Information and ideas in evolutionary research & academia.

sessile vs. petiolate submarginal wing cell

1/16/2017

A taxonomic key couplet distinguishes between a sessile wing cell and a petiolate wing cell -- but what does that mean? Look at the crossveins, not the shape of the cell itself.

Wing venation is a critical component of many insect keys. (I was accustomed to the reduced venation of Chalcidoidea but am now in a bee lab, dealing with larger and more venous hymenopterans.)
An anteriorly sessile versus anteriorly petiolate 2nd submarginal cell (2SM or SM2) is a character that is important in some sphecidoid and vespidoid groups. While working through keys and double-checking terminology, it was hard to find online guidance on the sessile/petiolate distinction.
I finally got smart and consulted the book 'Hymenoptera of the World' (Goulet & Huber 1993).

The wing on the left shows 2SM petiolate anteriorly, because it does not touch the marginal cell (M), but is connected to it by a crossvein (like a petiole). The wing on the right is an example of 2SM sessile anteriorly, because 2SM touches M, sharing a common vein.
Image from Hymenoptera of the World.

reference: Goulet, H. & Huber, J.T. (1993) Hymenoptera of the world: An identification guide to families. Agriculture Canada, Ottawa, Canada. [page 190, mutillid key]

1 Comment

Trees of Life

1/4/2017

0 Comments

As a visual history of evolution, Trees of Life (Pietsch 2012) is a captivating book. There are hundreds of figures, lending insight to how organisms' relatedness has been interpreted through the centuries -- from the fanciful hierarchical ladders drawn in the 1500s, to the dichotomous branching trees of today. Shown below are some pre-1900s illustrations.

The first conceptions of relationships of life on earth incorporated non-living things, for instance, stone, fire, and sky. 'The Great Chain of Being' (scalae naturae) is attributed to Aristotle. This figure above is "The Ladder of Ascent and Descent of the Intellect", from 1512. The idea of a ladder plays heavily into the early interpretation of life on earth, progressing from basic, lower beings to higher beings and then perfection, or Deus.

Below, this early diagram (Giseke 1792) shows the 'genealogico-geographical' affinities of plant families, based on the orders of Linnaeus. It is handy that the sizes of the circles give a measure of the number of genera included in each family, and the circles' positions and distances give an indication of the families' similarities.

Pictured to the left is the first evolutionary tree, from Lamarck in 1809. However this tree doesn't strictly adhere to our contemporary drawing of a phylogeny, since there is no root and there are extant groups at internal nodes. At the time, there were other illustrations similar to this one, but the difference was that evolutionary change was central to this tree concept. Lamarck believed in the transmutation of species, where one species could change into another. The ladder framework is retained here, and 'imperfect' animals are shown at the base of the tree (in this case at the top, with two separate groups).

the quinarian approach:

The quinarian system, popular in the early 1800s, is based on the belief that things existed in natural groups of five, at all levels. The objects touching indicate continuity. Left: Macleay 1821. Asterisks represent taxa not yet discovered but that must exist, to fulfill the assumptions of the quntuplet pattern. Right: Kaup 1854. The empty triangles are groups not yet discovered.

a couple of trees from Charles Darwin:

I wanted to include this rodent-marsupial tree figure below from Darwin (1850s) because I smile from reading his question to himself:
"Let dots represent genera ???".

Many people write themselves reminder notes and questions. Personally, I stop after two question marks. But I like how Darwin took it just a bit further.

This figure above is interesting due to the fact that it's Darwin's final tree, less common than the 'I think' from 1837 that we see so often. Darwin's last tree shown here is from 1868 and is a depiction of primate relationships. This is different than many other evolutionary interpretations in that 'Man' (far left branch) is not elevated in status.

reference: Pietsch, T. W. (2012). Trees of life: a visual history of evolution. JHU Press.

0 Comments

sessile vs. petiolate submarginal wing cell

Trees of Life

PhyloBlog

Archives

Categories

Elizabeth A. Murray, PHYLOGENETICS AND EVOLUTION of Hymenoptera

sessile vs. petiolate submarginal wing cell

Trees of Life

PhyloBlog

Archives

Categories

Elizabeth A. Murray, ​PHYLOGENETICS AND EVOLUTION of Hymenoptera

Elizabeth A. Murray, PHYLOGENETICS AND EVOLUTION of Hymenoptera