Poison Garden: Poison's In The Air

 

Dark glassy tiger butterfly (Parantica agleoides agleoides)

Great drama is unfolding in my Poison Garden. Here, you are looking at one of the most marvelous plant-animal relationship on Earth. What do you think this butterfly is doing? It is obviously not feeding on a flower, not laying eggs, and certainly not mating either.

 

 

This is a dark glassy tiger butterfly (Parantica agleoides agleoides) and it is sucking the juices out of my showy rattlepod (Crotalaria spectabilis, Fabaceae). If you recall my previous article, the showy rattlepod is deadly poisonous! But this poison is exactly what the butterfly wants, which it deliberately collects for its own good. 

 

Dark glassy tiger sipping at rattlepod.

 

The dark glassy tiger belongs to a group of butterflies we call the Danaids. They are generally very bold and beautiful because they can afford to fly around without being eaten. In fact, their beauty is a show-off of toxicity, we call this phenomenon aposematic colouration. The Latin name Danaid (Danaus) is based on Greek mythology. Danaus were daughters of the king of Argos who were assigned to kill their husbands on their wedding nights! Almost all Danaid butterflies are poisonous because their caterpillars feed exclusively on poisonous plants, and carry forward the plant toxins into butterfly-hood. Canonical examples include the Monarch butterfly and the plain tiger. For a long time scientists thought that Danaids obtained their poison from plants of the dogbane or milkweed family (Apocynaceae), but here's an exception.

 
The dark glassy tiger butterfly does not feed on plants that contain typical dogbane toxins called cardiac glycosides. Instead, it acquires a totally different group of toxin from the showy rattlepod called pyrrolizidine alkaloids. Even more remarkably, male glassy tigers tend to accumulate pyrrolizidine alkaloids more than the females. Scientists later found that the males fashion this toxin as a mating pheromone, which they use to attract females! Could this be a coincident, or a selection of fitness trait? The more poisonous male is a fitter mate? Nobody knows for sure. Many other Danaid butterflies and their females also exhibit pyrrolizidine alkaloid feeding behavior. This lead scientists to believe that it was not the milkweed, but pyrrolizidine alkaloid containing plants that were the ancestral evolutionary host of Danaid butterflies. In this second video, you see another species of Danaid, two crow butterflies (Euploea sp.), which are fighting with a glassy tiger over a rattlepod. And in the third video, we observe a plain tiger exhibiting pyrrolizidine alkaloid accumulating behavior. If you are keen, you would have noticed that the Danaid butterflies tend to flash their wings while feeding on the rattlepod. I am not sure why they exhibit this particular behavior, because they don't do it all that often when feeding on nectar, mating, or laying eggs. I suppose they either do it as an aposematic warning to predators, or to ward off competing individuals? If the latter is true, the butterflies are actually communicating with each other by flapping their wings in a particular way. I don't know! But I hope future entomologists will find out.

 

Crow butterfly (Euploea sp.)

Crow caterpillar chrysalis (Euploea sp.)

 

Despite its relatively dull appearance, the crow butterfly actually has a shinny chrysalis which is golden! However, the golden chrysalis gradually turns dark as the butterfly matures. I'm not sure if this conspicuous golden chrysalis is also a form of aposematic colouration. Perhaps it serves more of a disruptive action, because predators usually won't associate such colour with food. Anyways, that's all for today and next time, we will look at other poisonous beauties that my poison garden hosts.

Main reference: Edgar, J. A.; Boppré, M.; Schneider, D. Experentia. 1979, 35, 1447–1448.