A University of Liverpool study of ants across three continents has revealed that their colour and size is strongly influenced by their environment, and that the dominant1
colour and average body size can change from year to year as temperatures vary. This finding has implications for how ant communities will cope with rising global temperatures. Ants are ectotherms and so rely on the temperature of their surrounding environment to control their metabolic2
activity. Previous studies from individual locations or single species have found that larger bodied ectotherms with dark colouration do well in cold places. Large bodies retain heat whilst dark colours help individuals to gain heat quicker than their paler counterparts do. Combined, these two traits are highly beneficial as they allow ectothermic individuals to forage3
and remain active for longer even under cool conditions.
Researchers at the University's School of Environmental Sciences wanted to test whether these ideas of ectotherm thermoregulation held across species and at large geographic4
scales. They collected and analysed information on the abundance, body size and colour of ants on 14 different mountains from locations in South Africa, South America and Australia. Some of the sites were sampled repeatedly for up to seven years. This diversity of elevations5
provided a huge range of external ambient temperatures (from 0.5 to 35°C).
They found that the colder the external temperature is, the larger and darker ants were, and vice7
versa. Consequently, communities of ants in sites closer to the South Pole or near the tops of mountains, where it was colder, would tend to be dominated by dark and large bodied ants. In warmer places the ant species were smaller and lighter8
They also found that this effect depended on the amount of UV-B radiation present at the sites. Melanin, the pigment9
which makes ants darker, also protects against harmful UV-B rays. It effectively acts as a sunblock. This caused ants in the central Australian desert to be dark in order to counter the extremely high UV-B radiation. Ordinarily, the ants here should have been pale to reflect the harsh desert sun.