Tuesday, 16 February 2016

A Bug's Life

Social behaviours have allowed certain insects to become some of the most successful organisms in the planet's history. At the pinnacle of this select group are the ants. Some ant species form groups of just a dozen of so individuals, while others form colonies many millions strong. Their nests have the complexity of cities, while a single colony on the move is a powerful force, stripping all available resources in its path from leaves to living creatures. Ant colonies are highly territorial. Yet termites are a similarly large threat, capable of creating colonies which rival the ants in size and ferocity.

Two different ant species preserved in combat
in 100 million year old Burmese amber
The social behaviours displayed by ants, from cooperation to conflict, date back at least 100 million years. A recent study conducted on Burmese amber has led to the identification of a new species of Cretaceous ant which led a strongly cooperative lifestyle.

'We have one piece of amber with as many as 21 worker ants trapped, and that's significant because at this time period, ants are very rare to find in fossils,' said Dr Phillip Barden from Rutgers University. 'They make up less than one percent of all insects in amber, so to find 20 in one piece is highly suggestive of social behaviour.'

The ants themselves belonged to a lineage which is distinct from modern ants. Their ancient nature, however, suggests that social behaviours in the group are likely to be similarly ancient. These ants were certainly well equipped to defend territories they held, possessing tusk-like jaws which may have been used to impale prey.

'There's nothing like that alive today, especially not in the ant world' said Barden. 'It seems like they probably went extinct sometime in the 10 million years or so before or after dinosaurs went out. It could have been climate. We also think it's possible that the modern lineages actually out-competed these early ants.'

A member of the reproductive caste of Krishnatermes yoddha
In a separate study which included Barden, termites were identified in amber from the same Burmese deposit. This in itself is significant as it pushes back the evolutionary record of termites by an incredible 80 million years, The new species, named Krishnatermes yoddha, was represented by a number of individuals from winged soldier and worker castes - indicative of the termites' social nature.

Their presence in the same deposit as the ants opens up the possibility that the two species may have engaged in warfare, at the very least in defense of their respective territories. Ants today will often strip termite colonies of valuable resources, including the grubs which are then used as a food source. Such behaviours may also have been prevalent 100 million years ago.

Our views of past ecosystems often focus on megafauna. They are certainly impressive, but it is easy to forget about the multitude of species which dwell in the undergrowth and often in far greater numbers. Ants play a vital part in ecosystems today, engaging in multiple ecological roles from scavenging to pest control. They must have played similar crucial roles in the past. Further study of the fossil record, particularly of immaculate specimens preserved in amber, will shed light on how ants evolved to become colonial and even super-organismal entities and how this impacted on past ecosystems.