Ralph Tiedemann

In the African weakly electric fish genus Campylomormyrus, electric organ discharge signals are strikingly different in shape and duration among closely related species, contribute to prezygotic isolation, and may have triggered an adaptive radiation. We performed mRNA sequencing on electric organs and skeletal muscles (from which the electric organs derive) from 3 species with short (0.4 ms), medium (5 ms), and long (40 ms) electric organ discharges and 2 different cross-species hybrids. We identified 1,444 upregulated genes in electric organ shared by all 5 species/hybrid cohorts, rendering them candidate genes for electric organ–specific properties in Campylomormyrus. We further identified several candidate genes, including KCNJ2 and KLF5, and their upregulation may contribute to increased electric organ discharge duration. Hybrids between a short (Campylomormyrus compressirostris) and a …

Ecological speciation within the mormyrid genus Campylomormyrus resulted in sympatric species exhibiting divergence in their feeding apparatus and electric organ discharge (EOD). This study documents the overall diet of the genus Campylomormyrus and examines the hypothesis that the Campylomormyrus radiation is caused by adaptation to different food sources. We performed diet assessment of five sympatric Campylomormyrus species (C. alces, C. compressirostris, C. curvirostris, C. tshokwe, C. numenius) and their sister taxon Gnathonemus petersii with markedly different snout morphologies and EODs using hybrid capture/HTS DNA metabarcoding of their stomach contents. Our approach allowed for high taxonomic resolution of prey items, including benthic invertebrates, allochthonous invertebrates and vegetation. Comparisons of the diet compositions using quantitative measures and diet overlap …

Understanding the assembly of communities in separate patches with restricted connectivity is a central goal in spatial community ecology. In such meta-communities, several processes structure the local communities. Besides dispersal/drift and local processes, environmental filtering is often regarded as one important driver which refers to specific environmental characteristics of different patches that restrict the colonization and/or persistence of individual species. An aquatic example of a meta-community is a set of ponds scattered in the landscape. Many aquatic organisms disperse passively among ponds. As dispersal rates increase in a metacommunity, local environmental conditions primarily shape the zooplankton community structure. Local dynamics prevail and species generally exist in habitats where they are highly adapted to and in a few places where they are sub-optimally adapted (species sorting). Under high dispersal rates, spatial dynamics are more important to local densities than temporal, within-lake dynamics by frequently providing individual patches with immigrants (mass effects). We examine the influence of environmental filtering on the zooplankton community structure in a group of ponds within an agricultural landscape. We used an experimental approach to directly quantify environmental filtering and the potential local adaptation of individual species. We sampled four ponds in an agricultural matrix and measured the performance of the zooplankton community in their home and away environment. Common garden experiments revealed that the zooplankton communities developed differently in their home and away …

Ecosystems are continuously responding to both natural and anthropogenic environmental change. Lake sediments preserve local and global evidence of these ecological transitions through time. This archived information can yield crucial insights through the reconstruction of past changes over hundreds to many thousands of years. This chapter provides an overview on what lake sedimentary DNA (sedDNA) is, which biological groups can be detected with this novel paleoecological proxy, and the workflow and analytical techniques currently employed in sedDNA research. Finally, the implications of lake sedDNA studies are illustrated through five topics, illustrating how sedDNA can reconstruct lake response to environmental change.

The harbour porpoise (Phocoena phocoena), a highly mobile cetacean species of the Northern Hemisphere, inhabits basins that vary broadly in salinity, temperature, and food availability; such variation can drive divergent adaptation among local populations. To shed light on range-wide population structure and local adaptation, we generated ddRAD sequencing data spanning the entire North Atlantic and the Baltic Sea, as well as the Black Sea as an outgroup, and mapped this data to the high-quality draft genome of the species. We identified 11,978 genome-wide SNPs from 150 individuals, which we used for population genetic inferences. Our results support genetic differentiation between North Atlantic and Baltic Sea populations, with Kattegat as a transition zone. Across the North Atlantic the population differentiation is subtle from west to east, congruent with an isolation-by-distance pattern, but indicates a …

Despite decades of research, surprisingly little is known about the mechanism(s) by which an individual's genotype is encoded in odour. Many studies have focused on the role of the major histocompatibility complex (MHC) owing to its importance for survival and mate choice. However, the salience of MHC-mediated odours compared to chemicals influenced by the rest of the genome remains unclear, especially in wild populations where it is challenging to quantify and control for the effects of the genomic background. We addressed this issue in Antarctic fur seals by analysing skin swabs together with full-length MHC DQB II exon 2 sequences and data from 41 genome-wide distributed microsatellites. We did not find any effects of MHC relatedness on chemical similarity and there was also no relationship between MHC heterozygosity and chemical diversity. However, multilocus heterozygosity showed a significant …

We investigated structuring in a widespread livebearing fish, the Sailfin molly (Poecilia latipinna) combining genetic, life-history, and environmental data. Widespread species often experience significant environmental clines over the area the naturally occupy. This provides potential for genetic structuring, local adaptation and speciation. Sailfin mollies can be found in coastal freshwater habitats from roughly Tampico, Veracruz in Mexico to Wilmington, North Carolina, in the USA. In addition, they are found inland on the Florida peninsula. Using microsatellite DNA, we genotyped 168 individuals from 18 populations covering almost all of the natural range of the Sailfin molly. We further determined standard life history parameters for both males and females for these populations. Finally, we measured biotic and abiotic parameters as we collected. We find six distinct genetic clusters based on microsatellite data. Furthermore, there is very strong isolation by distance. We also found significant numbers of migrants between populations. The genetic clusters and the migration patterns do not match paleodrainages. Life histories vary between populations but are idiosyncratic. We suggest a role of humans in migration in the sailfin molly, for example in the form of a ship channel that connects southern Texas with Louisiana and might be a conduit for fish migration. Despite genetic structuring we did not find evidence of cryptic speciation.

Progressive habitat fragmentation threatens plant species with narrow habitat requirements. While local environmental conditions define population growth rates and recruitment success at the patch level, dispersal is critical for population viability at the landscape scale. Identifying the dynamics of plant meta-populations is often confounded by the uncertainty about dormant population compartments. We combined a landscape-scale assessment of an amphiphytic species’ population structure with measurements of dispersal complexity in time to track dispersal and putative shifts in functional connectivity. Using 13 microsatellite markers, we analyzed the genetic structure of extant Oenanthe aquatica populations and their soil seed banks in a kettle hole system to uncover hidden connectivity among populations in time and space. Considerable spatial genetic structure and isolation-by-distance (IBD) patterns suggest limited gene flow between sites. Spatial isolation and size of patches showed minor effects on genetic diversity. Local recruitment was prevalent, despite some evidence for spatial migration and recent colonization. Our findings uncover stepping-stone dynamics with source-sink effects based primarily on dispersal from persistent local to adjacent populations. Overall, spatiotemporal connectivity patterns provide support for meta-population dynamics in our system and highlight the importance of persistent seed banks as a long-term source of genetic diversity.