Climate and geographic trends in hatch delay of the treehole mosquito, Aedes triseriatus Say (Diptera: Culicidae)

Abstract

Eggs of Aedes triseriatus mosquitoes are stimulated to hatch when inundated with water, but only a small fraction of eggs from the same batch will hatch for any given stimulus. Similar hatching or germination patterns are observed in desert plants, copepods, rotifers, insects, and many other species. Bet hedging theory suggests that parents stagger offspring emergence into vulnerable life history stages in order to avoid catastrophic reproductive failures. For Ae. triseriatus, a treehole breeding mosquito, immediate hatching of an entire clutch leaves all of the parent's progeny vulnerable to extinction in the event of a severe drought. Natural selection has likely favored parents that pursued a bet hedging strategy where the risk of reproductive failure is distributed over time. Considering treehole mosquitoes, bet hedging theory could be used to predict that hatch delay would be positively correlated with the likelihood of drought. To test this prediction, we collected Ae. triseriatus from habitats that varied widely in mean annual precipitation and exposed them to several hatch stimuli in the laboratory. Here we report that, as predicted, Ae. triseriatus eggs from high precipitation regions showed less hatch delay than areas of low precipitation. This strategy probably allows Ae. triseriatus to cope with the wide variety of climatic conditions that it faces in its extensive geographical range. Journal of Vector Ecology 34 (1): 119-128. 2009.

Environmental effects on bet hedging in Aedes mosquito egg hatch

“…These results provide consistent support for the idea that delayed hatch is a critical evolutionary response to environmental conditions. Specifically, we propose that these results are consistent with a bethedging strategy that allows A. triseriatus populations to cope with intrinsic desiccation risk in its natural environment, effectively spreading risks over multiple instances as proposed by Khatchikian et al (2009). Developmental delay caused by environmental stochasticity, in this context, can constitute a ''cohort iteroparity'' (after Wilbur and Rudolf 2006).…”

“…At the end of the ninth stimulus, remaining unhatched eggs were checked for presence of viable embryos and total numbers were adjusted accordingly. A detailed description of site selection process, egg maintenance, hatching, and larval rearing procedures is presented elsewhere (see Khatchikian et al 2009). …”

“…In previous work, statistical modeling has shown that two indices of hatch delay, the proportion of eggs that hatch immediately and an index that captures the overall delayed hatch patterns through multiple hatch stimuli, were strongly correlated with temperature and precipitation (Khatchikian et al 2009). According to those multiple regression models, precipitation has a positive effect on immediate hatch, which is moderated by low temperatures within the domain of existing conditions.…”

“…However, some eggs in each batch do not hatch after the first inundation, but hatch progressively after subsequent hatch stimuli inundations (Livdahl and Koenekoop 1985). This strategy, which is common among container-breeding mosquitoes (Gillett 1955a, b), effectively scatters the egg cohort though time, and has been suggested as an evolutionary response to biological factors such as competition (Livdahl et al 1984), and to physical factors such as desiccation (Khatchikian et al 2009), or more generally, as an adaptation to unpredictable environmental conditions. In contrast, other factors such as shortened growing-season and predation may impose strong selection for immediate hatching.…”

The biology and demographic parameters of Aedes albopictus in northern peninsular Malaysia

“…This variability in hatching time has been documented in the species studied here [28,29] . This pattern of larval eclosion, known as erratic hatching is suggested as an evolutionary response to potential competitive interactions [30] and environmental adversities [31] . In fact, egg hatching patterns in container-breeding Aedes are modulated by the interactions temperature-larval environment and this has been well developed by Khatchikian et al [32] .…”