EVOLUTION: The Eureka Moment

The “eureka!” moment, when I saw the Pogonophora as the significant link of the two main divisions of higher animals, can be credited to the stimulation of reading Gans and Northcutt, 1983. 

Gans, Carl, and R. Glenn Northcutt.  1983.  Neural crest and the origin of vertebrates: a new head.  Science, 220:268-274. 

They placed the pogonophorans in line with the vertebrates based on development.  I was sure the evidence was overwhelming that pogonophorans were close to, or one of, the annelids.  But I also realized most scientists are honorable and truthful in their work and deserve to be taken seriously.  But how could Gans & Northcutt be right when the overwhelming evidence indicated pogonophorans were close to annelids and other protostomes?  Somehow, in an instant, I realized it could be true if pogonophorans were a connecting link.  A deluge of such evidence came to mind.  And, as I followed new, as well as some older, molecular and other evidence the connection became well supported. 

Engemann, Joseph G.  1968.  Pogonophora: the oldest living animals?  Pap. Mich. Acad. Sci., Arts, and Letters, 53:105-108.

Engemann, J. G.  1983.  Coelomate animals are monophyletic.  American Zoologist, 23(4):1008. Abstract # 753.  The Pogonophora have characteristics of both protostomes and deuterostomes and provide support for the annelid theory of origin of deuterostomes.

Understanding the extreme age of individual pogonophorans, suggested in the 1968 report above, was a result of preparing a new section on pogonophorans for the 1968 edition of Hegner and Engemann’s Invertebrate Zoology text.  It was reprinted in chapter 14 of the 1981 edition (Engemann and Hegner) which discussed the evidence making it very likely deep-sea animals typically have very extended lives and low respiratory rates.  My 1983 abstract noted above was reported shortly after Gans and Northcutt triggered my conclusion with their evidence. 

A full report of the paper was submitted to Nature.  The reviewers did not reject the paper but the editor decided not to publish it because it was not of wide enough interest.  I had given it a title suggesting pogonophorans were the protostome-deuterostome link.  He was not moved by my suggestion that a catchier title would have been “my ancestors were worms”.

Of course, there is a whole sequence of organisms from protozoans through sponges, jellyfish, flatworms, fish, amphibians, reptiles, insectivores, primates and closer relatives in our direct lineage.  But we don’t have direct ancestry through either nematodes, mollusks, arthropods, echinoderms, or many other groups.  If people squirm to think some ape-like primate was in our evolutionary ancestry, how much more appropriate to squirm for a worm.

What about extreme longevity of pogonophorans?

It helps explain their slow evolutioary rate, and thus, their close molecular relationship to diverse groups of animals.

What is so important about abyssal life of pogonophorans?

The slow pace of life at great depths, due to great pressure, low food and oxygen input to the depths, paucity of life, probable absorption of fossil nutrients from sediments, and isolation from many surface extinction factors makes them living "fossil" ancestors. [Note: really old people may live to see great, great, great grand-children]

What has pressure to do with it?

It has not been demonstrated but it is obvious that reduced diffusion based metabolism is probably the missing factor in reduced community respiration noted at great depths.  I await someone making observations of reduced Brownian movement and/or diffusion of dyes at great depths.  It may be a factor in extended submersion time for deep-diving whales.  Water is ever so slightly compressed at great pressures- it may be the cause.

Could circulatory systems increase activity and decease longevity at great depths?

Perhaps.  But whales presumably shut down some less essential portions of theirs.

What about the great difference in early embryology of the groups alleged to be connected by the pogonoporans?

That has been discussed in other posts.  Also, observation of isopod development in Tasmania and Michigan gives some clues to different rates of development associated with ecological factors.  Abyssal life put a species survival premium on shifting from protostome to deuterostome development.

Joseph G. Engemann    Emeritus Professor of Biology,  Western Michigan University, Kalamazoo, Michigan      December 14, 2017

EVOLUTION: OFFBEAT IDEAS

Evolution: Offbeat Observations

Georg Lichtenberg said “It is impossible to carry the torch of truth through a crowd without singeing someone’s beard”, according to James Geary (2005, The World in a Phrase, Bloombury Publishing, New York, 229 pp.).  It somewhat comforts me as I write about the multiple errors earnest and intelligent researchers of evolution have made, errors I am trying to replace with a more accurate depiction of the tree of life.

One, of the two worst research reports establishing a faulty superphylum, Ecdysozoa, had a lady as the primary author; it made me realize the sexist nature of the aphorism quoted above.  I also do not know if the gentleman first author of the publication setting up the other faulty superphylum, Lophotrochozoa, had a beard to be singed.

The most influential zoologist of the last hundred years could well be Libbie Hyman.  See http://evolutioninsights.blogspot.com/2015/03/abandoned-theories-and-libbie-hyman.html  She deserves the respect given her, mistakes in her work are minimal, and I also do not want to detract from other work by the two authors whose work is criticized in http://evolutioninsights.blogspot.com/2013/05/science-screw-up-no-1.html , after all, “to err is human”.  I guess that proves I am human too.

When offbeat becomes main-stream evolution

Three of the last four blog posts have had bits about the abyssal ocean.  There are several facts about the abyss that can help us understand major consequences for evolution shaping life today in unappreciated but interconnected ways.

One, the stability of the abyssal region offered refuge from numerous early extinction events.

The extreme pressure, lack of light for photosynthesis, low input of surface debris reaching the abyss, near-freezing temperature, and sparse populations were ecological factors leading to the long-life, low reproductive rates, and emphasis on survival adaptations characteristic of K-selected life styles.  They contrast to r-selected life styles of organisms where abundant food and high predation lead to short lives, high reproductive rates, rapid growth, and perhaps higher evolutionary rates of most organisms in lighted, warmer surface habitats.

Two, the abyssal affects on embryology and metabolic rates

The low reproductive potential in the deep sea put such a high priority on survival that it selected for delayed specification of embryonic fate of cells so loss of a cell from an early embryo would not prevent normal development.  This led the transition from protostomes to deuterostomes that have the ability to have an early embryo divide and produce two individuals instead of dying like a protostome embryo would.  Pogonophorans are at the junction where this happened and they have a mix of protostome and deuterostome features.

As I have noted elsewhere, the extreme pressure is probably a factor slowing metabolic rates and extending life-spans in the abyss.  Several studies have shown respiration is slowed greatly beyond what colder temperatures alone would depress rates.  One of the most enlightening clues was that a brown bag lunch contained a sandwich and an apple, that sank to the ocean bottom many months before they were retrieved with the sunken research vessel, Alvin, and were both in fresh condition.  Similar food in cold seawater decayed within a few days.

The ocean layer and circulation patterns described in a recent blog show that oxygen levels below the oxygen minimum layer would be impossible to exist if respiratory rates at abyssal pressures were anywhere near rates normal in shallow water below the photic zone.

Three, it’s a bit complicated, 

but the things above help show the role of the pogonophorans as an intermediate that also accounts for some features of our development and structure that were first accounted for by the annelid theory of chordate origin, an abandoned theory that is correct when adjusted for the role of the pogonophorans.

Joseph Engemann    Emeritus Professor of Biology, Western Michigan University, Kalamazoo, Michigan    September 30, 2017

DINOSAUR EXTINCTION

DINOSAUR EXTINCTION

A quick Google search confirmed my impression that the dinosaurs became extinct about 65,000,000 years ago at the end of the Cretaceous.  An exception was indicated by referring to the extinction as not including non-avian dinosaurs.  That distinction was made to satisfy scientists who have determined that bird’s ancestral reptilian roots was most likely in a specialized line of dinosaur-like ancestors.  It seems to me that it is unnecessary to continually repeat that connection in discussing non-phylogenetic issues.

Birds are sufficiently different from dinosaurs that they deserve their independency as a group.  Feather’s, no teeth, and homeothermy (maintaining a temperature independent of environmental temperature) may be avian characteristics that had a role in the survival of birds, but that is another topic.

THE MAJOR CAUSE, AN ASTEROID STRIKE

Multiple causes may have operated in making dinosaurs unable to survive the asteroid strike(s) that produced world-wide evidence of the disaster in the geological record found in sediments.  Several other major geological periods ended with similar disruptions, all also associated with the extinction of a large percentage of previously existing species.

In the several billion years of the earth’s existence earth has grown by the impact of space debris of varying sizes as indicated by the assortment of craters on the moon and other planets   Such bombardment was so intense in pre-Cambrian times that animals left a very skimpy fossil record, partially because large fossil forming animals seldom evolved or survived.

The abyss as a refuge during extinction events

The one place that had relatively stable conditions during extinction events was the abyssal region of the oceans.  There, any animals that could survive on the nutrients deposited in sediments had a better chance of survival in some location because most of the earth was covered with deep oceans.  The deep-water pogonophorans were one of the survivors.  The oxygenated region was so extensive and so slow to be replenished by polar surface waters that much of the fauna adapted to the region persisted to the present.  Those abyssal conditions made low metabolic rates and extended life cycles contribute to a very slow, almost absent, evolutionary rate for animals living there. (see 2015/05 listed at end of this post)

BEYOND THE ASTEROID IMPACT ZONE

Direct hits by the asteroid, its fragments, debris blasted from the impact zone did not even have to kill a single dinosaur.  But the world-wide atmospheric debris may have persisted for a year or more and made it difficult for significant plant growth of the type needed by large herbivores.  Carnivorous dinosaurs like T. rex would miss their normal food after large herbivores starved.  Continents isolated by oceans and partitioned by deserts or mountain rages would have made it difficult for the large dinosaurs to escape the drastic climatic shifts temporarily making their existing range uninhabitable.

POSSIBLE SECONDARY CAUSES OF DINOSAUR EXTINCTION

Pre-strike population declines or increases may have contributed to the death of many species.  Such declines may have been in the dinosaur species and/or other groups important in their food chains and are not limited to food organisms but could include microscopic disease organisms, parasites, and competitors of various types.  

The complexity of population changes resulting from decline or increase of one species is difficult to predict with certainty.  The decrease in one species may result in survival of more of those they prey upon and fewer of those feeding upon them. The changes can ripple up and down the food, predator, and parasite chains existing in the ecological community.  Add to these changes each of the physical changes produced by each species and the variability of possible community changes becomes astronomical.  If the vast number of buffalos grazing on our prairies had not been replaced by cattle, sheep, and farmers plowing- would much of it reverted to forest or scrubby vegetation providing homes for a different group of animals and plants?  Such changes had far reaching effects including soil erosion, flooding, less retention of water and less rainfall; all changes having additional effects on climate and life.

The cooling accompanying the atmospheric debris which reduced light energy and it warming effect makes a possible sufficient cause for extinction of many dinosaur species by shifting sex ratios of eggs hatching to all of one sex.  It is known that alligators and some other reptiles deposit large numbers of eggs in holes that they dig in the ground.  The holes are then covered over and the deeper the egg in the ground the cooler the temperature it experiences during embryonic development.  Higher temperatures induce one sex, cooler temperatures induce the other sex.  If cooler temperatures make all become the sex normally found in the deeper part of the nest, all will be of one sex.  It is not known if the phenomenon is the cause of alligators being restricted to warmer latitudes.

Cooler temperatures would make animals other than birds and mammals become inactive and unable to respond to egg predation or even being eaten by smaller animals with feather or fur insulation and higher metabolic rates maintaining body temperatures needed for activity.  The immense size of dinosaurs made them less susceptible to short term cold temperatures because it takes days for the largest to cool down, but the asteroid caused global cooling would persist so long it might have been sufficient to cause their demise, even those many other causes may have speeded the process of extinction.

Joseph Engemann     Kalamazoo, Michigan     October 20, 2016

http://evolutioninsights.blogspot.com/2014/03/science-extinctions-and-evolution.html

http://evolutioninsights.blogspot.com/2015/05/abyssal-ocean-environment-and-extreme.html 

ABYSSAL OCEAN ENVIRONMENT AND EXTREME AGE

THE WORLD'S OLDEST ANIMAL

In my post of June 13, 2014 I noted some evidence that pogonophorans can easily live to be over 10,000 years old.  A brief discussion of factors leading to extreme longevity in the deep sea was presented earlier in a post on June 22, 2013.  The importance of the pogonophorans as an over-looked link connecting chordates to annelid ancestors makes it important to understand deep-sea conditions better in order to understand the reality of that relationship.

OXYGEN, SALINITY, TEMPERATURE AND DEPTH OF THE OCEANS

My first clue to understanding the problem preceded my understanding of the pogonophorans.  When teaching a marine biology class in my early years at Western Michigan University I was examining one of the fifty volumes of Challenger Reports of deep-sea research done in the 1870's.  A map or graphs included distribution of oxygen, salinity and temperature by depth and latitude.

An oxygen minimum zone, with little or no oxygen, was centered at about 500 meters depth in temperate, sub-tropical, and tropical latitudes.  In contrast to eutrophic fresh-water lakes where the oxygen rich zone is seldom more than ten meters thick, the oceanic counterpart may be over 100 meters thick.  Oxygen was most abundant at the surface, but, after a brief, rapid increase below the oxygen minimum zone, gradually increased with depth below 1000 meters until, at the bottom a few miles lower, oxygen concentration was almost comparable to surface concentrations.

Temperature decreases with depth, salinity increases with depth.  The change is most rapid near the surface and very gradual with increasing depth.

THE MAIN CIRCULATION FACTOR

Density of ocean water increases with depth until about 2000 meters depth due to greater salinity and lower temperature.  So away from the polar regions bottom water is slowly rising with replacement from cold, salty, oxygen-rich water sinking along the bottom from polar regions at a relatively slow rate because of entrapment in the Arctic Ocean by shallower sea bottoms near most of its fringe.

The replacement of the sea-water beneath the oxygen-minimum zone takes over 10,000 years.  The rate can vary according to overall ocean levels and depth of sills where Arctic Ocean water spills over to sink and eventually reach topical latitudes.

THE CONSEQUENCE OF SLOW REPLACEMENT

Oxygen would be depleted and the deep ocean would be an anoxic wasteland if animals lived at the same rate they do in shallower waters.  Photosynthetic production of oxygen is limited to the first 100 meters or so of the ocean.  Enrichment from the atmosphere is the only other significant source of oxygen in the ocean and is limited to the surface and circulation by mostly wave induced surface currents.  The warmer surface and rain combine to lower density of water and make wave induced circulation ineffective below the thermocline (the zone of rapid drop in temperature).

AN ASIDE ABOUT HURRICANE SEVERITY

The thickness and depth of the thermocline can vary within the 50 to 300 meter depths of ocean water.  Presumably a very intense hurricane induced wave episode could mix the ocean to a greater depth and compress the thermocline.  That could perhaps store excess heat for a few years and reduce surface water temperatures so they have less heat energy to produce another mammoth hurricane for a few years.  So the complications of predicting global warming rates is increased.

OTHER FACTORS

The ocean is generally more productive, with nutrients and organisms abundant, in shallow regions fringing continents, and in areas of up-welling currents which bring colder nutrient rich water to the surface.  Sedimentation rates are generally very slow beyond the continental shelves.  Most of the open ocean can be thought of as biological desert, but some very small organisms may be more abundant than others that are better known.  More recent research indicates the small organisms may be more important than generally is known.

THAT OLDEST ANIMAL AGAIN

As long as its descendants stay in abyssal waters they will remain to help remind us of the stage that survived extinction episodes and enabled those moving to shallow water to adapt again to shorter lives and greater variety that includes the chordates.  The previous post has a figure that shows one of the annelid-like features of the pogonophora and their similarity to near chordate relatives, the hemichordates.

Molecular clocks fail to place pogonophorans in the correct position in the "tree of life".  The problem is addressed in the February 2, 2015 post; a better guess at the correct position is in the post
   http://evolutioninsights.blogspot.com/2014/12/our-evolutionary-lineage.html
and why the molecular clock estimates of phylogeny of phyla is wrong in the post
   http://evolutioninsights.blogspot.com/2013/05/science-screw-up-no-1.html

Inspiration for understanding evolutionary aspect of the embryological differences between protostomes and deuterostomes was presented in six posts from June 22, 2013 to June 30, 2013.

A MAJOR POINT OF THIS POST

The long residence time of bottom water of the ocean would make it anoxic if animals lived at the same rate we see occurring in shallow water.  The alternative explanation would be extremely low populations and/or biomass in the abyss.  Life is less abundant, but not nearly enough to account for the difference.  The stability of conditions made it an ideal refugium to allow survival of forms that could later repopulate surface waters after an extinction event bad enough to cause the demise of over 90 percent of living species.


Joseph G. Engemann   Emeritus Professor of Biology, Western Michigan University     May 17, 2015