Lise Meitner Group
Evolutionary Diversification and Innovation

There is an extraordinary diversity of life on earth. Yet, a closer look reveals that some traits readily evolve time and again, while others seem difficult if not impossible to evolve. Our research team aims to unravel what makes biological systems evolvable. Using lizards as study systems, we take an integrative approach to decipher the developmental rules that underpin evolutionary diversification and the emergence of novel colours, patterns and shapes.

Many of our projects involve Mediterranean wall lizards. The lizards’ rapid diversification in colouration and their persistence on tiny islets have puzzled naturalists since the 19th century. Recent theory and methods now allow us to understand why wall lizards are so successful, and to establish the causes of innovation, convergence, and the existence of hypervariable clades.

We believe that the diversity of evolutionary problems calls for a diversity of perspectives and tools to solve them. We therefore integrate ideas from evo-devo with other approaches, including evolutionary genomics, experimental developmental biology and field work, to understand how organisms work and how they shape their own evolution. Some of our current projects are described here.

Evo-Devo of Colors

Lizards show a dazzling diversity of colour patterns. Some patterns evolved frequently and repeatedly, others rarely or never. We believe that we can better understand the evolution of lizard colouration by unravelling how patterns form during development.

Our current projects focus on the repeated evolution of colour patterns in wall lizards and a diamond-vs-chevron polymorphism in the brown anole Anolis sagrei. Each system provides opportunities to understand how genetic variation and cellular behaviour give rise to macroscopic patterns, allowing us to connect development to phenotypic innovation and evolvability.

In lizards, chromatophores arise from neural crest cells, and we suspect that the migratory behavior of these cells are important for the formation of color patterns. We study these processes by combining genomic and developmental genetic approaches, theoretical modelling of pattern formation, and use comparative approaches to connect development and evolution of color patterns.

Evolution on Repeat

Naturalists that travelled the Mediterranean in the 19th century were struck by the wall lizards’ color patterns, which seemingly varied without any geographic structure. We are still trying to map this “chaos of variation”, but it is now clear that one reason for the confusion is that the same phenotypes have evolved again and again.

One example is the so-called ‘nigriventris syndrome’: large, stout and aggressive lizards with striking green backs, large blue spots on their flanks and black bellies. In the common wall lizards, we have uncovered the origin of this syndrome and followed its introgressive spread, and we are currently expanding this research into two main directions. One is taking a comparative approach to study similarities in the evolution of the syndrome across species, and the other is a developmental approach trying to understand why colour, morphology and behaviour co-evolve.

Hybridization – From Behaviour to Evolution

Individuals from independently evolving lineages occasionally mate and exchange genes. Can such hybridization promote adaptive change, induce novelties, and fuel diversification?

Our research suggests that the answer to all these questions could be yes. For example, in common wall lizards, sexual selection causes adaptive introgression of a novel phenotype. We have shown that introgression and climatic effects on the strength of sexual selection explains the confusing mosaic of diversity in colour and morphology.

It actually turns out that this is just the tip of an iceberg: hybridization was common throughout the evolutionary history of Mediterranean wall lizards. We now attempt to connect ancient hybridization with speciation, phenotypic innovation, and the bursts of diversification in colouration that made wall lizards famous.