That’s no plant

In the last few days, we have delved into the evolution and ecology of several different organismal groups. We have also had some remarkable experiences, including using a crane access system to experience the rainforest at the canopy level and hunting for electric fish in a rainforest river. There have been lots of new animals to see, such as the invasive peacock bass, sloths, butterflies, frogs, and one of my personal favorites, the velvet worm.

Edited Velvet Worm Picture

A velvet worm

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A brightly colored leafhopper

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One of many toads

One of my favorite topics of the last few days was sensory ecology. I am interested in mimickry and camouflage, both in general and in my study system of membracid treehoppers. Membracid treehoppers are amazing little insects that are part of the group Auchenorrhyncha, a suborder of the order Hemiptera which also includes leafhoppers, planthoppers, lanternflies, cicadas, froghoppers, and spittlebugs. Although the insects in this group are morphologically diverse, none are so unusual as the treehoppers. The pronotum of treehoppers, a structure on the dorsal thoracic surface, is common to insects but has been heavily modified in treehoppers to a variety of forms. The function of the pronotum is not well understood, and is something I hope to address in my research, but one hypothesis is that the pronotum serves as camouflage and thus a protection against predators.

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The incredible diversity of the treehopper pronotum (from Prud’homme et al. 2011).

This hypothesis was brought to my mind when I discovered an aggregation of treehoppers near Pipeline Road outside of Gamboa. The camouflage displayed by these insects was incredible. At first glance, the aggregation simply looked like part of the plant, and it was so convincing that I had to inspect the plant very closely to make sure that I was actually seeing insects.

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Perhaps it’s just a plant. 

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These are not plants.

This observation brought several questions to my mind. First, how effective is this display against actual predators? I had a hard time recognizing these insects immediately, and while I was actively looking for them, I don’t have to eat them to survive. Additionally, is the formation pattern of the group on the stem of adaptive significance? To my eyes, which I admit are rather ignorant of plants, the formation seems to match perfectly the pattern one would expect to see on the new growth portion of the plant. Members of the aggregation were clearly lined up with larger members with more prominent pronotol processes near the base and smaller, less ornamented members at the top. Would this pattern vary temporally with light or other environmental conditions? Additionally, how does the aggregation itself become established? Are they brothers and sisters, parents and offspring, a combination, or something else entirely? Are they all benefitting equally from this display, or are there some who are getting more out of it than others? Hopefully, my future research will be able to address some of these questions and contribute to a better understanding of both the biology of membracid treehoppers and sensory ecology.

Prud’homme et al. 2011.Body plan innovation in treehoppers through the evolution of an extra wing-like appendage. Nature. 473:83-86.

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