Image credit: Geometrid moth images assembled by Chuan-Kai Ho from The Moths of Borneo monograph series by Jeremy Holloway

Moths in Borneo show local reduction in size by movement and adaptation in response to climate warming

A new paper released today reveals that the increasing climate has affected the way that moths from Borneo have adapted to their environment, including becoming physically smaller. Led by Wu Chung-Huey from the National Taiwan University, the new study explores how the body-size, appendages and location of moth species collected over a 42-year gap (1965-2007) have changed in response to 0.7°C warming.

The resurvey data in 2007, from seven altitudes sampled in 1965, of over 8000 geometrid moths collected from Mount Kinabalu in Borneo, shows a significant wing-length reduction of 1.3% per species. The researchers also found the species had moved uphill by 67m on average, with movement by smaller species making the main contribution to observed size change.

Researchers including Chung-Huey Wu and I-Ching Chen from National Cheng Kung University, Taiwan, measured the collection of moths from 1965, which are part of the Natural History Museum’s entomology collection, to compare with those from the 2007 resurvey. As part of the new study, the research group used the same field protocols and sampled at the same sites to replicate as far as possible the previous survey from 1965.

Scientific Associate at the Natural History Museum and member of the 1965 survey, Dr Jeremy Holloway, said: “Mount Kinabalu was established as a Malaysian National Park in 1964, so the habitat remains largely undisturbed. We were thus able to compare the range shifts and body-size changes under climate warming with limited confounding factors.”

The study included measuring the forewing length as the metric of insect size, for 277 species (5536 individuals) and 219 species (3053 individuals) from the 1965 and 2007 surveys.

Dr Holloway continues: “Our main aim in 1965 was to see if the moths, as herbivores, reflected the interesting botanical mix in the flora of the higher altitude of the mountain. This was at least partially the case, particularly for the Geometridae, a family of moths used in the current study and now being sampled globally as prime environmental indicators. 42 years later, the new survey enabled assessment of whether general rules of a relationship between size and temperature and size within and between species applied in Borneo and had been affected by warming.”

Co-author of the study, Professor Chris Thomas from the Department of Biology at the University of York, said: "Moths becoming smaller could have two significant impacts: It will mean on average an insect having a smaller number of eggs, which will reduce the capacity to reproduce. Secondly, the size of the insect will affect how much they eat and so this will affect their energy value in the food chain.  If insect size changes become widespread, it could lead to functional changes across the ecosystem."

As the highest and most isolated mountain between the Himalayas and New Guinea, in one of the most biodiverse regions of the world, Mount Kinabalu is a globally important refuge for terrestrial species that become restricted to high altitudes by climate warming.

Co-author of the study, Professor Jane Hill from the Department of Biology at the University of York, added: "The area we studied on Mount Kinabalu is a protected national park but even in a place like this, we cannot protect insect communities from climate change, which is altering biological communities and ecosystem processes."

The paper is published by Nature on Thursday 10 October 2019.

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