Stick insects converge on tree lobsters

[Oolon Colluphid]

Just another nifty thing wot I spotted. (As usual, I've broken the abstract up into digestible chunks.)

Proc Biol Sci. 2009 Mar 22; 276 (1659): 1055-62.

Extreme convergence in stick insect evolution: phylogenetic placement of the Lord Howe Island tree lobster

Buckley, Attanayake and Bradler

The 'tree lobsters' are an enigmatic group of robust, ground-dwelling stick insects (order Phasmatodea) from the subfamily Eurycanthinae, distributed in New Guinea, New Caledonia and associated islands. Its most famous member is the Lord Howe Island stick insect Dryococelus australis (Montrouzier), which was believed to have become extinct but was rediscovered in 2001 and is considered to be one of the rarest insects in the world.

To resolve the evolutionary position of Dryococelus, we constructed a phylogeny from approximately 2.4 kb of mitochondrial and nuclear sequence data from representatives of all major phasmatodean lineages.

Our data placed Dryococelus and the New Caledonian tree lobsters outside the New Guinean Eurycanthinae as members of an unrelated Australasian stick insect clade, the Lanceocercata.

These results suggest a convergent origin of the 'tree lobster' body form. Our reanalysis of tree lobster characters provides additional support for our hypothesis of convergent evolution.

We conclude that the phenotypic traits leading to the traditional classification are convergent adaptations to ground-living behaviour. Our molecular dating analyses indicate an ancient divergence (more than 22 Myr ago) between Dryococelus and its Australian relatives.

Hence, Dryococelus represents a long-standing separate evolutionary lineage within the stick insects and must be regarded as a key taxon to protect with respect to phasmatodean diversity.

The main bugger in question looks like this:

http://upload.wikimedia.org/wikipedia/commons/thumb/8/81/Dryococelus_australis_02_Pengo.jpg/200px-Dryococelus_australis_02_Pengo.jpg

[DMB]

But of course they look similar but are very different genetically because they are the product of separate efforts of Intelligent Design, as any fule kno.

[Calilasseia]

I can see why they were placed in the Eurycanthinae taoxnomically though prior to this work on mtDNA. Because I've handled Eurycantha horrida and Eurycantha calcarata, two large stick insects from Papua New Guinea, which bear considerable morphological resemblance to the above insect. Here's Eurycantha horrida in all its glory (note this is an 8 inch stick insect when fully grown):

http://www.insectgems.com/phasmid/Eurycantha-horrida-female.jpg

as you can see, it bears considerable morphological resemblance to Dryococelus australis.

[RBH]

That's a mean looking bug, I gotta say.

[Calilasseia]

Oh I thought the image I was linking to was a single image of male and female side by side. It transpires that the web page had simply juxtaposed two separate images without a separating border so that the appeared to be a single image.

Here's the male. Take a look at those big spurs on the hindmost limbs. Not only used during mating to ensure a decent hold on the female, but also for defensive purposes, as I found out when I picked up a large male specimen with less than optimum care one day and he gave me a crash course in the use of those spurs for defence. Those things hurt when the male digs them into you, I can tell you.

http://www.insectgems.com/phasmid/Eurycantha-horrida-male.jpg