Museum specimens of 144 ant species reveal their colonisation history on the Fijian archipelago. PHOTO: PETER GINTER
Genome analysis of museum specimens sheds light on population history: native ant community on Fiji collapses following human arrival, whilst invasive species flourish.
He vast majority of ant populations found nowhere else on the Fijian islands have been declining since the arrival of humans, whilst the numbers of invasive species have increased dramatically, Japanese researchers write on 11 September in Science. According to the authors, the article is a response to alarming declines in insect populations worldwide, where a lack of historical monitoring data has left it unclear whether this ‘insect apocalypse’ is part of a long-term trend. The ant fauna of the archipelago now serves as a model system for exploring that question.
Colonisation history
With a few exceptions, the Japanese team did not directly monitor ant populations on Fiji over time. To nonetheless gain insight into historical changes, the team employs an alternative approach: they study DNA fragments from thousands of museum specimens representing 144 different ant species, collected by themselves and others over several decades. Because the genome contains evidence of population growth or decline, it is possible to use DNA analysis and genetic models to reconstruct the colonisation history of ants on the Fijian archipelago and track changes in the community over time.
Transport
The researchers identify 65 separate colonisation events. The first ant species reached Fiji millions of years ago through natural migration, subsequently evolving into the native ants the archipelago is home to today. The most recent species introductions are a direct consequence of human trade and transport. The study shows that 79 per cent of endemic species – found only on Fiji – are in decline. Their populations began to shrink following the first settlements around three thousand years ago. The decline accelerated from the 17th century onwards, coinciding with European colonisation, global trade, and the introduction of commercial agriculture. At the same time, species introduced by humans have increased explosively.
More adaptable
The study shows that native species with greater flexibility in their habitat preferences exhibit less decline than species restricted to a specific, low-disturbance environment. This is consistent with broader ideas about so-called biotic homogenisation: ecosystems become dominated by the same, widespread species, whilst unique, locally evolved organisms disappear. The findings extend beyond Fiji: ‘Because they are isolated ecosystems, islands feel the effects of human influence more quickly, making them function as a kind of canary in the coal mine’, the authors state. Habitat fragmentation could moreover cause mainland ecosystems to increasingly resemble islands.