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Consider the below phylogeny. taxon1 and 2 are sister taxa but: - share a brown color coat - differ from their closest common ancestor (light color coat)

Is this a case of homoplasy (Analogous trait)?enter image description here

MoBo
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    The definition of a homoplasy is a common characteristic to 2 or more branches, not shared by their common ancestors, so I'd say yeah, this qualifies as a homoplasy. – Joe Healey Aug 09 '17 at 08:18
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    @MoBo If you feel like one of the two answers answered your question, you can click on the check mark next to your favourite answer. – Remi.b Aug 10 '17 at 15:16

2 Answers2

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According to Furtado and Pessoa (2014):

Homology: A similarity due to common ancestry.

Homoplasy: A similarity not due to common ancestry.

And, according to Futuyma (2006):

Homology: Possession by two or more species of a character state derived, with or without modification, from their common ancestor.

Homoplasy: Possession by two or more species of similar or identical character state that has not been derived by both species from their common ancestor

Therefore, the answer is quite clear: the trait here is an homoplasy, since it's not present in the common ancestor of A and B.

PS: Homoplasy and analogy are not, technically speaking, synonyms. Analogy is a special case of homoplasy.

PPS: A clade is just a monophyletic group. For instance, the hominids form a clade, Mammalia is also a clade, Vertebrata is a clade, even Animalia is a clade. Therefore, a clade can be very exclusive or very inclusive. Because of that, I'm skipping the title of the question ("Could homoplasy occur within a clade?"), whose answer is obviously yes1, and focusing only on your second question: "Is this [image] a case of homoplasy?"

PPPS: Furtado is me, and that quote was translated from the original.

Sources:

  • Furtado, G. and Pessoa, F. (2014). Liçoes sobre sete conceitos fundamentais da biologia evolutiva. Brasília: Editora UnB. (translation: On seven fundamental concepts of evolutionary biology)
  • Futuyma, D. (2006). Evolutionary biology. New York: W.H. Freeman.

1For instance, my metamery and the metamery of an earthworm is an example of homoplasy. Both myself and the earthworm belong to a clade called Animalia. Therefore, there is homoplasy within a clade

  • Thank you Gerardo for your ample response and clarification. – MoBo Aug 09 '17 at 14:25
  • I added my own answer just because I wanted to emphasize a little bit on the concept of lineage and on the importance of not seeing a clade as something too atomic but your answer is good +1 – Remi.b Aug 09 '17 at 20:24
  • What exactly is the difference between a homoplasy and an analogy? – Hawkeye Aug 15 '17 at 20:19
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Could homoplasy occur within a clade?

Note that the all of life is a clade! A clade is any mono-phyletic tree. So any homoplasy observed on earth is necessarily within a clade!

Let's replace the term clade by species to further the discussion

Could homoplasy occur within a species?

Wether you consider two lineages as being part of the same species or not changes nothing to the question of whether their shared trait was already present in the common ancestor or not. You can have homoplasy within a species and even within a population. Of course, the lower level you go, the less likely it is to observe a clear case of homoplasy.

It is important not to view a clade (incl. species and subspecies) as something too atomic. As a whole and single clearly defined entity but rather a whole complex tree (or network) of lineages. Any lineage may have evolved a trait that has already evolved independently in another lineage whether the two lineages are very closely related (within the same subspecies) or very distantly related. In this regard, you might want to have a look at this post.

So, yes you can observe homoplasy when comparing lineages within a clade.

Remi.b
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