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Balkan Green Lizard. Lacerta trilineata.Photo Credit:
Kostas Sagonas
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Life on an island isn't always easy. To
make the most of the little there is to eat on many Greek islands, the
digestive system of s has evolved considerably compared to family members on
the mainland. Surprisingly, many of these insect-eating lizards even have
special valves that help to digest plants. These are some of the findingsĀ¹ from
a study led by Konstantinos Sagonas of the National and Kapodistrian University
of Athens in Greece, published in Springer's journal The Science of NatureĀ².
Reptiles
can adjust their digestive system and food preferences due to adverse
circumstances such as low rainfall and poor food supply. Previous studies, for
instance, show 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 larger stomachs. When the animals were dissected, the
researchers made an unusual discovery. Cecal valves, which slow down food
passage and provide fermenting chambers, were found in 62 percent of the
island-dwelling lizards, compared to 19 percent 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 percent
of their diet consists of plant material, compared to the 10 percent of the
mainland reptiles.
Their
evolved digestive system therefore makes it possible for island lizards to eat
more plants. Because of their longer digestive tract and the presence of cecal
valves, it takes up to 26 percent longer for the food of island lizards to pass
through their digestive system. In a process which is more common to
plant-eating lizards, the ingested food is ultimately exposed 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 colonize islands and maintain viable populations."
Citation
Sagonas K, Pafilis P., Valakos ED. Effects
of insularity on digestion: living on islands induces shifts in physiological
and morphological traits in island reptiles. The Science of Nature,
2015; 102 (9-10) DOI: 10.1007/s00114-015-1301-8