Abstract
Anopheles gambiae eggs generally hatch at the completion of embryo development; two-three days post oviposition. However, staggered or delayed hatching has been observed whereby a single batch of eggs shows marked variation in time-to-hatch, with some eggs hatching 18 days post oviposition or later. The mechanism enabling delayed hatch has not been clearly elucidated but is likely mediated by environmental and genetic factors that either induce diapause or slow embryo development. This study aimed to compare metabolic activity and embryonic development between eggs collected from sub-colonies of the baseline Anopheles gambiae GAH colony previously selected for early or late time-to-hatch. Egg batches from early and late hatch sub-colonies as well as from the baseline colony were monitored for hatching. For both time-to-hatch selected sub-colonies and the baseline colony the majority of eggs hatched on day two post oviposition. Nevertheless, eggs produced by the late hatch sub-colony showed a significantly longer mean time to hatch than those produced by the early hatch sub-colony. The overall proportions that hatched were similar for all egg batches. CO2 output between eggs from early and late hatch sub-colonies showed significant differences only at 3 and 7 days post oviposition where eggs from the early hatch and the late hatch sub-colony were more metabolically active, respectively. No qualitative differences were observed in embryo development between the sub-colonies. It is concluded that all viable embryos develop to maturity at the same rate and that a small proportion then enter a state of diapause enabling them to hatch later. As it has previously been shown that it is possible to at least partially select for late hatch, this characteristic is likely to involve genetic as well as environmental factors. Delayed hatching in An. gambiae is likely an adaptation to maximise reproductive output despite the increased risk of desiccation in an unstable aquatic environment.
Highlights
Anopheles gambiae sensu stricto is the nominal member of the Anopheles gambiae species complex
Cross-mating experiments [21] indicated that time-to-hatch did not follow a Mendelian mode of inheritance selection for late time-to-hatch increased the proportion of late hatching larvae to 30%
The last recorded hatching in the baseline colony was on day 18 post-oviposition, as was the case in the late time-to-hatch selected sub-colony (Fig. 1B) the numbers were very small
Summary
Anopheles gambiae sensu stricto is the nominal member of the Anopheles gambiae species complex. In An. gambiae, intra-species adaptive plasticity that enhances population survival in variable or unpredictable environments inadvertently maintains malaria parasite transmission. Some of those adaptive traits that likely affect vector capacity include larval development time, adult body size and adult longevity. Larval habitats typically selected by Anopheles gambiae tend to be small, temporary water bodies such as water-filled tyre tracks and hoof prints [8]. They can be described as unstable because they are prone to periodic desiccation and flooding
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
