Sunday, 12 June 2011

Fine young cannibal

ResearchBlogging.orgHave you ever come across ladybird eggs? Before today, I hadn't. They are really tiny, and the ones I found were cryptically laid on the yellow backgroun of a rose petal. I would easily have miss them but for the young larvae next to them. Look closely, and you will notice that the young ladybird larvae is eating an egg, likely its sibling. Far from odd, this is very common in ladybirds. Why would such behaviour get selected? surely ladybirds which do not canibalised their own siblings should be more successful. The key aspect is that newborn ladybirds can face substantial starvation risks. They are very small and do not move fast. Egg canibalism ensures easy access to a nutritious first meal and is likely to increases their survival. The second aspect is that this sibling cannibalism is actually arranged by their mother: they lay trophic eggs: unfertilised eggs produced for the purpose of being consumed by hatchlings. Right after hatching, ladybird larvae are soft, but after two hours or so they have hardened, and they start feeding on unhatched eggs. These include trophic eggs, but also other eggs that for some reason did not develop, or did not hatch in time: they do not discriminate between different egg types. Normally each newborn ladybird will have just one egg to feed on: the rest of the unhatched eggs will have probably been eaten by her siblings. Jennifer Perry and Bernard Roitberg showed that trophic egg production is an evolved maternal strategy in response to food availability, to minimise starvation risk of their young offspring, a long held hypothesis. In laboratory experiments, they showed that ladybird females adjust the proportion of trophic eggs they lay depending on the food conditions they have experienced. Ladybird females fed few aphids (low food conditions) produced 56% more trophic eggs than ladybirds fed on a plentiful supply of aphids. This way, ladybird mothers, despite abandoning their egg clutch are able to increase their offspring survival using information on the environment they themselves grew on.

Perry, J. & Roitberg, B. (2005). Ladybird mothers mitigate offspring starvation risk by laying trophic eggs. Behavioral Ecology and Sociobiology, 58 (6), 578-586 DOI: 10.1007/s00265-005-0947-1

1 comment:

Antje said...

Totally cool!