A social insect fertility signal is dependent on chemical context

Abstract

Identifying group members and individuals' status within a group are fundamental tasks in animal societies. For ants, this information is coded in the cuticular hydrocarbon profile. We manipulated profiles of the ant Odontomachus brunneus to examine whether the releaser and primer effects of fertility signals are dependent on chemical context. Fertility status is signalled through increased abundance of (Z)-9-nonacosene (Z9 : C29). Across the ant's distribution, populations have distinct hydrocarbon profiles but the fertility signal is conserved. Foreign queens and fertility-signal-treated workers from the same population, sharing a similar chemical background, elicited releaser effects from workers, whereas queens and fertility-signal-treated workers from different populations did not. Z9 : C29 presented without chemical background did not elicit releaser effects. A primer-effect experiment found that Z9 : C29, presented without a chemical background, did not inhibit worker reproduction. Our results demonstrate that a familiar chemical background is necessary for appropriate responses to fertility signals.

Keywords: cuticular hydrocarbon; fertility signal; queen pheromone.

Figure 1.

Releaser-effect experimental results showing submissive reactions of test workers to (a) queens, (b) workers treated with the fertility signalling compound Z9 : C₂₉ and (c) workers stripped of their hydrocarbon profiles and treated with Z9 : C₂₉ or C₂₇. (a: Cochran's Q-test, Q = 24.64, p < 0.001; same-population queen (SPQ) versus different population queen (DPQ) p = 0.013, SPQ versus nestmate worker (NMW) p = 0.007, nestmate queen (Q) versus DPQ p = 0.002, Q versus NMW p = 0.008, Q versus SPQ p = 0.24, DPQ versus NMW p = 1). (b: Cochran's Q-test, Q = 15.27, p < 0.001; NMW versus same-population worker (SPW) p = 0.61, SPW versus different population worker (DPW) p = 0.013, NMW versus DPW p = 0.004). (c: z = 0, p = 1). N = 12 for all groups.

Figure 2.

Tests of primer effects of the pure compounds C₂₇ (hydrocarbon control) and Z9 : C₂₉ showing days to egg-laying, relative to the hexane control group (zero). Dotted lines connect data from the same colonies, Friedman ANOVA χ² = 1.6, p = 0.46.