A standardized and statistically defensible framework for quantitative morphological analyses in taxonomic studies

Although body size correction and inferential statistics have been used in morphological studies for many decades, their applications are far from being ubiquitous. We performed a meta-analysis to quantify the extent of taxonomic papers that performed body size correction and implemented a statistical hypothesis testing framework during the analysis of morphological data. Our results indicate that in most papers, neither of these analyses were performed but instead, cursory comparisons of descriptive statistics were presented. With the development of numerous freely available and powerful statistical programs such as R, we find it prudent to outline a standardized and statistically defensible framework to enhance the workflow of morphological analyses in taxonomic studies. This 5-step approach can be applied to meristic and mensural data across a wide range of taxonomic groups. We include an easy-to-use companion R script to facilitate the implementation of this workflow. Our proposed framework is not rooted in phylogenetic or evolutionary theory and hence, should not be used in place of explicit species delimitation techniques. Nevertheless, it can be incorporated into a more robust integrative taxonomic framework and is particularly useful for identifying diagnostic characters for species diagnoses.

Diffuse sound absorption modelling of complex finite absorbers using a hybrid deterministic-statistical energy analysis approach

This contribution presents a numerical approach to quantify the response of an absorber in a diffuse reverberation room. Conventionally, this is done by considering an infinite absorber coupled to an acoustic halfspace. It is, however, well known that the diffuse absorption coefficient for a finite absorber can be quite different due to what is referred to in literature as the edge effect. A finite size correction has been developed previously, but it is only applicable to homogeneous absorbers and is based on a computationally costly quintuple integration. This contribution presents an alternative approach in which a deterministic model, e.g. using the finite element or modal transfer matrix method, is coupled with a statistical model of the room using a hybrid deterministic-statistical energy analysis framework. With this framework, also the theoretical uncertainty on this diffuse sound absorption that is inherent in the diffuse field assumption can be quantified, i.e. the variance of sound absorption results that can be theoretically expected across an ensemble of reverberation rooms of the same volume. The methodology is numerically and experimentally validated for several absorber types.

Correcting for Body Size Variation in Morphometric Analysis

Using an allometric growth model to correct for body size variation has been known for many decades to be superior to several other widely used methods such as ratios, analysis of covariance, principal components analysis, and residual analysis. However, this technique remains relatively obscure and rarely applied. We optimize the implementation of this method through a newly developed and easy-to-use R package GroupStruct and use empirical datasets to test its relative efficacy compared to several commonly used methods. Our results demonstrate the superiority of the allometric method and highlights the negative impacts of applying improper body size correction methods.

Finite-size correction for slab supercell calculations of materials with spontaneous polarization

The repeated slab approach has become a de facto standard to accurately describe surface properties of materials by density functional theory calculations with periodic boundary conditions. For materials exhibiting spontaneous polarization, we show that the conventional scheme of passivation with pseudo hydrogen is unable to realize a charge-neutral surface. The presence of a net surface charge induces via Gauss’s law a macroscopic electric field through the slab and results in poor size convergence with respect to the thickness of the slab. We propose a modified passivation method that accounts for the effect of spontaneous polarization, describes the correct bulk limits and boosts convergence with respect to slab thickness. The robustness, reliability, and superior convergence of energetics and electronic structure achieved by the proposed method are demonstrated using the example of polar ZnO surfaces.

Somewhere I Belong: Phylogenetic Comparative Methods and Machine Learning to Investigate the Evolution of a Species-Rich Lineage of Parasites

Metazoan parasites encompass a significant portion of the global biodiversity. Their relevance for environmental and human health calls for a better understanding as parasite macroevolution remains mostly understudied. Yet limited molecular, phenotypic, and ecological data have so far discouraged complex analyses of evolutionary mechanisms and encouraged the use of data discretisation and body-size correction. In this case study, we aim to highlight the limitations of these methods and propose new methods optimised for small datasets. We apply multivariate phylogenetic comparative methods (PCMs) and statistical classification using support vector machines (SVMs) to a data-deficient host-parasite system. We use continuous morphometric and host range data currently widely inferred from a species-rich lineage of parasites (Cichlidogyrus incl. Scutogyrus - Platyhelminthes: Monogenea, Dactylogyridae) infecting cichlid fishes. For PCMs, we modelled the attachment organ and host range evolution using the data of 135 species and an updated multi-marker (28S and 18S rDNA, ITS1, COI mtDNA) phylogenetic reconstruction of 58/137 described species. Through a cluster analysis, SVM-based classification, and taxonomic literature survey, we infered the systematic informativeness of discretised and continuous characters. We demonstrate that an update to character coding and size-correction techniques is required as some techniques mask phylogenetic signals but remain useful for characterising species groups of Cichlidogyrus. Regarding the attachment organ evolution, PCMs suggest a pattern associated with genetic drift. Yet host and environmental parameters might put this structure under stabilising selection as indicated by a limited morphological variation. This contradiction, the absence of a phylogenetic signal and multicollinearity in most measurements, a moderate 73% accordance rate of taxonomic approach and SVMs, and a low phylogenetic informativeness of reproductive organ data suggest an overall limited systematic value of the measurements included in most species characterisations. We conclude that PCMs and SVM-based approaches are suitable tools to investigate the character evolution of data-deficient taxa.

Patient Size Indices and Dose in Fluoroscopically Guided Lumbar Discectomy and Fusion: A Preliminary Study

Patient dose values varied significantly during interventional procedures, mainly due to the patient size, operators’ choices and clinical complexity. In this study, the effect of applying a previously described and validated size-correction method to normalise kerma-area product (KAP) and average KAP rate values of the whole procedure (KAP rate) and isolate variations in dose due to the patient size and complexity, during lumbar discectomy and fusion (LDF) procedures, was investigated. Fluoroscopy time (FT), KAP, KAP rate and patient size data (weight, height and equivalent diameter) were recorded, for 96 patients who underwent single or multilevel LDF procedures by three senior neurosurgeons, defining three different patient groups (surgeon 1, surgeon 2, surgeon 3). Simple linear regression and coefficients of determination were used to investigate the relationship between uncorrected and corrected KAP and KAP rate values and patient size indices in these groups. The results showed that the size correction decreased the influence of patient size and could contribute to the isolation of the variations in patient dose due to the patient size. From this point of view, dose surveys during lumbar spine interventions may include dosimetric data from all patients independently of their body size and not only for standard-sized patients, providing the advantage of accessible data collection for the establishment of local dose reference levels and optimisation purposes, within the framework of the radiation protection program in the Neurosurgery Department.