Flying ants mate close to home and produce inbred offspring

October 22, 2015

Ant queens stay close to home in their hunt for a mate and as a result produce thousands of inbred offspring, a study led by a University of Exeter biologist has found.

The research, published this week in the journal American Naturalist, found that that the queen will often only fly as far as 60 metres before finding a mate, and as a result may well be related to him. A queen mates only once, can live up to 30 years, and will continue re-producing long after her male mate is dead using the original sperm.

The one mating flight will therefore determine the fate of a colony for decades to come. Inbred colonies will produce fewer offspring and a queen who is herself inbred will have a much shorter lifespan.

In most ant species winged queens and males leave their colony to find a mate and this is thought to prevent inbreeding, so researchers have been puzzled by the fact that wild flying ant colonies were found to include inbred workers. This new study carried out at the University of Helsinki provides an explanation.

Dr Emma Vitikainen, a research fellow in the University of Exeter's Centre for Ecology and Conservation, and the principal researcher on the project, was surprised to find out just how close to home the ants stayed.

"Ninety per cent of queens flew a half a mile or less from their natal colony, with 60 metres being the average. Males flew further, 140 metres on average, probably because they are lighter and more agile than queens. Such differences between sexes are common in animals, and reduce the chances for inbreeding. Yet, with dispersal being limited, the sex difference in dispersal behaviour did not prevent inbreeding," she said.

Dr Vitikainen thinks that one explanation for the behaviour is that winged ants mature at different times in different colonies, limiting the pool of potential mating partners on a mating flight. As a result of this the queen would be force to find a mate closer to home and one to whom she may well be related.

"Inbreeding brings harmful effects in its wake. Understanding how animals disperse and avoid mating with relatives is therefore of crucial importance," she added.

"Ants are a really important part of the ecosystem, and they are vulnerable to habitat change and loss of genetic diversity. A colony may have thousands of workers, yet the numbers deceive: the workers are sterile and daughters of just one queen and her long-dead male mate, whose sperm she has kept alive in a storage organ."

The researchers spent three summers following the dawn mating flights of the narrow-headed ant Formica exsecta on islands at the University of Helsinki's Tvärminne Zoological Station in southern Finland. They collected newly mated ant queens and used genetic markers to trace the natal colony of queens and males (colony fathers). This allowed researchers to calculate the metric distances the ants had flown, and also to assess how closely related the mating partners were.
Natal Dispersal, Mating Patterns, and Inbreeding in the Ant Formica exsecta by Emma Vitikainen, Cathy Haag-Liautard and Liselotte Sundström is published in American Naturalist.


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About the University of Exeter

The University of Exeter is a Russell Group university and in the top one percent of institutions globally. It combines world-class research with very high levels of student satisfaction. Exeter has over 19,000 students and is one of the global top 100 universities according to the Times Higher Education World University Rankings 2015-16, positioned 93rd. Exeter is also ranked 7th in The Times and The Sunday Times Good University Guide 2016, 9th in the Guardian University Guide 2016 and 10th in The Complete University Guide 2016. In the 2014 Research Excellence Framework (REF), the University ranked 16th nationally, with 98% of its research rated as being of international quality. Exeter was named The Times and The Sunday Times Sports University of the Year 2015-16, in recognition of excellence in performance, education and research. Exeter was The Sunday Times University of the Year 2012-13.

The University has four campuses. The Streatham and St Luke's campuses are in Exeter and there are two campuses in Cornwall, Penryn and Truro. The 2014-2015 academic year marks the 10-year anniversary of the two Cornwall campuses. In a pioneering arrangement in the UK, the Penryn Campus is jointly owned and managed with Falmouth University. At the campus, University of Exeter students can study programmes in the following areas: Animal Behaviour, Conservation Biology and Ecology, English, Environmental Science, Evolutionary Biology, Geography, Geology, History, Human Sciences, Marine Biology, Mining and Minerals Engineering, Politics and International Relations, Renewable Energy and Zoology.

The University has invested strategically to deliver more than £350 million worth of new facilities across its campuses in the past few years; including landmark new student services centres - the Forum in Exeter and The Exchange at Penryn - together with world-class new facilities for Biosciences, the Business School and the Environment and Sustainability Institute. There are plans for further investment between now and 2016.

About the University of Exeter's Centre for Ecology and Conservation (CEC)

Staff at the Centre for Ecology and Conservation, based on the Penryn Campus, undertake cutting-edge research that focusses on whole organism biology. The CEC has three interlinked research groups: Behaviour, Ecology and Conservation, and Evolution which constitute 40 academics and over 100 early career researchers. It engages widely with businesses, charities and government agencies and organisations in Cornwall, the Isles of Scilly and beyond to translate its research into societal impact. Staff at the CEC deliver educational programs to some 500 undergraduate and 100 postgraduate students.

A new £5.5 million Science and Engineering Research Support Facility (SERSF) is currently under construction at the Penryn Campus. The facility will bring pioneering business, science and engineering together and will provide space for the growing CEC alongside the University of Exeter Business School, which is expanding into Cornwall, and the University's Marine Renewables team.

The University of Exeter and Falmouth University are founding partners in the Combined Universities in Cornwall (CUC), a unique collaboration between six universities and colleges to promote regional economic regeneration through Higher Education, funded mainly by the European Union (Objective One and Convergence), the South West Regional Development Agency and the Higher Education Funding Council for England, with support from Cornwall Council.

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