Thursday, November 13, 2014

Three polyphenic butterflies

This question mark hasn't given up on summer. (11/2/2014, Mission TX)
In an organism that is seasonally polyphenic, also termed seasonally polymorphic, the same genetic code produces different physical traits in response to environmental conditions. In butterflies this is quite common, and it is often expressed as "summer" and "winter"/"dry season" morphs. Day length and temperature seem to trigger these changes. Butterflies are most sensitive to these seasonal cues while they pupate, and they only get to choose their morph once (see comments).

Some researchers believe that polyphenism evolved as a solution to differing needs for camouflage and thermoregulation in summer vs. winter. Perhaps summer butterflies survive better on fresh green leaves in bright coats, while fall butterflies are more comfortable with darker coloration that allows them to soak up the weak winter sun. Fall butterflies also tend to live much longer-- some late-emergent butterflies hibernate for 9 months before reproducing, instead of the brief flight window and immediate reproduction of their summer kin.

Dainty sulphur. (11/8/14, Palo Pinto Co. TX)
I've encountered at least three polyphenic butterflies in the past couple weeks. Interestingly, these three butterflies couldn't agree on the season. Two were plainly marked for winter, while one insisted on hanging onto summer.

The question mark's dark morph is its summer form. In the winter, the hind wings lighten. Question marks don't typically nectar on flowers-- like the hackberry emperor, they prefer to feed on dung and rotten fruit. That's the reason you see the question mark perched on a log in the picture above- someone had smeared the log with bait. You'll notice s/he shares the perch with flies.

Another pic of the dainty sulphur
For the dainty sulphur, the summer morph is paler with more yellow markings, while the winter morph has a mostly sooty coloration, especially on its hind wings. Dainty sulphurs are the smallest member of their family found in North America.

In white peacocks, the winter morph is larger and whiter than those which emerge in summertime. White peacock males are notable for a behavior that is somewhat unusual in the butterfly family. They defend patches of their larval host plant in hopes of monopolizing any passing females. These harmless insects perch in their small territories and engage rivals in aerial duels. I'm not sure how a 'winner' is determined. Each participant is essentially incapable of harming the other, unless it is by exhaustion.

The seasonally confused question mark looked pretty fresh, not at all like some holdover from longer days and warmer weather. I wonder if he will suffer for his poor judgement? Perhaps he pupated during  a warm snap, confusing his cues. The verdict of the dainty sulphur and white peacock, and the arrival of an arctic front, tend to suggest that cooler weather is here to stay, at least for a little while.

White peacock (11/2/2014, Mission TX)

Wiklund, C., & Tullberg, B. S. (2004). Seasonal polyphenism and leaf mimicry in the comma butterfly. Animal Behaviour68(3), 621-627.

Lederhouse, R. C., Codella, S. G., Grossmueller, D. W., & Maccarone, A. D. (1992). Host plant-based territoriality in the white peacock butterfly, Anartia jatrophae (Lepidoptera: Nymphalidae). Journal of insect behavior5(6), 721-728.

Nylin, S. (2013). Induction of diapause and seasonal morphs in butterflies and other insects: knowns, unknowns and the challenge of integration. Physiological entomology38(2), 96-104.

Karlsson, B., Stjernholm, F., & Wiklund, C. (2008). Test of a developmental trade‐off in a polyphenic butterfly: direct development favours reproductive output. Functional ecology22(1), 121-126.


  1. So just to clear this up in my head -- "polyphenic" is a characteristic of the species, not an individual? I.e., the genes are expressed in an individual. Some butterflies are one form, some another, but an individual would change between them?

    1. Good question! Butterflies only get to choose their morph once- when they are pupating. They can't switch between morphs after they've committed.

    2. I updated the post to incorporate your question. I re-read it and realized it was a little vague. Thanks!