (unweighted pair‐group method using arithmetic averages) agglomerative hierarchical clustering having consistently the best performance. The UPGMA approach allows a tree‐like phenetic representation of the relative distances of regions and can be applied at different levels of taxonomic resolution. We find that the new quantitative biogeographical regions exhibit both striking similarities to and differences from the classic primary geographical divisions of the world’s biota. Specifically, our results provide evidence that the Sahara, northern Africa, the Arabian Peninsula and parts of the Middle East should be regarded as part of the Afrotropics. Further, the position of the New Guinean continental shelf, Lydekker’s Line, is supported as an appropriate border to separate the Oriental and Australian regions. Main conclusions We propose that this sort of new, quantitative delineation and relationship assessment across taxonomic and geographical grains is likely to offer opportunities for more rigorous inference in historical and ecological biogeography and conservation.     

A phylogeny of Cenozoic macroperforate planktonic foraminifera from fossil data

We present a complete phylogeny of macroperforate planktonic foraminifer species of the Cenozoic Era (∼65 million years ago to present). The phylogeny is developed from a large body of palaeontological work that details the evolutionary relationships and stratigraphic (time) distributions of species‐level taxa identified from morphology (‘morphospecies’). Morphospecies are assigned to morphogroups and ecogroups depending on test morphology and inferred habitat, respectively. Because gradual evolution is well documented in this clade, we have identified many instances of morphospecies intergrading over time, allowing us to eliminate ‘pseudospeciation’ and ‘pseudoextinction’ from the record and thereby permit the construction of a more natural phylogeny based on inferred biological lineages. Each cladogenetic event is determined as either budding or bifurcating depending on the pattern of morphological change at the time of branching. This lineage phylogeny provides palaeontologically calibrated ages for each divergence that are entirely independent of molecular data. The tree provides a model system for macroevolutionary studies in the fossil record addressing questions of speciation, extinction, and rates and patterns of evolution.     

The world's biogeographical regions: cluster analyses based on bat distributions

Aim Both floral kingdoms and faunal regions have so far been intuitively defined. This study was conducted to compare these with an analytical regionalization based on cluster analyses in a fairly homogeneous, globally distributed group of organisms: the bats (order Chiroptera). This comparison was used to discuss the possibilities of employing clustering techniques in global biogeography. Location The study considered bat distributions world‐wide. Methods Analyses were conducted both for presence/absence of genera and species, and for the number of species in each genus. Clusters distinguished at selected dissimilarity values were mapped. Results A set of c. 10 regional clusters recurred in the analyses, broadly corresponding not only to the world's accepted faunal regions and subregions, but also to the floral kingdoms and subkingdoms. Main conclusions This study is an analytical confirmation of the fact that similar global distribution patterns are to be found in different groups of organisms. Cluster analyses can be used to refine global regionalization schemes, and, with the accumulation of such data for different taxa and ecologically defined groups, shared patterns can be used to draft one common global biogeographical regionalization. At the same time, differences between the regionalization schemes derived for different groups can be used to partial out the role of dispersal abilities, body size, evolutionary age, etc., in determining global distribution patterns.     

The partitioning of Africa: statistically defined biogeographical regions in sub‐Saharan Africa

Aim To test whether it is possible to establish a common biogeographical regionalization for plants and vertebrates in sub‐Saharan Africa (the Afrotropical Region), using objective multivariate methods. Location Sub‐Saharan Africa (Afrotropical Region). Methods We used 1° grid cell resolution databases for birds, mammals, amphibians and snakes (4142 vertebrate species) and c. 13% of the plants (5881 species) from the Afrotropical Region. These databases were analysed using cluster analysis techniques to define biogeographical regions. A β(sim) dissimilarity matrix was subjected to a hierarchical classification using the unweighted pair‐group method with arithmetic averages (UPGMA). The five group‐specific biogeographical regionalizations were compared against a regionalization developed from a combined database, and a regionalization that is maximally congruent with the five group‐specific datasets was determined using a consensus classification. The regionalizations were interpreted against measures of spatial turnover in richness and composition for the five datasets as well as the combined dataset. Results We demonstrate the existence of seven well‐defined and consistent biogeographical regions in sub‐Saharan Africa. These regionalizations are statistically defined and robust between groups, with minor taxon‐specific biogeographical variation. The proposed biogeographical regions are: Congolian, Zambezian, Southern African, Sudanian, Somalian, Ethiopian and Saharan. East Africa, the West African coast, and the transitions between the Congolian, Sudanian and Zambezian regions are unassigned. The Cape area in South Africa, Afromontane areas and the coastal region of East Africa do not emerge as distinct regions but are characterized by high neighbourhood heterogeneity, rapid turnover of species and high levels of narrow endemism. Main conclusions Species distribution data and modern cluster analysis techniques can be used to define biogeographical regions in Africa that reflect the patterns found in both vertebrates and plants. The consensus of the regionalizations between different taxonomic groups is high. These regions are broadly similar to those proposed using expert opinion approaches. Some previously proposed transitional zones are not recognized in this classification.     

The evolution of endothermy in Cenozoic mammals: a plesiomorphic‐apomorphic continuum

The evolution of endothermy in birds and mammals was one of the most important events in the evolution of the vertebrates. Past tests of hypotheses on the evolution of endothermy in mammals have relied largely on analyses of the relationship between basal and maximum metabolic rate, and artificial selection experiments. I argue that components of existing hypotheses, as well as new hypotheses, can be tested using an alternative macrophysiological modeling approach by examining the development of endothermy during the Cenozoic. Recent mammals display a 10°C range in body temperature which is sufficiently large to identify the selective forces that have driven the development of endothermy from a plesiomorphic (ancestral) Cretaceous or Jurassic condition. A model is presented (the Plesiomorphic‐Apomorphic Endothermy Model, PAE Model) which proposes that heterothermy, i.e. bouts of normothermy (constant body temperature) interspersed with adaptive heterothermy (e.g. daily torpor and/or hibernation), was the ancestral condition from which apomorphic (derived), rigid homeothermy evolved. All terrestrial mammal lineages are examined for existing data to test the model, as well as for missing data that could be used to test the model. With the exception of Scandentia and Dermoptera, about which little is known, all mammalian orders that include small‐sized mammals (<500 g), have species which are heterothermic and display characteristics of endothermy which fall somewhere along a plesiomorphic‐apomorphic continuum. Orders which do not have heterothermic representatives (Cetartiodactyla, Perissodactyla, Pholidota, and Lagomorpha) are comprised of medium‐ to large‐sized mammals that have either lost the capacity for heterothermy, or in which heterothermy has yet to be measured. Mammalian heterothermy seems to be plesiomorphic and probably evolved once in the mammalian lineage. Several categories of endothermy are identified (protoendothermy, plesioendothermy, apoendothermy, basoendothermy, mesoendothermy, supraendothermy, and reversed mesoendothermy) to describe the evolution of endothermy during the Cenozoic. The PAE Model should facilitate the testing of hypotheses using a range of macrophysiological methods (e.g. the comparative method and the reconstruction of ancestral states).     

Accelerated evolution of early angiosperms: Evidence from ranunculalean phylogeny by integrating living and fossil data

The new discovery of angiosperm remains in the Jehol Biota of northeastern China contributes to our understanding of the origin and early evolution of flowering plants. The earliest eudicot genus with reproductive organs, Leefructus, was recently documented from the Lower Cretaceous Yixian Formation at 125.8–123.0 Ma, and was reconsidered to be close to the extant family Ranunculaceae based on gross morphology. However, this hypothesis has not been tested using a cladistic approach. To determine the possible allies of Leefructus within extant eudicots, we constructed a 66 morphological data matrix. Molecular and morphological analyses of extant Ranunculales combined with the fossil suggest that it has an affinity with the Ranunculaceae. The earliest fossil record of the eudicots is 127–125 Ma based on tricolpate pollen grains. Thus, we suggest a hypothesis that the basal eudicots might have experienced an accelerated evolution and diversification during the latest Barremian and earliest Aptian, leading to the stem groups of at least six extant families or lineages, 10–15 Myr earlier than currently documented. Angiosperms have undergone multiple uneven pulses of radiation since their origin. Many key character innovations occurred in different stages that could have triggered those radiations in concert with various biotic and abiotic factors.     

The first record of fossil Vitaceae wood from the Southern Hemisphere,a new combination for Vitaceoxylon ramunculiformis,and reappraisal of the fossil record of the grape family (Vitaceae) from the Cenozoic of Australia

Austrovideira dettmannaegen. & sp. nov. from the early Oligocene Capella Flora in central Queensland is the first fossil Vitaceae wood described from the Southern Hemisphere. A new combination, Stafylioxylon ramunculiformis (Poole & Wilkinson) Pace & Rozefelds for a Northern Hemisphere fossil wood is also proposed. Austrovideira and Stafylioxylon share with Vitaceoxylon secondary xylem with two diameter classes of vessels, wide vessels usually solitary, narrow vessels forming radial chains, very wide and tall rays, scanty paratracheal parenchyma and septate fibres. Austrovideira differs from Vitaceoxylon in having scalariform intervessel pits and homocellular rays composed exclusively of procumbent cells. This combination of features is seen in the Ampelocissus‐Vitis clade, and a clearly stratified phloem with fibre bands alternating with all other axial elements and phloem rays rapidly dilating towards the periderm is restricted to Parthenocissus and Vitis. Stafylioxylon shares with Austrovideira the presence of scalariform intervessel pits but it differs from that genus in both ray composition and bark anatomy, as it lacks a stratified phloem. These fossil wood genera demonstrate that the lianescent habit in the Vitaceae was established by the Eocene in the Northern Hemisphere and by the Oligocene in the Southern Hemisphere. The pollen and seed fossil record shows that the Vitaceae were in Australia by the Eocene and fossil seeds suggest that the family had radiated by this time. The Oligocene Capella flora with two seed taxa and fossil wood (Austrovideira) provides further evidence of an Australian radiation. The fossil evidence, suggests a significant Gondwanic history for the family.     

Evolutionary history of Spalacidae inferred from fossil occurrences and molecular phylogeny

1. The Spalacidae is a family of strictly subterranean rodents with a long evolutionary history. It is unclear how ecological changes have influenced the evolutionary history of these mammals, and the phylogenetic relationship of the subfamilies within Spalacidae is controversial.
2. Through compiling fossil records, reconstructing molecular phylogeny from molecular data, determining the date of divergence, and analysing their geographical evolution based on molecular data and fossil taxa, we explore the origin and evolutionary process of Spalacidae in detail. Diversification within Spalacidae dates to the Late Oligocene, approximately 25 million years ago, based on molecular data.
3. This family originated in South and East Asia in the Late Oligocene, and then split into four clades. The first clade includes Rhizomyinae, which was highly diversified in South Asia in the Early-to-Middle Miocene. Then Rhizomyinae from Asia migrated to northern Africa in multiple waves through the Afro-Eurasian land bridge. Its range largely contracted in the Late Miocene, notably in Central Asia. The second clade includes the extinct Tachyoryctoidinae, which was confined to East and Central Asia, and survived from the Late Oligocene to the Late Miocene. The third clade includes Spalacinae, which have remained around the Mediterranean region since the Late Oligocene with slight trend of northward expansion. The fourth clade is Myospalacinae. Ancient genera of this subfamily in East Asia dispersed eastward during the Late Miocene and reached northern China and south-east Russia.
4. The general distribution pattern of Spalacidae has persisted since the Late Miocene. Extinction of Tachyoryctoidinae and clear range contraction of Rhizomyinae in Central and East Asia are likely to have resulted from increased aridification, while the slight northward expansion of Myospalacinae and Spalacinae since the Quaternary was probably a response to a similar northward expansion of suitable vegetation for these animals.

     

基于SSR标记的琅琊山球孢白僵菌寄主专化性

球孢白僵菌Beauveria bassiana是一类常见的昆虫病原真菌,其自然侵染的寄主昆虫众多,达15目149科750种。为了解球孢白僵菌自然种群的遗传多样性,探讨种群异质性和寄主来源之间的关系,分析其寄主专化性的强弱,本研究利用SSR分子标记技术,比较了安徽琅琊山国家森林公园的85株球孢白僵菌（寄主种类涉及7目24种）群体遗传多样性差异,通过构建聚类树分析菌株基因型和寄主关联性。结果表明琅琊山球孢白僵菌群体Nei’s基因多样性指数h=0.2906,Shannon信息指数I_s=0.4510,多态位点百分率P为100%。不同寄主目球孢白僵菌遗传多样性水平由高至低为鞘翅目>膜翅目>同翅目>双翅目>鳞翅目>直翅目>半翅目,其中菌株数量较多的鞘翅目、膜翅目和同翅目3个亚种群的遗传多样性较高且水平接近。聚类分析发现8对SSR引物将85株球孢白僵菌分成29个基因型,并在遗传相似系数0.70处分别聚为3个分支。分析寄主类型发现相同基因型的株系可侵染不同目的寄主,而同一类型寄主也可被不同基因型的菌株侵染。球孢白僵菌种群的总体遗传多样性较高,遗传谱系与寄主来源无明显相关性,菌株的寄主专化性弱。     

The evolution of mammal body sizes: responses to Cenozoic climate change in North American mammals

Explanations for the evolution of body size in mammals have remained surprisingly elusive despite the central importance of body size in evolutionary biology. Here, we present a model which argues that the body sizes of Nearctic mammals were moulded by Cenozoic climate and vegetation changes. Following the early Eocene Climate Optimum, forests retreated and gave way to open woodland and savannah landscapes, followed later by grasslands. Many herbivores that radiated in these new landscapes underwent a switch from browsing to grazing associated with increased unguligrade cursoriality and body size, the latter driven by the energetics and constraints of cellulose digestion (fermentation). Carnivores also increased in size and digitigrade, cursorial capacity to occupy a size distribution allowing the capture of prey of the widest range of body sizes. With the emergence of larger, faster carnivores, plantigrade mammals were constrained from evolving to large body sizes and most remained smaller than 1 kg throughout the middle Cenozoic. We find no consistent support for either Cope's Rule or Bergmann's Rule in plantigrade mammals, the largest locomotor guild (n = 1186, 59% of species in the database). Some cold‐specialist plantigrade mammals, such as beavers and marmots, showed dramatic increases in body mass following the Miocene Climate Optimum which may, however, be partially explained by Bergmann's rule. This study reemphasizes the necessity of considering the evolutionary history and resultant form and function of mammalian morphotypes when attempting to understand contemporary mammalian body size distributions.     

Nemertean systematics and phenetic classification: an example from a group of hoplonemerteans

The applicability of numerical methods to the taxonomy of the Phylum Nemertea is assessed for a group of hoplonemertean species. The classifications obtained from various cluster and ordination methods are evaluated with reference to their predictability, i.e. the number of character or character states that can be predicted about species A knowing that it belongs to class a.     

Gradient versus cluster analysis of fossil assemblages: a comparison from the Ordovician of southwestern Virginia

Studies in modern ecology indicate that most species are distributed independently along environmental gradients according to their individual requirements. Steep gradients often produce species associations separated by discontinuities; gradual gradients produce broadly-overlapping distributions. Approaching the distribution of species populations as a continuum, using gradient analysis, avoids artificial subdivision of totally intergrading distributions, yet permits discontinuities to emerge where present. Faunas of the Martinsburg Formation (Ordovician) in southwestern Virginia offer an excellent opportunity to test the applicability of gradient analysis in a paleoecological setting. A broad spectrum of environments, from nearshore to open-marine, clastic to carbonate-dominated facies, provide both temporal and geographic variation against which to evaluate changes in species distributions. Variations of five classical, Petersen-type communities were recognized in the Martinsburg using cluster analysis: (1) Lingula, (2) bivalve, (3) Rafinesquina, (4) Onniella, and (5) Sowerbyella-dominated communities. Two gradient analysis techniques, ordination and Markov analysis, revealed the same basic associations. However, ordination and Markov analysis permit arrangement of these associations along one or more interpreted environmental gradients. Factors related to water depth and distance from clastic source areas, particularly bottom stability and disturbance frequency, appear to have been the most important of a complex of interrelated physical parameters. The high-stress, nearshore end of the Martinsburg gradient complex was occupied by a Lingula association, followed seaward by an association of bivalves adapted to less-stressed environments. Low-stress, open-shelf environments were occupied by Rafines-quina, Onniella, or Sowerbyella-dominated associations. Broad overlaps among these articulate brachio-pod associations reflect variations in the open-shelf habitat.     

Reticulate evolution in Thuja inferred from multiple gene sequences: implications for the study of biogeographical disjunction between eastern Asia and North America

The eastern Asia-North America disjunction is one of the most interesting biogeographical patterns, but its formation is still in much debate. Here nucleotide sequences of five cpDNA regions, nrDNA ITS and two low-copy nuclear genes (LEAFY, 4CL) were employed to reconstruct the phylogeny and to explore the historical biogeography of Thuja, a typical eastern Asia-North America disjunct genus. High topological discordance was observed between chloroplast and nuclear gene trees, even between different nuclear gene trees, suggesting that Thuja could have a reticulate evolutionary history due to multiple interspecific hybridization events. The eastern Asian species Thuja koraiensis might have obtained its chloroplast genome from the eastern North American species T. occidentalis by chloroplast capture, while the western North American species T. plicata is very likely to have inherited a recombinant cpDNA. Based on the phylogenetic analysis of multiple genes, DIVA-reconstruction of the distribution history, molecular clock estimation and fossil data, we inferred that Thuja could have originated from the high-latitude areas of North America in the Paleocene or earlier with subsequent expansion into eastern Asia through the Bering Land Bridge. The two eastern Asia species T. standishii and T. sutchuenensis have a sister relationship, and their split could have occurred in the Oligocene or early Miocene. In the present study, the selection of molecular markers in biogeographic studies was also discussed. Since most previous studies on the eastern Asia and North America disjunction are based on uniparentally inherited cpDNA and (or) directly sequenced nrDNA ITS data, the historical reticulate evolution in the studied groups might have been underestimated. Therefore, we suggest that multiple genes from different genomes, especially low-copy nuclear genes, be used in this research area in the future.     

The shape of pterosaur evolution: evidence from the fossil record

Abstract Although pterosaurs are a well‐known lineage of Mesozoic flying reptiles, their fossil record and evolutionary dynamics have never been adequately quantified. On the basis of a comprehensive data set of fossil occurrences correlated with taxon‐specific limb measurements, we show that the geological ages of pterosaur specimens closely approximate hypothesized patterns of phylogenetic divergence. Although the fossil record has expanded greatly in recent years, collectorship still approximates a sigmoid curve over time as many more specimens (and thus taxa) still remain undiscovered, yet our data suggest that the pterosaur fossil record is unbiased by sites of exceptional preservation (lagerstätte). This is because as new species are discovered the number of known formations and sites yielding pterosaur fossils has also increased – this would not be expected if the bulk of the record came from just a few exceptional faunas. Pterosaur morphological diversification is, however, strongly age biased: rarefaction analysis shows that peaks of diversity occur in the Late Jurassic and Early Cretaceous correlated with periods of increased limb disparity. In this respect, pterosaurs appear unique amongst flying vertebrates in that their disparity seems to have peaked relatively late in clade history. Comparative analyses also show that there is little evidence that the evolutionary diversification of pterosaurs was in any way constrained by the appearance and radiation of birds.     

Phylogeny of South American Bufo (Anura: Bufonidae) inferred from combined evidence

Despite the considerable research that has focused on the evolutionary relationships and biogeography of the genus Bufo, an evolutionary synthesis of the entire group has not yet emerged. In the present study, almost 4 kb of DNA sequence data from mitochondrial (12S, tRNA^Val, and 16S) and nuclear (POMC; Rag-1) genes, and 83 characters from morphology were analysed to infer a phylogeny of South American toads. Phylogenies were reconstructed with parsimony and maximum likelihood and Bayesian model-based methods. The results of the analysis of morphological data support the hypothesis that within Bufo , some skull characters (e.g. frontoparietal width), correlated with the amount of cranial ossification, are prone to homoplasy. Unique and unreversed morphological synapomorphies are presented that can be used to diagnose recognized species groups of South American toads. The results of all phylogenetic analyses support the monophyly of most species groups of South American Bufo . In most DNA-only and combined analyses, the South American (minus the B. guttatus and part of the ' B. spinulosus ' groups), North American, Central American, and African lineages form generally well-supported clades: ((((((((South America) (North America + Central America)) Eurasia) Africa) Eurasia) South America) West Indies) South America). This result confirms and extends prior studies recovering South American Bufo as polyphyletic. The biogeographical results indicate that: (1) The origin of Bufo predates the fragmentation of Gondwana; (2) Central and North American species compose the sister group to a large, 'derived' clade of South American Bufo ; and (3) Eurasian species form the sister group to the New World clade.  © 2006 The Linnean Society of London, Zoological Journal of the Linnean Society , 2006, 146 , 407–452.     

The early evolution of feathers: fossil evidence from Cretaceous amber of France

The developmental stages of feathers are of major importance in the evolution of body covering and the origin of avian flight. Until now, there were significant gaps in knowledge of early morphologies in theoretical stages of feathers as well as in palaeontological material. Here we report fossil evidence of an intermediate and critical stage in the incremental evolution of feathers which has been predicted by developmental theories but hitherto undocumented by evidence from both the recent and the fossil records. Seven feathers have been found in an Early Cretaceous (Late Albian, ca 100 Myr) amber of western France, which display a flattened shaft composed by the still distinct and incompletely fused bases of the barbs forming two irregular vanes. Considering their remarkably primitive features, and since recent discoveries have yielded feathers of modern type in some derived theropod dinosaurs, the Albian feathers from France might have been derived either from an early bird or from a non-avian dinosaur.     

The early Eocene birds of the Messel fossil site: a 48 million‐year‐old bird community adds a temporal perspective to the evolution of tropical avifaunas

Birds play an important role in studies addressing the diversity and species richness of tropical ecosystems, but because of the poor avian fossil record in all extant tropical regions, a temporal perspective is mainly provided by divergence dates derived from calibrated molecular analyses. Tropical ecosystems were, however, widespread in the Northern Hemisphere during the early Cenozoic, and the early Eocene German fossil site Messel in particular has yielded a rich avian fossil record. The Messel avifauna is characterized by a considerable number of flightless birds, as well as a high diversity of aerial insectivores and the absence of large arboreal birds. With about 70 currently known species in 42 named genus‐level and at least 39 family‐level taxa, it approaches extant tropical biotas in terms of species richness and taxonomic diversity. With regard to its taxonomic composition and presumed ecological characteristics, the Messel avifauna is more similar to the Neotropics, Madagascar, and New Guinea than to tropical forests in continental Africa and Asia. Because the former regions were geographically isolated during most of the Cenozoic, their characteristics may be due to the absence of biotic factors, especially those related to the diversification of placental mammals, which impacted tropical avifaunas in Africa and Asia. The crown groups of most avian taxa that already existed in early Eocene forests are species‐poor. This does not support the hypothesis that the antiquity of tropical ecosystems is key to the diversity of tropical avifaunas, and suggests that high diversification rates may be of greater significance.     

The evolution and loss of oil-offering flowers: new insights from dated phylogenies for angiosperms and bees

The interactions between bees that depend on floral oil for their larvae and flowers that offer oil involve an intricate mix of obligate and facultative mutualisms. Using recent phylogenies, new data on oil-offering Cucurbitaceae, and molecular-dating, we ask when and how often oil-offering flowers and oil-foraging bees evolved, and how frequently these traits were lost in the cause of evolution. Local phylogenies and an angiosperm-wide tree show that oil flowers evolved at least 28 times and that floral oil was lost at least 36–40 times. The oldest oil flower systems evolved shortly after the K/T boundary independently in American Malpighiaceae, tropical African Cucurbitaceae and Laurasian Lysimachia (Myrsinaceae); the ages of the South African oil flower/oil bee systems are less clear. Youngest oil flower clades include Calceolaria (Calceolariaceae), Iridaceae, Krameria (Krameriaceae) and numerous Orchidaceae, many just a few million years old. In bees, oil foraging evolved minimally seven times and dates back to at least 56 Ma (Ctenoplectra) and 53 Ma (Macropis). The co-occurrence of older and younger oil-offering clades in three of the four geographical regions (but not the Holarctic) implies that oil-foraging bees acquired additional oil hosts over evolutionary time. Such niche-broadening probably started with exploratory visits to flowers resembling oil hosts in scent or colour, as suggested by several cases of Muellerian or Batesian mimicry involving oil flowers.