EVOLUTION: NEMATODE WORMS

Nematode worms are typically long, round, unsegmented, gradually tapered at both ends.

"Nematodes have many species with relatively little difference in body form.  Many are parasitic and it is thought that most species of vertebrates may have one or more parasitic nematode species unique to them.  Nematodes parasitize many other groups of animals and plants.  Many live in the intestines of animals.  One free-living nematode species lives in organic rich soil but can also live as a parasite in humans. Rotting organic matter in soil is not so different from the intestinal contents of some animals.  Both are rich in bacteria that the nematodes can feed upon.  Adapting to the rich soil made them somewhat "pre-adapted" to life as an intestinal parasite. This adaptation included an ability to live in environments with oxygen so limited many other animals could not survive." (from my unpublished 2010 manscript)

The similarity of structure of different species disappears when the mouth end, and often the anal end, are examined microscopically.  Three jaws are present in some.  The pharanyx may have a muscular bulb that probably helps ingestion of food without losing pressure, the body contents act as a hydrostatic skeleton.  The cuticular covering of the body is molted or shed typically several times in early development.  During the process of development portions of the chromosomal material can be ejected from the chromosomes; this is perhaps a result of selection for the small size of ancestors living among the sand grains of soils. In one species the ejection of chromatin occurs in all cells except the stem cell until the 32 cell stage.  Body cells of many achelminths other than nematodes also seem to have the loss of ability to regenerate that is thought to be a result of the reduced chromosomal material in body cell nuclei (or nuclei when tissues are syncytial).  Near constant number of nuclei or cells of the species are present in the tissues of many aschelminths.

I was reviewing some of Libbie Hyman's work on Aschelminthes (not accepted as a valid cluster by many zoologists), but unfortunately she did not have the benefit of knowing about gnathostomulids (first described in 1956) which were later.  Gnathostomulids seem to be descendents of the simple early flatworms that are not flat, but are adapted to living in sediments that are often anoxic.  Reidel, 1969, suggests the gnathostomulids can be placed in either the Platyhelminthes or the Aschelminthes.  The gastrotrichs may be the connecting link to rotifers.  Nematodes may have been the termination of a line orginating early in the cluster of achelminth groups; but they have a complete lack of cilia, a fact that makes them unlikely to have given rise to any other groups since arthropods also lack cilia but are so clearly derived from annelids that do have cilia.  Thus the lack of cilia in nematodes and arthropods is an analagous, not homologous, trait.

The reason I referred to Hyman was to find out about the adhesive glands or pedal glands, commonly paired on most ashelminths' posteriors, but absent in the gnathostomulids.  The glands are very small and difficult to see, especially in nematodes.  I did not see them in some nematodes I had watched in water on a microscope slide at low magnification, but those nematodes were clearly adhering by their tail as the writhed around.  One researcher (Chitwood) divided nematodes into two groups depending on whether they had phasmids at their posterior.  The mouth area and anal areas of nematodes show great variation in microcopic details not conducive to casual observation.

Such fine details can be a great help in identifying species and often show revealing variation suitable for showing evolutionary relationships.  The October 20, 2017, issue of Science has a research report detailing such a fact with feather-like hairs on water-strider feet.  In the case of water-striders, the details are limited to very close relatives.  In arthropods, similar microscopic comparisons can be made of structures limited to closely related species of the same genus and sometimes of different orders.

When the very small and the very large features match, relationship seems more likely.  To determine evolutionary relationships, neither can be ignored.  Over-dependence on one may lead to error and demonstrate why the novice or student may see things the specialist or teacher does not see, a relationship affecting creativity as noted by Tinbergen.

Among the larger features distinctive for nematodes, that show them as a terminal group in an evolutionary sense, are the muscle cells of the body of the intestinal parasite, Ascaris.  All are longitudinal and each passes a muscle cell process to the nerve enervating the muscle.  Other lines of evidence that the Ecdysozoa are an invalid group are indicated by some of the references appended.

Ascaris can grow to a foot long during it time in the intestine.  It has a simple life cycle with transmission of eggs, typically ingested with fecal contaminated food, hatching in the intestine and larve going through tissue and blood to the lungs where they break out and get coughed up, swallowed, and then comlete their life in the intestine.  Another nematode parasite of humans is thought to be the fiery serpent mentioned by Moses.  It has a big name, Dracunculus medinensis, and is known as the guinea worm.  The adult female can be as much as a meter long and live in the subcutaneous tissue under the skin.  The larvae are discharged through a hole in the skin and, if ingested by an aquatic microcrustacean named Cyclops, complete their larval development and, if Cyclops is ingested by a human, eventually reach their location under the skin.

The great variations in size, number of host species needed to complete life cycles, and adaption to a single or limited number of final hosts of most vertebrates, as well as many invertebrates, seems to indicate an ancient origin for nematodes.

Joseph G. Engemann    Emeritus Professor of Biology, Western Michigan University, Kalamazoo, Michigan   October 30, 2017

REFERENCES (comments added)

Aguinaldo, Anna Marie A., James M. Turbeville, Lawrence S. Linford, Maria C. Rivera, James R. Garey, Rudolf A. Raff, and James A. Lake.  1997.  Evidence for a clade of nematodes, arthropods and other moulting animals.  Nature, 387:489-493. Unfortunately, textbooks have picked up their grouping of nematodes with arthropods and some other molting animals in a group they named Ecdysozoa; based on 18s ribosomal DNA sequences, it is inadequate to support such a group.  They even say “It was unexpected to find nematodes contained within the Ecdysozoa because in previous molecular studies they diverged deep in the protostome tree, even before the deuterostome-protostome bifurcation.”   -page 491 has discussion of unequal rates found in other nematode studies (documented and ignored) and their search for and choice of slowly evolving representatives [almost guaranteed to put an outgroup in where it doesn’t belong]

Fraser, Hunter B., Aaron E. Hirsh, Lars M. Steinmetz, Curt Sharfe, and Marcus W. Feldman.  2002.  Evolutionary rate in the protein interaction network.  Science, 296:750-752.  (26 Apr 2002)  “We show that the connectivity of well-conserved proteins in the network is negatively correlated with their rate of evolution.”  “interacting proteins evolve at similar rates.” - used “putatively orthologous sequences between Saccharomyces cerevisiae and the nematode Caenorhabditis elegans.” 

Halanych, Kenneth M.  1996.  Testing hypotheses of chaetognath origins: long branches revealed by 18S ribosomal DNA.  Syst. Biol., 45(223-246.   Well-done study but long branches and small sample size make result of relationships beyond the nematode-chaetognath affinity somewhat dubious.

Halanych, Kenneth M., John D. Bacheller, Anna Marie A. Aguinaldo, Stephanie M. Liva, David M. Hillis, and James A. Lake.  1995.  Evidence from 18S ribosomal DNA that the lophophorates are protostome animals.  Science, 267:1641-1643.  “we propose the node-based name (16)[K. de Queiroz and J. Gauthier, Syst. Zool. 39, 307 (1990)] Lophotrochozoa, which is defined as the last common ancestor of the three traditional lophorate taxa, the mollusks, and the annelids, and all of the descendants of that common ancestor.”  Note 10 includes the following statement “Regions that could not be readily aligned were excluded from the analyses.”  Their proposal is ridiculous when all data are considered.

Halanych, Kenneth M., and Yale Passamaneck.  2001.  A brief review of metazoan phylogeny and future prospects in Hox-research.  Amer. Zool., 41:629-639.  maintain Hox gene research supports the earlier ridiculous proposals of ecdysozoans and lophotrochozoans.  Has numerous references.

Hobert, Oliver, and Gary Ruvkun.  1998.  A common theme for LIM homeobox gene function across phylogeny?  Biol. Bull., 195:377-380.  neurogenesis regulatory genes and transcription factors are very similar in vertebrates, insects, and nematodes

Hobmayer, Bert, Fabian Rentzsch, Kerstin Kuhn, Christoph M. Happel, Christoph Cramer von Laue, Petra Snyder, Ute Rothbackerm, & Thomas W. Holstein.  2000.  WNT signaling molecules act in axis formation in the diploblastic metazoan Hydra.  Nature, 407:186-189.  the WNT signaling pathway had been found in nematodes, insects and vertebrates.

Kappen, Claudia.  2000.  Analysis of a complete homeobox gene repertoire: implications for the evolution of diversity.  Proc. Natl. Acad. Sci. USA, 97:4481-4486.  used the nematode, C. elegans

Sarnat, Harvey B.  1984.  Muscle histochemistry of the planarian Dugesia tigrina (Turbellaria: Tricladida): implications in the evolution of muscle.  Trans. Am. Microsc. Soc., 103(3):284-294.  Says striated muscle is in every metazoan phylum except Porifera and adult Platyhelminthes. (oblique striations in nematodes – Rosenbuth 1965, 67  Wright 62) 

Van Auken, Kimberly, Daniel C. Weaver, Lois G. Edgar, and William B. Wood.  2000.  Caenorhabditis elegans embryonic axial patterning requires two recently discovered posterior-group Hox genes.  Proc. Natl. Acad. Sci. USA, 97:4499-4503.  “essential embryonic patterning in C. elegans requires only Hox genes of the anterior and posterior paralog groups, raising interesting questions about evolution of the medial-group genes.” Three Hox genes in the nematode

LUTHER THEN AND NOW

Today's paper

A Washington Post article by Jonathan Kay, “Nobody Listened to Luther at first. That’s why he succeeded”, published in the Kalamazoo Gazette October 29, 2017, deserves reading to see an example of how momentous ideas develop.  Some similar circumstances surrounded Darwin’s ideas about natural selection.

Non-conformists may face problems

Today such factors as rapid communication and professional networks can, Kay writes, “make us more cautious, since we know that any new idea can expose us to instant censure from complete strangers in other parts of the world………. – This phenomenon goes by different names – group think, political correctness, herd mentality.  But in every form, it serves the interest of the orthodox and frustrates the heretic.” 

I sometimes feel like I am a group of one in terms of my findings.  I don’t expect to be in a group with Luther or Darwin, but I am not aware of much acceptance of what I thought were my best ideas about evolution.  I do appreciate the fact that my post about the coelom has received so many views.

An early post of mine-  http://evolutioninsights.blogspot.com/2014/02/creativity-brainstorming.html  has had zero page views. The post makes suggestions for solitary brainstorming that can substitute to some degree for the benefits of group brainstorming.

Nematodes

I have begun a draft of a post on nematodes.  It is hoped to be helpful in understanding the antiquity of their origin, far before the time the erroneous Ecdysozoa implies.  I was reviewing some of Libbie Hyman’s invertebrate volumes and will leave most related comments to the forthcoming post.  But the last two paragraphs of the post http://evolutioninsights.blogspot.com/2015/03/abandoned-theories-and-libbie-hyman.html  said some of the things I might have repeated.

Christian Unity

Today, about the 500^th anniversary of the event most associate with Luther’s long campaign, there is a mood that seems to have developed in recent years, of Protestants recognizing that Catholics have gotten past such blemishes as selling indulgences and killing heretics, and of Catholics thinking that Protestants have selectively departed from teachings of Jesus.  There is recognition of a common bond for many on both sides of the former divide; and if it has not been there before, that all humans are created by, and loved by, God.

Joseph Engemann      Kalamazoo, Michigan   October 29, 2017

The Economy

The blog post, “History Repeating”, that I posted in April of 2016 was copied from a journal entry I wrote in 2009.  It seems like history is still repeating in the economy, the political world, and perhaps other ways.  It seems like it is worth reading for those in the USA. 

If you want to read it you can get there by clicking the arrowhead before 2006, then April, then History Repeating.  I think you can also get there by clicking

https://www.evolutioninsights.blogspot.com/2016/04/history-repeating.html

Don’t let it depress you too much – repeating can be better than destroying.  It might be better to call it a cycle, or a day, year, or generation.  It can even make you happy when it is children or grandchildren.

If you apply natural selection theory to economic or political theory it might result in beneficial change.  It doesn't need to be as destructive as revolutionary change that people see in what Marx accomplished.  Gradual change is most likely to be both beneficial and successful.

Joe Engemann     Kalamazoo, Michigan    10/23/17

EVOLUTION: MAINSTREAM IDEAS

UPDATING MAINSTREAM IDEAS

About a half-century ago I was confused by the distinction between Darwinism and Neo-Darwinism.  The "Neo" prefix had been added to designate the discoveries of Darwin enhanced by understanding of hereditary or genetic principles clarifying the principles of natural selection.  Such proliferation of terms helps the specialists introducing them but brings confusion to the generalists.

Discovery of details of pogonophoran biology provides near certainty that the abandoned annelid theory of chordate ancestry was actually correct when modified as done in numerous posts on this evolutioninsights blog.  The separation of the chordate line from protostomes via the polychaete - pogonophora - hemichordate - chephalochordaate sequence has sufficient evidence to justify abandoning the old idea that the deuterostome departure from protostomes was near the flatworm level.

Updating the annelid theory

First, the original abandonment of the annelid theory on embryological grounds was dismissed by the drastic differences between protostome and deuterostome development.  This blog (June 24, 2013 etc.) is the only source showing a plausible reason for the change via the pogonophorans.

Second, the current popular distortion of animal phyla relationships is based on faulty research described in this site's blog of May 31, 2013.  The post on Evolution: Molecular Clocks on November 25, 2014 contains numerous citations to research showing the great variations possible in studies based on molecular clocks.

Third, the input from ecological and structural studies shows the simplicity of inversion of systems to deuterostome chordates from protostome annelids via tube-dwelling polychaetes noted in Evolution of systems inversion posted June 28, 2013.  Several other June 2013 posts should also be viewed.

Fourth, the post on EVOLUTION AND THE OLDEST ANIMAL, June 13, 2014, should be a great help understanding the unique evolutionary position of the pogonophorans and their position as a very important connecting link between the two major lines of higher animals.

Updating the Tree of Life

The June 30 2013 and subsequent posts to August 3, 2013 have information about the linking of mainstream invertebrate groups as well as arthropods and mollusks.  There are many important subgroups of sponges, cnidarians, and flatworms in the mainstream.  Interesting sideshoots include ctenophores, rotifers, nematodes.  The protonemerteans are a hypothetical descendent of flatworms preceding the polychaete annelids; they represent the most uncertain guess for continuity in the protozoan to people ancestral tree.  Arthropods and mollusks probably have separate origins from polychaete annelids.

Branches from uncertain places in the tree of life include lophophrates such as bryozoans and brachiopods, and echinoderms; they may be near the pogonophorans in origin.  Chaetognathan origins are uncertain, as are the origins of a number of unsegmented worms.


Joseph Engemann, Emeritus Professor of Biology, Western Michigan University, Kalamazoo, Michigan       October 20, 2017