Ladybirds - wolves in sheep's clothing
(麻豆淫院Org.com) -- CSIRO research has revealed that the tremendous diversity of ladybird beetle species is linked to their ability to produce larvae which, with impunity, poach members of 'herds' of tiny, soft-bodied scale insects from under the noses of the aggressive ants that tend them.
Reconstructing the evolutionary history of ladybird beetles (family Coccinellidae), the researchers found that the ladybirds鈥� first major evolutionary shift was from feeding on hard-bodied ("armoured") scale insects to soft-bodied scale insects.
鈥淪oft-bodied scales are easier to eat, but present a whole new challenge,鈥� says Dr Ainsley Seago, a researcher with the CSIRO鈥檚 Australian National Insect Collection.
鈥淭hese soft-bodied sap-feeding insects are tended by ants, which guard the defenceless scales and collect a 鈥榬eward鈥� of sugary honeydew. The ant tenders aggressively defend their scale insect 鈥榣ivestock鈥� and are always ready to attack any predator that threatens their herd.鈥�
Therein lay the evolutionary problem confronting ladybird beetles, whose larvae were highly vulnerable to ant attack.
To avoid being killed as they poach the ant鈥檚 scales, ladybird larvae evolved to produce two anti-ant defences: an impregnable woolly coat of wax filaments, and glands which produce defensive chemicals. Most of the ladybird family鈥檚 6,000 species are found in lineages with one or both of these defences.
鈥淲e found that most of ladybird species鈥� richness is concentrated in groups with these special larval defences,鈥� Dr Seago said.
鈥漈hese groups are more successful than any other lineage of ladybird beetle. Furthermore, these defences have been 鈥榣ost鈥� in the few species that have abandoned soft-scale poaching in favour of eating pollen or plant leaves.
鈥淭his is an unusual way for diversity to arise in an insect group.
鈥淚n most previous research, insect species richness has been linked to co-evolution or adaptive 鈥榓rms races鈥� with plants.鈥�
This research helps to place Australia鈥檚 ladybirds in the evolutionary tree of life for insects, and helps us to understand the complex system of mechanisms by which beetle diversity has arisen.
Provided by CSIRO
