Locomotor activity in males of Aedes aegypti can shift in response to females' presence

Abstract

Background: The study of physiological and behavioral traits of mosquito vectors has been of growing relevance for the proposition of alternative methods for controlling vector-borne diseases. Despite this, most studies focus on the female's traits, including the behavior of host seeking, the physiology of disease transmission and the site-choice for oviposition. However, understanding the factors that lead to males' reproductive success is of utmost importance, since it can help building new strategies for constraining population growth. Male behavior towards mating varies widely among species and the communication between males and females is the first aspect securing a successful encounter. Here we used an automated monitoring system to study the profile of locomotor activity of Aedes aegypti males in response to female's presence in an adapted confinement tube. We propose a new method to quantify male response to the presence of females, which can be potentially tested as an indicator of the success of one male in recognizing a female for mating.

Results: Locomotor activity varies in daily cycles regulated by an endogenous clock and synchronized by external factors, such as light and temperature. Our results show the previously described startle response to light, which is displayed as a steep morning activity peak immediately when lights are on. Activity drops during the day and begins to rise again right before evening, happening about 1.5 h earlier in males than in females. Most interestingly, males' activity shows a double peak, and the second peak is very subtle when males are alone and relatively more pronounced when females are present in the confinement tubes. The switch in the peak of activity, measured by the herein suggested Peak Matching Index (PMI), was significantly different between males with and without females.

Conclusions: The adapted monitoring system used here allowed us to quantify the response of individual males to nearby females in terms of the extent of the activity peak displacement. In this direction, we created the peak matching index (PMI), a new parameter that we anticipate could be interpreted as the inclination of males to respond to females' presence, and further tested as an indicator of the potential for finding females for mating.

Keywords: Aedes aegypti; Circadian activity; Mate recognition; Mosquitoes; Reproductive behavior; Vector control.

Fig. 1

Graphical scheme of the adapted confinement tube. a Plastic tube used as confinement for one female. b Cotton embedded in 10% sacarose solution. c Piece of tulle net used to separate male from female. d Glass cylinder placed in one of 32 rings of the activity monitor. e Each tube mounted is lodged in one of the monitor rings

Fig. 2

a Average profile of the locomotor/flight activity of Ae. aegypti males in different treatments, across 24 h. Average refers only to days 2, 3 and 4 in LD (12 h light/12 h dark). The first day in LD was not included because we considered males to be still adapting to the system. Error bars are shown for each 30 min interval. X-axis: Zeitgeber time refers to the number of hours after the light turns on inside the incubator; the white bar represents 12 h of light and the black bar represents 12 h of darkness. b Formula used for calculating the peak matching index (PMI)

Fig. 3

Plot of PMI values for each treatment, with mean and standard errors represented by innermost and outer bars, respectively. Comparison among treatments performed using ANOVA with Tukey’s post-hoc pairwise tests shown as lowercase letters. Abbreviations: M_VF, males with virgin females; M_IF, males with inseminated females

Fig. 4

Plot of total activity parameters for each treatment, with mean and standard errors represented by innermost and outer bars, respectively. Comparisons for the total activity in LD (graph c) were performed using ANOVA, with Tukey’s post-hoc pairwise tests shown as lowercase letters. The parameters total activity (a), total activity in DD (b) and proportion of activity in DD (d) were compared among treatments with the non-parametric Kruskal-Wallis test, with Dunn’s multiple comparisons test shown as lowercase letters. Abbreviations: M_VF, males with virgin females; M_IF, males with inseminated females

Fig. 5

Plot of parameters period and power, calculated when individuals are submitted to constant darkness conditions (see text for details). Mean and standard errors represented by innermost and outer bars, respectively. Comparison among treatments performed by Kruskal-Wallis test, with Dunn’s multiple comparisons test showing no difference among treatments. Abbreviations: M_VF, males with virgin females; M_IF, males with inseminated females

Fig. 6

Average profile of the locomotor activity of Ae. aegypti males and females with ablated organs, in different treatments, across 24 h (see text for details). X-axis: Zeitgeber time refers to the number of h after the light turns on inside the incubator; the white bar represents 12 h of light and the black bar represents 12 h of darkness

Fig. 7

Plot of activity values at evening peaks E1 (a) and E2 (b) and plot of the peak matching index (PMI) for each treatment (c), with means and standard errors represented by innermost and outer bars, respectively. Comparison among treatments performed using ANOVA, with Tukey’s post-hoc pairwise tests shown as lowercase letters. Abbreviations: M_abl_ant, males with ablated antennae; M_abl_ant_F, males with ablated antennae with females; M w/ F_abl_wng, males with females with ablated wings; M w/ F, males with females