Why do closely related animals look so different from one another? The cichlid fishes of East Africa have run that experiment for us. More than a thousand species live in the Great Lakes, many of them younger than the last ice age, and what separates them most obviously is color and pattern. They are close enough to compare and different enough for the differences to mean something.
Coloration is our way in, but the question underneath it is broader: how genetic change produces biological diversity by acting at every level of organization, from the identity of a single cell and the mix of cell types in a tissue, through the way those cells behave together and how the tissue is built, to the animal you can see. Color patterns are one of the few traits that can be followed the whole way along that chain, which is why we use them.
Two directions run through the work:
Because a genome acts through cells, the two directions are pursued together. Our work combines genomics, developmental biology, single-cell sequencing, imaging and behavioral experiments, and we develop new methods where established ones are not sufficient, including approaches that measure the appearance and the gene expression of the same cell. We apply these approaches beyond cichlids: across the ray-finned fishes, and in the endangered Saimaa ringed seal. The projects below are currently running. Each names the people mainly responsible; master's students, interns and visiting researchers contribute to most of them, and are listed on the
Every tissue is made of cell types, and evolution can change a tissue in two ways: by changing which cell types are present, or by changing the cells themselves. How much each of these contributes is largely unknown. Coloration is a useful place to look, because the colors of a fish are produced by a small, countable set of pigment cells, so a visible trait can be traced back to the cells that produce it.
We ask how pigment cell types differ between species, whether new ones appear, and what either would mean for how tissues change over evolutionary time.
Main team:
Funded by the European Research Council, Consolidator Grant IntEvoCell, 2027–2031.
In some cichlids the male and the female look so unlike each other that they were first described as separate species. They share a genome. Something in the way that genome is read has to differ between them, and it has to differ only in the skin, only in one sex, and only after a certain age.
We study how one set of genes produces two appearances, and how a difference like that evolves in the first place.
Main team:
Funded by the Research Council of Finland, Academy Research Fellowship, 2022–2027.
Development is noisy, yet it produces the same pattern again and again. The clearest way to measure how much noise gets through is to compare the two sides of a single animal. Left and right are built by the same genome, in the same individual, under the same conditions, so any difference between them comes from the process itself rather than from genes or environment. Biologists call that difference fluctuating asymmetry, and it is one of the few available measures of how robust development is.
Color patterns make it visible. A bar that sits a little further forward on one flank than the other is a record of where the process wavered. We compare left with right, and individual with individual, to ask what keeps pattern formation so dependable, which genes are involved, and what happens when conditions such as temperature change.
Main team:
Funded by the Research Council of Finland, Academy Project, 2025–2029.
Some cichlids change color faster than you can watch: a few seconds to go pale or dark, and back again when the situation changes. That is too fast for genes to be switched on and off, so it happens in the pigment cells themselves, under the control of the nervous system.
We study how that switch works, and what a fish is doing with it when it meets a rival or a mate.
Main team:
Funded by the Sigrid Jusélius Foundation, 2021–2024.
Bars, stripes and blotches are placed across the skin with a precision that is easy to admire and hard to explain. Where does a bar begin, what stops it, and why does the next one appear at that distance and no other?
How faithfully a pattern is reproduced varies, and that variation is itself informative. Some patterns come out almost the same in every individual, and even on the two sides of one fish: the outcome is close to deterministic. Others, blotches among them, differ every time, as though the same rules were run with different dice. Where a pattern falls between those extremes says how much of it is specified in advance and how much is settled as the tissue develops.
Cichlid skin is a good model for these questions, and they reach beyond fish: the same cell types and the same signals pattern human skin, and are involved in pigment disorders and in melanoma. We set out this framework in a recent
Main team:
Funded by the Sigrid Jusélius Foundation, 2024–2026, and the Research Council of Finland, Academy Project, 2025–2029.
Genomes change by more than point mutation. Genes are duplicated, lost, moved and put to new uses, and the genes behind color are an old family that has been through all of it. Across hundreds of genomes spanning the ray-finned fishes, we ask how that repertoire was assembled, how it differs between groups, and whether the lineages carrying the most color genes are the ones that became the most colorful.
Answering that needs genomes good enough to count genes in, which published assemblies often are not: duplicated genes are exactly what a short-read assembly collapses or misses. We generate our own long-read (PacBio) assemblies for the species we work on, and use them alongside public data.
Main team:
Part of the group's ongoing work at the University of Helsinki.
Comparing color across species sounds simple and is not. Photographs are taken under different light, patterns sit on a curved and moving animal, and much of what a fish sees is invisible to us. Many of the interesting questions in this field are limited by measurement rather than by ideas.
We build the methods and the tools that make color and pattern measurable in a way another lab can repeat, and we publish them for anyone to use.
Main team:
Funded by the Research Council of Finland, Academy Research Fellowship, 2022–2027 and Academy Project, 2025–2029, and by the Sigrid Jusélius Foundation, 2024–2026.
The Saimaa ringed seal has lived in one Finnish lake since the last ice age and numbers a few hundred animals. A population that small carries the marks of its history in its genome, in the variation it has lost and in the harmful variants it cannot easily shed, and those marks matter for how it is protected. We study the link between genetic and dental variation, and what deleterious variation means for the fitness of the population.
In the Baltic we work on the grey seal, a far more numerous relative with a different history. Baltic and Atlantic grey seals have been described as separate subspecies; using genomes from across the range we ask how distinct they really are, where they meet and hybridize, and what that means for how the two are managed. The first results are a
We work on both with colleagues in Finland and Denmark:
Main team:
Part of the group's ongoing work at the University of Helsinki, with collaborators.
Our research is carried out at the
Working next to groups asking related questions, with related methods, is much of what makes the work possible: genome and transcriptome sequencing, tissue analysis, imaging and behavioral experiments are all within walking distance. The institute hosts core facilities for genomics and sequencing, histology, and electron and light microscopy, with the staff who run them.
Our own space includes a fully equipped molecular laboratory, microscopes, a microinjection workstation, a room built for photographing and measuring color patterns, and a tropical fish facility of around 400 tanks.
We built the fish facility ourselves and wrote down how, so that other groups do not have to start from nothing:
The group's research is supported by the European Research Council (Consolidator Grant IntEvoCell, 101230417), the Research Council of Finland (347309 and 371328), the Sigrid Jusélius Foundation and the University of Helsinki. Members of the group hold personal fellowships of their own, including a Marie Skłodowska-Curie Postdoctoral Fellowship (101109896). Earlier work in the group was funded by the German Research Foundation.
Funded by the European Union (ERC, IntEvoCell, 101230417). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Council. Neither the European Union nor the granting authority can be held responsible for them.