Warmth shifts rather than speeds transcriptomic ageing in the malaria mosquito Anopheles gambiae

Abstract

Only older mosquitoes transmit malaria, so how warming changes mosquito ageing matters for disease. Warmer temperatures are known to make mosquitoes age faster, but 'faster' can mean two different things: the ageing clock ticks more quickly, or it is simply set forward. We distinguished these by reanalysing 115 whole-body RNA-sequencing libraries from female Anopheles gambiae kept at 27, 30 or 32 {degrees}C and sampled 1-15 days after emergence. A transcriptomic clock trained on 27 {degrees}C mosquitoes (error {+/-}0.9 days) read 32 {degrees}C mosquitoes as 2.4 days older (95% CI 1.9-2.9) and 30 {degrees}C mosquitoes as 1.1 days older. The gap opened by day 5 and then stopped growing: between days 5 and 15, warmth added 0.01 extra days per day (95% CI -0.16 to 0.19), well below the 0.29-0.45 expected if the clock ran faster. Genome-wide, warmth advanced genes that change late in life, notably melanisation and digestive genes, but moved early-maturation genes the opposite way. Many responses bent at 30 {degrees}C, and immune genes held until 30 {degrees}C before falling. Warmth therefore shifts mosquitoes to an older transcriptional state without accelerating its pace.