Monday, August 27, 2018

Appearances Can Be Deceiving

Right now I am primed to question appearances.  Partly to blame is the gripping political thriller Secret City in which no one, well, almost no one, is what he or she initially appears to be.  This Australian TV series (I recently binge-watched it on Netflix) raises the specter of a Chinese mole in the highest echelons of the Australian Government.  There’s a whiff of the Manchurian Candidate here.

The more I’ve thought about it, that questioning attitude about appearance is a fairly useful attitude to take toward nature in general where deceptive appearances, deliberate or otherwise, aren’t at all unusual.  This post is about three examples from this summer.

The first example, shown below, appears each summer in July near my summer cottage in a relatively unproductive and mostly untended flowerbed which lies in the shade cast by several oaks and hickories.

This is the Indian pipe (Monotropa uniflora), always a startling discovery in dim woodland light – pale white, waxy, and, in a strange way, softly ill-defined.  These particular specimens stand about 12 cm high.  In keeping with the theme of this post, it is, of course, not a fungus as it appears, and was long thought, to be.  This is a plant, a clever parasite, duping actual fungi that have a symbiotic relationship with tree roots into giving up their tree-derived nutrients.  As a result, the Indian pipe survives without chlorophyll altogether.  A very neat trick.  (A delightful essay by naturalist Dave Taft about the Indian pipe appeared in the New York Times this summer.)

Then there’s this recent visitor to one of my butterfly bushes.

Though this creature hovers and darts like a hummingbird, sips nectar like a hummingbird, sports colors reminiscent of a hummingbird, and even whirs like a hummingbird – it’s not.  Rather, it’s a widespread, diurnal moth – the hummingbird moth (genus Hemaris, this is probably H. thysbe)  (A good overview of this insect is available from the U.S. Forest Service.)

I speculate that this elaborate evolutionary mimicry is intended, in part, to deceive the usual moth predators.  Among others falling for this charade are many gardeners, myself included.

My third instance of appearances in nature belying reality is somewhat of a complex cheat.  Pictured below is a monarch butterfly (Danaus plexippus) I spotted a couple of days ago just down the street.

This monarch (a female it would appear) is just one of the countless I’ve seen in the Washington, D.C. area and on Long Island, New York, this summer.  It’s almost been so many that a sighting has become commonplace, no longer meriting comment . . . well, almost.  I still sound like an annoying public service announcement on an endless loop – “Attention everyone:  There goes a MONARCH.”

Now, the monarch is the subject of one of the classic examples of mimicry in nature.  The viceroy butterfly (Limenitis archippus), seen below, looks at first like a monarch.  (This image is from Wikimedia Commons (licensed under Creative Commons Attribution-Share Alike 3.0 Unported license), and posted by Lokai.  I have no picture of my own to post because I've never seen a live viceroy.)

But this act of mimicry is, itself, deception on several levels, raising the question of which species is mimicking which species.  Many years ago I was told that the viceroy evolved to appear similar to the monarch to capitalize on the fact that birds avoid the monarch because they find it noxious, stemming from the monarch's exclusive diet of milkweed as a caterpillar.  Turns out that’s probably wrong.  The viceroy is also distasteful to birds perhaps due to its diet of willow leaves or some capacity to generate its own toxins.  So this example of mimicry, once considered Batesian (the harmless copying the harmful), is now considered by many to be Müllerian – that is, both species evolving to resemble each other, thereby reinforcing their negative reputation among predators.  There’s another neat wrinkle to this story for the viceroy because the queen butterfly (Danaus gilippus), which appears a bit like the other two species and is also somewhat toxic, lives in regions where the viceroy and queen butterflies overlap, but the monarch is missing.  (There’s a nice overview of the viceroy, including its mimicry, posted by the “BugLady” at the University of Wisconsin, Milwaukee Field Station website.  See, also, Butterflies and Bad Taste by Tim Walker which appeared in Science News, June 1, 1991.)

Finally, back to the other monarch-related question of looks potentially being deceiving, that is, the apparent abundance of monarchs this summer in the northeast.  Should this give hope that the overwintering count in Mexico will rebound from the depressed level of last winter, or is this illusory?  To see, I checked in with the monarch status reports issued by biologist Chip Taylor who directs Monarch Watch.  Certainly, it’s too early to know whether the surfeit of monarchs here means good things in Mexico this coming winter, but the signs are good.

In the report issued July 24, 2018, Taylor begins with some cautionary words about the difficulty of estimating the scope of the monarch migration and the number of hectares (this is a metric measure of area; 1 hectare is approximately 2.47 acres) the butterflies will occupy in Mexico this winter.  The extent of overwintering coverage is a benchmark for the continued viability of the transcontinental migration in which these particular monarchs engage.

Taylor’s prediction for the northeast is that it will be “another good season, although not as good as last year.”  That’s a bit puzzling, since, at least in the areas where I’ve been in recent weeks in the northeast, there’s been a flood of monarchs, vastly more than I spotted last year.  Perhaps these aren’t the important areas in the northeast for the migration.  He also estimates that the monarch per hour counts at Cape May this fall will not match last year “but will still be well above the long-term average.”  With regard to the upper midwest, a critical part of the monarch flyway, Taylor’s estimation is quite rosy (though, he does caution that he greatly overestimated the production in this area last year).  Anyway, at least as of late July, Taylor feels there is a “real possibility that the overwintering population could hit 5 hectares once again” (that would be the largest area covered since 2008).

Taylor's assessment appears to be borne out in the news coming from the Journey North website whose founder, biologist Elizabeth Howard, reported on August 23, 2018, that the migration season is "off to an impressive start" with "overnight roosts" (where many monarchs gather to roost on their journey south) appearing earlier than usual and in large numbers.

In this case, I hope appearances are not deceiving.

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