Flexibility is often the key to success, and the ability to adjust to new environments often makes the difference between a new colony's survival and oblivion. Fabien Aubret from the Station d'Ecologie Expérimental du CNRS à Moulis and Richard Shine from the University of Sydney explain that, ‘adaptive developmental plasticity confers obvious benefits,’ but in well-established colonies, this ability to adjust is often lost. For example, when Australian tiger snakes occupy a new habitat they are initially able to adjust the size of their heads to match larger prey. But as time passes the head expansion becomes hard wired into their DNA, young are born with large heads and they lose their developmental plasticity. So why do they lose this ability? Aubret and Shine wondered whether the snakes pay a high fitness cost as a price for their plasticity. The duo decided to measure the consequences of the snake's versatility on their fitness to find out why they lose the ability to adjust head size (p. ).
Collecting two groups of newly hatched Australian tiger snakes, Aubret and Shine fed small mice to one group and larger meals to the other so that the first group developed small heads and the second group larger heads. Then, when the snakes were 255 days old, they changed the snakes' diets so that they were all on large lunches (from 46.7% to 95.9% of each snake's mass) and filmed the snakes as they attempted to get their meals down.
While the small-headed snakes struggled to swallow their larger meals, they eventually adjusted the size of their heads after 33 days to swallow the large snacks with ease. But what price did the snakes pay for the adjustment?
Measuring the reptiles' growth the duo realised that the growth rates of the small-headed snakes were reduced significantly while their heads enlarged because the reptiles missed meals while it was difficult for them to feed. However, Aubret and Shine explain that once the small-headed snakes had expanded their heads, they were better able to swallow large lunches and their growth rates accelerated to make up for the disadvantage they had faced earlier in life.
So the young of early settlers do incur costs as they adjust their head size, making it beneficial for subsequent generations to hard wire the adaptation into their DNA and this explains why well-established colonies lose the plasticity to remodel their heads.
