Limits...
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.

Show MeSH
Models used in the experiment i. Experiment 1 a. The first test comparing models with no eyespots (0) vs one eyespot (1) per hindwing. b. The second test comparing 1 eyespot (1) vs 5 eyespots (5) per hindwing. c. The third test comparing no eyespots (0) vs 5 eyespots (5) per hindwing. ii. Experiment 2. Comparison of models with a pair of natural sized eyespots (Area) vs a pair of eyespots of half the area (Area/2) iii. Experiment 3. Comparison of models with a pair of natural eyespots (Eyespot) vs a pair of fans (Fan) iv. Experiment 4. Comparison of models with symmetric eyespots (Symmetric) vs a pair of asymmetric patterns comprising an eyespot and a fan (Asymmetric) v. Experiment 5. Comparison of models with a pair of natural sized eyespots (Paired) vs a single eyespot with twice the area of the natural eyespot (Unpaired).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig5: Models used in the experiment i. Experiment 1 a. The first test comparing models with no eyespots (0) vs one eyespot (1) per hindwing. b. The second test comparing 1 eyespot (1) vs 5 eyespots (5) per hindwing. c. The third test comparing no eyespots (0) vs 5 eyespots (5) per hindwing. ii. Experiment 2. Comparison of models with a pair of natural sized eyespots (Area) vs a pair of eyespots of half the area (Area/2) iii. Experiment 3. Comparison of models with a pair of natural eyespots (Eyespot) vs a pair of fans (Fan) iv. Experiment 4. Comparison of models with symmetric eyespots (Symmetric) vs a pair of asymmetric patterns comprising an eyespot and a fan (Asymmetric) v. Experiment 5. Comparison of models with a pair of natural sized eyespots (Paired) vs a single eyespot with twice the area of the natural eyespot (Unpaired).

Mentions: The conspicuousness hypothesis predicts that the effectiveness of eyespots is determined by their total area. This experiment included three tests. In the first test (0 vs 1), 84 birds were given a choice between models with no eyespots and those with 1 eyespot on each hindwing. In the second test (1 vs 5), 93 birds were given a choice between models with one eyespot per hindwing and 5 smaller eyespots per hindwing, wherein the total area of the 5 eyespots equalled the area of the single eyespot. In the third test (0 vs 5), 89 birds were presented with a choice between models with no eyespots and models with 5 eyespots per hindwing (with the total area being equal to that of the single eyespot). Therefore, the total area of the conspicuous signal is conserved across treatments with eyespots. The eyespots were assumed to be circular; thus the radius of the original eyespot (9 mm diameter) was manipulated to make eyespots of 1/5th the area of the original one. Every day, the birds were divided into three groups for the corresponding tests (Figure 5 i.).Figure 5


What makes eyespots intimidating-the importance of pairedness.

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

Models used in the experiment i. Experiment 1 a. The first test comparing models with no eyespots (0) vs one eyespot (1) per hindwing. b. The second test comparing 1 eyespot (1) vs 5 eyespots (5) per hindwing. c. The third test comparing no eyespots (0) vs 5 eyespots (5) per hindwing. ii. Experiment 2. Comparison of models with a pair of natural sized eyespots (Area) vs a pair of eyespots of half the area (Area/2) iii. Experiment 3. Comparison of models with a pair of natural eyespots (Eyespot) vs a pair of fans (Fan) iv. Experiment 4. Comparison of models with symmetric eyespots (Symmetric) vs a pair of asymmetric patterns comprising an eyespot and a fan (Asymmetric) v. Experiment 5. Comparison of models with a pair of natural sized eyespots (Paired) vs a single eyespot with twice the area of the natural eyespot (Unpaired).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig5: Models used in the experiment i. Experiment 1 a. The first test comparing models with no eyespots (0) vs one eyespot (1) per hindwing. b. The second test comparing 1 eyespot (1) vs 5 eyespots (5) per hindwing. c. The third test comparing no eyespots (0) vs 5 eyespots (5) per hindwing. ii. Experiment 2. Comparison of models with a pair of natural sized eyespots (Area) vs a pair of eyespots of half the area (Area/2) iii. Experiment 3. Comparison of models with a pair of natural eyespots (Eyespot) vs a pair of fans (Fan) iv. Experiment 4. Comparison of models with symmetric eyespots (Symmetric) vs a pair of asymmetric patterns comprising an eyespot and a fan (Asymmetric) v. Experiment 5. Comparison of models with a pair of natural sized eyespots (Paired) vs a single eyespot with twice the area of the natural eyespot (Unpaired).
Mentions: The conspicuousness hypothesis predicts that the effectiveness of eyespots is determined by their total area. This experiment included three tests. In the first test (0 vs 1), 84 birds were given a choice between models with no eyespots and those with 1 eyespot on each hindwing. In the second test (1 vs 5), 93 birds were given a choice between models with one eyespot per hindwing and 5 smaller eyespots per hindwing, wherein the total area of the 5 eyespots equalled the area of the single eyespot. In the third test (0 vs 5), 89 birds were presented with a choice between models with no eyespots and models with 5 eyespots per hindwing (with the total area being equal to that of the single eyespot). Therefore, the total area of the conspicuous signal is conserved across treatments with eyespots. The eyespots were assumed to be circular; thus the radius of the original eyespot (9 mm diameter) was manipulated to make eyespots of 1/5th the area of the original one. Every day, the birds were divided into three groups for the corresponding tests (Figure 5 i.).Figure 5

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