Biology subjects

Wanzenboeck, J.

Publications and source records attributed to Wanzenboeck, J..

4 recordsLinked to original sources

bioRxiv2026

Achiasmatic meiosis underlies propagation of clonal genome and B chromosomes in hexaploid Carassius gibelio females but not males

Sexual reproduction in eukaryotes relies on meiosis, recombination, and fertilization, yet hybridization can lead to transitions to asexuality. Asexual vertebrate hybrids require modified gametogenesis to produce unreduced gametes, but the underlying mechanisms remain poorly understood in various hybrid complexes. Here, we investigated the Carassius gibelio complex, which combines clonal genome propagation to the offspring along with the transmission of B chromosomes. We analyzed meiotic progression and gametogenesis in sexual tetraploid and asexual hexaploid lineages, focusing on sex-specific differences. Cytological analyses of synaptonemal complexes and diplotene chromosomes revealed that both sexes in hexaploid lineages undergo achiasmatic meiosis, characterized by the absence of homologous pairing, recombination, and chiasmata. Chromosomes persist as univalents throughout meiotic prophase. Despite this shared meiotic program, outcomes differ between sexes: females complete oogenesis and produce unreduced eggs, whereas males exhibit disrupted spermatogenesis and reduced fertility. Females bypass the reductional division, enabling clonal gamete formation, while males fail to segregate univalents properly. Furthermore, B chromosomes were detected in both mitosis and meiosis of hexaploid males and females, but not in sexual lineages. B chromosomes were consistently present and varied in number among individuals. B chromosomes varied in number and consistently formed univalents during meiosis, similar to other chromosomes. Significance statementMeiosis normally depends on chromosome pairing and recombination, yet asexual vertebrates can bypass these processes. We demonstrate that asexual hexaploid Carassius gibelio reproduces through achiasmatic meiosis, in which chromosomes fail to pair and recombine. While females successfully produce unreduced clonal eggs, males display reduced fertility, revealing striking sex-specific differences in the ability to overcome meiotic dysfunction. We further show that B chromosomes persist as meiotic univalents and are stably inherited.

genetics↗

bioRxiv2021

DNA transposon expansion is associated with genome size increase in mudminnows

Genome sizes of eukaryotic organisms vary substantially, with whole genome duplications (WGD) and transposable element expansion acting as main drivers for rapid genome size increase. The two North American mudminnows, Umbra limi and U. pygmaea, feature genomes about twice the size of their sister lineage Esocidae (e.g., pikes and pickerels). However, it is unknown whether all Umbra species share this genome expansion and which causal mechanisms drive this expansion. Using flow cytometry, we find that the genome of the European mudminnow is expanded similarly to both North American species, ranging between 4.5-5.4 pg per diploid nucleus. Observed blocks of interstitially located telomeric repeats in Umbra limi suggest frequent Robertsonian rearrangements in its history. Comparative analyses of transcriptome and genome assemblies show that the genome expansion in Umbra is driven by extensive DNA transposon expansion without WGD. Furthermore, we find a substantial ongoing expansion of repeat sequences in the Alaska blackfish Dallia pectoralis, the closest relative to the family Umbridae, which might mark the beginning of a similar genome expansion. Our study suggests that the genome expansion in mudminnows, driven mainly by transposon expansion, but not WGD, occurred before the separation into the American and European lineage. Significance StatementNorth American mudminnows feature genomes about twice the size of their sister lineage Esocidae (e.g., pikes and pickerels). However, neither the mechanism underlaying this genome expansion, nor whether this feature is shared amongst all mudminnows is currently known. Using cytogenetic analyses, we find that the genome of the European mudminnow also expanded and that extensive chromosome fusion events have occurred in some Umbra species. Furthermore, comparative genomics based on de-novo assembled transcriptomes and genome assemblies, which have recently become available, indicates that DNA transposon activity is responsible for this expansion.

evolutionary biology↗

bioRxiv2020

Activity, energy use and species identity affect eDNA shedding in freshwater fish

The quantitative measurement of environmental DNA (eDNA) from field-collected water samples is gaining importance for the monitoring of fish communities and populations. The interpretation of these signal strengths depends, among other factors, on the amount of target eDNA shed into the water. However, shedding rates are presumably associated with species-specific traits such as physiology and behavior. Although such differences between juvenile and adult fish have been previously detected, the general impact of movement and energy use in a resting state on eDNA release into the surrounding water remains hardly addressed. In an aquarium experiment, we compared eDNA shedding between seven fish species occurring in European freshwaters. The investigated salmonids, cyprinids, and sculpin exhibit distinct adaptions to microhabitats, diets, and either solitary or schooling behavior. The fish were housed in aquaria with constant water flow and their activity was measured by snapshots taken every 30 s. Water samples for eDNA analysis were taken every 3 h and energy use was determined in an intermittent flow respirometer. After controlling for the effect of fish mass, our results demonstrate a positive correlation between target eDNA quantities as measured with digital PCR, fish activity, and energy use, as well as species-specific differences. For cyprinids, the model based on data from individual fish was only partly transferable to groups, which exhibited lower activity and higher energy use. Our findings highlight the importance of fish physiology and behavior for the comparative interpretation of taxon-specific eDNA quantities. Species traits should therefore be incorporated into eDNA-based monitoring and conservation efforts.

ecology↗

bioRxiv2020

Lateral and longitudinal fish eDNA distribution in dynamic riverine habitats

Assessing the status and distribution of fish populations in rivers is essential for management and conservation efforts in these dynamic habitats. Currently, methods detecting environmental DNA (eDNA) are being established as an alternative and/or complementary approach to the traditional monitoring of fish species. In lotic systems, a sound understanding of hydrological conditions and their influence on the local target detection probability and DNA quantity is key for the interpretation of eDNA-based results. However, the effect of seasonal and diurnal changes in discharge and the comparability of semi-quantitative results between species remain hardly addressed. We conducted a cage experiment with four fish species (three salmonid and one cyprinid species) in a glacier-fed, fish-free river in Tyrol (Austria) during summer, fall, and winter discharge situations (i.e. 25-fold increase from winter to summer). Each season, water samples were obtained on three consecutive days at 13 locations downstream of the cages including lateral sampling every 1-2 m across the wetted width. Fish eDNA was quantified by species-specific endpoint PCR followed by capillary electrophoresis. Close to the cages, lateral eDNA distribution was heterogenous and mirrored cage placement within the stream. In addition to the diluting effect of increased discharge, longitudinal signal changes within the first 20 m were weakest at high discharge. For downstream locations with laterally homogenous eDNA distribution, the signals decreased significantly with increasing distance and discharge. Generally, the eDNA of the larger-bodied salmonid species was less frequently detected, and signal strengths were lower compared to the cyprinid species. This study exemplifies the importance of hydrological conditions for the interpretation of eDNA-based data across seasons. To control for heterogenous eDNA distribution and enable comparisons over time, sampling schemes in lotic habitats need to incorporate hydrological conditions and species traits.

ecology↗