On page 94, Coyne discusses the idea of convergent evolution, and briefly discusses how convergent evolution is related to common ancestry, speciation, and natural selection. Some examples that Coyne gives of convergent evolution are the white coloration of arctic animals and the similarities of cacti and euphorbs.
Give another example of convergent evolution, discussing what environmental factors and characteristics of lifestyles that could have led to the similar traits.
Also, further expand upon and discuss the relationships between the three portions of the evolutionary theory mentioned above with convergent evolution.
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Another example of convergent evolution would be the superficial similarities between flying squirrels in North America and sugar gliders in Australia. Both mammals have “big eyes, a white belly, and a thin piece of skin stretched between their arms and legs” (http://evolution.berkeley.edu/evolibrary/article/analogy_02). However, flying squirrels are eutherians, or placental mammals, whereas sugar gliders are marsupials.
ReplyDeleteAlthough flying squirrels and sugar gliders look similar, they have different common ancestry. Flying squirrels share a closer common ancestor with other placental mammals, such as raccoons and mice. The different physical appearance of these placental mammals is due to speciation, where the common ancestor diverged into other species (Coyne 94). Likewise, sugar gliders share a closer common ancestor with other marsupials, such as kangaroos and opossums.
Sugar gliders and flying squirrels have analogous features, or traits that evolved independently from different ancestors (Campbell 465). For both species, similar environmental pressures resulted in similar adaptations. Both species use their patagia, the membrane between their arms and legs, to glide from tree to tree. (http://www.absoluteastronomy.com/topics/Flying_squirrel). Natural selection would have favored this trait as it gives the animals an efficient way to gather food and escape from predators. Another analogous trait is the large eyes, which makes it easier for the animals to see at night, when they are more active.
Convergent evolution exhibits the theme of “relationship between structure and function.” Although flying squirrels and sugar gliders evolved from different common ancestors, they share similar structures because they share a similar ecological niche.
We can see another example of convergent evolution in Marsupial moles of Australia and (placental) moles of the Americas. These two organisms are from two different places, and have fundamental differences but have similar traits.
ReplyDeleteTo start with, Coyne discusses the contrast in reproductive systems between the two moles, stating that “all marsupials have pouches and give birth to very undeveloped young, while placentals have placentas that enable young to be born at a more advanced stage,” (92) illustrating that by no means are the moles the same organism fundamentally. However, introduced to similar selective pressures, both groups of moles by the means of natural selection have evolved similarly to deal with these pressures. For example, burrowing behaviors in both marsupial moles and placental moles are very similar. Both have a similar “streamlined body shape, and modified forelimbs for digging,” (http://www.pbs.org/wgbh/evolution/library/01/4/pdf/l_014_02.pdf) to help an underground lifestyle focused on insect-searches for food. Additionally, both types of moles have velvety fur that natural selection has favored in both groups because it allows for smooth movement through the soil. (PBS)
Going back to the other part of Sam’s question, the three parts of evolutionary theory that relate to convergent evolution can be seen in the placental mole vs. marsupial mole example. Marsupial moles and placental moles respectively share a common ancestor, and this accounts for certain traits or features shared by and seen in all marsupial moles (for example, Coyne brings up the fact that all females have two vaginas and a double uterus) and different traits that all placental moles share (like a long-lasting placenta). Speciation comes in when this common ancestor “gives rise to many different descendants,” (94) leading to the creation of different species. Natural selection is what causes the actual phenomena we call convergent evolution, because when the moles’ environments show similar selective pressures that the moles have to deal with, both groups will evolve similarly since they are dealing with similar things (like the velvet fur, since both groups want to move smoothly through the soil).
To Jamie’s point, convergent evolution does in fact relate to the theme of relationship between structure and function, because both groups of moles (and more generally two groups that show convergent evolution) will develop similar traits and structures (like forelimbs) for similar functions (digging) even though their ancestors and origins are different, because of similar situations.
Another theme that would relate to BOTH Jaime’s and Radhe’s example would be science as a process. Scientists first gathered empirical data that two separate species living in two different geographical locations had similar structures that performed similar functions. Afterwards, the scientists found that they live in similar niches, which, they hypothesize, caused these two organisms to separately evolve. Then, after obtaining more examples as data, the scientists find that these data show that two separate species (which implies different geographical region) that live in similar niches have a high chance of having similar structures. Finally, the scientists drew their conclusion that these species coevolved, a theory that supports evolution. Q.E.D.
ReplyDeleteGive another example of convergent evolution, discussing what environmental factors and characteristics of lifestyles that could have led to the similar traits.
Also, further expand upon and discuss the relationships between the three portions of the evolutionary theory mentioned above with convergent evolution.
An example that is not mentioned in the book is the development of somewhat similar vascular systems in cephalopods and mammals. We have learned in class that cephalopods are the most evolved class of Phylum Mollusca, with a less evolved Class Bivalvia. Class Bivalvia has an open circulatory system because bivalves, such as clams, don’t move that much.
However, cephalopods are active predators that need a closed circulatory system, a circulatory system that has blood vessels. These predators need to move fast in the water to eat fish and survive. The circulatory system of cephalopods is similar to those of mammals, also having closed circulatory systems. Mammals such as tigers and lions are also active predators. These predators need the advantage of the closed circulatory system to capture and kill prey, just like cephalopods. Though cephalopods and mammals are totally different kinds of animals, these animals “experience similar selection pressures from their environment, so they may evolve similar adaptations” (94).
ancestry
Though there are profound morphological changes between cephalopods and other classes of mollusks, one could see similar characteristics such as the chitinous beak (found in squids and octopi) and the chitinous valves (found in clams). A scientists could see how these links show how these species are related, and how evolution has changed these species to different organisms.
Likewise, the mammalian closed circulatory system probably evolved all the way from chordates, which had open circulatory systems (Vassar). The leap to a closed circulatory system was established along later lines of evolution, and we have studied it as a class in fish such as chondrichthyans, which have a closed circulatory system with only one circuit. This closed circulatory system was modified over years of evolution, establishing the double circuit closed circulatory system that mammals have.
speciation
Speciation definitely happened along the evolutionary line, especially since cephalopods and mammals live in totally different geographic regions (one marine, one terrestrial). There are a huge diversity of cephalopods such as the blue ringed octopus, Humboldt squid as well as many mammals such as humans, jaguars, and tigers.
natural selection
To summarize, natural selection has narrowed down the many variety of different structures and functions that had been created through mutations into the circulatory system that could efficiently channel blood through the organism’s bodies. Both cephalopods and mammals show extraordinary life forms that are able to survive and reproduce with their useful circulatory system.
The theme structure and function is an active role in how well the closed circulatory system works. Since it is structured by vessels to bring only oxygenated blood to organs, this allows high efficiency when it comes to capturing prey, performing its function of bringing oxygen to organs.
Yet another example of convergent evolution is the convergent evolution of elephant shrews and true shrews. Elephant shrews were originally named shrews due to the elephant shrew's resemblance to shrews. However, genetic data indicates that elephant shrews diverged from the evolutionary path long ago and are more closely related to aardvarks and even elephants than they are to true shews. (http://evolution.berkeley.edu/evolibrary/news/080301_elephantshrew)
ReplyDeleteElephant shrews and true shrews did share a common ancestor far back in evolutionary history, when shrews and elephant shrews diverged from marsupials. However, elephant shrews and true shrews speciated long ago, and are as related to each other as the manatee is related to felines. However, similar environmental stresses caused natural selection to cause shrews and elephant shrews to evolve similar traits under convergent evolution.
Convergent evolution relates to interdependence in nature in that the convergent phenotype is a product of both environmental conditions and the organisms genes. True shrews and elephant shrews convergently evolved because true shrews and elephant shrews experienced similar environmental conditions and carried genes that could mutate into a similar phenotype in response.