Analysis of Ratios in Multivariate Morphometry

The analysis of ratios of body measurements is deeply ingrained in the taxonomic literature. Whether for plants or animals, certain ratios are commonly indicated in identification keys, diagnoses, and descriptions. They often provide the only means for separation of cryptic species that mostly lack distinguishing qualitative characters. Additionally, they provide an obvious way to study differences in body proportions, as ratios reflect geometric shape differences. However, when it comes to multivariate analysis of body measurements, for instance, with linear discriminant analysis (LDA) or principal component analysis (PCA), interpretation using body ratios is difficult. Both techniques are commonly applied for separating similar taxa or for exploring the structure of variation, respectively, and require standardized raw or log-transformed variables as input. Here, we develop statistical procedures for the analysis of body ratios in a consistent multivariate statistical framework. In particular, we present algorithms adapted to LDA and PCA that allow the interpretation of numerical results in terms of body proportions. We first introduce a method called the "LDA ratio extractor,” which reveals the best ratios for separation of two or more groups with the help of discriminant analysis. We also provide measures for deciding how much of the total differences between individuals or groups of individuals is due to size and how much is due to shape. The second method, a graphical tool called the "PCA ratio spectrum,” aims at the interpretation of principal components in terms of body ratios. Based on a similar idea, the "allometry ratio spectrum” is developed which can be used for studying the allometric behavior of ratios. Because size can be defined in different ways, we discuss several concepts of size. Central to this discussion is Jolicoeur's multivariate generalization of the allometry equation, a concept that was derived only with a heuristic argument. Here we present a statistical derivation of the allometric size vector using the method of least squares. The application of the above methods is extensively demonstrated using published data sets from parasitic wasps and rock crab

Classifying fossil Darwin wasps (Hymenoptera: Ichneumonidae) with geometric morphometrics of fore wings.

Linking fossil species to the extant diversity is often a difficult task, and the correct interpretation of character evidence is crucial for assessing their taxonomic placement. Here, we make use of geometric morphometrics of fore wings to help classify five fossil Darwin wasps from the Early Eocene Fur Formation in Denmark into subfamilies and often tribes. We compile a reference dataset with 342 fore wings of nine extant subfamilies and nine relevant fossil species. Since geometric morphometrics was mostly ignored in the past in Darwin wasp classification, the dataset is first used to examine differences and similarities in wing venation among subfamilies. In a next step, we used the reference dataset to inform the classification of the fossil species, which resulted in the description of one new genus and five new species, Crusopimpla weltii sp. nov., Ebriosa flava gen. et sp. nov., Entypoma? duergari sp. nov., Lathrolestes? zlatorog sp. nov., and Triclistus bibori sp. nov., in four different subfamilies. Carefully assessing data quality, we show that the fore wing venation of fossil Darwin wasps is surprisingly suitable to assign them to a subfamily or even lower taxonomic level, especially when used in conjunction with characters from other parts of the body to narrow down a candidate set of potential subfamilies and tribes. Our results not only demonstrate a fast and useful approach to inform fossil classification but provide a basis for future investigations into evolutionary changes in fore wings of ichneumonids. The high informativeness of wing venation for classification furthermore could be harvested for phylogenetic analyses, which are otherwise often hampered by homoplasy in this parasitoid wasp family

On the misidentification of chalcid (Hymenoptera: Chalcidoidea) parasitoids of the cabbage seedpod weevil (Coleoptera: Curculionidae) in North America

Previous identifications in North America of Trichomalus perfectus (Walker, 1835) and Mesopolobus morys (Walker, 1848) (Chalcidoidea: Pteromalidae), the principal chalcid parasitoids of the cabbage seedpod weevil (Ceutorhynchus obstrictus Marsham, 1802) in Europe, are shown to be misidentifications of Trichomalus lucidus (Walker, 1835) and Mesopolobus (Xenocrepis) moryoides sp. nov., respectively. Necremnus duplicatus Gahan, 1941 (Chalcidoidea: Eulophidae) is synonymized formally under Necremnus tidius (Walker, 1839) syn. nov., confirming a previous, tentative synonymy. Both sexes of N. tidius, M. moryoides, and T. lucidus are illustrated and compared with those of similar species using macrophotography and scanning electron microphotography. Hypotheses are offered to explain why the principal chalcid parasitoids of the cabbage seedpod weevil differ between North America and Europe and how the three treated species came to be in North Americ

Two species? - Limits of the species concepts in the pygmy grasshoppers of the Tetrix bipunctata complex (Orthoptera, Tetrigidae)

Today, integrative taxonomy is often considered the gold standard when it comes to species recognition and delimitation. Using the Tetrix bipunctata complex, we here present a case where even integrative taxonomy may reach its limits. The Tetrix bipunctata complex consists of two morphs, bipunctata and kraussi, which are easily distinguished by a single character, the length of the hind wing. Both morphs are widely distributed in Europe and reported to occur over a large area in sympatry, where they occasionally may live also in syntopy. The pattern has led to disparate classifications, as on the one extreme, the morphs were treated merely as forms or subspecies of a single species, on the other, as separate species. For this paper, we re-visited the morphology by using multivariate ratio analysis (MRA) of 17 distance measurements, checked the distributional data based on verified specimens and examined micro-habitat use. We were able to confirm that hind wing length is, indeed, the only morphological difference between bipunctata and kraussi. We were also able to exclude a mere allometric scaling. The morphs are, furthermore, largely sympatrically distributed, with syntopy occurring regularly. However, a microhabitat niche difference can be observed. Ecological measurements in a shared habitat confirm that kraussi prefers a drier and hotter microhabitat, which possibly also explains the generally lower altitudinal distribution. Based on these results, we can exclude classification as subspecies, but the taxonomic classification as species remains unclear. Even with different approaches to classify the Tetrix bipunctata complex, this case is, therefore, not settled. We recommend continuing to record kraussi and bipunctata separately

Incongruent molecular and morphological variation in the crab spider Synema globosum (Araneae, Thomisidae) in Europe

Establishing species boundaries is one of the challenges taxonomists around the world have been tackling for centuries. The relation between intraspecific and interspecific variability is still under discussion and in many taxa it remains understudied. Here the hypothesis of single versus multiple species of the crab spider Synema globosum (Fabricius) is tested. The wide distribution range as well as its high morphological variability makes this species an interesting candidate for re-evaluation using an integrative approach. This study combines information from barcoding, phylogenetic reconstruction based on mitochondrial CO1 and ITS2 of more than 60 specimens collected over a wide range of European localities, and morphology. The findings show deep clades with up to 6% mean pairwise distance in the CO1 barcode without any biogeographical pattern. The nuclear ITS2 gene did not support the CO1 clades. Morphological assessment of somatic and genital characters in males and females and a morphometric analysis of the male palp uncovered high intraspecific variation that does not match the CO1 or ITS2 phylogenies or biogeography either. Screening for endosymbiotic Wolbachia bacteria was conducted and only a single infected specimen was found. Several scenarios might explain these inconsistent patterns. While the deep divergences in the barcoding marker might suggest cryptic or ongoing speciation or geographical isolation in the past, the lack of congruent variation in the nuclear ITS2 gene or the studied morphological character systems, especially the male palp, indicates that S. globosum might simply be highly polymorphic both in terms of its mtDNA and morphology. Therefore, more data on ecology and behaviour and full genome sequences are necessary to ultimately resolve this taxonomically intriguing case

Review of the species of Trichomalus (Chalcidoidea: Pteromalidae) associated with Ceutorhynchus (Coleoptera: Curculionidae) host species of European origin

Six species of Trichomalus Thomson were reared as parasitoids of Ceutorhynchinae hosts in Europe during surveys in 2000-2004. Trichomalus rusticus (Walker) is treated as a valid species, resurrected from synonymy under T. lucidus (Walker), and T. lyttus (Walker) is transferred from synonymy under T. lucidus and newly placed in synonymy with T. rusticus. Illustrated keys to females and males are given to differentiate the six species (T. bracteatus (Walker), T. campestris (Walker), T. gynetelus (Walker), T. lucidus, T. perfectus (Walker), and T. rusticus) except for males of T. bracteatus and T. gynetelus. A lectotype female is designated for T. rusticus. Trichomalus campestris is newly recorded as a parasitoid of Ceutorhynchus cardariae Korotyaev. Implications of the host-parasitoid associations recovered by the surveys are discussed relative to introduction of species to North America for classical biological contro

Tiny wasps, huge diversity – A review of German Pteromalidae with new generic and species records (Hymenoptera: Chalcidoidea)

Despite their ecological and economic importance, hymenopteran parasitoids are severely understudied. Even in countries with a long taxonomic history such as Germany, dating back to the 18th century and including prolific figures like Christian Gottfired Nees von Esenbeck and Otto Schmiedeknecht, those species-rich groups are seldom the subject of comprehensive research efforts, leaving their true diversity unknown. This is often due to their small size of a few millimetres on average, leading to difficulties in their identification and examination. The chalcidoid family Pteromalidae is no exception to this neglect. So far, 735 species have been reported from Germany. Estimating the diversity of this group is not possible, but it has to be assumed that many more species are still to be discovered in Germany.With this study, we improve the knowledge on pteromalid diversity and present new records of 17 genera and 41 species, previously unknown to occur in Germany. We also match and describe previously unknown sexes of two species, based on DNA barcode data. The results of this study were generated as part of the German Barcode of Life Project. The newly-recorded species are illustrated and notes on the biology and distribution are given. The ecological significance of Pteromalidae and potential value as indicators for nature conservation efforts are briefly discussed

The Future of Swiss Hydropower A Review on Drivers and Uncertainties

Swiss Hydropower (HP) is currently facing a wide range of challenges that have initiated a debate about future prospects and its role within the envisioned energy transition. Building on this debate, this paper provides an overview of the status and prospects of Swiss HP by identifying and evaluating the different drivers and uncertainties that Swiss HP faces. Based on a review and the perceptions held by some of the main Swiss HP stakeholders the two main topics that need to be addressed are the market driven impacts and the political, legal and social aspects. While the market dynamics cannot directly be influenced by Swiss companies or authorities, the regulatory framework can and needs to be adjusted. However, this requires a comprehensive stakeholder process and is at least a medium-term process

Cuticular hydrocarbons on old museum specimens of the spiny mason wasp, Odynerus spinipes (Hymenoptera: Vespidae: Eumeninae), shed light on the distribution and on regional frequencies of distinct chemotypes

The mason wasp Odynerus spinipes shows an exceptional case of intrasexual cuticular hydrocarbon (CHC) profile dimorphism. Females of this species display one of two CHC profiles (chemotypes) that differ qualitatively and quantitatively from each other. The ratio of the two chemotypes was previously shown to be close to 1:1 at three sites in Southern Germany, which might not be representative given the Palearctic distribution of the species. To infer the frequency of the two chemotypes across the entire distributional range of the species, we analyzed with GC–MS the CHC profile of 1042 dry-mounted specimens stored in private and museum collections. We complemented our sampling by including 324 samples collected and preserved specifically for studying their CHCs. We were capable of reliably identifying the chemotypes in 91% of drymounted samples, some of which collected almost 200 years ago. We found both chemotypes to occur in the Far East, the presumed glacial refuge of the species, and their frequency to differ considerably between sites and geographic regions. The geographic structure in the chemotype frequencies could be the result of differential selection regimes and/or different dispersal routes during the colonization of the Western Palearctic. The presented data pave the route for disentangling these factors by providing information where to geographically sample O. spinipes for population genetic analyses. They also form the much-needed basis for future studies aiming to understand the evolutionary and geographic origin as well as the genetics of the astounding CHC profile dimorphism that O. spinipes females exhibit