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BackgroundThe order Hymenoptera (bees, ants, wasps, sawflies) contains about eight percent of all described species, but no analytical studies have addressed the origins of this richness at family-level or above. To investigate which major subtaxa experienced significant shifts in diversification, we assembled a family-level phylogeny of the Hymenoptera using supertree methods. We used sister-group species-richness comparisons to infer the phylogenetic position of shifts in diversification.ResultsThe supertrees most supported by the underlying input trees are produced using matrix representation with compatibility (MRC) (from an all-in and a compartmentalised analysis). Whilst relationships at the tips of the tree tend to be well supported, those along the backbone of the tree (e.g. between Parasitica superfamilies) are generally not. Ten significant shifts in diversification (six positive and four negative) are found common to both MRC supertrees. The Apocrita (wasps, ants, bees) experienced a positive shift at their origin accounting for approximately 4,000 species. Within Apocrita other positive shifts include the Vespoidea (vespoid wasps/ants containing 24,000 spp.), Anthophila + Sphecidae (bees/thread-waisted wasps; 22,000 spp.), Bethylidae + Chrysididae (bethylid/cuckoo wasps; 5,200 spp.), Dryinidae (dryinid wasps; 1,100 spp.), and Proctotrupidae (proctotrupid wasps; 310 spp.). Four relatively species-poor families (Stenotritidae, Anaxyelidae, Blasticotomidae, Xyelidae) have undergone negative shifts. There are some two-way shifts in diversification where sister taxa have undergone shifts in opposite directions.ConclusionsOur results suggest that numerous phylogenetically distinctive radiations contribute to the richness of large clades. They also suggest that evolutionary events restricting the subsequent richness of large clades are common. Problematic phylogenetic issues in the Hymenoptera are identified, relating especially to superfamily validity (e.g. "Proctotrupoidea", "Mymarommatoidea"), and deeper apocritan relationships. Our results should stimulate new functional studies on the causes of the diversification shifts we have identified. Possible drivers highlighted for specific adaptive radiations include key anatomical innovations, the exploitation of rich host groups, and associations with angiosperms. Low richness may have evolved as a result of geographical isolation, specialised ecological niches, and habitat loss or competition.

2007: Between a rock and a hard place: arthropod trackways and ichnotaxonomy. Lethaia , Vol. 40, Several challenges exist in ichnotaxonomy: overcoming the perceived distinction between invertebrate and vertebrate ichnotaxonomy, standardizing terminology, rationalizing the plethora of ichnotaxa already in existence, and developing principles for diagnosing new ichnotaxa. Ichnotaxa should be based on morphology, and this morphology incorporates three key components; the behaviour expressed, the producer, and the substrate. Invertebrate and vertebrate ichnotaxa can both be accommodated within this framework, but they differ in the relative contributions of these components. The key to justifying the synonymy of existing ichnotaxa is the recognition of intergrading specimens. However, this is only the case for minor morphological variants (i.e. those representing minor differences in behaviour, such as gait parameters or stance; or minor differences in preservation, such as undertrack fallout or slight differences in substrate conditions). Intergrading specimens should not be used to justify synonymy between major morphological variants (i.e. those representing major behavioural differences, defined herein as ethological categories; or major differences in preservation, such as formation in soup, soft and firmgrounds), and such specimens should be denoted as hybrids (e.g. Cruziana × Rusophycus ). New ichnotaxa should ideally be based on observations of large samples of material, so that recurrence is demonstrable, and morphological continuums, or subset relationships, representing minor morphological variation, are identified. Ichnotaxa may only be erected on the basis of limited material if they truly represent a unique morphology. These principles have been developed with arthropod trackways in mind, but it is hoped that they will be of more general utility. ᮀ Computer simulation , ichnology , ichnotaxobases , neoichnology , nomenclature , trace fossils .Nicholas J. Minter [N.J.Minter@bris.ac.uk], Simon J. Braddy [S.J.Braddy@bris.ac.uk], and Robert B. Davis [rbd501@york.ac.uk]