Tuesday, April 15, 2014

Metazoan Embryos From Terminal Neo-Proterozoic Early Cambrian Himalayas

In Current Science Sabhyasachi Shome et al  and in Journal of Geological Society of India V.K Mathur et al report fossilized cellular remains in phosphatic chert sediments from the Krol Group (Terminal Neo-Proterozoic ~ 590 -543 mya) and Tal Group (Early Cambian ~ 540 mya) from the Lesser Himalayan sequences exposed in the Kamlidhar syncline north west of Mussorie. These they interpret as metazoan (multicellular animals) eggs and embryos. The findings are significant because they are some of the earlier known examples of body fossils of animals and will add to our understanding of the timing and nature of early animal evolution.

The Krol Group and the succeeding Tal Group represents sedimentation taking place in shallow to mid shelf environments along a passive continental margin that would in the future after Gondwanaland split up become the northern edge of the Indian continent facing the Tethys ocean.

The stratigraphic sequence is depicted in the image below with the position of the reported metazoan remains marked in red. 


Modified from:  Jiang et al 2003


The Krol Group has been interpreted as representing an evolving carbonate platform that shows a change from an early sloping ramp style geometry to a rimmed shelf to an open flat shelf profile over the course of tens of millions of years. This platform was north north-west facing i.e. the shoreline was to the south and the open deep ocean towards the north. Only the facies representing the shallower environments have been preserved in the study area. The deeper water equivalents are likely to be found in the High Himalayas in what are called the Tethyan Sequence exposed at great heights. The reported embryos are preserved in phosphatic chert lenticular bodies in a sandstone from the lowermost unit of the Krol sedimentary sequence. Younger units also contain evidence of multicellular animal life in the form of Ediacaran biota and sponge spicules.

The Tal Group represents more restricted conditions with algal buildup and lagoonal facies with deposits of phosphatic limestone, black shale and fine sandstone. From the sediments, phosphatized globular to sub-oval metazoan eggs with distinctively ornamented covering and polar lobe forming embryos have been found. They are associated with Small Shelly Fossils, a name given to a diverse array of fossils forms which are probably the dis-articulated remains of organisms like sponges, brachiopods, echinoderms, significant because they represent one of the earliest examples of metazoan biomineralization i.e. the ability to secrete hard skeletons from calcium carbonate.

The picture below from the Krol Group sediments shows a CT scan of the metazoan embryos at a two cell division stage. These have been interpreted as blastomeres representing the blastula stage embryos of animals.


Source: Sabhyasachi Shome et al -2014

And here are some more pictures of interpreted metazoans embryos from an earlier study of the Krol Group.


Source: R. Babu et al 2013 - Open Access- Description - a, Embryo showing cytoplasm, arrow showing air chamber;  b, Embryo showing developmental stage comparable to gastrula, arrow showing multicelled structure; c, Lower enlarged part of (b) (embryo), arrow showing two-layered wall (epidermis and endodermis); d, Embryo, arrow showing cleavages of blastula stage infilling homogenous organic matter (? proteineous in nature); e, Embryo showing cleavages; f, Upper enlarged part of (b) showing multicelled structure;


Some time back a friend asked me whether there is any chance of finding a Burgess Shale like Cambrian fossil bonanza in India. The Burgess Shale fossil locality in the Canadian Rocky Mountains is a Lagerstatte.. which means it represents an event of sudden entombment of the animal and/or plant life. This may be due to a submarine mud and silt flows burying the animal and plant communities in soft sediment leading to a snapshot of life at that particular moment. Rapid burial prevents degradation on the sea floor of organic remains. This means that even details of soft tissue along with hard parts are preserved as impressions on sediment. 

My answer to the question was that in Peninsular India sedimentation stopped by terminal Neo-Proterozoic. There were no Cambrian basins. But along the northern margin of proto-India in a basin which in the future would be deformed and uplifted to become the Himalayas, sedimentation continued in the Paleozoic. Which means Cambrian sediments are present, although I remarked they may be metamorphosed and destroyed. That is not the case however. The Krol and Tal Group do contain a Neo-Proterozoic to Early Cambrian fossil record with Ediacaran biota, sponge spicules and small shelly fossils indicating presence of metazoans. Their deeper water equivalents may be found in the High Himalayas! So, there is always a change of a spectacular fossil find either in or near more familiar places like Mussorie or Nainital where the Krol and Tal Groups are exposed or along the frigid heights of the Himalayan snow giants -for explorers brave enough to venture there.


Thursday, April 10, 2014

Are Himalayan Glaciers Retreating?

Open Access in Current Science- A remote sensing survey of 2018 glaciers across the Himalayan arc for the time period 2001 -2010 was carried out. Change in snout position was compared. The majority of glaciers over the last ten years show stable snout positions. About 12% show retreat and only 0.9% show advancement. Himalayan glaciers are retreating though. Studies that cover larger time periods have shown that studied glaciers have been in retreat over all of the last century with the largest retreats from the mid 1970's to the late 1990's. Glaciers have been naturally shrinking since the last Ice Age ended with few reversals such as the younger Dryas and the Little Ice Age, but the past 100 years or so are of interest to us due to the impact of anthropogenic global warming.

Glacial retreat may have slowed down in the last decade and no doubt given the complex response of ice masses to their situation in a particular topographic setting and temperature changes such variations in rates of change of glacier decay will continue as the earth warms. Besides, as other water experts have pointed out , the big problem with interpreting the true significance of Himalayan glacier behavior is the lack of crucial baseline data for a) the amount of snowfall in the various Himalayan glacial source areas and b) much of the reporting of changes in glaciers present area changes and not changes in volume. The volume of ice corresponds to the volume of water held, so any assessment of damage to north Indian river supply must study volume change of ice as glacial melt contributes substantially to Himalayan river water flow. Furthermore, such data if it does exist and that collected in the future must be made public to be examined by as many experts as needed and not kept secret as has been the case with Himalayan river water data in the past. So, a lot more work in terms of basic data gathering needs to be done. 

In any case such larger scale studies are useful pointers to regional trends and for pinpointing areas deserving more detailed studies.

Abstract:

The Himalayan mountain system to the north of the Indian land mass with arcuate strike of NW–SE for about 2400 km holds one of the largest concentration of glaciers outside the polar regions in its high-altitude regions. Perennial snow and ice-melt from these frozen reservoirs is used in catchments and alluvial plains of the three major Himalayan river systems, i.e. the Indus, Ganga and Brahmaputra for irrigation, hydropower generation, production of bio-resources and fulfilling the domestic water demand. Also, variations in the extent of these glaciers are understood to be a sensitive indicator of climatic variations of the earth system and might have implications on the availability of water resources in the river systems. Therefore, mapping and monitoring of these fresh  water resources is require d for the planning of water resources and understanding the impact of climatic variations. Thus a study has been carried out to find the change in the extent of Himalayan glaciers during the last decade using IRS LISS III images of 2000 /01/02 and 2010/11. Two thousand and eighteen glaciers representing climatically diverse terrains in the Him a-laya were mapped and monitored. It includes glaciers of Karakoram, Himachal, Zanskar, Uttarakhand, Nepal and Sikkim regions. Among these, 1752 glaciers (86.8%) were observed having stable fronts (no change in the snout position and area of ablation zone), 248 (12.3%) exhibited retreat and 18 (0.9%) of them exhibited advancement of snout. The net loss in 10,250.68 sq km area of the 2018 glaciers put together was found to be 20.94 sq km or 0.2% (2.5 % of 20.94 sq km).

Tuesday, April 8, 2014

What Ails Indian Science

A strongly worded article by Mathai Joseph and Andrew Robinson in Nature points the finger at the bureaucratic stranglehold over Indian research institutes.

Some snippets...

The basic problem is that Indian science has for too long been hamstrung by a bureaucratic mentality that values administrative power over scientific achievement. And, to preserve local control, research is still done mostly by small teams working in isolation rather than through collaboration — a key generator of impact.

..Nearly 60% of India's science budget2 is now spent on the CSIR, scientific departments and the Defence Research and Development Organisation (DRDO) — an enormous and impenetrable empire set up in 1958. None of these national institutions has stimulated scientific excellence..

..The problems at the national level are mirrored in institutions. First, scientists are promoted on the basis of years of service, rather than achievement, and once at the top they stay until retirement age; long after, in some cases.

.. limited foreign travel and no travel support for research students, ruling out regular participation in leading conferences and research gatherings.

..the movement of researchers from one institution to another is discouraged, because administrators prefer senior positions to be filled by internal promotion rather than lateral hiring.

and 4 steps for change-

a) empowered funding agency
b) rotation of institutional role and responsibility
c) trans-institute groups (collaboration)
d) more money for State Universities that produce most of the country's PhD's.

..also worth reading is an older  article by Gautam Desiraju which takes a more detailed look on the current state of Indian science education and research.
 
..

Monday, March 31, 2014

Natural Selection And Punctuated Equilibrium

A reader asks-

I am still curious as to the mechanism and speed with which evolution by natural selection itself happened, like was it "punctuated equilibrium" or was it a slow and steady (continuous) mode of evolution, or was it a combination of the two, or some altogether third process. Not many programs discuss this unfortunately..

I left a short answer in a comment. Some additional thoughts:

Well.. Natural Selection and Punctuated Equilibrium are not directly connected with each other. Natural selection along with random genetic drift are mechanisms of evolution. Populations change in their genetic character and morphology due to natural selection or random genetic drift or a combination of the two. Punctuated equilibrium on the other hand refers to the tempo and pattern of morphological change seen in the fossil record and its significance. As was originally proposed by Eldridge and Gould it said that morphological change is concentrated in short bursts during cladogenesis i.e. when a new species buds off from an ancestral species. This change in morphology can be driven via natural selection or drift. So Punctuated Equilibrium says nothing about the primacy of any particular mechanism of evolution. Rather the emphasis is on the observed long periods of statis or little directional change in morphology in a lineage interrupted by geologically rapid bursts of change interpreted to be coupled to cladogenesis.

Gould later retracted somewhat from this position. He accepted the explanation for the pattern of Punctuated Equilibrium put forth by evolutionary biologist Douglas Futuyama which was that change could occur at any time during the life of a species but it is only when a small population gets reproductively isolated from its parent population i.e when the two populations stop exchanging genes that any directional change may get fixed or become permanent enough to show up in the fossil record.

Then there are examples of lineages changing in a slow and steady fashion too.. so can't generalize.. Nature has examples of both.

Regarding why programs don't cover this-its true that television programs have to my knowledge not covered this topic. My sense is programs on evolution and fossils stick to popular topics like the discovery of fossils of recognizable creatures like dinosaurs, the first tetrapods, proto-whales or on dramatic events in the history of life such as mass extinctions. A debate that uses detailed morphometric analysis of creatures like trilobites and foraminifers to reveal the pace of evolution (two organisms used extensively to test for patterns of punctuated equilibrium due to their abundance) may be thought of as too arcane to make for great television.

Having said that punctuated equilibrium got its fair share of attention in the print media and mostly for the wrong reasons for it was widely misinterpreted by the media as some kind of alternative to conventional evolution. The biggest mistakes made were in thinking that punctuated equilibrium means that new species form due to large morphological changes that occur suddenly. The primary authors Eldridge and Gould never advocated this, but the garbled version promoted in popular press made it seem so and large changes meant that some unknown genetic mechanism (macromutations?) may be at work. In reality, some of the demonstrated cases of punctuated equilibrium from trilobites showed that the new species differed only slightly from the ancestral species, nothing that could not be explained by well understood processes in an evolving population. So, an interesting theory that sought to explain patterns of appearances of new species in the fossil record as an example of allopatric speciation and migration became sensationalized as an alternative to "Darwin's theory" of evolution.

Creationists loved it,  palaeontologists banged their heads in frustration and much of the reading public have been confused ever since.

 

Tuesday, March 25, 2014

Neil deGrasse Tyson's Cosmos On Evolution

This past Sunday in India the second episode of Neil deGrasse Tyson's Cosmos was broadcast on National Geographic. The title was "What Molecules Can Do" and it was all about the evolution of life on earth. I quite enjoyed it. .. Just a couple of quibbles.

Dog evolution was showcased as an example of artificial selection which then Dr. Tyson used to argue for the efficacy of natural selection. It was depicted in cartoon form and the dog cartoons though showed quite a modern looking dog barking and scaring a wolf away from a campsite. This was meant to show the very early relationship  between dogs and humans. Early dogs wouldn't have looked as depicted in that frame. Its hard to point to modern dog breeds and find an analogue for the earliest dogs because they have changed so much and so late in their history. Still, a more smaller version of a wolf with a stubbier face would have been a best representative of early dogs, and not the hairier house pet looking one.

Later in the show Dr. Tyson wanting to emphasize that evolution is true says that the the "theory of evolution is a fact". That is a little confusing.  Evolution is a fact. Life has changed over the past 4 billion years and the theory of evolution is a theory that attempts to explain how it happened. There are many theories of evolution. Some like Lamarck's theory rely on organisms responding to environmental stimuli and the inheritance of acquired characters to explain change. Creationists in their garb of Intelligent Design have faith in an unknown intelligence guiding natural processes. Modern evolutionary theory that adds on to Darwin's and Wallace's insights is the most successful one.