Question

Suppose you are studying a population of an animal or plant. You wonder if this population is genetically distinct from neighboring populations (i.e., an ecotype). Briefly state several ways by which you could determine if your population is indeed a locally adapted ecotype. Then describe in some detail how this ecotype could have evolved to be distinct from neighboring populations. Include the concepts of mutation, natural selection, gene flow (migration), genetic drift and inbreeding.

Answer 1

Answer ) Characteristics of locally adapted ecotypes:

1. Ecotypes of a species, though genotypically distinct, are always inter-fertile.

2. They retain their original features when cultivated in a natural habitat.

3. Ecotypes are genetically fixed.

4. A species with wide ecological amplitude can be distinguished on the basis of morphological and physiological characters into different habitat forms or ecotypes.

5. They occur in distinct habitats.

6. Ecotypes are discrete entities with clear differences which separate one ecotype from another.

7. The differences are not due to plastic response to change in environment but are actually due to natural selection of locally adapted populations.

The ways by which ecotypes evolved are:

1. Hybridization:

It is produced by the natural cross between two species. For example, when Spartia stricta is naturally crossed with S. altemiflora, the new hybrid S. townsendii results which eliminates both the parents from their natural habitats owing to its greater adaptability.

2. Mutation:

Due to natural mutation and recombination small gene pools accumulate in a segregating population which make it better adapted to the particular habitat or environment. Some new ecotypes also arise by cultivation or protected growth as it eliminates competitive selection.

3. Chromosomal changes:

Structural changes in the chromosomes such as translocation, inversions, and loss or addition of chromosome segments produce changes in genotypes and phenotypes resulting in the formation of new ecotypes. Polyploidy also leads to the formation of new ecotypes because polyploids hardly exhibit ecological tolerance as their parents do.

Now a days following techniques have been applied to differentiate ecotypes:

(i) Morphological features:

In this case morphological or physiological features of several individuals are studied at random in different populations of a species and one or few characters are considered and the results obtained are shown in the graph. Unimodal curve shows homogenous population, bimodal, trimodal and multimodal curves show two, three and many ecotypes in the population respectively.

(ii) Anderson’s Scatter Diagrams:

This was devised by Anderson (1940) to delimit ecotypes. For this some measurable characters are taken into consideration. One character (for example, leaf length) is plotted on one axis of the graph and other character (for example leaf breadth) is plotted on another axis. In this way large number of characters are taken from different localities.

(iii) Cytological behaviour.

In this case karyotypes and their behaviour are observed in different forms. The differences in cytological behaviour show the existence of distinct ecotypes.

(iv) Transplantation experiment:

In this experiment plants from all the different localities are grown under uniform environmental conditions and their morpho-physiological characters are compared with plants growing in natural habitat. If the characteristic features are not changed in the neutral area, the existence of particular ecotypes is confirmed.

(v) Breeding experiments:

In this case, crossing is done between different forms of variable nature followed by self-fertilization to determine the characteristic features of variable forms. If the characteristic features show segregation in the offspring’s, the presence of distinct ecotypes can be proved.