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MaxKatt

Head hunters & Eyes

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Conventional wisdom is that eyes on plugs don't matter, and thus are often left off.

 

At the same time, it's also conventional wisdom that stripers are "head hunters."

 

There appears to be a breakdown in logic here.  If something is programed to "hunt heads" it has to be able to locate and target that head for a strike. 

 

I Googled a bit.  Eyes matter.  Obviously, you can do well on "blind" plugs stripers detect based on silhouette, vibration, sound, and ability to determine direction of prey  (particularly at night and/or low light conditions...but the presence of a dot or eye can only marginally INCREASE the likely hood of getting bit...not decrease it or be immaterial.

 

 

Bottom line:   Eyes and decoy spots matter. 

 

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"....With these experiments, we have demonstrated a possible anti-predator function of eyespots in aquatic prey against predation by fish. As all sticklebacks used in these experiments were naive (i.e. had no previous experience of predators, or prey with eyespots), any behavioural responses they showed at least during their first encounter with a spotted prey can be considered innate. The strong response in the first experiment that tested for the diverting effect of eyespots indicates that eyespots very effectively manipulate the behaviour of three-spined sticklebacks and direct their attacks towards them. This is an important finding, because it indicates that eyespots can be used to manipulate the behaviour of aquatic predators and direct their attacks towards the eyespots for protective purposes.

Importantly, the results from experiment 1b revealed that there was no difference in attack latency between the spotted and the spotless prey, indicating that the spotless area of the prey was not markedly more difficult to detect than the eyespot. Consequently, the diverting effect was not simply a result of the spotless part of the prey being more concealed than the eyespot. This may not be that surprising, considering that although both the prey and the background were speckled, the density of the dots in the background was twice as high as on the prey. Importantly, these two experiments demonstrated that the fish were attracted to attack towards the eyespot rather than being directed away from the spotless half of the prey. Our results are also in accordance with a recent study by Vallin et al. [15], who presented artificial prey items to passerine birds. Vallin et al. [15] used prey items that had a small marginal eyespot and presented these items to birds on backgrounds that were either concealing or exposing. Although the effect was not very strong, their result showed that small eyespots directed the attacks of birds towards them, regardless of how well the rest of the prey body blended into the background [33].

Why would the attack-directing effect of eyespots be advantageous for a prey? Particularly in Lepidoptera, it has been argued that if attacks are directed to the small eyespots located near the wing margins of many species instead of the more vital parts, such as the head or the body, the prey is more likely to escape and survive the attack [3,8,9,14,34]. Torn wing edges in Lepidoptera are not very costly damage, but many other species do not have body parts that would be likely to tolerate an attack and enable a successful escape [6,34]. However, it has been observed in butterflyfishes (Chaetodontidae) that some individuals that have lost up to 10% of their posterior body region (probably in an attack by a predator) have still been able to survive, recover, and be reproductively active after this type of damage [4].

In addition to redirecting attacks towards less vital body parts, eyespots could also be used to direct attacks in a direction that, in combination with the escape trajectory of the prey, would increase the chance of a successful escape [35]. For example, many fishes (e.g. members of ChaetodontidaePomacentridaeGobiidaeLabridaeApogonidae and Pomacanthidae [36]) have spots located in the areas on, or close to, their caudal fins, and because fish primarily swim head first, an attack directed towards the posterior region could facilitate the escape of a fish [4]. Interestingly, in many species of fish that have an eyespot in the posterior region, the real eye is obscured by an eye stripe (a stripe running through the eye [4,8,35]) or the eyespot is larger than the real eye, which might also indicate that competition for the predator's visual attention between the eyespot and the real eye may influence the evolution of colour patterns. This also raises the question of whether such eyespots rely on eye mimicry (i.e. that the posterior eyespot gives the appearance that the head is located at that end of the body; cf. the false head hypothesis [2,23,37]) or whether the pattern attracts attention and directs attacks. Dale & Pappantoniou [38] suggest that eye mimicry might be important for the anti-predator function of eyespots against eye-picking predators (such as the cutlip minnow, Exoglossum maxillingua), but unfortunately their study lacks proper statistical analysis [6]. Importantly, our findings from the two first experiments suggest that even though eyespots effectively divert the attacks of fish towards them, eyespots do not necessarily make an individual more susceptible to predation risk by increased conspicuousness. It is clear, however, that the function of divertive eyespots against fish predators warrants further experimental studies. For example, although we have shown that the eyespot pattern has a divertive effect against fish, we cannot exclude that also some other patterns might have similar effect. Future studies could investigate which properties of markings (e.g. eyelikeness) are important for predator response.

Gagliano [13] interpreted the lack of bite marks towards the eyespot on the posterior dorsal fin of recaptured reef fish (Pomacentrus amboinensis) as evidence against the diversion hypothesis, but as we state, another possibility is that the lack of bite marks instead indicated that the eyespots increased the chance of successfully avoiding an attack [39]. Similarly, McPhail [40] suggested that diversion marks could also increase the probability of a prey successfully avoiding predator attacks, and not only direct attacks towards less vital or defended parts of the prey body. McPhail [40] concluded that caudal, simple spots found in many fish may function as such diversion marks. Unfortunately, as already pointed out [6], sections on McPhail's [40] experimental methods and data analysis are incomplete, and his data suffered heavily from pseudo-replication. Thus, even though the idea that eyespots in aquatic prey may serve to misdirect predator attacks towards them is widely spread [4,6,40], we contend that our study is the first to present firm experimental support for this.

As our second question, we investigated whether large eyespots could have an intimidating effect against attacking fish. Our result from experiment 2 did not lend support for the intimidation hypothesis. This is interesting, considering the strong support this hypothesis has received in numerous terrestrial studies using passerine predators and butterflies as prey [17,19,20,22,41]. It has also been suggested multiple times that spots could have an intimidating effect in fish [4,16,42]. Yet, at least so far, experimental evidence to support this hypothesis in aquatic environments remains scarce (but see [16]).

It is noteworthy, however, that the fish that received spotless prey items in both the detectability and the intimidation experiment decreased their attack latency with successive trials, whereas the fish that received a spotted prey did not. This may suggest that even though we did not find any increased attack latency owing to intimidation caused by the eyespots, eyespots might interfere with learnt improvement of attack performance.

One possible explanation for why the large eyespots did not induce any immediate flight response is that, when viewed from the front, in (predatory) fish the projection of eyes is quite different owing to their lateral placement compared with many terrestrial predators, such as birds of prey. Therefore, an eyespot may not mimic a threat owing to the presence of a predator as closely in aquatic environments as it does in many terrestrial systems. Clearly, this is based on the assumption that eye mimicry is important for the intimidating effect of eyespots ([3,7,16,43,44], but see also [45,46]). Moreover, in experiment 2, the artificial prey items had only one eyespot, and one possibility is that two spots could be more likely to cause an intimidating effect in fish, because it might better reflect a more honest signal about potential threat by mimicking the frontal view of an approaching predator [16,43].

Another possibility is that our experiment lacks some condition such as movement. Many butterflies enhance their intimidating effect of an eyespot by a startle display, that is, by suddenly revealing it and also by moving so that the projection of the spot will be maximized towards the predator [3,17,47]. There are also anecdotal notes that fish appear to turn sideways towards a predator to present their lateral eyespot [4,48]. However, it is important to note that even fixed displays without such additional behaviours have been shown to elicit a response in birds encountering a butterfly [19,22].

Collectively, our results clearly showed that eyespots effectively draw the attacks of fish towards them, although our experiment does not exclude the possibility that also other markings could have a similar effect. Nevertheless, our results suggest that the existence of eyespots in many aquatic prey species may be explained by the diversion hypothesis. This finding also suggests that the diverting effect in fish may not only select for the occurrence of eyespots in aquatic prey, but it may also select for the location, possibly because directing a predator towards the opposite direction in which a prey is moving might enhance the probability of a successful escape.

 

 

 

 

 

 

 

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Edited by MaxKatt

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Plug building rule:

If the plug has a lot of roll, no eyes, like a danny. Eyes going up and down like that are un-natural

Not much roll, like a pikie, definitely eyes.

Edited by Sudsy

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