Biology subjects

Tratkiewicz, K.

Publications and source records attributed to Tratkiewicz, K..

4 recordsLinked to original sources

bioRxiv2026

Exotic catenulid flatworms (Platyhelminthes, Catenulida) and where to find them in a temperate climate - a field study in a botanic garden

Catenulids are free-living flatworms, common in eutrophic freshwaters such as ponds, ditches, or peatbogs, with most of the diversity described from tropical regions to date. Although the majority of the species have been described from warmer climates, most molecular studies have been done on specimens from temperate zones in Europe. We addressed this gap by sampling for exotic species in localities available in a temperate climate. In this study, we investigated catenulid diversity in the greenhouses at the University of Warsaw Botanic Garden and recorded two species known only from tropical areas (Stenostomum paraguayense and Suomina evelinae) and one exotic species recorded previously from a greenhouse in Poland (Stenostomum corderoi). Additionally, in the latter species, we provide evidence for environmentally induced coloration of sensory pits, which has not been reported thus far. We placed the collected species on a phylogeny using barcoding of 18S, 28S, and COI genes and retrieved paraphyly of the family Catenulidae, with S. evelinae forming a sister group to the genus Paracatenula, and hence we propose a revision of its systematic position. In total, we recorded six species, including three with a wide cosmopolitan distribution (C. turgida, S. grande and S. tuberculosum), and provided sequences for five of them, three of which had no previous molecular records (S. paraguayense, S. evelinae and S. corderoi). Thus, we confirm that greenhouses represent an important source of exotic species for taxonomic work on microscopic invertebrates.

zoology↗

bioRxiv2026

Excessive feeding induces development of a colony-like body plan in paratomous flatworms

Colonial animals rely on agametic reproduction to generate repeated colony modules (zooids). Although zooid development has been extensively studied in fully colonial species, such as cnidarians, bryozoans, or tunicates, it provides limited insight into how and why animals transition from solitary asexual fission to colony formation. Here, we fill this gap by studying the dynamics of asexual development in the microscopic flatworm Stenostomum, which can alternate between asexual fission and colony-like linear chains, composed of several zooids connected tail-to-head. Combining ecological, developmental, physiological, and transcriptomic analyses, we demonstrate that in four species of Stenostomum, chain formation can be triggered by manipulating food availability. This ecological input changes the balance between somatic longitudinal growth and head morphogenesis rate, generating a transient modular organism without requiring a new developmental program. We found no evidence for division of labor among zooids or for enhanced predation avoidance of the worms in chains, indicating that chain formation might be a developmental byproduct without obvious adaptive value. Together, these findings suggest that a neutrally evolving developmental byproduct of food-modulated allometric growth may provide a mechanistic route from asexual reproduction to coloniality.

evolutionary biology↗

bioRxiv2025

Molecular phylogeny of Catenulida (Platyhelminthes) with special focus on their diversity in Poland

Catenulida is a clade of free-living flatworms found abundantly in freshwater habitats across the globe. Despite their ubiquitous distribution, catenulids remain poorly studied; most of the species are known only from the asexual forms that lack distinct, taxonomically useful characters. Accordingly, the studies of catenulid diversity require application of integrative methods that combine morphological and molecular data. Here, we report the survey of catenulid diversity in Central and Western Europe, with a special focus on the species found in Polish freshwaters. We collected and identified 13 distinct morphotypes that were subsequently sequenced for four molecular markers - 18S, 28S, COI and ITS-5.8S. The obtained sequences, together with reference data from other catenulid species, were used to infer the comprehensive phylogeny of the clade. The analysis revealed several well-supported clades within the largest catenulid family, Stenostomidae, highlighting the major challenges in catenulid taxonomy, such as unresolved species complexes of Stenostomum leucops and Stenostomum simplex. By tracing evolution of morphological, developmental and ecological characters on the phylogeny our study provides insight into major character transitions in the key lineages of catenulids.

zoology↗

bioRxiv2025

Spontaneous ectopic head formation enables reversal of the body axis polarity in microscopic flatworms

In most of the animals the antero-posterior axis is specified during early embryogenesis. However, in the organisms that undergo somatic asexual reproduction constant re-establishment of the body axis occurs during each asexual act in the context of the fully formed adult body. In microscopic flatworms from the genus Stenostomum the new head and tail structures are inserted in the pre-existing body plan during the asexual process known as paratomy. Here, we report a spontaneously occurring developmental error that results in the formation of the worms with double heads at the opposite ends of their bodies that misses the posterior pole identity. In the set of experiments, we show that the double head phenotype is not heritable on the organismal level. Worms originating from the sectioning or fission of the double head animals give rise to the healthy populations that do not display the erroneous asexual development. We also demonstrate that the posterior piece of the double head worm can survive, regenerate the tail on its previously anterior pole and resume the asexual reproduction. Effectively, such regeneration allows reversal of the body axis polarity without impairment of the survival or reproductive abilities of the animal, an exceptionally rare phenomenon among bilaterians.

developmental biology↗