Adaptive Plasticity in Wild Field Crickets’ Acoustic Signaling

Adaptive Plasticity in Wild Field Crickets’ Acoustic Signaling

A new article in PLOS ONE written by

Susan Bertram, Sarah Harrison, Ian Thomson, and Lauren Fitzsimmons

Click here for a copy of our PLOS ONE article

Click here for the Bertram Lab website

http://science.nature.nps.gov/im/units/ucbn/monitor/sagegrouse/sagegrouse.cfm

Figure 1: Changes to the density of competitors is an example of environmental variability commonly faced by organisms in the wild.

Environmental change is a common obstacle that animals have to overcome. Temporal or spatial changes in the weather, food availability, predator density, mate availability, or competitor density are just some examples of the environmental variability commonly faced by animals in the wild (Figure 1).The optimal phenotype (an organism’s morphology, physiology, behavior etc.) for a given environment often changes as environmental conditions change. For example, a caterpillar feeding on oak flowers will develop into a mimic of an oak catkin, while a sibling caterpillar feeding on leaves will develop into a mimic of a twig (Figure 2). These caterpillars may avoid predation by camouflaging themselves to match their environments.

Photo source: Whitman and Agrawal

Figure 2: Nemoria arizonaria caterpillars: (a) summer broods feed on oak leaves and
Develop to resemble oak twigs, (b) while spring broods feed on and resemble oak catkins (Whitman and Agrawal 2009).

Figure 3: Hydrangea macrophylla flowers grown in acidic soil produces blue flowers, while flowers grown in neutral or alkaline soil produce pink flowers.

Figure 3: Hydrangea macrophylla flowers grown in acidic soil produces blue flowers, while flowers grown in neutral or alkaline soil produce pink flowers.

If individuals are unable to adapt to changes in their surroundings, they may experience reduced survival or reproductive success compared to individuals who are able to adapt.Phenotypic plasticity is the ability to change behaviour, appearance, or other characteristics in response to environmental change. For instance, Hydrangea macrophylla produce either blue or pink flowers depending on soil alkalinity (Figure 3). Phenotypic plasticity may be adaptive as long as environmental variation is predictable and the benefits of plasticity outweigh the costs. For instance, phenotypic plasticity in sexually selected traits may be particularly adaptive if there are frequent predictable changes to the socio-sexual environment (e.g. fluctuation in mate density).

In our study, recently published in PLOS ONE, we examined the phenotypic plasticity of male field crickets’ sexually selected acoustic signals for two species: the fall field cricket, Gryllus pennsylvanicus and the spring field cricket, G. veletis (Figure 4).

Figure 3: The fall field cricket (Left- G. pennsylvanicus male) and the spring field cricket (Right- G. veletis male) are both found throughout North America.

Figure 4: The fall field cricket (Left- G. pennsylvanicus male) and the spring field cricket (Right- G. veletis male) are both found throughout North America.

Male crickets produce acoustic signals by raising their forewings and rubbing them together, each closing stroke producing a pulse of sound with 3-4 pulses grouped into a chirp (Figure 5). These acoustic calls are used to attract females, and females choose mates on the basis of the quantity and fine-scale structure of these signals. Female movement and sexual receptivity in the wild often follows predictable fluctuations throughout the day (diel rhythms), which may partially be explained by hourly fluctuations in the biotic (predator and parasite density) and abiotic (light and temperature levels) environment. Therefore, males that synchronize their daily signalling rhythms to match female mating activity are likely to have higher reproductive success. Here we examined how male acoustic signalling in the laboratory changes over the course of the day and compared this to the known reports of diel rhythms in female mating activity in the wild.
We captured wild males and brought them to our laboratory at Carleton University where we recorded their acoustic signalling for 2-4 days. We found that both spring and fall field crickets exhibited phenotypically plastic signalling behavior, with most males signalling more often and more attractively during the time of day when female mating activity is the highest in the wild (fall field cricket: night time and early morning; spring field cricket: early morning and afternoon). Most male crickets (from both species) chirped more often during the time of the day that female mating activity is highest in the wild (Figure 5). However, a few males of each species signalled in a seemingly maladaptive manner during times when female mating activity is lowest in the wild. Diel rhythms in signalling also differed across species, which may be beneficial in preventing lethal hybridization when spring and fall field crickets overlap temporally and spatially in mid-summer.

Figure 4: Waveforms of long-distance mate attraction signals of one G. pennsylvanicus and one G. veletis male.  Figures show typical long-distance mate attraction signal for each species and how signaling typically changes during time periods indicative of low (A & B) and high (C & D) mating activity in the wild. Signal fine-scale properties are indicated as follows: ChD = chirp duration; IChD= interchirp duration; PPCh = pulses per chirp; PD = pulse duration; IPD = interpulse duration; and PP = pulse period, which combines PD and IPD.

Figure 4: Waveforms of long-distance mate attraction signals of one G. pennsylvanicus and one G. veletis male. Figures show typical long-distance mate attraction signal for each species and how signaling typically changes during time periods indicative of low (A & B) and high (C & D) mating activity in the wild. Signal fine-scale properties are indicated as follows: ChD = chirp duration; IChD= interchirp duration; PPCh = pulses per chirp; PD = pulse duration; IPD = interpulse duration; and PP = pulse period, which combines PD and IPD.

Overall, our findings suggest that male field crickets exhibit phenotypically plastic mate attraction signals and that diel rhythms in these signals are synchronized so that they are in phase with diel rhythms in female mating activity, suggesting that signalling plasticity may be adaptive. We have yet to determine how the costs and benefits of the phenotypic plasticity we observed in our species of field cricket ultimate affect fitness.

References:

Whitman, D. W. and A. A. Agrawal. What is Phenotypic Plasticity and why is it Important? Pages 1-63 in: D. W. Whitman and T. N. Ananthakrishna (editors), Phenotypic plasticity of insects: Mechanisms and consequences. Science Publishers, Inc, Enfield, NH

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Male crickets change their behaviour when watched by an audience

Playing to an audience: The social environment influences aggression and victory displays

A new article in Biology Letters by Lauren Fitzsimmons and Susan Bertram

Click here for a copy of our Biology Letters article

Click here for the Bertram Lab website

Click here for Lauren’s website

http://wallpaperscraft.com/download/stag_beetle_fight_male_female_36738

Figure 1. Two male stag beetles fight while a female watches

In nature, many animals fight for dominance, territories, and mates, and fights often occur when others are watching (Figure 1). For example, eavesdropping fish are more likely to initiate fights with a loser than a winner, imposing an immediate cost to the loser. Fighters also sometimes change their behaviour when they know they are being watched.

Figure 2. Football players are famous for their victory celebrations after a touchdown.

Figure 2. Football players are famous for their victory celebrations after a touchdown.

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Humans do this regularly: consider the classic victory dance following a touchdown in a football game (Figure 2). Fish do this too: male fish have been shown to change their female preference in the presence of a potential competitor.

We conducted the first investigation of how audiences affect fighting and victory displays in an invertebrate, the spring field cricket (Gryllus veletis; Figure 3). Male field crickets frequently engage in fights over resources (see video here).

Winning a fight increases a male’s mating success through dominance which provides access to mate attraction territories, and because females usually prefer to mate with dominant males. Cricket fight winners often advertise their success using victory displays of aggressive songs and body jerks (shown after the fight in the video linked above). Because cricket densities can be high in field crickets, and mate attraction and fights occur in close proximity, many fights are likely to occur with female and male audiences nearby.

Figure 3. Two male spring field crickets (Gryllus veletis) engaged in a fight (photo credit: Louis Gagnon).

Figure 3. Two male spring field crickets (Gryllus veletis) engaged in a fight (photo credit: Louis Gagnon).

We investigated aggression and victory display behaviour in both field-captured and laboratory-reared crickets to explore the effect of rearing environment on these behaviours. We predicted that males with social experience would change their behaviour depending on the social context, whereas inexperienced lab-reared males would be less likely to respond to the presence of an audience. We found that the type of audience and the rearing environment (field or lab) were important predictors of how males behaved during and after fights. Field-captured winners were more aggressive than laboratory-reared winners in the presence of an audience (Figure 4).

Figure 4. Field-captured males are more aggressive with an audience present than with no audience, while lab-reared males are less responsive to the social environment. Field-captured males are also more aggressive than lab-reared males when an audience is present but similar when no audience is present.

Figure 4. Field-captured males are more aggressive with an audience present than with no audience, while lab-reared males are less responsive to the social environment. Field-captured males are also more aggressive than lab-reared males when an audience is present but similar when no audience is present.

Field-captured winners produced more victory displays in the presence of a male audience compared to no audience, whereas the victory display behaviour of lab-reared males was similar across audiences and highly variable among males within audience conditions (Figure 5). Our results suggest that field-captured winners, in particular, dynamically adjust their fighting behaviour to potentially gain a reproductive benefit via female eavesdropping and may deter future aggression from rivals by advertising their aggressiveness and victories.

Female mating decisions and male fighting decisions may be influenced by information communicated during contests, and females may represent a valuable resource for the winner, providing advantages to elevated aggression by winners during fights. Indeed, we found that contest winners elevate aggression in the presence of a female audience compared to no audience. Contest winners may be selected to be more aggressive and give more victory displays with male audiences because these displays reduce the likelihood of future contests; victory displays may also advertise additional energy that could be used against potential rivals. It is unknown whether cricket audiences gain information through eavesdropping, but our results suggest potential payoffs for both victorious males and eavesdroppers.

Figure 5. Field-captured males elevate victory display behaviour when a male audience is present, indicating a potential browbeating function (boasting their victory to other males to deter future aggression).

Figure 5. Field-captured males elevate victory display behaviour when a male audience is present, indicating a potential browbeating function (boasting their victory to other males to deter future aggression).

The relative lack of response to audience treatments for lab-reared males may reflect a lack of social experience. Our findings suggest that experiments on naive lab-reared individuals may not accurately reflect the behaviour of wild animals in nature, and add to evidence that social experience is important in shaping the development of dynamic behaviours. Field-captured males may be better able to adjust their dynamic behaviours to different social environments after experiencing both their own aggressive encounters and observing interactions between other males.

Our study provides the first evidence that invertebrates modify their contest behaviour in the presence of an audience. The ability to perceive the presence and sex of an audience and adjust behaviour accordingly is thus not restricted to vertebrates and may be more common across animals than previously recognized. Our study also provides the first evidence of an audience effect on victory display behaviour, and highlights the importance of the social environment in shaping animal behaviour.

Dr. Lauren Fitzsimmons

Dr. Lauren Fitzsimmons

ResearchBlogging.orgFitzsimmons, L.P. and S.M. Bertram (2013). Playing to an audience: The social environment influences aggression and victory displays. Biology Letters