Читать книгу Extreme Insects - Richard Jones - Страница 24

NAME	ten-spot ladybird Adalia decempunctata
LOCATION	Europe
ATTRIBUTE	over 80 different named colour or pattern forms

Naming plants and animals should be a relatively straightforward procedure. Since the Swedish naturalist Karl von Linné (also Latinised to Carolus Linnaeus) developed the binomial (two-name) system, each organism has been given two names. Thus, for the seven-spot ladybird we have one name for the genus, Coccinella, meaning ladybird, and one for the particular species, septempunctata, meaning seven-spotted.

Except that nothing in nature is that straightforward. The common seven-spot always has seven spots, but the closely related ten-spot ladybird, Adalia decempunctata, very rarely has ten. In fact it can have anything down to no spots. It can be red with black flecks, black with yellow shoulder marks, chequered, netted, speckled or barred. When early naturalists put Linnaeus’s binomial system into use, they went to town with ladybirds.

There was sexmaculata and sexpunctata for six-spotted ones; octopunctata had eight spots, quadripunctata four; semicruciata was halfway to having a cross on its back; semifasciata had half a stripe; centromaculata had spots down the middle; triangularis had three marks; subpunctata had small spots; obscura was obscurely marked. There was only one small problem – all these were the same species.

There are over 80 different named forms of the ten-spot ladybird, many once thought to be separate species, but now recognised as one species featuring different genetically controlled colour patterns. Geneticists are still trying to work out how these patterns are controlled at the level of the genes and the DNA.

These are not races or subspecies, where particular colour-ways occur in discrete geographical zones or different places around the world. The different patterns often occur together, and in breeding experiments many different patterns can appear in the offspring of identical ‘normal’ ten-spotted parents.

One selection pressure that can drive the evolution of a diversity of forms is the presence of predators that hunt by favouring one precise colour-way. Birds, in particular, hunt using a ‘search-image’ in their brains, seeing targets that match the image but missing others that look slightly different. By having many different patterns, at least some individuals should survive to reproduce. The only trouble with this theory in this case is that all ladybirds are brightly coloured to remind birds not to eat any of them because they taste horrid. Quite why the ten-spot ladybird should have such versatile patterns is still open to debate.