Degraded salt marsh: scientific illustration

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Degraded salt marsh: scientific illustration

A drawing I did that became a figure in a scientific paper published in PLoS One. This is what many salt marshes in Cape Cod look like, and recently, many in Rhode Island. Read more about salt marsh die-off here: http://www.bertnesslab.com/.

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A new paper from the Bertness Lab!

The paper, “Herbivory drives the spread of salt marsh die-off” was published in PLoS One and documents the findings of work in our lab that I helped out with last summer.

Finding a Voice for Non-Human Persons

I wrote a guest post for Ursa Sapiens, the Triple Helix’s blog, about dolphins and other non-human persons! Check it out here: http://ursa.browntth.com/the-blog/finding-a-voice-for-non-human-persons

Now you see me, now you don’t: insect mimicry and crypticity

All living things possess a fundamental drive to avoid being eaten, but there are a plethora of methods by which an organism can achieve this goal.  Insects have evolved various anti-predator mechanisms and behaviors, some of which are more successful than others.  Many insects utilize anti-predator defenses that involve trickery, such as crypticity and mimicry, to avoid notice by predators.  So many insects have evolved these defense mechanisms that one can assume they are highly profitable to the continuation of insect clades or these forms would have been culled out by natural selection.  However, why choose mimicry over crypticity, or vice versa?  There are inherent benefits and downfalls to utilizing one mechanism versus the other, but which is more profitable?  There may not be one right answer, but I argue that crypticity is a more favorable option than mimicry because of the riskiness inherent in the mimic’s utter dependence on the model and because crypticity could be considered more evolutionarily advantageous because of its higher frequency of occurrence in nature.

leaf bug

Both crypticity and mimicry deceive the beholder into believing that the insect is something that it is not.  Crypticity typically involves an insect avoiding detection through colors and patterns and can be visual, olfactory, or auditory (Stevens & Merilaita 2009).  Visual crypticity can include camouflage, disruptive coloration, and background-matching, and can be quite striking.  Crypticity is distinguished from a similar phenomenon, masquerading, in that masquerading involves the matching of specific inanimate object like twigs or rocks rather than matching the general background (Gullan & Cranston 2010).  Olfactory crypticity involves an insect camouflaging its odor in order to blend in to the myriad of odors present in its surroundings.  For example, the death’s head hawk moth mimics the pheromones of bees to enter its hive and steal nectar (Dettner & Liepert).  This is not mimicry because the moth’s aim is to blend in with its surroundings in an anti-predatory defense mechanism to avoid detection.

Mimicry is the similarity of one species to another to the benefit of one or both species. Two types of mimicry include Batesian and Mullerian, although these forms of mimicry should be considered two ends of a spectrum with various forms of mimicry in between.  In Batesian mimicry, the insect is essentially a sheep in a wolf’s clothing in that the mimic (a palatable species) parasitically resembles a model (an unpalatable species) (Balogh et al. 2008).  Mullerian mimics, on the other hand, involve two or more poisonous species that have evolved to mimic each other’s aposematic coloration or warning signals (Balogh et al. 2008).

While both mimicry and crypticity have served insects well, there are advantages and disadvantages for each anti-predation strategy. Mimicry is advantageous in that it is a reliable way to prevent predation in that an animal will normally not try to eat an unpalatable meal.  On the other hand, animals that are not fooled might still eat the mimic and learn the difference between the mimic and the model.  Another advantage of mimicry is that it allows the mimic to move about and avoid predation without having to stay still, as is often the case in camouflage.  Mimicry can also be used as an aggressive rather than defensive strategy; parasitic Phengaris arion (Large Blue butterfly) caterpillars mimic ant predators so as not to be detected by them when they invade the ant nests and eat their larvae and eggs (Witek et al. 2008).  However, mimicry that involves pheromones and aposematic coloration or other warning signals can be costly to the organism (Blount et al. 2008).  Furthermore, if the model species goes extinct, migrates, becomes less toxic, or evolves to look different than the mimic, then the mimic could find itself in a highly unfavorable situation.

flower bug mimics

Crypticity is a more commonly occurring phenomenon among insects than mimicry (according to my general observation and knowledge).  This could indicate that crypticity is a more highly evolutionarily advantageous adaptation than mimicry, simply by comparing the abundances of forms that employ each strategy.  Animals blending into their surroundings will be seen by fewer predators than those that use mimicry, and therefore bypass the problem of having to use costly warning signals or avoiding predators that are not fooled by mimicry.  Although camouflage can only be used in one type of environment, insects are generally found in an environment with a specific background and can adapt to their surrounding if they change, sometimes at fast rates (e.g. the famous industrial melanism of peppered moths described by Cook et al. 2004).  However, cryptic organisms may be cryptic to others of their own species, which could hinder such activities as mating.  This particular disadvantage is bypassed by various other means of communication such as olfaction and audition.

Crypticity and mimicry are both useful mechanisms to avoid predator detection.  However, I argue that crypticity is a more profitable anti-predatory mechanism because it is more abundant and comes with fewer inherent risks.  If I were an insect and I had to perform a cost-benefit analysis, I would exclude mimicry as an option because although it is highly effective for some clades, I would consider crypticity to be more favorable because of its higher frequency of occurrence in nature, and because I would expend too much energy using warning coloration and using a risky mechanism that depends entirely on the model species’ stability, spatial distribution, morphology, and toxicity.

Works Cited 

Balogh, A.C.V., G. Gamberale-Stille & O. Leimar. 2008. Learning and the mimicry spectrum: from quasi-Bates to super-Muller. Animal Behaviour 76:1591-1599.

Blount, J.D., M.P. Speed & G.D. Ruxton. 2008. Warning displays may function as honest signals of toxicity. Proceedings of the Royal Society B 276:871-877.

Cook, L. M., R. L. H. Dennis, and M. Dockery.  2004.  Fitness of insularia morphs of the peppered moth Biston betularia.  Biological Journal of the Linnean Society 82:359-366.

Dettner, K. & C. Liepert.  1994. Chemical Mimicry and Camouflage.  Annual Review of Entomology.  39: 129-154.

Gullan, P.J. & P.S. Cranston.  The Insects.  Ed. 4.  Wiley-Blackwell: UK, 2010.

Stevens, M. & S. Merilaita. 2009. Animal camouflage: current issues and new perspectives. Philosophical Transactions of the Royal Society B 364:423-427.

Witek, M., E. Gliwieska, P. Skorka, P. Nowicki, M. Wantuchi, V. Vrabeck, J. Settele, & M. Woyciechowski.  2008.  Host ant specificity of large blue butterflies Phengaris (Maculinea) (Lepidoptera: Lycaenidae) inhabiting humid grasslands in East-central Europe.  European Journal of Entomology.  105: 871-877.