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.

Tuesday, October 21, 2014

Meteorite Impact May Have Triggered Largest Pulse Of Deccan Basalt Eruptions

What caused the mass extinction 65 million years ago?

a) It was a meteorite impact and the resulting environmental crises.
b) No,  it was the Deccan basalt eruptions and the resulting environmental crises.
c) It was both, the meteorite impact and the eruptions.

The two mechanisms were distinct. One, a calamity from space and the other a gigantic eruption whose cause was from deep within the earth.

Now, it seems they may be more intimately linked. The meteorite impact may have triggered the largest pulse of the Deccan volcanic eruptions. Be careful here. The impact did not initiate Deccan volcanism. That was caused by India rifting away from Madagascar (88 mya) and Seychelles (66 mya). The rifting and an unusually hot mantle underneath resulted in copious amounts of melt being generated in the mantle which found its way to the surface via the great tensional cracks formed when continents separate. The impact though may have resulted in increasing the permeability of the mantle underneath thus making it possible for larger amounts of magma to make its way to the surface.

Abstract- 2014 GSA Annual Meeting, Vancouver:

New constraints on the timing of the Cretaceous-Paleogene (K-Pg) mass extinction and the Chicxulub impact, together with a particularly voluminous and apparently brief eruptive pulse toward the end of the “main-stage” eruptions of the Deccan continental flood basalt province, suggest that these three events may have occurred within less than about a hundred thousand years of each other. Partial melting induced by the Chicxulub event does not provide an energetically-plausible explanation for this coincidence, and both geochronologic and magnetic-polarity data show that Deccan volcanism was underway well before Chicxulub/K-Pg time. However, historical data document that eruptions from existing volcanic systems can be triggered by earthquakes. Seismic modeling of the ground motion due to the Chicxulub impact suggests that the impact could have generated seismic energy densities of order 0.1-1.0 J/m3 throughout the upper ~200 km of the Earth’s mantle, sufficient to trigger volcanic eruptions worldwide based upon comparison with historical examples. Triggering may have been caused by a transient increase in the effective permeability of the existing deep magmatic system beneath the Deccan province, or mantle plume “head.” It is therefore reasonable to hypothesize that the Chicxulub impact might have triggered the enormous Poladpur, Ambenali, and Mahabaleshwar (Wai sub-group) lava flows that account for >70% of the Deccan Traps main-stage eruptions. This hypothesis is consistent with independent stratigraphic, geochronologic, geochemical, and tectonic constraints, which combine to indicate that at approximately Chicxulub/K-Pg time a huge pulse of mantle plume-derived magma passed through the crust with little interaction, and erupted to form the most extensive and voluminous lava flows known on Earth. High-precision radioisotopic dating of the main-phase Deccan flood basalt formations may be able either to confirm or reject this hypothesis, which in turn might help determine whether this singular outburst within the Deccan Traps (and possibly volcanic eruptions worldwide) contributed significantly to the K-Pg extinction.

Elsewhere in a GSA special issue on volcanism, impacts and mass extinctions more evidence that Deccan volcanism had a significant impact on the fauna and flora.

Chronology of the volcanic episodes is improving and pointing to a scenario wherein the volcanism coincided (or was causally connected) to within a hundred thousand years of the Chicxulub impact and overlapped the stratigraphic horizon defined as the Cretaceous -Paleogene boundary. Looks like everyone is going to be partially right on this one.

Multiple causes for the mass extinction.

Tuesday, October 14, 2014

A Small Note On Animal Fossils Before The Cambrian "Explosion"

Every now and then there appears a news story about metazoan fossil findings that expresses great astonishment and surprise that there is NOW... THIS TIME.. new evidence that multicellular animals evolved long before their celebrated preservation in the Chengjiang and Burgess shale Lagerstatte.

But we have known that for a long time.  The Neo-Proterozoic and early Cambrian fossil record is so much better and is improving and paleo-biologists and palaeontologists have recognized in it the gradual increase in complexity of metazoans over a 50-60 million year period before the exceptional preservation windows of Chengjiang and Burgess shale gives us a false impression of a sudden appearance of complex multicellular animals. This artifact has been exploited by creationists who claim that the fossil record actually supports their creation story of a sudden origin, under some intelligent guidance, of complex animals in the Cambrian, summarized in books like Darwin’s Doubt: The Explosive Origin of Animal Life and the Case for Intelligent Design. The best rebuttal I have come across of the creationists many misunderstandings of early animal evolution is this excellent article by Nick Matzke.

Let me just post this invaluable figure below which summarizes the Neo-Protoerozic - Cambrian metazoan fossil record. This is from James Valentine's book On The Origin Of Phyla.  It shows clearly that metazoan complexity and diversity increased gradually over time. Molecular phylogeny which aims to reconstruct the last common ancestor of animals based on genetic similarities and differences also tells us that the origin of multicellular animals goes back at least 600 million years ago, maybe even more, a good 80-100 million years before the evolution of calcium carbonate skeletonization made their existence obvious in early Cambrian. Next time a news item appears that claims that somehow fossil embryos or fossil burrows from the Neo-Proterozoic times are some shocking new finding that will change our understanding of animal evolution - don't believe it.


Source: On The Origin Of Phyla

Thursday, October 2, 2014

How Are Diagenetic Studies Useful In Understanding Sedimentary Basin History

I dusted of my PhD dissertation last week for two reasons. A friend insisted that she wanted to see my research.. and then this paper in the Journal of Sedimentary Research (behind paywall):

Diagenetic Evolution of Selected Parasequences Across A Carbonate Platform: Late Paleozoic, Tengiz Reservoir, Kazakhstan by J. A. D. Dickson and J. A. M. Kenter

The work is eerily similar to what I did for my PhD which was carrying out a detailed study of cementation patterns in Middle and Late Ordovician carbonate parasequences from the southern Appalachians.

Dickson and Kenter use petrographic techniques along with cathodoluminescence to tease apart the cementation sequence and pore space modification of the carbonate rocks. Hydrocarbon reservoir quality depends in part on how reaction of sediment with water either dissolves material to create pore space or precipitates cements to modify pore space. So, understanding the timing of these events in the context of the burial history of the sediment pile on a basin wide scale can help geologists predict reservoir quality.

Ok, so what are Parasequences?