Genetic study reveals extensive mixing of wall lizard lineages in German cities.
Lately, I have been writing quite a lot about hybridization in South America, featuring among others jacamars, siskins, and ruddy ducks. But you don’t need to venture into the dense jungle of Colombia or Bolivia to see hybrids. Sometimes you can find them right under your nose, in the city for example. A recent study in Proceedings of the Royal Society explored hybrid lizards in German cities.
Apart from pigeons and jackdaws, you can also find reptiles in cities, such as the common wall lizard (Podarcis muralis). Joscha Beninde and his colleagues collected no less than 826 of these little critters in four German cities: Trier, Saarbrucken, Freiburg and Mannheim. They genotyped all of these individuals using a mitochondrial marker (cytochrome b) and 17 microsatellites.
The wall lizard comprises a number of distinct genetic lineages that originated from multiple regions in the Mediterranean and spread across Europe. The researchers wanted to know how many lineages can be found in each of the cities and if individuals from different lineages are interbreeding.
Each city houses a native lineage (the so-called ‘Eastern France’ lineage), but in several cities you can also find some non-native lineages. In Mannheim, for instance, the researchers found representatives of the Southern Alps and the Venetian lineages. More detailed genetic analyses revealed that these lineages are mixing, giving rise to hybrid swarms (i.e. a population comprised of two or more genetic lineages).
The researchers also applied some landscape genetic analyses, to explore how cityscape structures influence patterns of gene flow. Water bodies turned out to be strong barriers, whereas railway tracks are conducive to gene flow. Surprising, only the genes of the admixed populations flow along railway tracks. It thus seems that non-native lizards are spreading by railway, not by taking the train but by travelling along the railway enbankments.
It will be interesting to see how the genetic make-up of lizards in these cities will develop. Indeed, the authors conclude that: ‘cities are likely to become major playgrounds for hybridization.’
Beninde, J., Feldmeier, S., Veith, M. & Hochkirch, A. (2018) Admixture of hybrid swarms of native and introduced lizards in cities is determined by the cityscape structure and invasion history. Proceedings of the Royal Society B 285, 20180143.