Zombie ants cling to the aerial vegetation and spend months spores of their parasitic fungi, but researchers have noticed that they do not always clamp on the same part of the plant. Now researchers know that the choice of leaves or branches is related to the climate and that climate change has forced the mushrooms to adapt to local conditions.
"In tropical areas, zombie ants bite on leaves, but in temperate areas they bite branches or bark," said David P. Hughes, Associate Professor of Entomology and Biology, Penn State.
Zombie ants are actually different types of carpenter ants that are infected with a parasitic fungus. About half of the types of carpenter ants can become infected and each species has its own mushroom. The zombie ant phenomena are present on all continents around the world, except in Europe. However, a fossil zombie anteater was found in Germany, so that it once existed in Europe.
"They are not likely to be in Europe because the forests are being managed there," Hughes said. "Probably they died there locally."
Zombie ant spores fall on ants from above and the fungus proliferates in the ant body and uses it as a food source. Finally, the fungus manipulates the ant to climb high in the branches and pinch by biting. If an infected ant dies in the colony or on the ground, it has no chance to infect another ant. Therefore, it is essential for these fungi to position the ant bodies, where fungi can be widely distributed.
"In late summer and early fall, leaves and branches are where the ants live," said Raquel G. Loreto, postdoctoral fellow in entomology, Penn State. "But in temperate areas, the trees are deciduous and lose their leaves in the fall, where the ants bite on twigs."
Tropical forests are almost always evergreen and remain leafy throughout the year. Many temperate forest trees drop all leaves in autumn.
The German fossil, dated about 47 million years ago, shows the ant biting into a leaf. During this time, wet evergreen forests reached from the equator almost to the north and south poles. Since all the woods were evergreen, all zombie ants would have decided to bite into leaves.
As the climate cooled, temperate forests grew in the northernmost and southernmost areas of the world. Zombie ants in the areas that bit on leaves would have landed quickly on the ground as the leaves fell. The fungus that manipulated its host on leaves would not breed successfully. This implies that a strong force of natural selection had an effect on the ant's manipulation. Over time, the fungi developed to manipulate zombie ants in temperate zones to bite on twigs or bark.
"Some of the ants do not just bite the branches, but wrap their hind legs around the branch and hold it tight," said Loreto, "Probably they do that because biting twigs are not enough to hold them."
This Manipulative behavior developed in temperate zones around the world.The researchers report the results of their study in the current issue of Evolution .
They looked at three separate areas.First, they have determined that tropical zombie ants always exist Leaves bite and moderate zombie ants always bite twigs and bark, and 90 percent of the dead temperate ants have their legs wrapped around the branches.
They then found that biting the leaf instead of biting the branch was the ancestor form – the approach that was originally used When the world was much warmer, they also found that the biting behavior at different times varied developed into different places, making it a convergent developed feature in temperate areas that emerged independently from different locations – in this case, North America and Japan.
Much of the work involved viewing samples of zombie ants wherever they may be found – museums, other collections, photographs, and previously compiled datasets.
"We had a big advantage here, Kim Fleming," Hughes said. "Kim is a civic scientist whose possessions in South Carolina are adorned with zombie ants on trees." "As an excellent photographer and naturalist, Kim spent over 18 months collecting detailed data on the zombie ants by continuously taking pictures of them valuable data that would have been very hard to collect.
"Kim is an author of this article, but perhaps the greatest recognition of its significance is that the fungal species that infested carpenter ants in South Carolina Ophiocordyceps kimflemingiae .
The researchers also investigated the phylogenetic relationships of the various fungi by examining extracted DNA from as many samples as possible, genetically, biting and infecting. The coating was independently developed to adapt the fungi to the temperate vegetation.
"We can estimate that these changes took place 40 to 20 million years ago," Hughes said. Because of the scarcity of zombie ant fossils, we can not be more specific than that at the moment. "
Whenever the climate changes, either warmer or colder, wetter or drier – plants and animals adapt or die out. Zombie ant mushrooms also adapted well to the changing environment and their manipulation of carpenter ants ensured their survival to this day.
"Noteworthy here is that we have shown that the complex manipulation of an animal by microbe has responded to selective pressures that the climate imposes on animals and plants," says Hughes. "That was a cool finding that really got us excited."
The zombie ant mushroom is attacked, it says in the research