Question

1. Homology refers to the presence of a feature in two taxonomic groups due to shared common ancestry – that is, the evolutionary origin of the feature in a common ancestor of the two taxa. Homoplasy, on the other hand, refers to the opposite situation – the presence of similar features due to independent convergent or parallel evolution in two groups.

   1. Describe three features that we discussed in class that are homoplastic (i.e., they have arisen independently in at least two different plant lineages). What are these features, why are they significant, and which groups share them via homoplasy?

   2. If we use these observations to pose the hypothesis that plants are more prone to homoplasy than animals, what differences in the biology of plants and animals might explain higher levels of homoplasy in plants?

Answer 1

Homoplay is the result of convergent evolution for same function but are not derived from common evolutionary lineage. Convergence was defined by Edward Wiley as “the development of similar characters from different pre-existing characters.”

These characters evolve independently in different taxonomic group which have no close evolutionary link to each other. Homoplastic characters are mostly evolved as adaptation to the environment and these are not present in their common ancestors. Eg.

1. Fins and streamline body is evolved in both shark (cartilaginous fish) and dolphins (mammals) is Homoplastic characters since they are not common in their ancestors.
2. Similarly the wings of birds, bats and insects perform same function but have no common evolutionary lineage.
3. The thorns developed in different plants are modifications of different plant parts but perform same function. eg thorns developed in Downy hawthron (Crataegus mollis) are the modified from axillary buds while the spines of japanese blue berry (Elaeocarpus decipiens) is a modified leaf
4. Two succulent plant genera, Euphorbia and Astrophytum, are only distantly related, but the species within each have converged on a similar body form
5. Sieve tubes play role in long distance transport of food in tall plants. In algae no sieve tubes are found, but brown algae have these. Brown algae are found as some giant forms as kelps (up to 100 mt) and it appears that the adaptation is to facilitate the movement of food.

Immotile nature of plants is likely to be the most promising reason for more homoplasy in plants than animals. Evolution proceeds in the direction of least resistance. Homoplasy points to selection thus leading to these evolutionary changes