Aquatic Ecology & Evolution

Fishes are the most diverse group of vertebrates, are key players in aquatic ecosystems, provide a diverse set of ecosystem services, and are sensitive to environmental change. We study their ecology, evolution and conservation. We work with fish diversity from traits and genes in populations to the diversity of species assemblages, their change through time and the ecosystem consequences. We are particularly interested in understanding the evolution of endemic diversity within individual ecosystems, such as the radiations of cichlid fish in African lakes and the radiation of whitefish in the lakes around the European Alps. We are a single research group led by Ole Seehausen at the University of Bern but Ole also leads the Department Fish Ecology and Evolution at the Eawag Center for Ecology, Evolution and Biogeochemistry, Kastanienbaum, where we currently host four other research groups that are all associated with the IEE too. The work of the Eawag department is motivated by the aim to contribute to the emerging synthesis between evolutionary biology and ecosystems ecology. There we also host the Swiss Fisheries Advisory Service. Researchers in the department of vertebrates at the Natural History Museum Bern, NMBE, are also affiliated with our University division.

News

In the spotlight!

Our postdoc Alexus has been chosen for a recent "scientist spotlight" in Ichthyology & Herpetology (formerly Copeia). Read her inspiring interview here...

AmNat - Replicated Functional Evolution in Cichlid Adaptive Radiations

Our postdoc Alexus has recently published a new paper in American Naturalist with her colleagues from University of California studying the functional and morphological diversification in 300 species of cichlid fishes from the East African Great Lakes and the Neotropics. While they do find similarities between the different radiations with early bursts, they also find differences such as a much faster rate of functional evolution in Lake Victoria cichlids compared to the other radiations. Read more here...

PhDone! Congratulations to Dr. Leighton King

Congratulations to Dr. Leighton King who defended her PhD last Monday! Like Nare, she was part of the big Sinergia team that dug deep into Lake Victoria's last 20'000 years of evolution, studying remains of plankton and other organisms in sediment cores. You can read one of her papers on "Anthropogenic eutrophication drives major food web changes" by clicking here.

PhDone! Congratulations to Dr. David Alila!

Congratulations to Dr. David Alila on defending his PhD on trophic ecology and community ecology of annual killifishes of the genus Nothobranchius. A big part of his work focused on testing criteria testing for ecological character displacement. He managed to satisfy 5 out of 6 criteria with his study system which only 3 other studies have achieved so far. Read more here...

SCNAT Communications - Ausbau erneuerbarer Energien biodiversitäts- und landschaftsverträglich planen

The Swiss academy of natural sciences has published a new communications issue on how to accommodate aspects of biodiversity and landscape conservation in the planning of the production of renewable energy. Several people from our research group have contributed to this publication (in German). Read more by clicking on this box.

PhDone! Congratulations to Dr. Nare Ngoepe!

Nare finished and defended her PhD last Friday, congratulations! It was about reconstructing the evolutionary history of the last 20'000 years of Lake Victoria cichlids based on fossils found in sediment cores. One of her papers was published in Nature end of last year. Read more here...

Endangered fishes on new Swiss post stamp

Two new post stamps of the Swiss Post focus their attention on the endangered underwater biodiversity. One is depicting a whitefish with Chara algae (stonewort) and a pond mussel and the other shows the rarest fish in Switzerland from the Doubs river, the apron (Zingel asper). together with white-clawed crayfish and common water moss. Read more here...

Frontiers in EnvSci - Ecosystem services of mangroves on Brazilian coast

Margaret Owuor and her international team of researchers mapped for the first time the ecosystem services in Brazilian Amazon mangroves to people living in the area. They identified the spatial changes in the flow of services across coastal landscapes, including urban, agricultural upland areas and coastal natural protected areas. They also show that the adjacent coastal upland habitats such as forests and croplands are important to support many provisioning
ecosystem services to coastal villagers that would otherwise be obtained from mangroves, suggesting that protecting these connected habitats and supporting small-scale agriculture may help to avoid deforestation of mangrove forests.

Evolution - ECD in Tanzanian killifish

David recently published a paper from his PhD on ecological character displacement (ECD) in the Tanzanian killifish from the genus Nothobranchius. Coastal Tanzania is a diversity hotspot for killifishes from that genus. N. melanospilus is a widespread species that sometimes is the only species in a pond or co-occurs with other species, often N. eggersi. He shows that N. melanospilus that co-occur with N. eggersi are much bigger and hence have stronger jaws and feed on harder prey items than when they are alone in a pond. The data satisfies four out of six criteria usually used to test for ECD. His results suggest that competition is the main driver of the observed divergence between the two N. melanospilus populations.

Evolution - Testing for a role of postzygotic incompatibilities in rapidly speciating Lake Victoria cichlids

Anna recently published that last chapter of her PhD in the journal Evolution. She investigated the potential role of intrinsic postzygotic hybrid incompatibilites in the adaptive radiation of Lake Victoria cichlids. These incompatibilites are usually negative epistatic interactions of alleles from the two parental genomes. She inferred such potential epistatic interactions from systematic patterns of genotype ratio distortions using both experimental crosses as well as wild individuals. Overall there was little evidence for a major role of incompatibilities, however, she found putative loci coinciding with islands of differentiation between species that diverged early in the radiation suggesting that such incompatibilities may have played an important role in the early burst of the radiation.

Prof. Margaret Owuor explored coastal mangroves in the mouth of the Amazon

Margaret Owuor and other National Geographic Explorer colleagues studied the coastal mangroves of the mouth of the Amazon to investigate the value not only from a biological but also from a sociological perspective. The most astonishing finding was a mangrove forest in freshwater! Typically mangroves only grow in seawater. Many among the local inhabitants understand the value of mangrove forests, however, they are also frustrated by basic living conditions and lack of services.

Science - Cycles of fusion and fission enabled rapid parallel adaptive radiations in African cichlids

In a new paper published in Science this month, Joana Meier and others reconstruct the evolutionary history and genetic basis of the fastest known vertebrate adaptive radiation, that of the haplochromine cichlid fish in Lake Victoria that radiated into 500 endemic species in the 16'000 years since the lake filled up. Meier et al show that the radiation was seeded by three distinct refugial cichlid lineages that merged into a single hybrid population when they colonized the newly filling lake. Each of these was of older hybrid origin between distant lineages from Nile and Congo, and each of them added unique genes to the mix that were subsequently combined in many new ways enabling an explosive radiation across the food web

Nature - A continuous fish fossil record reveals key insights into adaptive radiation

Nare Ngoepe and colleagues published a paper in Nature showing the sequence of fish colonization in Lake Victoria using fish teeth fossils. They collected sediment cores reaching down to 8m into sediment layers with an age of up to 17'000 years old and found a staggering 7'623 fish tooth fossils which were assigned to six major fish taxa. The fossil record shows that from the onset of the modern lake, multiple fish taxa were present, challenging the hypothesis that the first lineage to arrive benefits most. Surprisingly, the haplochromine cichlids which radiated in the lake did not even dominate the fish assemblage when the lake formed. Their findings suggest a combination of genetic makeup and ecological versatility of cichlids, which persisted in various habitats including the novel deep open water, contributed to the success of the haplochromine cichlid fish in Lake Victoria.

Paper - Constraints to speciation despite divergence

Claudio Müller and colleagues studied the divergence in an old haplochromine species, Astatoreochromis alluaudi, which is widespread across various habitats in and around Lake Victoria. It has been around as long as the 500+ haplochromine species of Lake Victoria but has not radiated. Behavioural experiments revealed the absence of behavioural assortative mating despite genetic and phenotypic differentiation between ecotypes. The authors suggest that the lack of coupling of female mating preference and phenotypic divergence constrains speciation in this cichlid.

Paper - Variation in parasite infection between replicates of speciation in Lake Victoria cichlid fish

Tiziana Gobbin studied in her PhD patterns of parasite infections in the adaptive radiation of Lake Victoria cichlids. It has been hypothesised that parasites may, through their strong eco-evolutionary interactions with their hosts, enhance or initiate diversification. Tiziana indeed found consistent differences in parasite infections between species. However, the infection differences were significant only between the oldest, most strongly differentiated species pair. This is inconsistent with parasite-driven speciation.

Paper - Transgressive segregation in mating traits drives hybrid speciation

This completely new theoretical mechanism was discovered by Kotaro discovered while studying hybrid speciation models. This model is unusual in that it generates speciation by completely neutral mechanisms (transgressive segregation and genetic drift) in the face of gene flow, while most previous theory implies that speciation in the face of gene flow requires divergent selection. Kotaro found that hybrid speciation occurred most frequently when a hybrid population received moderate continued immigration from parental species. We suggest that recurrent transgressive segregation of mating phenotypes may offer possible explanations for hybrid speciation and radiations that do not show much ecological diversification.

"Good science has to be open, diverse and inclusive"

Tomorrow, 11 February, is the International Day of Women and Girls in Science, an initiative supported by UNESCO encouraging women and girls to pursue a career in science and promoting diversity in research.

How giants became dwarfs

Pooja Singh recently published together with Michael Taborsky and Katie Peichel a paper on the genetic sex determinism mechanism in a Lake Tanganyika cichlid, Lamprologus callipterus, which has two types of males: giant, territorial males that collect empty snail shells in which the females of this species spawn their eggs, and tiny dwarf males - even smaller than the females - that fit into the snail shells to attempt to fertilize the eggs from inside the shell. Read more about the story on this link.

Paper - Introgression from extinct species facilitates adaptation to its vacated niche

David Frei published the first paper of his PhD thesis on speciation and its genomics in alpine whitefish. In Lake Constance, an endemic profundal whitefish species went extinct during a period of anthropogenic eutrophication. In the process of extinction, this species hybridized with three surviving whitefish species of Lake Constance, resulting in introgression of genetic variation that is potentially adaptive in deep-water habitats. The results are consistent with the syngameon hypothesis, proposing that hybridization between members of an adaptive radiation can promote further niche expansion and diversification. Furthermore, these findings demonstrate that introgression from extinct into extant species can be a source of evolvability enabling rapid adaptation to environmental change and may contribute to the ecological recovery of ecosystem functions after extinctions.

NatComm - A functional vulnerability framework for biodiversity conservation

Conor published a paper in Nature Communications together with a large group of international researchers on a new tool to quantify the vulnerability of species communities. This framework also incorporates uncertainty and reference conditions into a generalizable tool. Combined with future ecosystem risk assessment studies, this tool should help decision-makers identify management priorities and guide protection efforts where they are most needed.

PRSB - Climate, immigration and speciation shape terrestrial and aquatic biodiversity in the European Alps

Luiz and many colleagues from Eawag, WSL, NMBE and the IEE discuss the relative contribution of immigration, speciation and extinction to the assembly of biodiversity in island-like habitats. They detect biogeographic and genetic signatures associated with two mechanisms, namely (i) a glacial species pump where isolation in glacial refugia accelerates allopatric speciation and (ii) adaptive radiation in underused adaptive zones during ice-free periods. A high proportion of the endemic Alpine biodiversity is very young making it very vulnerable to climate change. The mechanisms and consequences of species loss will likely differ for different species groups with different evolutionary history.

NatComm - Genomic architecture of adaptive radiation and hybridization in Alpine whitefish

Rishi and many colleagues from our research group recently published one of his PhD chapters in Nature Communications. They address questions revolving around the roles of the genomic architecture and hybridization in the Alpine whitefish radiation, using a whole-genome dataset that includes multiple individuals of each of the 22 species belonging to six ecologically distinct ecomorph classes across several lake-systems. The results reveal that repeated ecological and morphological diversification along a common environmental axis is associated with both genome-wide allele frequency shifts and a specific, larger effect, locus. They further highlight the role of introgression between species from different lake-systems in facilitating the evolution and persistence of species with unique trait combinations and ecology.

photo of Pooja Singh by Christian Dinkel

Interview with Pooja Singh - The genome of 100'000 African species will be decoded

Africa is home to a large part of the world's biodiversity. Many species are native only to this continent. So far, the genome of only a tiny proportion of them has been decoded, but this is an important prerequisite for their protection. The large-scale African BioGenome Project, in which Eawag researchers are also involved, now aims to change this.

PRSB - Genetic architecture of adaptive radiation across two trophic levels

In most young fish radiations, transitions between invertivory and herbivory are unusual. Haplochromine cichlid fish of the African Great Lakes are exceptional in this regard. Lake Victoria was colonized by an insectivorous generalist and in less than 20 000 years, several clades of specialized herbivores evolved. Anna and Ole investigated components of the genetic architecture of a suite of traits that distinguish invertivores from algae scrapers by QTL mapping based on a second-generation hybrid cross. There were indeed indications of linkage/pleiotropy within trait complexes. However, QTLs for distinct traits were distributed across several unlinked genomic regions. Thus, a mixture of independently segregating variation and some pleiotropy may underpin the rapid trophic transitions.

JEB - Multispecies colour polymorphisms associated with contrasting microhabitats in two Mediterranean wrasse radiations

Sarya, Ole and colleagues studied Mediterranean wrasses of the tribe Labrini which evolved two species radiations each harbouring several species with a brown and a green morph. The colour morphs occur in complete sympatry in mosaic habitats with rocky outcrops and Neptune grass patches. With genome-wide data for almost all Labrini species, we show that species with colour polymorphisms are distributed across the phylogeny, but show evidence of hybridization. This suggests that the colour morphs are either ancient and have been lost repeatedly, that they have evolved repeatedly or have been shared via hybridization.

Projet Lac synthesis report published!

Today the synthesis report of the Projet Lac is published. It summarises the work of over 10 years in which 35 peri-alpine lakes in Switzerland and neighbouring countries were quantitively fished to the first time resulting in a great fish inventory for the alpine region.
One result is the recognition that the large and deep lakes of the region have exceptionally rich fish assemblages because they combine species-rich warm water and species-rich cold water faunas in a unique way: The combination of cold, deep and well oxygenated lakes with geographical proximity to the southern European glacial refugia for warm water fish has led to biogeographical "hybrid communities" rich in warm water species that inhibit the littoral zones and rich in locally endemic cold water species that dominate the open and deep waters (the Galapagos for cold water fish). It is this "hybrid fauna" that explains the richness. It is also the cause of the extreme vulnerability of many species to climate warming and lake pollution.

Nature - The ecological and genomic basis of explosive adaptive radiation

Analysing a phylogeny of all 1700 described cichlid fish species and whole genomes of 100 species endemic to Lake Victoria, Matt, Joana, David, Salome, Remy, Laurent and Ole, together with collaborators in Tanzania, Uganda and the US, have investigated the striking variation observed in cichlid fish speciation rates. Their analyses reveal that Lake Victoria cichlids diversify orders of magnitude faster than most other cichlids, and that exchange of ancient genetic variants between species dramatically accelerates the origin of new species – given favourable ecological conditions.

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