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Embryonic development and rates of metabolic activity in early and late hatching eggs of the major malaria vector Anopheles gambiae.

Kaiser ML, Duncan FD, Brooke BD - PLoS ONE (2014)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Wits Research Institute for Malaria, School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa; Centre for Opportunistic, Tropical & Hospital Infections, National Institute for Communicable Diseases, NHLS, Johannesburg, South Africa.

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.

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Related in: MedlinePlus

Embryos photographed at different ages and developmental stage post oviposition.a) early 4 hours post oviposition b) late 4 hours post-oviposition c) early 20 hours post oviposition d) late 20 hours post oviposition e) early 24 hours post oviposition f) late 24 hours post oviposition g) early 48 hours post oviposition h) late 48 hours post oviposition i) early 4 days post oviposition j) late 4 days post oviposition k) early 6 days post oviposition l) late 6 days post oviposition.
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pone-0114381-g003: Embryos photographed at different ages and developmental stage post oviposition.a) early 4 hours post oviposition b) late 4 hours post-oviposition c) early 20 hours post oviposition d) late 20 hours post oviposition e) early 24 hours post oviposition f) late 24 hours post oviposition g) early 48 hours post oviposition h) late 48 hours post oviposition i) early 4 days post oviposition j) late 4 days post oviposition k) early 6 days post oviposition l) late 6 days post oviposition.

Mentions: Approximately 30 images of eggs per age group (1–8 days post oviposition) were obtained from both early and late time-to-hatch selected sub-colonies. Using the degree of definition in embryo segmentation as a visual cue for development, no obvious differences were observed in the rates of embryo development between the eggs from the early and late time-to-hatch sub-colonies (Table 2 and Fig. 3). Most of the embryos from both groups of eggs were fully developed by two to three days post oviposition. Both groups also had eggs that hatched on day two post oviposition. The majority of eggs hatched between days two and four as previously described. Many embryos did not develop. The mean rate to full embryonic development across the ages 24 hours to 8 days was 44.88% in the early time-to-hatch sub-colony and 46.75% in the late time-to-hatch sub-colony.


Embryonic development and rates of metabolic activity in early and late hatching eggs of the major malaria vector Anopheles gambiae.

Kaiser ML, Duncan FD, Brooke BD - PLoS ONE (2014)

Embryos photographed at different ages and developmental stage post oviposition.a) early 4 hours post oviposition b) late 4 hours post-oviposition c) early 20 hours post oviposition d) late 20 hours post oviposition e) early 24 hours post oviposition f) late 24 hours post oviposition g) early 48 hours post oviposition h) late 48 hours post oviposition i) early 4 days post oviposition j) late 4 days post oviposition k) early 6 days post oviposition l) late 6 days post oviposition.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4257673&req=5

pone-0114381-g003: Embryos photographed at different ages and developmental stage post oviposition.a) early 4 hours post oviposition b) late 4 hours post-oviposition c) early 20 hours post oviposition d) late 20 hours post oviposition e) early 24 hours post oviposition f) late 24 hours post oviposition g) early 48 hours post oviposition h) late 48 hours post oviposition i) early 4 days post oviposition j) late 4 days post oviposition k) early 6 days post oviposition l) late 6 days post oviposition.
Mentions: Approximately 30 images of eggs per age group (1–8 days post oviposition) were obtained from both early and late time-to-hatch selected sub-colonies. Using the degree of definition in embryo segmentation as a visual cue for development, no obvious differences were observed in the rates of embryo development between the eggs from the early and late time-to-hatch sub-colonies (Table 2 and Fig. 3). Most of the embryos from both groups of eggs were fully developed by two to three days post oviposition. Both groups also had eggs that hatched on day two post oviposition. The majority of eggs hatched between days two and four as previously described. Many embryos did not develop. The mean rate to full embryonic development across the ages 24 hours to 8 days was 44.88% in the early time-to-hatch sub-colony and 46.75% in the late time-to-hatch sub-colony.

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Wits Research Institute for Malaria, School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa; Centre for Opportunistic, Tropical & Hospital Infections, National Institute for Communicable Diseases, NHLS, Johannesburg, South Africa.

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.

Show MeSH
Related in: MedlinePlus