Abstract
Signals of fighting indicate an animal's intention to attack and so they serve to prevent costly aggressive encounters. However, according to theory, a signal that is different in design (i.e. a novel signal) but that fails to inform fighting intentions will result in negative fitness consequences for the bearer. In the present study we used males of the territorial damselfly Hetaerina americana, which have a red wing spot during territory defense that has evolved as a signal of fighting ability. By producing a novel signal (covering the red spot with blue ink) in territory owners, we investigated: a) the behavioral responses by conspecific males; b) survival cost and c) three physiological mediators of impaired survival: muscular fat reserves, muscle mass and immune ability. We predicted that males with the novel signal would be attacked more often by conspecifics as the former would fail to convey fighting ability and intentions adequately. This will result in lower survival and physiological condition for the novel signal bearers. We found that, compared to control males (males whose red spot was not changed), experimental males had reduced survival, were less able to hold a territory, and had a reduced muscle mass. It seems that spot modified males were not able to effectively communicate their territory tenancy, which may explain why they lost their defended sites. Our results provide support for theoretical models that a novel signal that fails to informing fighting ability may lead to a fitness cost for bearers.
Highlights
Animal signals convey information to conspecifics and are frequently used to mediate aggressive conflicts
If there is a mismatch between the signal and the behavior and fighting intentions of the signaler, this may lead to a fitness cost for bearers via enhanced aggression by conspecifics [1,2,3,4]
We evaluated the behavioral responses of their competing conspecific intruders, field survival of experimental animals [23,24], and the three key indicators of physiological condition we explained above, as causative of impaired survival: fat reserves, thoracic muscle mass, and immune ability
Summary
Animal signals convey information to conspecifics and are frequently used to mediate aggressive conflicts. One example is the use of signals during territorial defense: a resident animal will use a signal to communicate its intention to chase away a conspecific intruder. If the intruder persists on taking the resident’s territory, the resident will attack. This way of communication supposes that the signal is needed as a pre-requisite for preventing aggressive behavior. If there is a mismatch between the signal and the behavior and fighting intentions of the signaler, this may lead to a fitness cost for bearers via enhanced aggression by conspecifics [1,2,3,4]. The reason for the fitness cost is that conspecifics would fail to relate the fighting intention of the bearer when assessing the bearer’s novel signal (i.e., [5])
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