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What makes eyespots intimidating-the importance of pairedness.

Mukherjee R, Kodandaramaiah U - BMC Evol. Biol. (2015)

Bottom Line: However, contrary to previous, outdoor experiments, we found that the total area of eyespots did not affect their effectiveness.Non-eye-like, fan shaped patterns derived from eyespots were found to be just as effective as eye-like circular patterns.Furthermore, we did not find a significant effect of symmetry of patterns, again in discordance with previous work.

View Article: PubMed Central - PubMed

Affiliation: School of Biology, Indian Institute of Science Education and Research Thiruvananthapuram, CET campus, Trivandrum, 695016, India. ritwika@iisertvm.ac.in.

ABSTRACT

Background: Many butterflies possess striking structures called eyespots on their wings, and several studies have sought to understand the selective forces that have shaped their evolution. Work over the last decade has shown that a major function of eyespots is their ability to reduce predation by being intimidating to attacking predators. Two competing hypotheses seek to explain the cause of intimidation, one suggesting 'eye-mimicry' and the other their 'conspicuousness' as the reason. There is an on-going debate about which of these better explains the effectiveness of eyespots against predation. We undertook a series of indoor experiments to understand the relative importance of conspicuousness and eye-mimicry, and therefore how predator perception may have influenced the evolution of eyespots. We conducted choice tests where artificial paper models mimicking Junonia almana butterflies were presented to chickens and their preference of attack recorded.

Results: We first established that birds avoided models with a pair of eyespots. However, contrary to previous, outdoor experiments, we found that the total area of eyespots did not affect their effectiveness. Non-eye-like, fan shaped patterns derived from eyespots were found to be just as effective as eye-like circular patterns. Furthermore, we did not find a significant effect of symmetry of patterns, again in discordance with previous work. However, across all experiments, models with a pair of patterns, symmetric or asymmetric, eyelike or non-eye-like, suffered from fewer attacks compared with other models.

Conclusions: The study highlights the importance of pairedness of eyespots, and supports the hypothesis that two is a biologically significant number that is important in prey-predator signalling. We discuss the implications of our results for the understanding of eyespot evolution.

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Related in: MedlinePlus

Boxplot describing the latency between the first and second attack (in seconds) of the birds. The dark horizontal line within the box represents the median with the box denoting the first and third quartiles and the whiskers being the minimum and maximum values observed. Upon being presented with no vs 1 eyespot per hindwing (No eyespots: m = 20 s, IQR = 51 s; 1 eyespot/hindwing: m = 5.5 s, IQR = 11.25 s), the latency was significantly higher when the birds attacked the model with 1 eyespot/hindwing after attacking model with none (Mann–Whitney U Test: W = 942, P = 0.0276).
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Fig2: Boxplot describing the latency between the first and second attack (in seconds) of the birds. The dark horizontal line within the box represents the median with the box denoting the first and third quartiles and the whiskers being the minimum and maximum values observed. Upon being presented with no vs 1 eyespot per hindwing (No eyespots: m = 20 s, IQR = 51 s; 1 eyespot/hindwing: m = 5.5 s, IQR = 11.25 s), the latency was significantly higher when the birds attacked the model with 1 eyespot/hindwing after attacking model with none (Mann–Whitney U Test: W = 942, P = 0.0276).

Mentions: In the first test, birds that preferred to attack the eyespot-less model first, attacked the second model (with 1 eyespot per wing) after a significantly longer time than birds that attacked the models in a reverse order (Mann–Whitney U Test: W = 942, P = 0.0276) (Figure 2). However, this difference between treatments in terms of duration from first to second attacks was not significant in the next two tests (1 vs 5 eyespots/hindwing: W = 1005, P = 0.9367; 0 vs 5 eyespots/hindwing: W = 1009, P = 0.8361).Figure 2


What makes eyespots intimidating-the importance of pairedness.

Mukherjee R, Kodandaramaiah U - BMC Evol. Biol. (2015)

Boxplot describing the latency between the first and second attack (in seconds) of the birds. The dark horizontal line within the box represents the median with the box denoting the first and third quartiles and the whiskers being the minimum and maximum values observed. Upon being presented with no vs 1 eyespot per hindwing (No eyespots: m = 20 s, IQR = 51 s; 1 eyespot/hindwing: m = 5.5 s, IQR = 11.25 s), the latency was significantly higher when the birds attacked the model with 1 eyespot/hindwing after attacking model with none (Mann–Whitney U Test: W = 942, P = 0.0276).
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4374370&req=5

Fig2: Boxplot describing the latency between the first and second attack (in seconds) of the birds. The dark horizontal line within the box represents the median with the box denoting the first and third quartiles and the whiskers being the minimum and maximum values observed. Upon being presented with no vs 1 eyespot per hindwing (No eyespots: m = 20 s, IQR = 51 s; 1 eyespot/hindwing: m = 5.5 s, IQR = 11.25 s), the latency was significantly higher when the birds attacked the model with 1 eyespot/hindwing after attacking model with none (Mann–Whitney U Test: W = 942, P = 0.0276).
Mentions: In the first test, birds that preferred to attack the eyespot-less model first, attacked the second model (with 1 eyespot per wing) after a significantly longer time than birds that attacked the models in a reverse order (Mann–Whitney U Test: W = 942, P = 0.0276) (Figure 2). However, this difference between treatments in terms of duration from first to second attacks was not significant in the next two tests (1 vs 5 eyespots/hindwing: W = 1005, P = 0.9367; 0 vs 5 eyespots/hindwing: W = 1009, P = 0.8361).Figure 2

Bottom Line: However, contrary to previous, outdoor experiments, we found that the total area of eyespots did not affect their effectiveness.Non-eye-like, fan shaped patterns derived from eyespots were found to be just as effective as eye-like circular patterns.Furthermore, we did not find a significant effect of symmetry of patterns, again in discordance with previous work.

View Article: PubMed Central - PubMed

Affiliation: School of Biology, Indian Institute of Science Education and Research Thiruvananthapuram, CET campus, Trivandrum, 695016, India. ritwika@iisertvm.ac.in.

ABSTRACT

Background: Many butterflies possess striking structures called eyespots on their wings, and several studies have sought to understand the selective forces that have shaped their evolution. Work over the last decade has shown that a major function of eyespots is their ability to reduce predation by being intimidating to attacking predators. Two competing hypotheses seek to explain the cause of intimidation, one suggesting 'eye-mimicry' and the other their 'conspicuousness' as the reason. There is an on-going debate about which of these better explains the effectiveness of eyespots against predation. We undertook a series of indoor experiments to understand the relative importance of conspicuousness and eye-mimicry, and therefore how predator perception may have influenced the evolution of eyespots. We conducted choice tests where artificial paper models mimicking Junonia almana butterflies were presented to chickens and their preference of attack recorded.

Results: We first established that birds avoided models with a pair of eyespots. However, contrary to previous, outdoor experiments, we found that the total area of eyespots did not affect their effectiveness. Non-eye-like, fan shaped patterns derived from eyespots were found to be just as effective as eye-like circular patterns. Furthermore, we did not find a significant effect of symmetry of patterns, again in discordance with previous work. However, across all experiments, models with a pair of patterns, symmetric or asymmetric, eyelike or non-eye-like, suffered from fewer attacks compared with other models.

Conclusions: The study highlights the importance of pairedness of eyespots, and supports the hypothesis that two is a biologically significant number that is important in prey-predator signalling. We discuss the implications of our results for the understanding of eyespot evolution.

Show MeSH
Related in: MedlinePlus