A total-evidence approach to dating with fossils, applied to the early radiation of the hymenoptera.

Phylogenies are usually dated by calibrating interior nodes against the fossil record. This relies on indirect methods that, in the worst case, misrepresent the fossil information. Here, we contrast such node dating with an approach that includes fossils along with the extant taxa in a Bayesian total-evidence analysis. As a test case, we focus on the early radiation of the Hymenoptera, mostly documented by poorly preserved impression fossils that are difficult to place phylogenetically. Specifically, we compare node dating using nine calibration points derived from the fossil record with total-evidence dating based on 343 morphological characters scored for 45 fossil (4--20 complete) and 68 extant taxa. In both cases we use molecular data from seven markers (∼5 kb) for the extant taxa. Because it is difficult to model speciation, extinction, sampling, and fossil preservation realistically, we develop a simple uniform prior for clock trees with fossils, and we use relaxed clock models to accommodate rate variation across the tree. Despite considerable uncertainty in the placement of most fossils, we find that they contribute significantly to the estimation of divergence times in the total-evidence analysis. In particular, the posterior distributions on divergence times are less sensitive to prior assumptions and tend to be more precise than in node dating. The total-evidence analysis also shows that four of the seven Hymenoptera calibration points used in node dating are likely to be based on erroneous or doubtful assumptions about the fossil placement. With respect to the early radiation of Hymenoptera, our results suggest that the crown group dates back to the Carboniferous, ∼309 Ma (95% interval: 291--347 Ma), and diversified into major extant lineages much earlier than previously thought, well before the Triassic. [Bayesian inference; fossil dating; morphological evolution; relaxed clock; statistical phylogenetics.].

Phylogenetic relationships among superfamilies of Hymenoptera.

The first comprehensive analysis of higher-level phylogeny of the order Hymenoptera is presented. The analysis includes representatives of all extant superfamilies, scored for 392 morphological characters, and sequence data for four loci (18S, 28S, COI and EF-1α). Including three outgroup taxa, 111 terminals were analyzed. Relationships within symphytans (sawflies) and Apocrita are mostly resolved. Well supported relationships include: Xyeloidea is monophyletic, Cephoidea is the sister group of Siricoidea + [Xiphydrioidea + (Orussoidea + Apocrita)]; Anaxyelidae is included in the Siricoidea, and together they are the sister group of Xiphydrioidea + (Orussoidea + Apocrita); Orussoidea is the sister group of Apocrita, Apocrita is monophyletic; Evanioidea is monophyletic; Aculeata is the sister group of Evanioidea; Proctotrupomorpha is monophyletic; Ichneumonoidea is the sister group of Proctotrupomorpha; Platygastroidea is sister group to Cynipoidea, and together they are sister group to the remaining Proctotrupomorpha; Proctotrupoidea s. str. is monophyletic; Mymarommatoidea is the sister group of Chalcidoidea; Mymarommatoidea + Chalcidoidea + Diaprioidea is monophyletic. Weakly supported relationships include: Stephanoidea is the sister group of the remaining Apocrita; Diaprioidea is monophyletic; Ceraphronoidea is the sister group of Megalyroidea, which together form the sister group of [Trigonaloidea (Aculeata + Evanioidea)]. Aside from paraphyly of Vespoidea within Aculeata, all currently recognized superfamilies are supported as monophyletic. The diapriid subfamily Ismarinae is raised to family status, Ismaridae stat. nov. © The Will Henning Society 2011.

Evolution of the hymenopteran megaradiation.

The Hymenoptera--ants, bees and wasps--represent one of the most successful but least understood insect radiations. We present the first comprehensive molecular study spanning the entire order Hymenoptera. It is based on approximately 7 kb of DNA sequence from 4 gene regions (18S, 28S, COI and EF-1α) for 116 species representing all superfamilies and 23 outgroup taxa from eight orders of Holometabola. Results are drawn from both parsimony and statistical (Bayesian and likelihood) analyses, and from both by-eye and secondary-structure alignments. Our analyses provide the first firm molecular evidence for monophyly of the Vespina (Orussoidea+Apocrita). Within Vespina, our results indicate a sister-group relationship between Ichneumonoidea and Proctotrupomorpha, while the stinging wasps (Aculeata) are monophyletic and nested inside Evaniomorpha. In Proctotrupomorpha, our results provide evidence for a novel core clade of proctotrupoids, and support for the recently proposed Diaprioidea. An unexpected result is the support for monophyly of a clade of wood-boring sawflies (Xiphydrioidea+Siricoidea). As in previous molecular studies, Orussidae remain difficult to place and are either sister group to a monophyletic Apocrita, or the sister group of Stephanidae within Apocrita. Both results support a single origin of parasitism, but the latter would propose a controversial reversal in the evolution of the wasp-waist. Generally our results support earlier hypotheses, primarily based on morphology, for a basal grade of phytophagous families giving rise to a single clade of parasitic Hymenoptera, the Vespina, from which predatory, pollen-feeding, gall-forming and eusocial forms evolved.

Parasitoidism, not sociality, is associated with the evolution of elaborate mushroom bodies in the brains of hymenopteran insects.

The social brain hypothesis posits that the cognitive demands of social behaviour have driven evolutionary expansions in brain size in some vertebrate lineages. In insects, higher brain centres called mushroom bodies are enlarged and morphologically elaborate (having doubled, invaginated and subcompartmentalized calyces that receive visual input) in social species such as the ants, bees and wasps of the aculeate Hymenoptera, suggesting that the social brain hypothesis may also apply to invertebrate animals. In a quantitative and qualitative survey of mushroom body morphology across the Hymenoptera, we demonstrate that large, elaborate mushroom bodies arose concurrent with the acquisition of a parasitoid mode of life at the base of the Euhymenopteran (Orussioidea + Apocrita) lineage, approximately 90 Myr before the evolution of sociality in the Aculeata. Thus, sociality could not have driven mushroom body elaboration in the Hymenoptera. Rather, we propose that the cognitive demands of host-finding behaviour in parasitoids, particularly the capacity for associative and spatial learning, drove the acquisition of this evolutionarily novel mushroom body architecture. These neurobehavioural modifications may have served as pre-adaptations for central place foraging, a spatial learning-intensive behaviour that is widespread across the Aculeata and may have contributed to the multiple acquisitions of sociality in this taxon.

Inconsistency of maximum parsimony revisited.

Felsenstein (1978, Syst. Zool. 27:401-410) showed that the method of maximum parsimony can be inconsistent, i.e., lead to an incorrect result with an infinite amount of data. The situation in which this inconsistency occurs is often called the "Felsenstein zone," the phenomenon also known as "long-branch attraction." Felsenstein derived a sufficient inconsistency condition from a model for four taxa with only two different parameters for the probability of change on the five branches connecting the four taxa. In the present paper, his approach is used to derive the inconsistency condition of maximum parsimony from the most general model for four taxa, i.e., with five different parameters for the probabilities of change on the five branches and, for the first time, for characters with k states (k = 2, 3, 4, 5, 6, ...) This is used to determine the factors that can cause the inconsistency of maximum parsimony. It is shown that the probability of change on all five branches and the number of character states play a role in causing inconsistency.

Comparative and phylogenetic analysis of developmental sequences.

Event pairing has been proposed for the optimization of developmental sequences (event sequences) on a given phylogenetic hypothesis (cladogram) to determine instances of sequence heterochrony. Here, we show that event pairing is faulty, leading to the optimization of impossible hypothetical ancestors, the underestimation of the lengths of the developmental sequences on the tree, and the proposition of synapomorphies that are not supported by the data. When used for phylogenetic analysis, event pairing can even produce cladograms that are inconsistent with the data. These errors are caused by the fact that event pairing treats dependent features as if they were independent. We present a new method for comparative and phylogenetic analysis of developmental sequences that does not exhibit these errors. Our method applies Search-based character optimization and treats the entire developmental sequence as a single character that is then analyzed by using an edit cost function, which specifies the transformation cost between pairs of observed and unobserved character states, and dynamic programming. In other words, the developmental sequence is directly optimized on the tree. We used event pairing as an edit cost function, but others are possible.

Simultaneous analysis of the basal lineages of Hymenoptera (Insecta) using sensitivity analysis.

The first simultaneous analysis of molecular and morphological data of basal hymenopterans that includes exemplars from all families is presented. DNA sequences (of approximately 2000-2700 bp for each taxon) from the nuclear genes 18S and 28S and the mitochondrial genes 16S and CO1 have been sequenced for 39 taxa (four outgroup taxa, 29 symphytans, and six apocritans). These DNA sequences and 236 morphological characters from Vihelmsen [Zool. J. Linnean Soc. 131 (2001) 393] were analyzed separately as well as simultaneously. All analyses were performed on unaligned sequences, using the optimization alignment (= direct optimization) method. Sensitivity analysis sensu Wheeler [Syst. Biol. 44 (1995) 321] was applied by analyzing the data under nine different combinations of analysis parameter values. The superfamily level relationships of basal hymenopterans as proposed by Vilhelmsen [Zool. J. Linnean Soc. 131 (2001) 393] and Ronquist et al. [Zool. Scr. 28 (1999) 13] are mostly confirmed, except that Pamphilioidea is the sister group to Tenthredinoidea s.l. and that Anaxyelidae (i.e., Syntexis libocedrii) and Siricidae are supported as a monophyletic group, partly reestablishing the traditional concept of Siricoidea. The resulting hypothesis that best represents the combined evidence from morphology and DNA sequences is (Xyeloidea (Tenthredinoidea s.l. Pamphilioidea) (Cephoidea (Siricoidea (Xiphydrioidea (Orussidae Apocrita))))), with Siricoidea = Anaxyelidae +Siricidae. The phylogenetic system within Tenthredinoidea s.l., derived from the combined evidence, is (Blasticotomidae (Tenthredinidae including Diprionidae (Cimbicidae (Argidae Pergidae)))).