The morphological diversity of Mymaridae (Hymenoptera): an atlas of scanning electron micrographs. Part 2. Structure of the mesosoma

This is the second in a series of studies that aim to provide a comprehensive overview of the morphological diversity of Mymaridae (Hymenoptera) or fairyflies, a monophyletic family of small parasitic wasps postulated to be the sister group of all other Chalcidoidea. The external morphology of the mesosoma of about 6575 taxa, representing 5565% of the 115 currently valid described genera and subgenera, is described and illustrated with almost 269 scanning electron micrographs, including 77 micrographs of the dorsal, 71 micrographs of the lateral, 59 micrographs of the ventral, 53 micrographs of the anterior, and 9 micrographs of the posterior views of the mesosoma. Twenty annotated figures of the external and major internal structures are given. Two appendices list the morphological terms used, and names of the 75 genera and subgenera of Mymaridae illustrated. The variety of characters and their features that could be used to help define morphologically the genera, and possibly also the species, of Mymaridae is discussed.

Morphology and evolution of the mesopleuron in Bethylidae (Hymenoptera: Chrysidoidea) mapped on a molecular phylogeny

The mesopleuron of Bethylidae has morphostructural characters that remain poorly understood, explored, and defined. The wide range of variability of this sclerite has generated confusion both in taxonomic and cladistic studies. Aiming to solve this issue, we describe the general mesopleural anatomy of Bethylidae. Our goal is to propose primary homologies by matching external and internal structures (muscles and apodemes). We reconstruct the ancestral state of the main mesopleural structures by applying the maximum-likelihood method on ten selected character states. The phylogeny of Bethylidae is built by analyzing a dataset of COI and 28S sequences, using maximum-likelihood and Bayesian inference methods. The Bethylidae and all subfamilies are recovered as monophyletic in both resulting phylogenies, with high clade support values. Although the two analyses yielded similar results, we used the tree resulting from the Bayesian inference to map the evolution of the morphological characters, as it is better supported. The study of mesopleural anatomy allows exploration and discussion of the evolution of characters and their present states in Bethylidae and Hymenoptera in general. Reconstruction of the ancestral states shows that many characters arose independently in Bethylidae subfamilies.

A new lineage of Cretaceous jewel wasps (Chalcidoidea: Diversinitidae)

Jewel wasps (Hymenoptera: Chalcidoidea) are extremely species-rich today, but have a sparse fossil record from the Cretaceous, the period of their early diversification. Three genera and three species, Diversinitus attenboroughi gen. & sp. n., Burminata caputaeria gen. & sp. n. and Glabiala barbata gen. & sp. n. are described in the family Diversinitidae fam. n., from Lower Cretaceous Burmese amber. Placement in Chalcidoidea is supported by the presence of multiporous plate sensilla on the antennal flagellum and a laterally exposed prepectus. The new taxa can be excluded from all extant family level chalcidoid lineages by the presence of multiporous plate sensilla on the first flagellomere in both sexes and lack of any synapomorphies. Accordingly, a new family is proposed for the fossils and its probable phylogenetic position within Chalcidoidea is discussed. Morphological cladistic analyses of the new fossils within the Heraty et al. (2013) dataset did not resolve the phylogenetic placement of Diversinitidae, but indicated its monophyly. Phylogenetically relevant morphological characters of the new fossils are discussed with reference to Cretaceous and extant chalcidoid taxa. Along with mymarid fossils and a few species of uncertain phylogenetic placement, the newly described members of Diversinitidae are among the earliest known chalcidoids and advance our knowledge of their Cretaceous diversity.

Two new fossil genera and species of Cerocephalinae (Hymenoptera, Chalcidoidea, Pteromalidae), including the first record from the Eocene

Cerocephalinae (Chalcidoidea, Pteromalidae) is a small group of parasitoid wasps characterized by a number of derived diagnostic features. Their hosts are endophytic beetles. So far, 43 species of Cerocephalinae have been described, including one fossil species from the Miocene. In this study, we add two new genera and species from Baltic and Dominican amber to the fossil record. Tenuicornus dominicus gen. et sp. n. is the second genus described from Dominican amber, and Pteropilosa lailarabanorum gen. et sp. n., described from Baltic amber, represents the oldest record of the subfamily, pushing the minimum age of Cerocephalinae back to the Eocene. Diagnostic characters of both species are discussed in comparison with other Cerocephalinae. An updated key to extant and fossil Cerocephalinae is presented.

A Nonstationary Markov Model Detects Directional Evolution in Hymenopteran Morphology

Directional evolution has played an important role in shaping the morphological, ecological, and molecular diversity of life. However, standard substitution models assume stationarity of the evolutionary process over the time scale examined, thus impeding the study of directionality. Here we explore a simple, nonstationary model of evolution for discrete data, which assumes that the state frequencies at the root differ from the equilibrium frequencies of the homogeneous evolutionary process along the rest of the tree (i.e., the process is nonstationary, nonreversible, but homogeneous). Within this framework, we develop a Bayesian approach for testing directional versus stationary evolution using a reversible-jump algorithm. Simulations show that when only data from extant taxa are available, the success in inferring directionality is strongly dependent on the evolutionary rate, the shape of the tree, the relative branch lengths, and the number of taxa. Given suitable evolutionary rates (0.1-0.5 expected substitutions between root and tips), accounting for directionality improves tree inference and often allows correct rooting of the tree without the use of an outgroup. As an empirical test, we apply our method to study directional evolution in hymenopteran morphology. We focus on three character systems: wing veins, muscles, and sclerites. We find strong support for a trend toward loss of wing veins and muscles, while stationarity cannot be ruled out for sclerites. Adding fossil and time information in a total-evidence dating approach, we show that accounting for directionality results in more precise estimates not only of the ancestral state at the root of the tree, but also of the divergence times. Our model relaxes the assumption of stationarity and reversibility by adding a minimum of additional parameters, and is thus well suited to studying the nature of the evolutionary process in data sets of limited size, such as morphology and ecology.

Skeletal morphology of Opius dissitus and Biosteres carbonarius (Hymenoptera: Braconidae), with a discussion of terminology

The Braconidae, a family of parasitic wasps, constitute a major taxonomic challenge with an estimated diversity of 40,000 to 120,000 species worldwide, only 18,000 of which have been described to date. The skeletal morphology of braconids is still not adequately understood and the terminology is partly idiosyncratic, despite the fact that anatomical features form the basis for most taxonomic work on the group. To help address this problem, we describe the external skeletal morphology of Opius dissitus Muesebeck 1963 and Biosteres carbonarius Nees 1834, two diverse representatives of one of the least known and most diverse braconid subfamilies, the Opiinae. We review the terminology used to describe skeletal features in the Ichneumonoidea in general and the Opiinae in particular, and identify a list of recommend terms, which are linked to the online Hymenoptera Anatomy Ontology. The morphology of the studied species is illustrated with SEM-micrographs, photos and line drawings. Based on the examined species, we discuss intraspecific and interspecific morphological variation in the Opiinae and point out character complexes that merit further study.