Tuesday, November 18, 2014

Evolutionary History Of Insects

When the biologist J B S Haldane was asked if anything can be learned about the Creator from studying natural history, he is said to have quipped that "God has an inordinate fondness for beetles". There are about 300,000 species of beetles compared to 10,000 species of birds and about 5,400 species of mammals. Overall, there are about 1 million described species of insects and estimates range from 6 million to 10 million for the total number of living insects species. Insects may represent up to 90% of animal forms on earth.

Now a new genomic study aims at teasing out aspects of their evolutionary history such as the timings of their origin, the timing of winged flight and the timing of major diversification events. This is a big deal. On Science Friday, Michelle Trautwein from the California Academy of Sciences gives a lively presentation of this research. The amount of data used is staggering... a comparison of about 1500 genes. Working out evolutionary relationships and nodes of diversification.. essentially building an insect family tree took months of number crunching on supercomputers. Insects evolved from a lineage of crustaceans, an arthopod group that includes lobsters, crabs and shrimp. Segmented animals seem to be very speciose (propensity to evolve new species), dominating both marine and terrestrial ecosystems.

Here is the summary from the paper-

Insects are the most speciose group of animals, but the phylogenetic relationships of many major lineages remain unresolved. We inferred the phylogeny of insects from 1478 protein-coding genes. Phylogenomic analyses of nucleotide and amino acid sequences, with site-specific nucleotide or domain-specific amino acid substitution models, produced statistically robust and congruent results resolving previously controversial phylogenetic relations hips. We dated the origin of insects to the Early Ordovician [~479 million years ago (Ma)], of insect flight to the Early Devonian (~406 Ma), of major extant lineages to the Mississippian (~345 Ma), and the major diversification of holometabolous insects to the Early Cretaceous. Our phylogenomic study provides a comprehensive reliable scaffold for future comparative analyses of evolutionary innovations among insects.

Holometabolous insects are those that undergo metamorphosis, insect development is made up of 4 stages of egg, larva, pupa and adult.

Those who like to wade into the details check out the image below. I like the footer which places the evolution of different insect groups in the context of major geological events and plant evolution.

The earliest terrestrial vegetation on earth in the mid late Ordovician Period about 450-470 million years ago was mosses and lichen which hugged the ground. Correspondingly, the earliest insects were ground dwelling. As vegetation gained height by the Devonian Period, insects evolved the ability to fly. Co-evolution with plants is the common theme of the insect story of life. And these creatures are old ... old.. consider this that the extant lineages of mammals began diversifying only about 100 million years or so. All the major living groups of insects originated more than 300 million years ago. Sometimes our perspective of animal life on earth is skewed towards too much attention to mammals even though in antiquity and diversity insects do dominate.

Do listen to the talk on Science Friday. 

Thursday, November 6, 2014

Early Chinese History Told Through Maps And Poetry

I am really enjoying Jerry Brotton's A History Of The World In 12 Maps. One richly rewarding chapter is on early Chinese map making traditions and inevitably you end up learning quite a bit of history as well.

The Song dynasty (907- 1276 AD) struggled with keeping the empire unified and intact and faced particularly strong challenges from the Jurchen Jin a confederacy of Tungusic tribes from northern Manchuria. In the middle of the 12th century the Song were forced to sign a peace treaty with the Jurchen Jin ceding to them nearly half their northern territory.

Subsequent imperial maps drawn up by the Song never showed this division. Rather, an idealized geography that the Song kept dreaming of based on earlier classical texts like Yu Gong, that of a unified empire to which foreign barbarian rulers paid tribute was portrayed. Using maps as a tool for political propaganda is an old trick! 

What maps did not depict though, poetic license did.

This beautiful passage from the book:

Poetry describing maps either side of the traumatic division of the Song also captures their power to first acknowledge, and then lament the loss of territory. Writing more than 100 years earlier, the ninth century Tang poet Cao Song describes 'Examining " The Map of Chinese and Non Chinese Territories"':

With a touch of the brush the earth can be shrunk;
Unrolling the map I encounter peace.

The Chinese occupy a prominent position;
Under what constellation do we find the border areas!

On this occasion the almost meditative act of unrolling the map and seeing a unified Chinese dynasty at its center evokes emotions of security and assurance. Later Southern Song poets used a similar conceit, but with very different emotions. Writing in the late twelfth century, the celebrated Lu You (1125-1210) lamented:

I have been around for seventy years, but my heart has 
remained as it was in the beginning, 
Unintentionally I spread the map, and tears come gushing forth.

The map is now an emotive sign of loss and grief, and perhaps a 'template for action', a call to unite what has been lost.