Effects of larval growth condition and water availability on desiccation resistance and its physiological basis in adult Anopheles gambiae sensu stricto

Abstract

Background: Natural populations of the malaria mosquito Anopheles gambiae s.s. are exposed to large seasonal and daily fluctuations in relative humidity and temperature, which makes coping with drought a crucial aspect of their ecology.

Methods: To better understand natural variation in desiccation resistance in this species, the effects of variation in larval food availability and access to water as an adult on subsequent phenotypic quality and desiccation resistance of adult females of the Mopti chromosomal form were tested experimentally.

Results: It was found that, under normal conditions, larval food availability and adult access to water had only small direct effects on female wet mass, dry mass, and water, glycogen and body lipid contents corrected for body size. In contrast, when females subsequently faced a strong desiccation challenge, larval food availability and adult access to water had strong carry-over effects on most measured physiological and metabolic parameters, and affected female survival. Glycogen and water content were the most used physiological reserves in relative terms, but their usage significantly depended on female phenotypic quality. Adult access to water significantly influenced the use of water and body lipid reserves, which subsequently affected desiccation resistance.

Conclusions: These results demonstrate the importance of growth conditions and water availability on adult physiological status and subsequent resistance to desiccation.

Figure 1

Effect of larval nutritional stress and water availability on survival. Effects of larval food availability at the larval stage and hydric stress at the adult stage on the survival (h) of female mosquitoes subsequently challenged with constant desiccation. Manipulation of larval food availability resulted in female of 'Good' and 'Poor' phenotypic quality, and females were provided with constant access to water (24 h) or for 16 h per day only (16 h).

Figure 2

a-e - Direct and carry-over effects of phenotypic quality and water availability on physiological and metabolic parameters. Fig. 2a-e. Effects of mosquito phenotypic quality induced by larval nutritional stress and water availability on 5 physiological and metabolic parameters of females at the end of the 7-day hydric stress experiment (grey bars), the end of 7 d + desiccation challenge experiments (white bars), and the percentage difference between the two experiments (black bars - right axis). All parameters were corrected for body size. Confidence intervals are indicated and P-values for Mann-Whitney tests comparing parameters between the two experiments in each experimental groups are shown as * P < 0.05, ** P < 0.01, *** P < 0.001, NS not significant.