Growing Pains

Mid-semester is always a busy time. The bugs don't care, though, so here's a nice find from last week:

Coral Hairstreak (Satyrium titus), Illinois Beach SP, Lake Co, IL 7/9/2014

This is a Coral Hairstreak, (Satyrium titus). They're quite common around here, and always a welcome sight in July.

Here's what one looked like last month:

Coral Hairstreak (Satyrium titus), Illinois Beach SP, Lake Co, IL 6/14/2014

Everyone knows that caterpillars turn into butterflies, right? (Well, most of them turn into moths, but that's a story for another day.) But what about other insects?

Dragonfly Nymph (order Odonata), College of Lake County, IL, 7/16/2012

Many groups undergo metamorphoses similar to butterflies. This frightening critter is a young dragonfly. (Dragonfly nymphs are very hard to ID to species, I'm afraid.)

Racket-tailed Emerald (Dorocordulia libera), Gander Mt. Forest Preserve,
Lake Co, IL 5/23/2012

And here's an adult, in this case a Racket-tailed Emerald (Dorocordulia libera).

Seaside Grasshopper (Trimerotropis maritima), Illinois Beach SP,
Lake Co, IL 7/21/2013

Here's a Seaside Grasshopper (Trimerotropis maritima). Despite the name, they're quite common in the old sand dunes at Illinois Beach State Park. And here's a young one:

Seaside Grasshopper (Trimerotropis maritima), Illinois Beach SP,
Lake Co, IL 6/12/2014

You can tell it's young by the short, stiff wing pads, compared to the long, mobile wings of the adult. Clearly, though, grasshoppers (like the rest of the order Orthoptera) don't undergo a full metamorphosis. Neither do the true bugs in the order Hemiptera.

So there is variation in metamorphosis in insects. (We don't see it at all in Arachnids - young spiders or scorpions look like tiny versions of their parents.) Any time we see variation across a group, it provides a possible test of evolutionary mechanisms. In this case, Kukalova-Peck discussed the fossil record of insects back in 1978, concluding that metamorphosis had evolved separately in several different lineages. (1) Thirty years later, Belles agreed, arguing that we can trace the more complete, holometabolan lineages through hemimetabolan fossil stages, (2) while still concluding that the story is murky at best.

In 2001, Yang used insect metamorphosis to test the hypothesis that organisms with modular developmental strategies (like metamorphic insects) should show more diversification over time. They found that, indeed, holometabolan lineages showed more diversification than ametabolan or hemimetabolan ones. (3)

(1) Kukalova‐Peck, J. (1978). Origin and evolution of insect wings and their relation to metamorphosis, as documented by the fossil record. Journal of Morphology, 156(1), 53-125.

(2) Belles, X. (2011). Origin and evolution of insect metamorphosis. eLS.

 

(3) Yang, A. S. (2001). Modularity, evolvability, and adaptive radiations: a comparison of the hemi‐and holometabolous insects. Evolution & development, 3(2), 59-72.