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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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Barplots illustrating the number of first attacks on models used in the 5 experiments. An asterisk indicates significance (P <0.05) i. The first test in experiment 1: no eyespots vs one eyespot/hindwing. ii. The second test in experiment 1: 1 eyespot vs 5 eyespots/hindwing iii. The third test in experiment 1: no eyespot vs 5 eyespots/hindwing iv. Second experiment; natural sized eyespots vs eyespots with half the area v. Third experiment: natural eyespots vs fan-like eyespots vi. Fourth experiment: symmetric eyespots vs asymmetric eyesopts vii. Fifth experiment: paired vs unpaired single eyespot.
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Fig1: Barplots illustrating the number of first attacks on models used in the 5 experiments. An asterisk indicates significance (P <0.05) i. The first test in experiment 1: no eyespots vs one eyespot/hindwing. ii. The second test in experiment 1: 1 eyespot vs 5 eyespots/hindwing iii. The third test in experiment 1: no eyespot vs 5 eyespots/hindwing iv. Second experiment; natural sized eyespots vs eyespots with half the area v. Third experiment: natural eyespots vs fan-like eyespots vi. Fourth experiment: symmetric eyespots vs asymmetric eyesopts vii. Fifth experiment: paired vs unpaired single eyespot.

Mentions: The first experiment consisted of three trials employing a total of 266 birds. Each bird was presented a pair of prey items, and no bird was used more than once. In the first test (0 vs 1 eyespot per wing), birds significantly preferred to first attack the eyespot-less model over the eyespotted model (Binomial Test: N = 84; P = 0.0001) (Figure 1 i.), with a significantly higher attack latency for the eyespotted model (Wilcoxon signed-rank test: V = 798; P = 0.000011; N = 84). In the second test (1 vs 5 eyespots per wing, where the area of each eyespot in the latter treatment was reduced such that the total eyespot size was equal in both treatments), birds preferred to first attack the model with 5 eyespots (Binomial Test: N = 93; P = 0.0220) (Figure 1 ii.), taking significantly lesser time to attack the one with 5 eyespots (Wilcoxon signed-rank test: V = 2716; P = 0.0422; N = 93). In the third test (0 vs 5 eyespots per wing) both models suffered similar rates of first attacks (N = 89; P = 0.5250) (Figure 1 iii.) and attack latency (V = 1820; P = 0.4559; N = 89).Figure 1


What makes eyespots intimidating-the importance of pairedness.

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

Barplots illustrating the number of first attacks on models used in the 5 experiments. An asterisk indicates significance (P <0.05) i. The first test in experiment 1: no eyespots vs one eyespot/hindwing. ii. The second test in experiment 1: 1 eyespot vs 5 eyespots/hindwing iii. The third test in experiment 1: no eyespot vs 5 eyespots/hindwing iv. Second experiment; natural sized eyespots vs eyespots with half the area v. Third experiment: natural eyespots vs fan-like eyespots vi. Fourth experiment: symmetric eyespots vs asymmetric eyesopts vii. Fifth experiment: paired vs unpaired single eyespot.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig1: Barplots illustrating the number of first attacks on models used in the 5 experiments. An asterisk indicates significance (P <0.05) i. The first test in experiment 1: no eyespots vs one eyespot/hindwing. ii. The second test in experiment 1: 1 eyespot vs 5 eyespots/hindwing iii. The third test in experiment 1: no eyespot vs 5 eyespots/hindwing iv. Second experiment; natural sized eyespots vs eyespots with half the area v. Third experiment: natural eyespots vs fan-like eyespots vi. Fourth experiment: symmetric eyespots vs asymmetric eyesopts vii. Fifth experiment: paired vs unpaired single eyespot.
Mentions: The first experiment consisted of three trials employing a total of 266 birds. Each bird was presented a pair of prey items, and no bird was used more than once. In the first test (0 vs 1 eyespot per wing), birds significantly preferred to first attack the eyespot-less model over the eyespotted model (Binomial Test: N = 84; P = 0.0001) (Figure 1 i.), with a significantly higher attack latency for the eyespotted model (Wilcoxon signed-rank test: V = 798; P = 0.000011; N = 84). In the second test (1 vs 5 eyespots per wing, where the area of each eyespot in the latter treatment was reduced such that the total eyespot size was equal in both treatments), birds preferred to first attack the model with 5 eyespots (Binomial Test: N = 93; P = 0.0220) (Figure 1 ii.), taking significantly lesser time to attack the one with 5 eyespots (Wilcoxon signed-rank test: V = 2716; P = 0.0422; N = 93). In the third test (0 vs 5 eyespots per wing) both models suffered similar rates of first attacks (N = 89; P = 0.5250) (Figure 1 iii.) and attack latency (V = 1820; P = 0.4559; N = 89).Figure 1

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