ABSTRACTThe decline of central European salmonid populations is exacerbated by global warming impacts on disease and interspecific competition. In this context, sympatric naturally reproducing populations of rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta were sampled in three rivers in southern Germany where the myxozoan parasite T. bryosalmonae, the causative agent of the temperature‐associated proliferative kidney disease (PKD), is widely distributed. As expected, parasite prevalence and kidney hyperplasia increased from summer to autumn while decreasing with fish total length. Parasite infection intensity was greater in brown trout than in rainbow trout. With ongoing climate change, this difference in species vulnerability may lead to higher prevalence of PKD in brown trout creating a competitive disadvantage.

Successful conservation of cryptic species such as representatives of the genus Cobitis presents a challenge for fishery managers. Only Cobitis taenia L. is currently assumed to occur in southwest Germany, where it is classified as critically endangered. Established genetic markers and eDNA analysis identified three Cobitis species in the study area. Cobitis taenia and Cobitis elongatoides were widely distributed in the Rhine River system, primarily forming hybrid species complexes in which polyploid individuals dominate but coexist with diploid parent species. A third non-native species, Cobitis bilineata, has recently become established in the southern part of the Rhine to which it probably migrated naturally via the connected Aare River system. In the Danube River catchment, two populations, including one previously thought to be extinct, comprise both diploid and polyploid representatives of C. elongatoides. Our results provide an important basis for more targeted conservation strategies for Cobitis species currently found in the region.

Changes in day-length entrain the endogenous clock of organisms leading to complex responses to photoperiod. In long-lived organisms experiencing several seasons this response of the clock to photoperiod is phenotypically plastic. However, short-lived organisms often experience a single season without pronounced changes in day-length. For those, a plastic response of the clock to different seasons would not necessarily be adaptive. In aquatic ecosystems, zooplankton species like Daphnia live only for some weeks, i.e. one week up to ca. two months. However, they often show a succession of clones that are seasonally adapted to environmental changes. Here, we found that 16 Daphnia clones per each of three seasons ( = 48 clones) from the same pond and year differed in clock gene expression with a homogenous gene expression pattern in ephippia-hatched spring clones and a bimodal expression pattern in summer and autumn populations indicating an ongoing adaptation process. We clearly demonstrate that spring clones were adapted to a short, and summer clones to a long photoperiod. Furthermore, we found that gene expression of the melatonin-synthesis enzyme AANAT was always lowest in summer clones. In the Anthropocene, Daphnia's clock might be disturbed by light-pollution and global warming. Since Daphnia is a key-organism in trophic carbon transfer, a disruption of its clock rhythm would be devastating for the stability of freshwater ecosystems. Our results are an important step in understanding the adaptation of Daphnia's clock to environmental changes.

Sedimentary ancient DNA has by now become a recognized source of information on past biodiversity change, but our understanding of its dynamics and taphonomy is still limited. While for environmental DNA in water, dedicated investigations on its provenance and degradation are being increasingly carried out, we know very little about sedimentary DNA, in particular with respect to aquatic organisms. We are therefore conducting investigations on the distribution of DNA in surface sediments and a short sediment core, with a focus on aquatic communities in the large and heterogeneous Lake Constance. Targeted organisms range from phyto- and zooplankton to fish and waterbirds. Initial results and comparison with sightings of rare species indicate that the DNA is not distributed uniformly or widely across the lake, especially for multicellular animals, but rather linked to the local presence of the organisms. This has implications for our understanding of how DNA enters the sediment and for paleoecological inferences derived from these records.