The role of cuticular hydrocarbons in male attraction and repulsion by female Dawson s burrowing bee, Amegilla dawsoni

Transcription

1 The role of cuticular hydrocarbons in male attraction and repulsion by female Dawson s burrowing bee, Amegilla dawsoni Emily Traughber, Keegan Romig, and Sai Movva

2 Overview - What is CHC? CHC (cuticular hydrocarbons) are long chains of fatty acids and their derivatives, which protect insects from desiccation (drying out) as well as maintaining female bee attractiveness. CHC has been observed in bees, ants, field crickets, and acridid grasshoppers. CHC is significant in sex recognition as well as reproduction, especially in virgin female bees. Nesting females lack a certain CHC blend which makes them unattractive to males. However, some recently mated females may still have some of this initial blend. This cannot be compensated by adding virgin CHC blends to these bees, the responses are weak overall.

3 The Reproductive Biology of Bees Chemical signals are relevant not only to reproductive behavior, but also to kinship between bees. This prevents males from mating with their sisters, and vice versa. Newly emerging female bees produce sex pheromones that attract males and stimulate copulation. Females may become unattractive due to changes in their own olfactory cues or due to antiaphrodisiacs administered by sexually active males.

4 Breeding Ecology Whether a chemical signal is an attractant or repellant depends on the bees breeding ecology. Purpose of paper: Hypothesis: to analyze CHC blends in order to identify the specific compounds involved in mate attraction/avoidance. to test bees and their pheromones in order to see how low/highly localized emergence sites affect the distance and volatility of their signals. Finally, to see if attractiveness in nesting/mated females can be restored. CHCs play a potential role in sexual communication in Amegilla dawsoni bees.

5 For females, they are monandrous - meaning that they do not mate a second time. Dawson s Burrowing Bee (Amegilla dawsoni) Large, ground nesting bees found in the arid (dry) regions of central northwestern Australia. Males emerge in early spring, up to 2 weeks before females. Large males patrol the emergence sites to look for females, while small males patrol the peripheral area where females must pass. This creates competition among males, where the larger males acquire the most mates % of females are detected quickly by males, who ride the female's back to the peripheral vegetation to mate.

6

7 The same process was done for mated and nesting females. CHC Removals (Experiment 1) Researchers took 8 pairs of virgin bees and washed half of them off to remove CHC from the cuticles. They were then soaked in 2 ml hexane for 5 min, and rinsed again. Half remained unwashed. The amount of times that the males touch the female bees was counted, as well as how long the males tried to copulate Time mounted x the number of males mounted + 1s per touch (but didn t mount) = male seconds The location of the decoys was changed for each trial to avoid memorization by searching males.

8 Figure 2: The unwashed virgin and mated females are more attractive than their washed counterparts. Hexane washing had no effect on the attractiveness of female nesting bees.

9 2 washed nesting females as decoys one with 1 ml virgin extract and the other CHC Additions (Experiments 2 and 3) Purpose: To see whether washed virgin bees can be found attractive when adding CHC extracts derived from the previously washed bees. Experiment 2: 1 bee was administered 1ml clean hexane, while the other was administered 1 ml of hexane wash from either a nesting or virgin bee. 7 decoy pairs used to compare attractiveness between hexane and virgin extract 6 decoy pairs used to compare attractiveness between hexane and nesting extract Experiment 3: (to see if we can restore attractiveness to nesting females)

10 Figures 3 and 4: Attractiveness Washed virgin females with virgin extract >> washed females with hexane > washed females with nesting female extract Adding virgin female extract to a washed nesting bee was inconclusive. The effect of the virgin extract was very low.

11 Analysis of Hexane Washes In total, the washes from 7 virgin females, 8 nesting females, and 9 males were analysed. CHC peaks were labelled by scan number (each # = a chemical), which also corresponds to their retention times (fig 1). Overall, the GC (gas-liquid chromatography) produced 28 peaks. The area of each peak in a given sample was divided by the sum of all peak areas in that sample to give a relative concentration of each compound in the extract. (table 1)

12 The graph above shows a chemical profile from a female Dawson s burrowing bee.

13 PC3 - separated virgin females from nesting females and males The scatter plot shows (top) PC2 vs. PC1, and (bottom) PC3 vs. PC2. PC1 - separated nesting from virgin females and males PC2 - separated males from females

14 Results Unwashed virgin females attracted more attention than washed females. Hexane washing had no effect on the attractiveness of nesting bees, which were ignored by the patrolling males. Washed virgin females that received clean hexane were more attractive than washed virgin females that were administered nesting female extract. Overall, there seemed to be considerable differences in the CHC blends between males, virgin females, and nesting females. The test could not prove that addition of virgin extract increased the attractiveness of nesting females.

15 Discussion What s the advantage of males and females differing in their CHC blends? The ability to recognize females and males save patrolling males the energy that it takes to fight, considering that there is plenty of competition between them. This also saves males more time as they know not to wait for a bee to emerge that may also be male. Virgin females actively signal their receptivity due to their compounds being of such higher concentration, there are two benefits of this: Virgin females are essentially guaranteed a mate (up to 90%) This creates competition among patrolling males, meaning that the most superior males are the most likely to copulate with females once they emerge. This means that their offspring will have a good phenotype and possible genotype.

16 (continued) There are two possible explanations for changes in female attractiveness: It may be an adaptation in males to avoid sperm competition (instead they administer an antiaphrodisiac that makes females unattractive) It may also be an adaptation in females to avoid unwanted harassment from searching males. Males often try to mate with recently mated females, as they are still attractive compared to nesting females. This saves time and energy associated with attempted mating and female resistance. Since recently mated females were as attractive as newly emerged females, it s inconclusive whether mating is what is responsible for odour change. Instead, there could be signals in the male s ejaculate that turns off production of attractive

17 Thank you!