Biology 302- Systematic Botany Case Studies in Taxon Delimitation and Speciation
ID: 188034 • Letter: B
Question
Biology 302- Systematic Botany Case Studies in Taxon Delimitation and Speciation Patterns The following case studies are derived from the taxonomic literature. For each, determine a classification using the given information. Be aware that many of the determinations will be based on concepts of speciation including patterns of isolation and reproduction. Also you may have to make a decision based on incomplete data - in that way this is like real life Case Study I: Asteraceae Problem: Provide a classification for the taxa A-D using any or all of the following categories, species, subspecies, variety, and form. Materials and Methods: The taxa under study have been rarely collected however 72 specimens have been obtained from herbaria and field studies examined 13 populations having the distribution shown in Fig. I Initial variation based on geographic location and slight morphological differences suggests that there may be four independent taxa at some level. To identify chromosome numbers flower buds were taken from the populations #700,703 and 705 and compared with one published count for population 698 and all were found to have a value of n 12 A thorough morphological investigation found that selective characters of the stems and leaves were the most diagnostic for segregating the groups (Fig. 2a &b;). Quantitative measurements of these characters (Fig. 3) were taken from 20 individuals in each of the 13 sampled populations. One typical lower leaf per stem was used for blade width, length, and length/width measurements The total upper surface of these leaves was examined in order to determine the minimum and maximum trichome lengths, and all stem heights were accounted for in attempting to evaluate the variation in the size of the plants. A summary of the most significant differences separating the taxa is presented in Table 1 -- ' c … @ * · .. | Figure 1. Map showing distributions of taxa A-D Taxon A = triangles; Taxon B-blackened circles; Taxon C-circles; Taxon B-C intermediates -half blackened circles; Taxon D squares. Numbers indicate locations of sampled populations.Explanation / Answer
1. The four taxa are mainly based on their morphological features like the position of the leaves on the stem, whether it is at the apex or in between, also the nature of the stem surface, whether it is pubescent, number of florets and number of disc florets etc.
The reasons for my classification are the distinctive features expressing in all the four taxas.The branching of stem, the differences in the stem thickness, its aerial roots, the shape of the flower, branching pattern in all the 4 taxa is different.
Allopatric speciation is observed in the above model experiment as the biological population of the same species become isolated , so much so that it prevents any firther genetic exchange. Thus due to this isolation the population evolve to become distinct species.
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