Greek lizards change their digestive tracts to cope with food shortages
With little to eat on many Greek islands, Balkan green lizards have evolved their digestive systems considerably compared to members of the same species on the mainland.
Even more surprisingly, these insect-eating lizards have also developed special valves to help them to digest plants.
These facts have emerged from a study led by Konstantinos Sagonas of the National and Kapodistrian University of Athens in Greece and published in Springer’s journal The Science of Nature.
The new study confirms how some reptiles can adjust their digestive system and food preferences in response to adverse circumstances such as low rainfall and poor food supply.
Previous studies have shown that insect-eating Balkan green lizards (Lacerta trilineata) surviving in the harsh environments of various Greek islands have broadened their diet to include more plants.
To extend this research, Sagonas’ team set out to compare groups of these lizards on the islands of Andros and Skyros with two other populations in mainland Greece.
They found that the island lizards have a longer small intestine and hindgut compared to their mainland counterparts.
Those collected from the island of Skyros also have longer stomachs.
Cecal valves, which slow down food passage and provide fermenting chambers, were found in 62 per cent of the island-dwelling lizards, compared to 19 per cent of the mainland ones. This was a fact not previously known for green lizards.
Cecal valves are typically found in plant-eating lizards, and host micro-organisms that help to ferment and break down plant material into fatty acids.
When these structures do occur in insect-eating lizards, it is generally among populations that have started to eat a varied diet that also includes plants.
Sagonas believes the presence of cecal valves among the island lizards therefore reflects their higher consumption of plant material.
About 30 per cent of their diet consists of plant material, compared to the 10 per cent of the mainland reptiles.
So because of their longer digestive tract and the presence of cecal valves, it takes up to 26 per cent longer for the food of island lizards to pass through their digestive system and the ingested food is exposed for far longer to digestive enzymes.
“Such adaptations allow insular populations to take advantage of the limited food resources of the islands and, eventually, overcome food dearth,” explains Sagonas.
“Energy flow in insular environments, the digestive performance of insular populations and the connections within them, provide insights into how animals are able to colonise islands and maintain viable populations.”