Firstly, I apologise for the lack of posts recently but I've been revising a lot for my uni exams! I thought I would start back with writing about harvester ants which I saw in Mallorca. Ants are an incredible insect with such a complex social structure that is truly fascinating. I have learnt a lot about them during uni and I wouldn't have imagined finding them so interesting so I'm hoping that I can pass this on to more people. Ant colonies will either have one or multiple queens which may be singly or multiply mated. They also have males whose role is just to mate after which they die, and workers which are all females and do not mate. Typically, harvester ants will accept multiple queens, despite reducing the relatedness between the colony and increasing queen conflict. They do this because genetic diversity is mediated by queen number in these colonies such that susceptibility to parasites is lessened and the ants can diverge to specialise in a wider range of tasks (such as defending the territory, collecting food or nursing young). However, new queens will almost always still be related to the colony. If the new queen was unrelated, the colony would not benefit from helping care for their brood. This is because with a related queen to whom they share many genes, they are indirectly passing on their own genes so caring for them is advantageous. Did you know that queens and females are genetically identical?
If you have ever seen a queen ant, you will know that they are much bigger than the female workers (which can also differ) so how can they be genetically the same? Caste (morphologically different ants) fate of an ant is determined either in the egg or larval stages and is determined by the environment and nutrition of each ant. Epigenetic factors (differential expression of the same gene) also determine this. For example, more insects than seeds in the diet of the Florida harvester ant results in a larger caste - i.e. it becomes a queen, and then a major worker and then a minor worker depending on the amount of insects fed. As the workers control the environment of the colony, they determine caste fate. Major workers are also known as soldier ants and play a role in defence as well as to crack open strong, hard seeds by using their large heads to do so. Minor workers will typically either be nursers for the young produced or they will be foragers of food and have a role in the maintenance of the colony. The difference between being a nurser or forager is also due to a different expression of some genes - including the 'foraging' gene. Finding their way home When out foraging, the worker harvester ants will leave a scent trail along their way so that they can track their way home again. This trail is produced from the poison gland and is also made so that they do not have any aggressive interactions with other competing ants. This scent trail is also used by other ants in the colony when some workers return with food. This means that a large amount of food can then be collected as all of the workers cooperate to improve their maximal returns. Harvester ants as well as other ants, bees, wasps and the only two known mammals that are truly eusocial (naked mole rat and Damaraland mole rat) have truly incredible social structures that allow them to increase the fitness of the colony. I hope that this article has made you excited about ants, as learning about it did for me - especially how ants with the same genetic make up can manifest into such different morphological groups! ©
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