Biology subjects

Schardt, L.

Publications and source records attributed to Schardt, L..

3 recordsLinked to original sources

bioRxiv2025

Genomes of ancient asexual mites appear streamlined in their architecture

The long-term persistence of obligate asexual lineages represents one of the most enduring and critical paradoxes in evolutionary biology. Sexual reproduction, through meiotic recombination and segregation, enables the efficient removal of deleterious mutations and facilitates rapid adaptation to shifting environmental pressures. Lineages that lose sex are therefore classically predicted to experience genomic decay and face rapid extinction. Oribatid mites (Acari, Sarcoptiformes) represent a unique system for testing these predictions, as they feature multiple, ancient, and independent transitions to asexuality, providing a natural experiment on the evolutionary fate of asexual genomes. We compared four sets of sister sexual and asexual species using high-quality nuclear genome assemblies to investigate the genomic consequences of long-term asexuality. Our study revealed a profound, reproductive-mode-dependent dichotomy in the evolution of genome architecture. Contrary to their expected genomic decay, asexual species have mostly streamlined genomes with less novel genes than their sexual sister species. In contrast, sexual species have acquired genetic innovations, encompassing both gene and transposable element content. These results challenge classical expectations of genomic deterioration in asexual species and might explain the long-term evolutionary persistence of oribatid mites.

genomics↗

bioRxiv2025

Two decades of compositional restructuring of soil biodiversity in Germany despite stable a- and b-diversity indices

Soil ecosystems host some of the most taxonomically and functionally diverse biological communities on Earth, yet long-term trends in their biodiversity remain poorly understood. Here, we analysed soil biodiversity dynamics over 20 years with samples archived in the German Environmental Specimen Bank. We assessed temporal and spatial patterns in -diversity and {beta}-diversity with shotgun metagenomics across bacteria, fungi, and metazoa. We found no statistically significant temporal trends in -diversity for any group. Total {beta}-diversity also appeared temporally stable. However, decomposing {beta}-diversity into its balanced variation and abundance gradients revealed taxon-specific compositional restructuring. Bacterial and fungal communities showed signs of compositional homogenisation, while metazoan communities remained more stable. Spatial structuring was pronounced across all groups. Land use emerged as a key spatial predictor of community composition for bacteria and fungi, and geographic locality for metazoans. Our findings show that apparent stability in standard biodiversity indices may mask significant underlying community change. This highlights the need for integrative, taxonomically inclusive approaches to biodiversity monitoring. The combination of environmental specimen banking with metagenomic sequencing offers a powerful framework for uncovering hidden biodiversity trends in soil ecosystems and identifying the drivers of ecological reorganisation under global change.

ecology↗

bioRxiv2021

Rapid diversification of the Australian Amitermes group during late Cenozoic climate change

Late Cenozoic climate change led to the progressive aridification of Australia over the past 15 million years. This gradual biome turnover fundamentally changed Australias ecosystems, opening new niches and prompting diversification of plants and animals. One example is the Australian Amitermes Group (AAG), consisting of the Australian Amitermes and affiliated genera. Although it represents the most speciose and diverse higher termite group in Australia, little is known about its evolutionary history. We used ancestral range reconstruction and diversification analyses to illuminate 1) the origin and phylogenetic relationships of the AAG, 2) biogeographical processes leading to the current continent-wide distribution, and 3) timing and pattern of diversification in the context of late Cenozoic climate change. By estimating the first time-calibrated phylogeny, we show that the AAG is a monophyletic group, whose ancestor arrived ~11-10 million years ago from Southeast Asia. Ancestral range reconstruction indicates that Australias monsoon region was the launching point for a continental radiation that has been shaped by range expansions and within-area speciation rather than vicariance. We found that multiple arid species diversified from mesic and tropical ancestors in the Plio-Pleistocene, but also observed diversification in the opposite direction. Finally, we show that two pulses of rapid diversification coincided with past climate change during the late Miocene and early Pliocene. Consistent with rapid diversification, species accumulation slowed, likely caused by progressive niche saturation. This study provides a stepping stone for predicting the future response of Australias termite fauna in the face of human-mediated climate change.

evolutionary biology↗