Linking individual phenotype to density-dependent population growth: the influence of body size on the population dynamics of malaria vectors

Abstract

Understanding the endogenous factors that drive the population dynamics of malaria mosquitoes will facilitate more accurate predictions about vector control effectiveness and our ability to destabilize the growth of either low- or high-density insect populations. We assessed whether variation in phenotypic traits predict the dynamics of Anopheles gambiae sensu lato mosquitoes, the most important vectors of human malaria. Anopheles gambiae dynamics were monitored over a six-month period of seasonal growth and decline. The population exhibited density-dependent feedback, with the carrying capacity being modified by rainfall (97% wAICc support). The individual phenotypic expression of the maternal (p = 0.0001) and current (p = 0.040) body size positively influenced population growth. Our field-based evidence uniquely demonstrates that individual fitness can have population-level impacts and, furthermore, can mitigate the impact of exogenous drivers (e.g. rainfall) in species whose reproduction depends upon it. Once frontline interventions have suppressed mosquito densities, attempts to eliminate malaria with supplementary vector control tools may be attenuated by increased population growth and individual fitness.

A dynamic model of some malaria-transmitting anopheline mosquitoes of the Afrotropical region. I. Model description and sensitivity analysis

“…This is in line with observations by Paaijmans et al [83]. The number of new eggs is simplified to a function of the number of gravid mosquitoes in each age group and their size (measured as wing length) based on observations [55,84-86]. The critical size is set to a wing length of 2.6 mm, which is less than that observed by Lyimo and Takken [85] but greater than observations by Yaro et al [87].…”

Seasonal variation in metabolic rate, flight activity and body size of Anopheles gambiae in the Sahel

“…Considering the abundance of flowers and fruits during the dry season (Müller et al, 2010), continued availability of human hosts and the hospitable temperature range, mosquitoes may amass nutritional reserves until they can later allocate them to reproduction. It is possible that these seasonal shifts in body size are mostly due to the drying of larval sites at the end of the wet season, which in turn affects larval density and thus food availability and larval growth patterns, as it is well known that growing conditions affect adult size (Lanciani, 1992;Fischer and Fiedler, 2002;Chown and Klok, 2003;Aboagye-Antwi and Tripét, 2010;Russell et al, 2011). In the riparian population, body mass was also increased in the transition period and early dry season, but fell starting in the late dry season, indicating that aestivation predictions were not closely met.…”

“…To determine the unique effect of season, we used sequential multivariate ANCOVAs, adding in the effects of seasonal temperature and other seasondependent variables such as flight activity and body size (wing length) one at a time and determining the remaining effect of season. Wing length was used as the primary indicator of body size instead of dry mass, because mass varies greatly with blood digestion or time since the last sugar meal (Lanciani, 1992;Aboagye-Antwi and Tripét, 2010;Russell et al, 2011), wing length was found to be at least as good a predictor of metabolic rate as dry body mass in our previous study , and wing length measurements were available for larger sample sizes.…”

Eliminating malaria vectors

“…Even recent models assuming the kind of linear dependence of emergence rates upon mean longevity [43] that would only be expected far below the carrying capacity of available larval habitat [44,45], predict the dominance of Anopheles arabiensis as a vector of residual transmission at high ITN coverage (Figure 1) but fail to capture the dramatic collapse of An . gambiae populations that is often observed in practice [36-38,46,47].…”