Saturday, October 4, 2008

Who Knew?

I’ve been thinking a lot about migrations. Right now we have migrating birds, awhile back we had migrating monarch. Monarch Butterflies have an interesting story. Who knew?

As most prey-species do, these butterflies possess several defensive measures:

  • Color - bright ‘warning’ colors indicate foul or poisonous taste
  • Numbers - they migrate and hibernate in great numbers (up to 10 million butterflies per hectare!)
  • Mass Startle Effect - roosting monarchs, when disturbed, fall from their perches all at once, behavior that seems to confuse and disorient predators and allow escape

  • Defensive Chemical Compounds - known to be both distasteful and toxic to most predators.

Male Monarch Butterfly
Slightly larger and with
more narrow black veining on wings

The chemical compounds are gleaned from the plants both caterpillars and butterflies feed upon and are toxic to vertebrate predators. As caterpillars, monarchs gain cardiac glycosides (Asclepiadaceae (milkweed.)) from the plants they eat.

Female Monarch Butterfly
Somewhat smaller and with
wider black veining on wings

This toxin is passed on from caterpillar to butterfly, and stored primarily in the cuticle (the outer, non-cellular layer of an insect’s exoskeleton), as well as in the abdomen and thorax. However, the toxin lessens with the age of a butterfly. To help with its toxicity, another compound, pyrrolizidine alkaloid, is gained by the butterfly through the flowers it chooses to feed from (Astraea (Euphorbiaceae family)). As a result, most monarchs face little predation from frogs, lizards, mice, and birds.

Mature Monarch Caterpiller
Most toxic form of the Monarch

While there are a few other predators who occasionally eat a monarch butterfly or two, it is primarily just two birds and one mouse that seem to prey extensively on them. The birds are the Black-headed Grosbeak and the Black-backed Oriole. In smaller colonies, predation levels by birds reached as high as 44%.

Male (L) and female (R) Black-headed Grosbeak

The levels of toxins in adult monarchs reflect the levels in their host plants making some monarchs not so bitter-tasting. Some predators have learned to measure the toxins by taste and reject butterflies with high cardiac glycosides contents, eating only the ones with low cardiac glycosides contents. Some predators are able differentiate these lower-toxic parts and consume only the most palatable ones. None have perfected this so well as has the Black-backed Oriole, which will ‘unzip’ a butterfly and eat only the abdomen and thorax. The Black-headed Grosbeak leaves only the wings.

Who knew?

Research:

All photos on this post from Wikipedia


4 comments:

Bosque Bill said...

Add this to your "Who Knew" file:

Although the transformation from caterpillar to butterfly or moth is a dramatic state change, turns out there may be some memory transfer from one stage to the other. This according to researchers at Georgetown University:

"Insects that undergo complete metamorphosis experience enormous changes in both morphology and lifestyle. The current study examines whether larval experience can persist through pupation into adulthood in Lepidoptera, and assesses two possible mechanisms that could underlie such behavior: exposure of emerging adults to chemicals from the larval environment, or associative learning transferred to adulthood via maintenance of intact synaptic connections."

See: Retention of Memory through Metamorphosis: Can a Moth Remember What It Learned As a Caterpillar?.

A report in Scientific Blogging may be a little easier to digest.

Beverly said...

OMG...I already HAVE that one! LOL

I even mentioned it on Julie Zickefoose's blog when she discussed her monarchs (9/25). I believe the testing was actually on moths (and with finger-nail polish of all things)...but same same, huh? I'd said:

"BTW...considering the caterpillar morphs from one creature into another…I find it astounding they can ‘remember’…in fact learn things as a creepy-crawly that they take into flight!

I had always thought life in the chrysalis a kind of primordial soup, but I guess not, if memories and minds remain.

Who knew?"


I left three links, too; but no one even commented! I was so surprised; I found it the information astounding!

I'm so tickled to correspond with you...you are every bit as inquisitive as I am and interested in sharing information, too. I really like that! Thanks a bunch, pal...and keep those great ideas coming!

Beverly

lkw said...

Geez, and I was at a program last week where the 'expert' suggested that monarchs navigated with some sort of magnetic 'memory' -- he wasn't a scientist, but knowledgeable.

It's really quite amazing to think about.

Beverly said...

I have read some, that birds may be doing the same thing! The research is interesting, to say the least!

Thanks for visiting again! :)