Remarkable mimicry

2017-07-19-15.27.39 ZS PMax

Spider that mimics a frog in our Rio Zunac Reserve. Photo: Lou Jost/EcoMinga.

I’ve been away again, this time gone for almost three weeks with a great group of students from Stanford University led by Dr Margaret (Minx) Fuller. We spent most of our time in the Amazonian lowland rainforest, but I also took them to EcoMinga’s Rio Zunac and Rio Anzu Reserves. Throughout the trip we found amazing examples of mimicry. The most unusual mimic was this spider, which was found by students Dylan Moore and Natalia Espinoza on our Rio Zunac trip. At first they thought it was a frog. It holds its forelegs in a position reminiscent of the hind legs of a frog, and its abdomen mimics a frog head, complete with eyes. I imagine that small birds or insects that would catch a spider might not want to waste energy or risk their lives trying to catch a frog.This spider seems to be related to the famous “bird poop spiders” but I don’t really know. If an arachnologist reads this, perhaps he or she could add some information about this?

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Above and below: Spider that mimics a frog in our Rio Zunac Reserve. Click to enlarge. Photo: Lou Jost/EcoMinga.

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Note added July 26 2017: Andreas Kay in nearby Puyo reports that he has also found this spider twice, and thinks it is in the genus Stephanopis; see his picture here:

https://www.flickr.com/photos/andreaskay/31583234000/in/photolist-Q7UkjN-Q7Uk8f-HpMphQ-HpRUzt-JkQCzc-JkQCbr-HBPABf-HEcfA6-eXy7XX-eXy7Ta-eXKv1S-egc5ed-dmufYw-dmucGX-bVDV1V-bPbYgn-bPbYeX

It is always a pleasure to browse his site, Ecuador Megadiverso.

I found another exquisite mimic in our Rio Anzu Reserve the next day. This leaf-mimic katydid would have passed unnoticed except that when we walked past, it went into its hiding pose and moved its two antennae together so that they appeared as one. That motion caught my attention, but it still took me a minute to see the katydid.

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A leaf-mimic katydid in our Rio Anzu Reserve. Click to enlarge. Photo: Lou Jost/EcoMinga.

The best way to see exotic katydids, grasshoppers, and crickets is to walk in the forest at night. Here are some others we found in the eastern lowlands on this trip.

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Dead-leaf katydid in the Amazon. Click to enlarge. Photo: Lou Jost/EcoMnga.

 

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Grasshopper in the Amazon. Click to enlarge. Photo: Lou Jost/EcoMinga.

 

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Amazonian nymph katydid. Click to enlarge. Photo: Lou Jost/EcoMimnga.

Mimicry is not limited to insects and arachnids, though. Birds can can also disguise themselves. The hardest birds to spot in these forests are the potoos, which look like dead stubs on tree branches. When some species of potoo sense danger, they even lift their heads to point straight up, enhancing the illusion. They sit all day on their chosen perch, and only hunt at night, sallying for large flying insects. The females lay their single egg carefully balanced on the broken-off tip of a branch, and the baby grows up looking just like an extension of the branch.

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Great Potoo. Click to enlarge. Photo: Lou Jost/EcoMinga.

 

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Common Potoo. Click to enlarge. Photo: Lou Jost/EcoMinga.

Thanks for looking,

Lou Jost, EcoMinga Foundation.

Interspecific plumage mimicry in toucans

Mimicry among co-existing toucans: White-throated and Channel-billed Toucans live together in the Amazon and look the same. Chestnut-mandibled and Choco Toucans live together in the lowlands west of the Andes and look the same. Nevertheless, the Chestnut-mandibled Toucan's closest relative is the very dissimilar White-throated Toucan, and the Choco Toucan's closest relative is the very dissimilar Channel-billed Toucan. Modified from Ridgely and Greenfield's Aves del Ecuador.

Mimicry among co-occurring toucans: White-throated and Channel-billed Toucans live together in the Amazon and look the same. Chestnut-mandibled and Choco Toucans live together in the lowlands west of the Andes and look the same. Nevertheless, the Chestnut-mandibled Toucan’s closest relative is the very dissimilar White-throated Toucan, and the Choco Toucan’s closest relative is the very dissimilar Channel-billed Toucan. Modified from Ridgely and Greenfield’s Aves del Ecuador.

Evolutionary biologist Jerry Coyne (author of Why Evolution is True and coauthor of Speciation) kindly posted my photos of the Plate-billed Mountain-Toucan  (Andigena laminirostris) on his website today. Earlier today I wrote a post about the striking similarity of color patterns in the Plate-billed Mountain-Toucan  and the Toucan-Barbet (Semnornis ramphastinus), and  I mentioned this mimicry in the comments on Jerry’s site. Reader Bruce Lyon responded to my comment by reminding me that there are other remarkable examples of plumage mimicry among the toucans.

Co-existing Amazonian toucans: Left, Channel-billed Toucan (a croaker); right, White-throated Toucan (a yelper. Photos from Roger Ahlman.

Co-occurring Amazonian toucans: Left, Channel-billed Toucan, a croaker; right, White-throated Toucan, a yelper. Photos from Roger Ahlman.

For example, here in the lowlands of Amazonian Ecuador two large Ramphastos toucans co-occur, the White-throated Toucan (Ramphastos tucanus) and the Channel-billed Toucan (R. vitellinus). They have very different songs: the larger White-throated Toucan is a “yelper” while the slightly smaller Channel-billed Toucan is a “croaker”. However, both species have virtually identical plumages. If they are not singing it can be very difficult to tell them apart, except by the bill proportions (the Channel-billed Toucan has a smaller bill relative to its head).

Co-existing  Choco lowland toucans: Left, Chestnut-mandibled Toucan, a yelper; right, Choco Toucan, a croaker. Photos from Roger Ahlman.

Co-occurring Choco lowland toucans: Left, Chestnut-mandibled Toucan, a yelper; right, Choco Toucan, a croaker. Photos from Roger Ahlman.

On the other side of the Andes, in the western Choco lowlands, there is another pair of co-occurring Ramphastos toucans: a “yelper”, the Chestnut-mandibled Toucan (R. swainsonii), and a slightly smaller “croaker” Choco Toucan (R. brevis). These also have plumages that are identical to each other, but they are completely different from the plumages of the Channel-billed and White-throated Toucans on the other side of the Andes.

Judging only by their appearances, anyone would think that the identical-looking Chestnut-mandibled and Choco Toucans of the western  lowlands were each other’s closest relatives. Anyone would also think that the White-throated and Channel-billed Toucans of the eastern (i.e Amazonian) lowlands were also each other’s closest relatives, since they are almost identical to each other and very different-looking from the western pair of toucans.

However, bill shape and song link the big western species to the big eastern species, and the smaller western species to the smaller eastern species, in spite of their very different colors. DNA analysis (Weckstein 2005) conclusively proves that bill shape and song, not the birds’ colors, are the phylogenetically informative characters in this case. (One of the most exciting things about DNA analysis is that it teaches taxonomists which morphological characters indicate evolutionary history.) The croakers on each side of the Andes are each other’s closest relatives, and the yelpers on each side of the Andes are each other’s closest relatives. This means the nearly perfect match between plumages of the coexisting species has come about through natural selection rather than inheritance from a common ancestor. There must be a very strong survival advantage to looking as they do, for one or both coexisting species.

Ramphastos toucan phylogeny, from Weckestein (2005), with toucan heads from Ridgely and Greenfield, Aves de Ecuador.

Ramphastos toucan phylogeny, from Weckestein (2005), with toucan heads from Ridgely and Greenfield, Aves de Ecuador.

What could the advantage be? One possibility, proposed especially by Prum (2014), is to reduce interspecific social dominance interactions. If larger toucans drive away smaller species of toucans feeding in the same tree, then it is advantageous for the smaller species to resemble the larger species. This might defuse the larger species’ instinctive aggression against non-conspecifics. An alternative theory relies on the observation that toucans are nest raiders. Most birds fear the largest toucans and do not put up a fight when they raid a nest. Perhaps if the smaller toucan looks like the larger and more fearsome species, other birds will mistake the smaller species for the larger one and flee more often.

Note added July 25: It remains possible that both species in each region have evolved these colors because they are regionally advantageous to both species. However, it is difficult to imagine what regional selective pressures, other than pressure for mimicry, would make the two co-occurring species so precisely similar to each other in each region. In the comments on my last post, in response to a question by Peter Tobias, I suggest some experimental tests of the mimicry hypothesis. End of note.

This kind of near-perfect apparent mimicry is rather rare in birds. It is probably facilitated in this case by the genetic similarity of the species involved. A pattern that is easy to evolve in one member of the pair should also be easy to evolve in the other member of the pair, since their genetic architectures are so similar. Perfection would be harder to achieve in more distantly-related mimicry pairs, like the Plate-billed Mountain-Toucan / Toucan-Barbet pair I wrote about in the previous post.

The Toucan-Barbet (left, photo by Roger Ahlman) and the Plate-billed Mountain-Toucan (right, photo by Lou Jost) occur in the same forests and have  similar plumage colors and patterns.

The Toucan-Barbet (left, photo by Roger Ahlman) and the Plate-billed Mountain-Toucan (right, photo by Lou Jost) occur in the same forests and have similar plumage colors and patterns.

There are other apparent cases of mimicry in Neotropical birds. The Kiskadee-like flycatchers, those nemeses of beginner birdwatchers, are possible examples. However, it can be hard to separate phylogenetic constraints (inherited genetic architecture) from actual mimicry. The toucan case seems nearly ironclad, now that we know their phylogeny. Now that we know are pretty sure mimicry happens in birds, we should be on the lookout for other examples, and I think the Toucan-Barbet case I mentioned in my last post is best interpreted this way.

Prum, R. (2014) Interspecific social dominance mimicry in birds. Zoological J of the Linnean Society 172: 910-941.

Weckstein, J. (2005) Molecular Phylogenetics of the Ramphastos Toucans: Implications for the Evolution of Morphology, Vocalizations, and Coloration.The Auk 122: 1191-1209.

Lou Jost (www.loujost.com)