獵物群落結構影響捕食者對於穆氏擬態之選擇

Ihalainen E, Rowland HM, Speed MP, Ruxton GD, Mappes J. 2012 Prey community structure affects how predators select for Mullerian mimicry. Proc Biol Sci. DOI:10.1098/rspb.2011.2360 [Full]

Keywords: aposematism; avoidance learning; Batesian mimicry; generalization

The protective value of conspicuous signals is not impaired by shape, size, or position asymmetry

The protective value of conspicuous signals is not impaired by shape, size, or position asymmetry

Behavioral Ecology (2009) Vol. 20, No. 1, 96-102
Martin Stevens, Sarah A. Castor-Perry, and Jessica R.F. Price
Department of Zoology, University of Cambridge

Various conspicuous signals in nature promote initial and learned avoidance by predators. It is widely thought that such signals are most effective when highly symmetrical in features such as size and shape, supported by recent laboratory experiments with domestic chicks and artificial prey. However, no study has investigated the effect of asymmetry on conspicuous signals in a natural setting, where viewing distances, angles, predator species, and light conditions vary and where predators encounter prey sequentially rather than simultaneously. We undertook 2 field experiments with artificial gray-scale prey, marked with a pair of white markings presented to wild avian predators, to test the effect of asymmetry on the survival value of conspicuous signals in the field. Experiment 1 had treatments with symmetrical spots or with spots asymmetrical in area between 5 and 50%. All marked
treatments survived better than unmarked controls, but there was no benefit of being symmetrical. Experiment 2 tested the effect of possessing markings asymmetrical for shape or position and any additive effect of these 2 features. Again, symmetry conferred no benefit and targets with markings asymmetrical for position and/or shape survived equally well as those with symmetrical arrangements. These findings indicate that asymmetry in warning signals may not be costly to prey in nature or be of less importance compared with other features of the signal, such as color and overall size.

Keywords: antipredator coloration, aposematism, birds, eyespots, predation, symmetry.

[Article]Learning and the mimicry spectrum: from quasi-Bates to super-Müller

Learning and the mimicry spectrum: from quasi-Bates to super-Müller

Alexandra C.V. Balogh^{, a,} , Gabriella Gamberale-Stille^a and Olof Leimar^a

^aDepartment of Zoology, Stockholm University, Sweden

Müllerian mimicry is the mutualistic resemblance between two defended species, while Batesian mimicry is the parasitic resemblance between a palatable species (the mimic) and an unpalatable one (the model). These two kinds of mimicry are traditionally seen as extreme ends of a mimicry spectrum. For the range in between, it has been suggested that mimetic relations between unequally defended species could be parasitic, and this phenomenon has been referred to as quasi-Batesian mimicry. Where a mimetic relation is placed along the mimicry spectrum depends on the assumptions made about predator learning. We used a variant of the Rescorla–Wagner learning model for virtual predators to analyse the different possible components of the mimicry spectrum. Our model entails that the rate of associative learning is influenced by variation in the stimuli to be learned. Variable stimuli, that is, unequal defences, can increase the predator learning rate and thus lead to an increased level of mutualism in a mimetic relation. In our analysis, we made use of the concepts of super-Müllerian mimicry, where the benefit of mimicry is even greater than in traditional Müllerian mimicry, and quasi-Müllerian mimicry, where mimicry by a palatable mimic is mutualistic. We suggest that these types of mimicry should be included in the mimicry spectrum along with Müllerian, Batesian and quasi-Batesian mimicry.

Keywords: associative learning; mutualism; Müllerian mimicry; quasi-Batesian mimicry; Rescorla–Wagner model

[Article]Multimodal warning signals for a multiple predator world

Nature 455, 96-99 (4 September 2008) | doi:10.1038/nature07087; Received 10 February 2008; Accepted 14 May 2008

Multimodal warning signals for a multiple predator world

John M. Ratcliffe^1,3 & Marie L. Nydam^2,3

1. Center for Sound Communication, Institute of Biology, University of Southern Denmark, DK-5230 Odense M, Denmark
2. Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York 14853, USA
3. These authors contributed equally to this work.

Correspondence to: John M. Ratcliffe^1,3Marie L. Nydam^2,3 Correspondence and requests for materials should be addressed to M.L.N. (Email: mln32@cornell.edu) or J.M.R. (Email: jmr@biology.sdu.dk).

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Abstract

Aposematism is an anti-predator defence, dependent on a predator's ability to associate unprofitable prey with a prey-borne signal¹. Multimodal signals should vary in efficacy according to the sensory systems of different predators; however, until now, the impact of multiple predator classes on the evolution of these signals had not been investigated^{2, 3}. Here, using a community-level molecular phylogeny to generate phylogenetically independent contrasts, we show that warning signals of tiger moths vary according to the seasonal and daily activity patterns of birds and bats—predators with divergent sensory capacities. Many tiger moths advertise chemical defence^{4, 5} using conspicuous colouration and/or ultrasonic clicks^{3, 6}. During spring, when birds are active and bats less so, we found that tiger moths did not produce ultrasonic clicks. Throughout both spring and summer, tiger moths most active during the day were visually conspicuous. Those species emerging later in the season produced ultrasonic clicks; those that were most nocturnal were visually cryptic. Our results indicate that selective pressures from multiple predator classes have distinct roles in the evolution of multimodal warning displays now effective against a single predator class. We also suggest that the evolution of acoustic warning signals may lack the theoretical difficulties associated with the origination of conspicuous colouration.

[Practice]變色龍適合拿來當成predator嗎?

今天以台灣茶斑蛾(Eterusia taiwana)當成prey, 丟給高冠變色龍, 日守宮和攀蜥試試, 原本的想像是--高冠會因為吃到可怕的東西而生氣變色, 這樣我們就知道高冠是否覺得那個東西unpalatable, 這樣不是很棒嗎? 結果丟了斑蛾給四隻高冠, 四隻看了兩眼, 連試也不試, 就走了, 是因為不餓嗎? NO! 丟蟋蟀下去馬上就被吃掉了, 因此那四隻高冠並不是因為不餓才不吃的啊. 接下來再試一次, 仍然只觀察, 但完全不予理會. 所以使用高冠變色龍做為predation test中的naive predator的夢想破碎.

接下來使用的是日守宮. 日守宮看見斑蛾後會馬上下來咬, 但咬完就放開. 看起來是好的開始. 接下來使用攀蜥也有一樣的效果. 但是馬上再拿給同一隻日守宮再試一次, 牠又咬了一次, 然後又放開沒吃. 這代表什麼呢? 表示這個stimulus的強度不足? 不足以讓日守宮產生警戒? 還是第一次的取食失敗並沒有伴隨明顯的視覺警訊 (那隻斑蛾是羽化失敗的 大多數翅紋沒有顯示)? 或者是日守宮的記憶力不好? 之後我們又試了瑤山鱷蜥, 一樣是咬了後馬上吐出來. 因此日行性的斑蛾對日行性的蜥蜴是unpalatable是確認的. 然而這些蜥蜴是否能夠成為predator test裏的naive predator則需要更多的測試.

[Article: Predation]Predators Make (Temporary) Escape from Coevolutionary Arms Race

Predators Make (Temporary) Escape from Coevolutionary Arms Race

Liza Gross

Citation: Gross L (2008) Predators Make (Temporary) Escape from Coevolutionary Arms Race. PLoS Biol 6(3): e75 doi:10.1371/journal.pbio.0060075

Published: March 11, 2008

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Arguably cute and spanning at most 20 cm from head to tail, the rough-skinned newt packs pretty near the most poisonous punch known to the animal kingdom. Taricha granulosa, like all species in its genus, exudes an exceptionally potent neurotoxin, tetrodotoxin (TTX) from its skin glands. Some Taricha newts could wipe out thousands of mice or a clutch of humans with their toxic issue. But why produce enough poison to kill a potential predator several times over? To discourage the one predator—the common garter snake (Thamnophis sirtalis)—that's resistant enough to the poison to count on newts as a food source.

URL: http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0060075

Phenotypic Mismatches Reveal Escape from Arms-Race Coevolution

Charles T. Hanifin^1¤*, Edmund D. Brodie Jr.¹, Edmund D. Brodie III²

1 Department of Biology, Utah State University, Logan, Utah, United States of America, 2 Department of Biology, University of Virginia, Charlottesville, Virginia, United States of America

Because coevolution takes place across a broad scale of time and space, it is virtually impossible to understand its dynamics and trajectories by studying a single pair of interacting populations at one time. Comparing populations across a range of an interaction, especially for long-lived species, can provide insight into these features of coevolution by sampling across a diverse set of conditions and histories. We used measures of prey traits (tetrodotoxin toxicity in newts) and predator traits (tetrodotoxin resistance of snakes) to assess the degree of phenotypic mismatch across the range of their coevolutionary interaction. Geographic patterns of phenotypic exaggeration were similar in prey and predators, with most phenotypically elevated localities occurring along the central Oregon coast and central California. Contrary to expectations, however, these areas of elevated traits did not coincide with the most intense coevolutionary selection. Measures of functional trait mismatch revealed that over one-third of sampled localities were so mismatched that reciprocal selection could not occur given current trait distributions. Estimates of current locality-specific interaction selection gradients confirmed this interpretation. In every case of mismatch, predators were “ahead” of prey in the arms race; the converse escape of prey was never observed. The emergent pattern suggests a dynamic in which interacting species experience reciprocal selection that drives arms-race escalation of both prey and predator phenotypes at a subset of localities across the interaction. This coadaptation proceeds until the evolution of extreme phenotypes by predators, through genes of large effect, allows snakes to, at least temporarily, escape the arms race.

URL: http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0060060

[Article]Can experienced birds select for Müllerian mimicry?

link: http://tinyurl.com/2m6zlz
Ihalainen, E. et al. 2008. Behav. Ecol. 19: 362-368
Abstract: Field experiments have shown that avian predators in the wild can select for similarity of warning signals in aposematic prey (Müllerian mimicry) because a common signal is better protected than a signal that is novel and rare. The original theory of Müllerian mimicry assumes that the mechanism promoting mimicry is predator learning; by sharing a signal, the comimic species share the mortality that is due to sampling by inexperienced predators. Predation events have not been observed in the wild, and learning experiments with naive bird predators in a laboratory have not unambiguously shown a benefit of a uniform signal compared with different signals. As predators in the field experiments are likely to be more experienced compared with previous laboratory experiments, we studied selection by experienced predators on a novel imperfect mimic. We trained great tits Parus major to avoid artificial aposematic models and subsequently introduced perfect and imperfect mimics at different frequencies. Birds with prior experience on the models selected against the imperfect mimics that were at a disadvantage also in a memory test conducted a week after their introduction. Selection against the imperfect mimics was antiapostatic. However, the imperfect mimics also benefited from some signal generalization to the models and possibly gained protection because the birds were familiar with the alternative cryptic prey that was also present. Our results suggest that experienced predators might be more important to the evolution of mimicry than the learning-based theory assumes.

[Article]Cognitive Dimensions of Predator Responses to Imperfect Mimicry

Link: http://0rz.tw/633Np
Abstract: Many palatable animals, for example hoverflies, deter predators by mimicking well-defended insects such as wasps. However, for human observers, these flies often seem to be little better than caricatures of wasps—their visual appearance and behaviour are easily distinguishable from those which they are attempting to mimic. This imperfect mimicry baffles evolutionary biologists, because one might expect natural selection to do a more thorough job. Here we discuss two types of cognitive processes that might explain why distinguishable mimics could enjoy increased protection from predation. Speed–accuracy tradeoffs in predator decision making might give imperfect mimics sufficient time to escape, and predators under time constraint might avoid time-consuming discriminations between well-defended models and inaccurate edible mimics and instead adopt a “safety first” policy of avoiding insects with similar appearance. Categorisation of prey types by predators could mean that wholly dissimilar mimics may be protected, provided they share some common property with noxious prey. If predators use experience with multiple prey types to learn rules rather than just memorising the appearance of individual prey types, it follows that different individual predators should form different categories, each including separate types of novel prey. Experimental studies to test these hypotheses should be straightforward, because we can use the relatively simple signals (e.g., striped patterns) with which prey manipulate predator behaviour as tools for investigating cognitive processes that underlie decision making and object recognition in animals' daily lives.