Ten lizards carried between two Adriatic islands in 1971 became the starting point for an unusually revealing comparison. Their descendants did more than establish a population: they ate differently and developed a different feeding apparatus.

The transfer involved five male and five female Italian wall lizards, moved from Pod Kopište to Pod Mrčaru in Croatia. A University of Massachusetts Amherst account of the research described differences in head shape, bite strength and digestive anatomy after just 36 years. The animals remained Italian wall lizards, now generally called Podarcis siculus and called P. sicula in the original paper.

The striking part was how much had changed within that short span.

A different menu on the new island

In the 2008 PNAS paper, Anthony Herrel and colleagues reported that plants accounted for about 34% of stomach-content volume in spring and 61% in summer on Pod Mrčaru. Corresponding figures on Pod Kopište were roughly 7% and 4%. The introduced population was eating a mixed diet with a substantial plant component, rather than becoming exclusively vegetarian.

Both sexes had stronger bites. The researchers also found cecal valves in all the Pod Mrčaru specimens they examined, including a hatchling and a young juvenile, but not in the source population. These intestinal structures can slow the movement of food and support fermentation.

The authors interpreted the differences as rapid adaptive divergence, while explicitly calling for tests of environmental plasticity and maternal effects. The observations did not, by themselves, identify the genes responsible.

The jaws offer a mechanical explanation

A later 2023 study of skull form and function examined the connection between head anatomy and feeding performance in more detail. Its modeling compared jaw mechanics across different mouth-opening angles and combinations of skull shape and musculature.

The analysis suggested that the Pod Mrčaru skull configuration improved bite performance at wider gapes. That adds a mechanical dimension to the earlier field measurements: head shape affects how muscle force becomes force at the bite point.

A larger head alone would be an incomplete explanation. The useful questions concern the arrangement of the jaws, the muscles acting on them and the performance that results. Measuring an animal’s outline, measuring its bite and modeling its feeding apparatus provide different kinds of evidence that can be compared with one another.

A later diet experiment complicated the picture

The gut story became more interesting in a 2010 follow-up by Bart Vervust and colleagues. They reported longer food-passage times and higher apparent digestive efficiency in the Pod Mrčaru population, along with differences in tooth width and digestive-tract dimensions.

They also compared wild-caught animals with specimens from the same island that had spent 15 weeks eating only arthropods in captivity. Cecal valves were present in 12 of 16 freshly caught Pod Mrčaru lizards examined, but absent from all 20 specimens in the captive dietary group. Gut tissue also differed between the groups.

The authors treated this as preliminary evidence that some features associated with the dietary shift were plastic, meaning responsive to environmental conditions. The comparison was not a series of before-and-after dissections of the same living animals.

This matters because finding a distinctive structure does not automatically establish that it is permanently fixed by a new mutation. An inherited capacity to respond to diet and evolutionary changes in that capacity are separate questions. The follow-up gave researchers a reason to investigate both.

What the genetic evidence added

A 2023 genomic study examined the populations using approximately 82,000 sampled genomic loci. It detected a founder effect associated with the introduction and little neutral genetic differentiation between the introduced population and its source.

Despite reduced genetic variation, the introduced population had expanded. The researchers also identified candidate genomic regions potentially associated with adaptation. They discussed a combination of plastic responses and directional selection as an explanation consistent with the evidence.

Candidate regions are leads for further investigation, not a complete genetic explanation for every feature of the animals. A population can be closely related to its source while differing in traits relevant to its new conditions. Conversely, documenting a genetic difference does not establish what that difference does without additional functional evidence.

A short experiment with a long scientific afterlife

The value of the island comparison lies in its documented starting point. Researchers knew where the introduced animals came from, roughly when the separation began and where to find a population for comparison. Later teams could return with questions the original transfer had never been designed to answer.

The findings now span diet, anatomy, feeding mechanics, digestive performance and genetics. These measurements should not be collapsed into a single claim that an animal simply grew whatever organ it needed. They describe a biological response whose components can be investigated separately.

The original contrast remains striking, but its explanation has become richer with follow-up work. Observing a difference starts the investigation; changing the diet, examining the mechanics and analyzing the genome help reveal how that difference could arise and persist.

Ten transported lizards left scientists much more than a head count to follow.