1a. Two species that possess a homologous trait are frogs and lizards with their forelimbs. Frogs are amphibians that mostly live near moist wetlands while lizards are reptiles that live in more dry regions.
1b. The forelimbs of a frog are used for a multitude of things, but most notably for locomotion (both land and water), balance when standing/sitting and absorbing shock from high impact stress on the body.
The forelimbs of a lizard are used almost strictly for locomotion on land, however, there are other lesser known uses for them such as hunting, scavenging and feeding.
2a. Two species that share an analogous trait are humans and octopi. Both species use eyes for seeing, but both sets of eyes have adapted for completely different environments.
2b. Human eyes are used only for vision. They are adapted mostly for environments where sunlight or some substitute is present. There is a clear periphery where vision gets blurred and blind spots where the eye cannot see due to placement on the human.
Octopus eyes are also only used for vision. However, they are adapted for the deep sea where there is not sunlight. Also different from humans is that they do not have a blind spot, meaning that they can see everything around them.
2c. The common ancestor between these two must have the analogous trait because both of the structures are used for the same thing (vision), however they act different because they are adapted differently to their respective environments.
Good description of the functional differences between the frog and lizard forelimb, but how is that reflected structurally? You have images, but you needed to explain how that anatomy/shape/structure was changed because of its functional differences.
ReplyDeleteWith regard to ancestry, the frog is an amphibian and reptiles like lizards arose from amphibian ancestors. So the common ancestor was an archaic amphibian that possessed this ancestral limb structure and passed it onto these two descendents.
The eye is a wonderful example of an analogous trait, as it has evolved independently numerous times in earth's history.
"The common ancestor between these two must have the analogous trait..."
Really? For traits to be analogous, they need to arise through independent evolution (parallel evolution), NOT through common descent. So the ancestor likely didn't possess this trait, otherwise both octopus eyes and human eyes would have genetic and structural similarities traceable to this common ancestor. That isn't the case. That is why these are analogous and not homologous traits.
Good images.
How interesting that you decided to compare the eye. I found your posting on this to be very good. When thinking of things for my post, it never occurred to me to think about the eye. I had no idea that octopi did not have blind spots! Very interesting, and very true on their different adaptations but similar uses. Good job!
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