HOW THE ENVIRONMENT AFFECTS NATURAL SELECTION
The environment makes no conscious effort to select traits of an animal or plant beneficial to itself or the organisms resident in its habitats. If the location is in a suitable part of the range the animal occupies, it can contribute to survival and reproduction of the animal, especially of genetic variants having the genetic features best adapted to the environment. An animal may select the environment, although it may not be a conscious act. Foraging to new areas is less likely to occur when food and housing are abundant so a search does not take the organism to new areas.
Some examples of how the environment passively results in natural selection of animal features you are already familiar with-
the streamlined shape of fish (and birds), tapered at each end so resistance to movement through water (air) is minimized. The obvious exceptions, as in baleen whales, occur when feeding or some other benefit is more important in their lives.
coloration blending with the visual background. Again, exceptions occur when attracting a mate or warning predators of your toxic properties is more beneficial to survival.
fur or feathers aiding temperature regulation at the same time providing physical protection such as abrasion resistance, flotation, and a mechanism for seasonal color change.
appendage modification improving function for climbing (claws), digging, feeding, and locomotion to name a few.
THE LUNG AND BONY SKELETON CONNECTION
A less familiar example, unless you have a background in evolution and marine biology, is the difference between the cartilaginous and modern bony fishes and the role of air breathing fish in the evolution of bony skeletons. Survival of fish in anoxic ponds or ones that temporarily dried up, selected fish having more mouth surface able to extract oxygen from water or air. Ultimately, a pocket becoming the lung of lung fishes, then of amphibians and eventually reptiles, birds, and mammals in one line and from the fishes the early lung was adapted to the air bladder/swim bladder enabling evolution of the modern bony fishes.
It is interesting that the bony fish in the ocean had their origin in fresh water. Sharks and other cartilaginous fish do not have fresh water fish in their ancestry. The flotation provided modern fish by the air bladder offsetting the extra weight produced by bone, as compared to the weight of sea water, is partially provided by oil and/or fat stores for cartilaginous fish for excess of weight of bodies heavier than sea water. Some compensate by continuous swimming providing "lift" from wing-like pectoral fins or body shape.
SUBTERRANEAN AND ABYSSAL SIMILARITIES
The deep sea abyssal region and subterranean aquatic environments have both similarities and differences. The similarities usually include absence of light, stability of temperature, no green plants, low input of food, low predator density, cool temperatures.
In response to those features of the environment there is no selection eliminating loss of vision, pigmentation, and defensive weapons. Slender, elongated appendages provide some adaptation for loss of vision, They may also enable walking on soft, unstable sediment accumulations and sensory input for feeding.
SUBTERRANEAN AND ABYSSAL DIFFERENCES
The abyss
Soft sediments dominate abyssal environments and currents probably cause less erosion and relocation of sediment. Temperature away from thermal vents are slightly above the freezing temperature of water. Invertebrate species present are from major groups first found in sediments from older sediments that were in near shore environments (Jablonski et al., 1983; see references at end of the June 22, 2013 post of this blog).
This trend to migrate to deeper water and newer related groups evolve in shallower sea areas was not documented for abyssal species but seems to be a reasonable projection.
Temperate Zone Caves
Numerous instances of cave dwelling crustaceans were originally lumped into one or a few species with what were thought to be their closest relatives in other caves. Later research showed their closest relatives were in surface waters adjacent to the caves; the rapid adaptation to cave dwelling led to similar loss of pigmentation and vision of less value in showing their evolutionary origin in post-glacial times. This is one example of how rapidly evolution can occur to bring about the loss of characteristics of little use but essential to survival in a different environment.
EXTREME PRESSURE
https://evolutioninsights.blogspot.com/2013/06/evolution-in-deep-sea.html
notes the factors thought to be responsible for slow metabolism and increased longevity in abyssal animals. I speculate that the slight compression of water at great depths decreases molecular mobility and so called Brownian movement noted with oil immersion microscopic viewing of cells and related particles; this could be a major factor in the slow pace of life and evolution in the abyss. I have not searched the literature for related research for many years, One suggestion in an older article about pressure interference with cell activities was the variable rate of compression of organic compounds could stop or reverse the direction of action toward the product most greatly compressed. If so I would think alternative metabolic pathways might evolve, but oh so slowly under abyssal conditions.
It seems to me that it would be simple for a physicist or chemist with access to equipment with extreme pressure to compare the rate of diffusion from a grain of dye, or the rate of sedimentation of fine particles, or both to a range of pressures. ( see blog noted above for reference to Yayanos, Dietz, and Boxtel 1979 study of pressure effects on growth)
My nebulous account of factors enabling understanding of the pogonophoran story is, unfortunately, not easily told in a concise way. The scattered threads that lead to understanding of the story is perhaps inaccessible to many viewing one of the disconnected bits I provide. It took a lifetime for me to see the things I present. I hope others do it more easily and find the trip interesting. If you see what I am attempting to say, I encourage you to point it out to Wikipedia. You will need to include a few scientific journal references noted elsewhere in this blogsite to have any hope of others resisting the urge to expunge the entry as not being in sync with existing views. It is normally good, but preserving the status quo can be a major stumbling block to creativity.
Joseph Engemann Kalamazoo, Michigan March 4, 2019
Showing posts with label temperature. Show all posts
Showing posts with label temperature. Show all posts
Monday, March 4, 2019
Thursday, May 3, 2018
EVOLUTION: OCEAN CIRCULATION
CURRENTS AND DENSITY
Currents of major impact on the ocean are profoundly influenced by density differences due to salinity and temperature differences. The heavier water sinks and the lighter water rises. Surface currents can be wind driven. Gravity and inertia impact currents. At the interface of moving currents, or a current and still water, turbulence and mixing can be induced.
Pure water is most dense at about four degrees centigrade. So progressively warmer water is usual found from near the bottom to near the surface. Salt concentration of the water may make the temperature stratification vary in other ways. For example, Mediterranean Sea water entering the Atlantic Ocean near the Straights of Gibraltar sometimes goes to an intermediate depth based on density level of the ocean of the same density, but with different temperature and salinity.
Most of us are familiar with the affect of the Gulf Stream on climate in Europe, by its movement north along the western Atlantic that veers east and provides milder climates to northern Europe. A similar current affects climates in the north Pacific. While such currents catch our attention, one of greater consequence has had a profound affect on evolution as it has no doubt persisted and survived assaults by asteroids, volcanic disruptions, continental drift, and variations in solar radiation. It involves a cycle of circulation that takes ten thousand or more years to complete - from icy polar water settling to abyssal depths of temperate, sub-tropical, and tropical parts of the ocean where it slowly warms and rises until it ultimately mixes with warmer surface waters and completes the cycle by returning to polar regions via currents and evaporation and precipitation. A pause in polar ice caps can exceed the ten thousand plus year trip from abyss to sea surface.
A PERSISTENT CIRCULATION PATTERN
polar region temperate - sub-tropical regions
The visual above is not to scale but indicates the North Atlantic pattern of circulation from polar regions on the left to tropical regions on the right. Similar but variable profiles would be found in the North Pacific and Southern Ocean region of Atlantic, Pacific, and Indian Oceans. The flows would diminish and seem to disappear as they meet under tropical waters.
S represents the ocean floor or sediment with a sill regulating flow from (the sometimes ice covered) Arctic Ocean water. A rise in sea level, or a subsidence of the sill can allow a greater volume of flow to the abyss of the Atlantic.
C represents the cold salt water of high density that sinks to the depths of the ocean of such great volume that the warming water rises slowly, taking ten thousand or more years to mix with the warmer and less dense overlying water.
M represents the oxygen minimum zone separated from W, the warm surface water, by a thinner mixing zone, the thermocline. The thermocline is identified by rapid change in temperature. A shallow thermocline may result in more light for photosynthesis penetrating beyond the mixing zone so the oxygen minimum will be somewhat deeper. Also, storms may produce sufficient turbulence at depths to make the oxygen minimum zone deeper. The extent of the oxygen minimum zone also responds to organisms living there and bacteria utilizing organic debris settling from the photosynthetic zone near the surface.
W, the warm water is where oxygen is replaced by photosynthesis as well as by diffusion from the atmosphere.
Hurricanes
The thickness of the thermocline is greatly affected by wave action. Calm seas may have a thermocline within a hundred meters of the surface. Hurricanes and storms can produce turbulence to make the thermocline much deeper and provide a thicker zone of warm water and heat storage that may prolong or increase subsequent storms.
The H.M.S. CHALLENGER EXPEDITION
The first major oceanographic expedition occurred from late 1873 to early 1876. One of its many accomplishments was measuring depths, temperatures, and salinity of the oceans. I had examined part of one of the fifty some volumes of its researches published later that century while I was teaching a marine biology class about a hundred years after the voyage. I don't know how many years it took me to realize that the temperature profile that I have crudely illustrated above meant that the presence of oxygen and long residence time of the deep water beneath the thermocline meant either extremely low biological activity or very few organisms.
Subsequent oceanographic work has provided more complete coverage of the oceans and greater precision in measurements without changing the basic importance of the early expedition.
The time factor
Sediment cores show the vast percentage of abyssal sediments accumulate very slowly. That helped me understand the extreme age of some bottom dwelling animals as indicated by their tubes position in sediments. The embedding in sediments was inferred from the rarity of finding their posterior ends in dredge samples, absence of tube rings on a posterior branch of the fork of branched tubes, and funnel-like rings on some species with rims oriented toward the anterior end (the exposed tentacle bearing ends giving rise to the common name, beard worms, of the Pogonophora).
My paper describing the evidence for the beard worms extreme age - Engemann, Joseph G. 1968. Pogonophora: the oldest living animals? Pap.Mich. New York
Currents of major impact on the ocean are profoundly influenced by density differences due to salinity and temperature differences. The heavier water sinks and the lighter water rises. Surface currents can be wind driven. Gravity and inertia impact currents. At the interface of moving currents, or a current and still water, turbulence and mixing can be induced.
Pure water is most dense at about four degrees centigrade. So progressively warmer water is usual found from near the bottom to near the surface. Salt concentration of the water may make the temperature stratification vary in other ways. For example, Mediterranean Sea water entering the Atlantic Ocean near the Straights of Gibraltar sometimes goes to an intermediate depth based on density level of the ocean of the same density, but with different temperature and salinity.
Most of us are familiar with the affect of the Gulf Stream on climate in Europe, by its movement north along the western Atlantic that veers east and provides milder climates to northern Europe. A similar current affects climates in the north Pacific. While such currents catch our attention, one of greater consequence has had a profound affect on evolution as it has no doubt persisted and survived assaults by asteroids, volcanic disruptions, continental drift, and variations in solar radiation. It involves a cycle of circulation that takes ten thousand or more years to complete - from icy polar water settling to abyssal depths of temperate, sub-tropical, and tropical parts of the ocean where it slowly warms and rises until it ultimately mixes with warmer surface waters and completes the cycle by returning to polar regions via currents and evaporation and precipitation. A pause in polar ice caps can exceed the ten thousand plus year trip from abyss to sea surface.
A PERSISTENT CIRCULATION PATTERN
polar region temperate - sub-tropical regions
The visual above is not to scale but indicates the North Atlantic pattern of circulation from polar regions on the left to tropical regions on the right. Similar but variable profiles would be found in the North Pacific and Southern Ocean region of Atlantic, Pacific, and Indian Oceans. The flows would diminish and seem to disappear as they meet under tropical waters.
S represents the ocean floor or sediment with a sill regulating flow from (the sometimes ice covered) Arctic Ocean water. A rise in sea level, or a subsidence of the sill can allow a greater volume of flow to the abyss of the Atlantic.
C represents the cold salt water of high density that sinks to the depths of the ocean of such great volume that the warming water rises slowly, taking ten thousand or more years to mix with the warmer and less dense overlying water.
M represents the oxygen minimum zone separated from W, the warm surface water, by a thinner mixing zone, the thermocline. The thermocline is identified by rapid change in temperature. A shallow thermocline may result in more light for photosynthesis penetrating beyond the mixing zone so the oxygen minimum will be somewhat deeper. Also, storms may produce sufficient turbulence at depths to make the oxygen minimum zone deeper. The extent of the oxygen minimum zone also responds to organisms living there and bacteria utilizing organic debris settling from the photosynthetic zone near the surface.
W, the warm water is where oxygen is replaced by photosynthesis as well as by diffusion from the atmosphere.
Hurricanes
The thickness of the thermocline is greatly affected by wave action. Calm seas may have a thermocline within a hundred meters of the surface. Hurricanes and storms can produce turbulence to make the thermocline much deeper and provide a thicker zone of warm water and heat storage that may prolong or increase subsequent storms.
The H.M.S. CHALLENGER EXPEDITION
The first major oceanographic expedition occurred from late 1873 to early 1876. One of its many accomplishments was measuring depths, temperatures, and salinity of the oceans. I had examined part of one of the fifty some volumes of its researches published later that century while I was teaching a marine biology class about a hundred years after the voyage. I don't know how many years it took me to realize that the temperature profile that I have crudely illustrated above meant that the presence of oxygen and long residence time of the deep water beneath the thermocline meant either extremely low biological activity or very few organisms.
Subsequent oceanographic work has provided more complete coverage of the oceans and greater precision in measurements without changing the basic importance of the early expedition.
The time factor
Sediment cores show the vast percentage of abyssal sediments accumulate very slowly. That helped me understand the extreme age of some bottom dwelling animals as indicated by their tubes position in sediments. The embedding in sediments was inferred from the rarity of finding their posterior ends in dredge samples, absence of tube rings on a posterior branch of the fork of branched tubes, and funnel-like rings on some species with rims oriented toward the anterior end (the exposed tentacle bearing ends giving rise to the common name, beard worms, of the Pogonophora).
My paper describing the evidence for the beard worms extreme age - Engemann, Joseph G. 1968. Pogonophora: the oldest living animals? Pap.
The extreme longevity of deep sea animals is part of a circular argument that suggests the slow replacement of the cold deep water of the ocean, which in return, suggests the extreme age of the organisms there. Fortunately, other evidence is available to augment the invalid circular reasoning. The most dramatic bit was discovery of unspoiled fruit and sandwich on a lunch recovered from the Alvin submersible research vessel many months after it sank to great depth. Several studies involving respiratory rates of deep sea organisms show greatly slowed rates compared to comparable organisms of shallow seas.
Evolutionary implications
Some major implications are discussed in numerous past posts. Two major ones are-
- the error compounded in molecular phylogeny studies (especially establishment of the Ecdysozoa concept), and the unique missing link role that the pogonophorans fulfill.
The permanence of the ocean stratification in tropical through temperate zones has provided stable environments where the extremely slow metabolism resulting from low temperature and immense pressure allowed those that slowly adapted to the abyssal region to survive. The pogonophorans are one of the most significant, but little known, groups. Neopilina is an important indicator of molluscan relationships and their annelid ancestry. Brittle stars are abundant on many areas of the ocean bottom and help us understand the selective pressures giving rise to shallow water relatives. The coelocanth fish was found at intermediate depths but is a living relative of what is otherwise known from fossils.
Will the enormous area and depth protect marine life there from the assault of a constant flow of debris and chemicals we dump from ships, atmospheric contamination and polluted streams?
The permanence of the ocean stratification in tropical through temperate zones has provided stable environments where the extremely slow metabolism resulting from low temperature and immense pressure allowed those that slowly adapted to the abyssal region to survive. The pogonophorans are one of the most significant, but little known, groups. Neopilina is an important indicator of molluscan relationships and their annelid ancestry. Brittle stars are abundant on many areas of the ocean bottom and help us understand the selective pressures giving rise to shallow water relatives. The coelocanth fish was found at intermediate depths but is a living relative of what is otherwise known from fossils.
Will the enormous area and depth protect marine life there from the assault of a constant flow of debris and chemicals we dump from ships, atmospheric contamination and polluted streams?
Joseph G. Engemann Emeritus Professor of Biology, Western Michigan University, Kalamazoo, Michigan May 3, 2018
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