MUSCLES AND EVOLUTION

MUSCLES

Muscles are almost the definition of the animal kingdom.  The larger the animal the larger its proportion of muscle.  It is a consequence of the strength of a muscle being proportional to its cross-sectional area which increases in amount with the square of lineal dimensions.  The strength needed to move its mass increases with the cube of the lineal dimensions.  Thus muscles scale up in size with increasing animal size faster than do most animal organs.

Two types of muscle are found in vertebrates and most other advanced groups of animals.  Striated muscle, often referred to as skeletal muscle in vertebrates, is usually the most abundant.  Intestines and blood vessels are the major locations of smooth muscle.  The sliding filaments of actin and myosin are aligned in the fibrils of the muscle fiber so striations are evident, keeping their orientation as they contract or relax and lengthen as the biochemical reactions powering the movement is regulated by control by voluntary nerves.  Smooth muscle is the other type of muscle and is controlled mostly by nerve fibers of the autonomic nervous system.  Smooth muscle is the muscle type responsible for contraction of veins and intestines.  Like skeletal muscle it works only by contracting.

A special type of striated muscle, not associated with the skeleton, is found in the heart and called cardiac muscle.  Cardiac muscle fibers branch and fuse forming a network.  The network probably is needed to prevent blood from separating fibers and pushing through the wall of the heart.  The fibers of cardiac muscle are partitioned at intervals by intercalated disks.  Intercalated disks are also found in some protostome hearts thus providing some evidence supporting the annelid ancestry of advanced protostomes and deuterostomes.

MUSCLE ATTACHMENTS

Bone
Skeletal muscles, which do their work by contracting as do all muscles, have an origin on a bone at one end and an insertion at the other end on an adjacent bone that is moved when the muscle contracts.  To move the bone back to its original position and opposing muscle must contract on the other side of the bones and joint.

Soft tissue
So how do we stick out our tongue.  We do it by contracting other muscles within the tongue oriented in directions other than the length of the tongue in which muscles are relaxing.  If they relax more on one side the tongue will curve more to the other side.

Hydrostatic or hydraulic skeletons
The earthworm provides a good example of this type of skeleton.  Under the cuticle and epidermis, the outer layer of muscle is circular muscle.  The soft tissue and fluid in the coelom is forced by contractions of the circular muscle into lengthening the worm as it gets thinner in the segments containing the contracting muscle.  Interior to the circular muscles are longitudinal muscles that lengthen.  If all the segments lengthen, the worm gets long and thin, the total worm volume remains the same.  Conversely, when the longitudinal muscles contract the worm shortens and gets much thinker, but total volume remains the same.

The leech also is dependent on the muscular system using the transmission of fluid and flexible soft tissue moved by the opposing contractions of outer circular and inner longitudinal muscles.  But the body is flattened by transverse muscles connected to dorsal and ventral surface tissues.  Thus movement involves less lengthening and shortening but more up and down bending to either swim by undulations of the body or move along surfaces my bringing the posterior sucker up close to the attached anterior sucker which is then released as the body straightens its bend to attach it further forward.

The photo above is a cross-section of a portion of a leech showing the thin layer of circular muscles under the cells of the epidermis.  Bundles of longitudinal muscles underlie the circular muscles.  A few transverse muscles are shown as dark tracts, some with lighter connections passing between longitudinal muscle bundles to tissue associated with the circular muscles.  The coelom is mostly filled with soft organs.

Hydras do much the same, but the interior of the hydra is fluid filled and the body has the circular muscle fibrils of the gastrodermal cells inside the longitudinal fibrils of the epidermal cell where the fibrils are in more of a network.  The fibrils of both layers of the layers are in close association with the thin layer of connective tissue separating the two cell layers.

Resolving the evolutionary switch from outer longitudinal to outer circular muscle

It is evident that the cnidarian medusa to planarian flatworm suggested in earlier posts and illustrated in [ http://evolutioninsights.blogspot.com/2015/03/evolution-quiet-pre-cambrian-genes.html ] provides a plausible mechanism for the transition.

I gained some insight into the functioning of hydra's hydrostatic skeleton when I had students study the feeding reaction of hydra.  When a weak solution of glutathione is introduced into the water near a hungry hydra it will start moving its tentacles toward its mouth in the same manner it would do if a small crustacean had been captured by a tentacle.  I was amazed to see that the mouth was wide open.  I was thinking it was impossible for it to maintain its posture if the fluid in the gastrovascular cavity was not prevented from exiting the open mouth.  Examination of hydra sections, in particular the tentacles, showed the gastrodermal cells were very large, almost balloon like, and the cavities in the tentacles were almost non-existent.

It made sense that each gastrodermal cell had a single circular muscle fibril so that contraction would be most directly applied to the cell and not slip between cells.  And the thick gasterodermis near the mouth allowed longitudinal fibers of the epidermis to open the mouth more efficiently.

Although the bloated gastrodermal cells may be a more important part of hydra's hydrostatic skeleton, large anthozoan anemones do utililize the fluid filling the gastrovascular cavity to a much greater extent.  Many have one or two siphonoglyphs which are ciliated grooves of the gastrodermis extending from near the mouth to near the basal disk.  Siphonoglyphs enable the anemone to remain inflated and/or reinflate itself after major contractions reducing size for self-protection.

Nematode muscles and evolution

The muscular system of large nematodes such as Ascaris is unique in that the muscles of the body wall are all longitudinal muscles.  The fibrils are enclosed in cells that are long tapering tubes with the nuclei containing part projecting into the pseudocoel.  From the bulbous part containing the nucleus, a slender tubular extension runs to one of two major nerves extending the length of the worm in dorsal or ventral positions; the synaptic connection to the nerve is made at the nerve by the muscle cell rather than at the muscle as in most organisms.  The muscular pharynx is a characteristic of nematodes important in maintaining fluid volume of the worm enabling its hydrostatic skeleton to function.  The cuticle is strong enough to keep the fluid retained for its function as a skeleton.  As a result, when the muscles of dorsal and ventral halves of the worm alternate contractions, the nematode bends or undulates up and down.

The peculiarity of the muscular system of nematodes and their lack of motile cilia are reason enough to reject the Ecdysozoa as a legitimate phylogenetic group.  The molecular basis for its formation is unsustainable if the evidence presented in [ http://evolutioninsights.blogspot.com/2013/05/science-screw-up-no-1.html  ]  is known.

Joseph G. Engemann     Kalamazoo, Michigan     January 28, 2016

KARYOTYPES, TELOMERES, AND EVOLUTION UPDATE

A BRIEF LITERATURE SEARCH ON THE INTERNET

Despite my disdain for looking for molecular phylogenies that fail to consider generation time when relating phyla, I did a quick look at what was going on in telomere and karyotype contributions to evolutionary knowledge.  There seems to be a lot more research done than I anticipated in http://evolutioninsights.blogspot.com/2016/01/karyotypes-telomeres-and-evolution.html .  The references cited by the reports below could be a start.

Elsa Vera, Bruno Bernardes de Jesus, Miguel Foronda, Juvana M Flores, and Maria A. Blasco had a Cell Press Open Access report in Cell Reports 2, 732-737. Oct. 25, 2012 entitled-
"The Rate of Increase of Short Teleomeres Predicts Longevity in Mammals", included the finding from, I think rodents, that as the telomeres are reduced there is a reduction in longevity.

Jana Fulneckova, Tereza Sevcikova, Jifi Fajkus, Alena Lukesova, Martin Lukes, Cestmin Vicek, F. Franz Lang, Eunsoo Kim, Marek Elies, and Eva Syborova had "A broad phylogenetic survey unveils the diversity and evolution of telomeres in eukaryotes" published in Genome Biology and Evolution, Advance Access published February 9, 2013 dol:10.1093/gbe/cut 019.  The human type nucleotide repeat sequence of a telomere was considered to be TTAGGG.  The same sequence appears to be quite common in mammals but modified and often longer in each telomere of primitive monads and other protists.

"The genome diversity and karyotype evolution of mammals" was reviewed in Molecular cytogenetics.org/content/4/1/22 by Alexander S. Graphodatsky, Vladimir A. Trefonov, and Roscoe Stayor.  It was the one I particularly wanted to look at more closely, but I think I accidentally deleted the download and couldn't find the search terms to get back to it when I Googled it.

Many of the author names had special marks on some of the letters.  I also couldn't read my own handwriting very well, but if you Google anything like it with telomeres, karyotypes, and evolution you may find them and many more.  Its my third week with my new tablet and I still haven't mastered much of it, especially the touch screen.  The "OK GOOGLE" voice command seems to do better than I can with the keyboard entry for a search.

Joe Engemann    Kalamazoo, Michigan    January 18, 2016

KARYOTYPES, TELOMERES, AND EVOLUTION

It happened in Tasmania

Karyotypes are the representations of the chromosomes of cells typically in one plane with the chromosomes spread out and stained so shape is evident and numbers and sizes can be determined.  Ideally, the numbers and the individual chromosomes can be identified by size and silhouette for comparisons that may be useful in determining relationships.

 A photo of Ken Burns helping Dr. Rao collect podocarp materials for his karyotype research.  The remains of the glacier that eroded the tarn shelf is visible behind them on a mountain in central Tasmania.

 A photo showing Mr. Burns sampling in the region with the tarns (glacial pools) on the shelf behind him.

A view from Clemes Tarn on a ridge leading to Mt. Field, Tasmania.  The mountainous region was forested all the way to the ocean at that time in the mid 1950's

Telomeres are repeated terminal groups on the ends of chromosomes.  The early cells in development typically start with the greatest numbers of telomeres.  One from each group is generally removed at each division.  As a result, cells of older individuals have fewer telomeres.

The reduction may be a cause of aging.  When telomeres are gone, there is greater likelihood of the ends a chromosome fusing with another such chromosome.  Such an result could reduce the number of chromosomes so the karyotype of the next generation would have a reduced number of chromosomes but the same number of genes would be transmitted.  Such an event would probably be accompanied by a reduction of spindle fibers to match the number of chromosomes.

Karyotypes are probably best at showing relationships of closely related species.  But like most characteristics showing relationships, they are best used in conjunction with other species defining characteristics.

Considering just the number aspect of  karyotypes, change can occur rapidly.  Related groups sometimes differ by having chromosomes with a variable whole number divisible by the haploid number of the group with the fewest chromosomes.

Karyotype examples 

Animal examples and diploid chromosome numbers  [selected and combined from a table in Wikkipedia]

Chicken – 78;  dog – 78

Horse – 64;  female echidna – 64

Elephant – 56;  house mouse – 40

Gorilla – 48;  chimpanzee – 48

Capuchin monkey – 54;  silkworm – 54

Human – 46;  rhesus monkey – 42

Tiger – 38;  cat – 38

Honey bee – 32;  mosquito – 6
The Tasmanian Devil, a marsupial, was near the bottom with a 14.

The above comparisons are almost meaningless but may illustrate similar numbers do not assure close relationship, nor do different numbers always indicate less relationship.  A few of the same organisms were included in the table comparing protein coding DNA and random DNA between genes with humans in post 98 [ http://evolutioninsights.blogspot.com/2015/03/evolution-god-100-nature-science-0.html  ] and was first presented in [  http://evolutioninsights.blogspot.com/2015/03/evolution-quiet-pre-cambrian-genes.html ].

Mammals have benefited, versus invertebrates, in speed of evolution by having multiple similar genes where invertebrates have only a single gene per family of genes.  It relaxes the selective pressure to get a change right the first time when a gene mutates.

A lame apology

I am uninformed on the details of karyotypes and telomeres, but use the topic as an excuse to include the three pictures from  Tasmania taken in 1956 or 1957 when I accompanied Dr. Sundar Rao on his trip to tarn shelves on Tasmanian mountains to get tissue samples from primitive plants of the Podocarpaceae for their karyotypes.  My minimal knowledge in the area may give me room to ask some possibly creative questions.

Do the telomeres of pogonophorans from abyssal and slope species show significant differences accompanying longevity differences?

Do karyotypes show similarities that might be expected to be evident in transitions of phyla proposed in some classifications better than other classifications accompanying family trees of phyla?

Chromosomal rearrangements would be expected to exhibit greater change in karyotypes than genotypes in evolutionary transitions.

My thanks to the University of Tasmania for making the above picture taking possible.


Joseph G. Engemann     Kalamazoo, Michigan     January 11, 2016

THE MOON: ORIGIN, IMPACT ON US, AND DEMISE

WHY THE MOON?

Two days ago I was watching an episode of How the Universe Works, on the Science Channel.  Its original air date was 8/18/2015.  The title of the episode was "Secret History of the Moon".  There was a considerable amount of new information for me, especially the evidence of much more water, volcanic activity and resulting lava tubes that may possibly be used for establishing self sustaining colonies as a base of more distance space exploration.

It was somewhat oversold for its emphasis on possible dramatic explanations of its origin and ultimate demise taking us with it.  The end involves the expansion of the Sun billions of years from now.  Also, the hypothesis of a twin star of the Sun circling with us in a pattern that will provoke peaks of comets and meteors from the Oort Cloud beyond the known planets to endanger us with a cycle of recurrences every 20 some millions of years, is very speculative.  Such a periodic event would be much more regular than past extinction peaks indicate.

MOON ORIGIN

 It is reasonable that the moon's origin was part of the condensation of the early protoplanetary disk around the Sun and aggregation of particles.  The process would continue with greater efficiency, due to gravity increasing with mass, until the results were established in orbits around the sun as they are today.  Probably there were multiple small moons during an early phase, but the compactness of orbits close to the Sun made them more likely to collide and grow into the single moon the earth has.  The dozens of moons of Jupiter and Saturn and more distant planets shows moon accretion is probably a common process.

My contention that the asteroid belt between Jupiter and Mars seems consistent with the possible collision of two planets producing the fragments of the asteroid belt.  The fragments have been mostly swept from orbits of nearby planets - Jupiter, Mars, Earth and its moon.  This origin is consistent with the outer layers of moon and Earth having the same geology that has, probably erroneously, been considered evidence of the moon resulting from a collision with earth causing the similarity.

THE MOON'S IMPACT ON US AND EVOLUTION

I've heard or read that there is a peak of violent acts resulting in increased emergency room visits during the days around the Full Moon.  The word lunatic gets its origin from the phenomenon.  There is no bad magic about it, probably just an impact of poor sleeping with the greater night-time light.  But the approximate 28 days of the lunar cycle has probably selected the duration found in menstrual cycles.  The cycles of growth some marine mollusks show in their shells can reflect the lunar cycle.  They can also show the daily growth and seasonal growth so we know that near the beginning of the fossil record there were more days in a year before the tidal tug of moon on earth and/or a slowing due to space debris accretion made the days longer, but the year shorter in terms of number of days.

The craters on the moon seem better evidence of asteroid impacts than of volcanoes.  But the side facing us has the clearest evidence of volcanic activity.  The smaller size of the moon, compared to the earth, is consistent with an earlier cooling and lessening of volcanic activity.  The earth's greater size means it would collect more space debris (asteroids etc.) than the moon.  A Pre-Cambrian peak of that type of activity was probably a major selective force during extinction peaks shaping the pogonophoran link as noted in the post [ http://evolutioninsights.blogspot.com/2013/06/evolution_28.html ].

The post [ http://evolutioninsights.blogspot.com/2013/05/asteroid-strikes.html ] was my second post on this blog and enlarges on the comments of the evolutionary impact of asteroids and the deep sea as a refugium enabling the evolutionary events leading to the pogonophoran link of deuterostomes to protostomes.

If you think the collision of two planets causing the asteroid belt is improbable, check the graded spacing of planets and the gap between Mars and Jupiter.

Joseph G. Engemann  Kalamazoo, Michigan    January 7, 2016