Biology subjects

Helm, C.

Publications and source records attributed to Helm, C..

6 recordsLinked to original sources

bioRxiv2025

Convergent evolution of sensory palps in Scalibregmatidae (Annelida)

Scalibregmatidae are deposit feeders inhabiting muddy or sandy sea floors at considerable depths, and usually lack head appendages common in many other marine annelids. Surprisingly, one lineage within this family bears palp-like structures comparable to anterior head appendages in other Annelida. Nevertheless, a homology of the scalibregmatid appendages with those of other annelids is highly questionable. Using an integrative morphological approach including immunohistochemistry, azan-histology, and 3D reconstruction, we examined the neural innervation of the anterior head region in one travisiid and two scalibregmatid species: Travisia sp. (without appendages), Scalibregma celticum (lateral, prostomial horns), and Axiokebuita cavernicola (palp-like appendages). Scalibregma and Axiokebuita show an innervation pattern of their appendages different from that of palps in other annelids, while no prominent prostomial innervation is present in Travisia. The short, lateral horn-like appendages of S. celticum possess a quite diffuse neuronal scaffold extending from distinct neurite bundles originating from multiple regions of the brain. The elongated palp-like head appendages of A. cavernicola exhibit a neuronal innervation pattern comparable with that of thin sensory antennae known from other annelid groups. Thus, innervating neurites solely originate in the dorsal part of the brain, a pattern not observable for "true" feeding- or sensory palps of other taxa. We also shed new light on the mysterious "neck organ" in scalibregmatids, which are shown to be ventral dublications of the olfactory nuchal organs considering the level of external features and nervous innervation. These results, combined to previous phylogenetic studies, show that Scalibregmatidae are the only so far known annelids to have re-evolved palp-like sensory head structures after a secondary loss. Thus, this is the first example of convergent evolution of palps, a character complex hitherto showing similar overall innervation patterns and considered homologous across all annelids.

evolutionary biology↗

bioRxiv2025

New insights into the evolution of Charlie Chaplin worms (Histriobdellidae, Eunicida, Annelida)

Histriobdellidae, the so-called Charlie Chaplin worms, is an enigmatic group of microscopic commensal annelids associated with crustaceans. They crawl by alternately attaching their adhesive anterior appendages and left and right huge lateral feet, and bear a complex jaw apparatus in the ventral muscular pharynx. Although histriobdellids were always thought to be a part of the jaw-bearing clade Eunicida, their exact placement within the annelid tree is still debated due to their highly derived external morphology and long branch attraction artefacts in molecular analyses. In this study we employ morphological and molecular comparative approaches in order to gain new insights into the evolution of Histriobdellidae and its aberrant traits. Our phylogenetic analyses of Eunicida including 52 species and four molecular markers yield further support for Histriobdellidae being the sister group to the eunicid family Dorvilleidae. The detailed morphology of Histriobdella homari Van Beneden, 1858, a commensal of the European lobster, was examined using standard immunohistochemical stainings and subsequent confocal laser scanning microscopy (CLSM) as well as scanning electron microscopy (SEM). Integrative analyses allow us to compare in detail with other eunicidans and unravel extensive anatomical transformations in Histriobdellidae. Neural innervation patterns help verify the presence of antennae and true annelid palps on the histriobdellid prostomium. The arrangement of ganglia and the neuronal scaffold innervating the anterior end supports the presence of a buccal segment (peristomium) in Histriobdella. Additionally, based on our comprehensive investigations we newly propose their adhesive anterior locomotory appendages to be homologous with parapodia, and their posterior-most adhesive locomotory appendages to be homologous with the pygidial lobes of other Annelida. Detailed studies of this highly deviating family of annelids not only exemplify how to reconstruct extreme transformation of canonical annelid characters such as parapodia, but again also highlight the exceptional evolutionary plasticity of the annelid body plan.

zoology↗

bioRxiv2024

Anthelmintic resistance against benzimidazoles and macrocyclic lactones in strongyle populations on cattle farms in northern Germany

Anthelmintic resistance (AR) in cattle gastrointestinal nematodes (GIN) is an increasing global concern, with low to moderate levels recently documented in Central Europe. This study reports on resistance against both macrocyclic lactones (MLs) and benzimidazoles (BZs), highlighting that AR is spreading. The Fecal Egg Count Reduction Test (FECRT) remains the primary tool for AR assessment, yet differing methodologies and recent guideline updates complicate resistance interpretation across studies. Statistical methods, such as Bayesian approaches used by eggCounts and bayescount, yield varying confidence intervals, further influencing results. Notably, the nemabiome analysis identified Ostertagia ostertagi and Cooperia oncophora as predominant species in the region, though unexpected diversity among farms with additional GIN species occurring sometimes even at high frequency, suggests morphological analysis of coprocultures may underestimate species prevalence. Detecting AR against both drug classes on some farms underscores the urgency of implementing sustainable strategies, such as targeted selective treatment and combinations of anthelmintics with different mode of action, to prevent scenarios of multi-drug resistance observed elsewhere. Effective resistance management requires immediate discussions with veterinarians and stakeholders to steer toward informed, preventive measures in cattle farming.

microbiology↗

bioRxiv2024

A genome resource for the marine annelid Platynereis dumerilii

The marine annelid Platynereis dumerilii is a model organism used in many research areas including evolution and development, neurobiology, ecology and regeneration. Here we present the genomes of P. dumerilii (laboratory culture reference and a single individual assembly) and of the closely related P. massiliensis and P. megalops (single individual assembly) to facilitate comparative genomic approaches and help explore Platynereis biology. We used long-read sequencing technology and chromosomal-conformation capture along with extensive transcriptomic resources to obtain and annotate a draft genome assembly of [~]1.47 Gbp for P. dumerilii, of which more than half represent repeat elements. We predict around 29,000 protein-coding genes, with relatively large intron sizes, over 38,000 non-coding genes, and 105 miRNA loci. We further explore the high genetic variation ([~]3% heterozygosity) within the Platynereis species complex. Gene ontology reveals the most variable loci to be associated with pigmentation, development and immunity. The current work sets the stage for further development of Platynereis genomic resources.

genomics↗

bioRxiv2024

Model-Based Estimation of Active and Passive Muscle Forces Using MRE in Forearm Muscles During 2-DOF Wrist Tasks

Magnetic resonance elastography (MRE)-based muscle force estimation methods have been proposed to estimate individual muscle forces based on measurements of shear wave speed and joint torque in multiple postures. To estimate both the slope and offset parameters of the relationship between shear wave speed and muscle force, it is necessary to collect measurements in a plethora of postures in case of substantial muscle redundancy. However, anisotropic MRE requires a structural and diffusion-tensor imaging scan in each posture, which is infeasible given the time constraints of MRI imaging. The objectives of this work were to develop a muscle force estimator with sufficient accuracy that would only require a limited set of postures, and to evaluate its effectiveness under a variety of measurement conditions. We developed a novel MRE-based muscle force estimator, which decouples shear wave speed into its active and passive components and solves for the slope and offset parameters, independently. We assessed the effectiveness of the proposed estimator under different simulated measurement conditions, with varying levels of noise, and compared it to the original MRE-based estimator. The proposed estimator results in a reduction in the estimation error for the offset parameter, for all muscles, without significant degradation in the estimation error for the slope parameter. However, the proposed muscle force estimator does not improve the goodness-of-fit or the cross-validation error compared to the original estimator. In conclusion, the proposed MRE-based muscle force estimator improves the estimation of muscle-specific parameters and may yield increased muscle force estimation performance.

bioengineering↗

bioRxiv2018

Breaking the ladder: Evolution of the ventral nerve cord in Annelida

A median, segmented, annelid nerve cord has repeatedly been compared to the arthropod and vertebrate nerve cords and became the most used textbook representation of the annelid nervous system. Recent phylogenomic analyses, however, challenge the hypothesis that a subepidermal rope-ladder-like ventral nerve cord (VNC) composed of a paired serial chain of ganglia and somata-free connectives represents neither a plesiomorphic nor a typical condition in annelids.\n\nUsing a comparative approach by combining phylogenomic analyses with morphological methods (immunohistochemistry and CLSM, histology and TEM), we compiled a comprehensive dataset to reconstruct the evolution of the annelid VNC. Our phylogenomic analyses generally support previous topologies. However, the so far hard-to-place Apistobranchidae and Psammodrilidae are now incorporated among the basally branching annelids with high support. Based on this topology we reconstruct an intraepidermal VNC as ancestral state in Annelida. Thus, a subepidermal ladder-like nerve cord clearly represents a derived condition.\n\nBased on the presented data, a ladder-like appearance of the ventral nerve cord evolved repeatedly, and independently of the transition from an intraepidermal to a subepidermal cord during annelid evolution. Our investigations thereby question a common origin of the bilaterian median ganglionated VNC and propose an alternative set of neuroanatomical characteristics of the last common ancestor of Annelida or perhaps even Spiralia.

evolutionary biology↗