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Altruistic defence behaviours in aphids.

Wu GM, Boivin G, Brodeur J, Giraldeau LA, Outreman Y - BMC Evol. Biol. (2010)

Bottom Line: The altruistic nature of anti-predatory behaviours is often difficult to establish because the actor can obtain direct fitness benefits, or the behaviour could result from selfish coercion by others, especially in eusocial animals.Smeared parasitoids, however, spent proportionately more time grooming and less time foraging, which resulted in a decreased host-encounter and oviposition rate within the host patch.Moreover, the use of cornicle secretions was consistent with their altruistic nature, because the occurrence of this behaviour increased with the size of indirect fitness benefits, the number of clone-mates that can benefit.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Natural Resource Sciences, McGill University, 21,111 Lakeshore Road, Ste-Anne-de-Bellevue, QC, H9X 3V9, Canada. mick.wu@mail.mcgill.ca

ABSTRACT

Background: Altruistic anti-predatory behaviours pose an evolutionary problem because they are costly to the actor and beneficial to the recipients. Altruistic behaviours can evolve through indirect fitness benefits when directed toward kin. The altruistic nature of anti-predatory behaviours is often difficult to establish because the actor can obtain direct fitness benefits, or the behaviour could result from selfish coercion by others, especially in eusocial animals. Non-eusocial parthenogenetically reproducing aphids form colonies of clone-mates, which are ideal to test the altruistic nature of anti-predatory defence behaviours. Many aphids release cornicle secretions when attacked by natural enemies such as parasitoids. These secretions contain an alarm pheromone that alerts neighbours (clone-mates) of danger, thereby providing indirect fitness benefits to the actor. However, contact with cornicle secretions also hampers an attacker and could provide direct fitness to the actor.

Results: We tested the hypothesis that cornicle secretions are altruistic by assessing direct and indirect fitness consequences of smearing cornicle secretions onto an attacker, and by manipulating the number of clone-mates that could benefit from the behaviour. We observed parasitoids, Aphidius rhopalosiphi, foraging singly in patches of the cereal aphid Sitobion avenae of varied patch size (2, 6, and 12 aphids). Aphids that smeared parasitoids did not benefit from a reduced probability of parasitism, or increase the parasitoids' handling time. Smeared parasitoids, however, spent proportionately more time grooming and less time foraging, which resulted in a decreased host-encounter and oviposition rate within the host patch. In addition, individual smearing rate increased with the number of clone-mates in the colony.

Conclusions: Cornicle secretions of aphids were altruistic against parasitoids, as they provided no direct fitness benefits to secretion-releasing individuals, only indirect fitness benefits through neighbouring clone-mates. Moreover, the use of cornicle secretions was consistent with their altruistic nature, because the occurrence of this behaviour increased with the size of indirect fitness benefits, the number of clone-mates that can benefit. This study provides evidence for a case of kin-directed altruistic defence outside eusocial animals.

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Parasitoid oviposition rate within patch visits against smearing frequency. Box plots show the distribution of oviposition rates for patches containing 2 (white), 6 (grey), and 12 (black) aphids. Boxes show the inter-quartile range (50% of observations) in which the horizontal bar is the median. Whiskers extend 1.5 times the interquartile range beyond the median. Dots show individual observations lying outside this interval. Box widths are proportional to the square root of sample sizes.
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Figure 2: Parasitoid oviposition rate within patch visits against smearing frequency. Box plots show the distribution of oviposition rates for patches containing 2 (white), 6 (grey), and 12 (black) aphids. Boxes show the inter-quartile range (50% of observations) in which the horizontal bar is the median. Whiskers extend 1.5 times the interquartile range beyond the median. Dots show individual observations lying outside this interval. Box widths are proportional to the square root of sample sizes.

Mentions: Oviposition rate within patches (Figure 2) decreased significantly with increasing smearing frequency (Wald = 13.1, df = 1, p = 0.0003), and increased significantly with aphid density (Wald = 42.3, df = 1, p < 0.0001). Encounter rate with aphids (Figure 3a) decreased significantly with increasing smearing frequency (Wald = 11.5, df = 1, p = 0.0007), but increased significantly with aphid density (Wald = 66.7, df = 1, p < 0.0001). The proportion of encounters resulting in oviposition (Figure 3b) did not vary significantly with smearing frequency (Wald = 0.03, df = 1, p = 0.87) or aphid density (Wald = 1.84, df = 1, p = 0.17). Similarly, handling time of ovipositions in a patch (Figure 3c) did not vary significantly with smearing frequency (Wald = 0.27, df = 1, p = 0.60) or aphid density (Wald = 0.16, df = 1, p = 0.69).


Altruistic defence behaviours in aphids.

Wu GM, Boivin G, Brodeur J, Giraldeau LA, Outreman Y - BMC Evol. Biol. (2010)

Parasitoid oviposition rate within patch visits against smearing frequency. Box plots show the distribution of oviposition rates for patches containing 2 (white), 6 (grey), and 12 (black) aphids. Boxes show the inter-quartile range (50% of observations) in which the horizontal bar is the median. Whiskers extend 1.5 times the interquartile range beyond the median. Dots show individual observations lying outside this interval. Box widths are proportional to the square root of sample sizes.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2823731&req=5

Figure 2: Parasitoid oviposition rate within patch visits against smearing frequency. Box plots show the distribution of oviposition rates for patches containing 2 (white), 6 (grey), and 12 (black) aphids. Boxes show the inter-quartile range (50% of observations) in which the horizontal bar is the median. Whiskers extend 1.5 times the interquartile range beyond the median. Dots show individual observations lying outside this interval. Box widths are proportional to the square root of sample sizes.
Mentions: Oviposition rate within patches (Figure 2) decreased significantly with increasing smearing frequency (Wald = 13.1, df = 1, p = 0.0003), and increased significantly with aphid density (Wald = 42.3, df = 1, p < 0.0001). Encounter rate with aphids (Figure 3a) decreased significantly with increasing smearing frequency (Wald = 11.5, df = 1, p = 0.0007), but increased significantly with aphid density (Wald = 66.7, df = 1, p < 0.0001). The proportion of encounters resulting in oviposition (Figure 3b) did not vary significantly with smearing frequency (Wald = 0.03, df = 1, p = 0.87) or aphid density (Wald = 1.84, df = 1, p = 0.17). Similarly, handling time of ovipositions in a patch (Figure 3c) did not vary significantly with smearing frequency (Wald = 0.27, df = 1, p = 0.60) or aphid density (Wald = 0.16, df = 1, p = 0.69).

Bottom Line: The altruistic nature of anti-predatory behaviours is often difficult to establish because the actor can obtain direct fitness benefits, or the behaviour could result from selfish coercion by others, especially in eusocial animals.Smeared parasitoids, however, spent proportionately more time grooming and less time foraging, which resulted in a decreased host-encounter and oviposition rate within the host patch.Moreover, the use of cornicle secretions was consistent with their altruistic nature, because the occurrence of this behaviour increased with the size of indirect fitness benefits, the number of clone-mates that can benefit.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Natural Resource Sciences, McGill University, 21,111 Lakeshore Road, Ste-Anne-de-Bellevue, QC, H9X 3V9, Canada. mick.wu@mail.mcgill.ca

ABSTRACT

Background: Altruistic anti-predatory behaviours pose an evolutionary problem because they are costly to the actor and beneficial to the recipients. Altruistic behaviours can evolve through indirect fitness benefits when directed toward kin. The altruistic nature of anti-predatory behaviours is often difficult to establish because the actor can obtain direct fitness benefits, or the behaviour could result from selfish coercion by others, especially in eusocial animals. Non-eusocial parthenogenetically reproducing aphids form colonies of clone-mates, which are ideal to test the altruistic nature of anti-predatory defence behaviours. Many aphids release cornicle secretions when attacked by natural enemies such as parasitoids. These secretions contain an alarm pheromone that alerts neighbours (clone-mates) of danger, thereby providing indirect fitness benefits to the actor. However, contact with cornicle secretions also hampers an attacker and could provide direct fitness to the actor.

Results: We tested the hypothesis that cornicle secretions are altruistic by assessing direct and indirect fitness consequences of smearing cornicle secretions onto an attacker, and by manipulating the number of clone-mates that could benefit from the behaviour. We observed parasitoids, Aphidius rhopalosiphi, foraging singly in patches of the cereal aphid Sitobion avenae of varied patch size (2, 6, and 12 aphids). Aphids that smeared parasitoids did not benefit from a reduced probability of parasitism, or increase the parasitoids' handling time. Smeared parasitoids, however, spent proportionately more time grooming and less time foraging, which resulted in a decreased host-encounter and oviposition rate within the host patch. In addition, individual smearing rate increased with the number of clone-mates in the colony.

Conclusions: Cornicle secretions of aphids were altruistic against parasitoids, as they provided no direct fitness benefits to secretion-releasing individuals, only indirect fitness benefits through neighbouring clone-mates. Moreover, the use of cornicle secretions was consistent with their altruistic nature, because the occurrence of this behaviour increased with the size of indirect fitness benefits, the number of clone-mates that can benefit. This study provides evidence for a case of kin-directed altruistic defence outside eusocial animals.

Show MeSH
Related in: MedlinePlus