Part 5 of 7 - Speciation
Question 1 of 4
Your friend has recently been given a short sequence of homologous DNA from several species; you know there are some polymorphisms (nucleotide
differences) in this sequence between some of the organisms. She takes the data and excitedly builds a phylogenetic tree; her end result is based on the
principle of parsimony. You note that the tree she produced has a polytomy in which three different species appear to radiate from one common ancestor at
the same time. What could explain this polytomy in the tree? Pick ALL that apply,
A. Adaptive radiation, i.e., the rapid evolution of a species into multiple new speices, initiated when the parent population was split into three isolated
groups by a major flood.
B. Convergent evolution in a less-related species, which misled your friend into grouping the less-related species with two other species that are closely
related to each other and which do share a common ancestor.
C. The three species don’t actually form a polytomy, but instead, you don’t have fine-enough resolution in the tree and in the genetic data to determine
the order in which the three species evolved over a relatively short amount of time.
D. Although none of the traits are homoplasies, one of the organisms in the polytomy actually represents an outgroup, thus leading to the presence of an
Mark for Review
Question 2 of 4
Let’s take a journey to Lake Stanford. Long ago, there was only one species of cichlid fish inhabiting the lake. Over time, though, you notice that five different
cichlid species have evolved from it, each with its own peculiar fin structure corresponding to particular niches in the environment. Stanford soon builds a dam
across the lake, though, to generate electricity for FroSoCo. This divides the lake into two unequal portions, and the fish cannot cross from one portion to the
other. After some time, you notice that although the five species in the smaller portion of the lake don’t appear to change, the fish in the larger portion are
beginning to look different, developing new fin shapes, etc., even though the selective pressures remain the same for both portions of the lake.
are no longer able to mate with fish from the first portion of the lake, even when artificially introduced to each other.
Soon after this dam is built, a new predator -
- is introduced to the area. You notice, though, that a new fish morph (form), with a pectoral fin as the
shape of a tree, has arisen in both portions of the lake. You investigate and discover that this fin shape confers upon it better fitness to avoid
is really scared of tree shapes.
Given this scenario (and this is the only information you know about these fish), choose all the terms that can definitively be said to be in play for the evolution
of cichlid fish in this situation.