Evolution Lecture No. 13: The Origins Of Life
October 10 , 2012
The Mode Of Speciation In Drosophila:
-As earlier noted, the more ancestral Drosophila species were found in the western, older islands of the
Hawaiian archipelago. By examining the phylogeny of this example, we see that the most derived
synapomorphy includes the most recent taxa of the tree (D. silvestris and D. heteroneura). The species
with the most derived traits is always the most recent in evolutionary time. By using phylogenetic
means, we provide evidence for speciation in allopatry via dispersal.
The Mode Of Speciation In Snapping Shrimp:
-In the morphologically identical sister species of snapping shrimp (separated by the Panama isthmus
some few million years ago), we see the phylogenetic tree showing double the amount of distinct
shrimp species (through the phylogenetic species concept). Due to this phylogeny, evidence is present
regarding the speciation in allopatry via vicariance.
The Coevolution Of Two Species Of Heliconius:
-Coevolution refers to interacting species evolving adaptations (and counter-adaptations) in parallel. This
was most eloquently observed in the wing patterning of butterflies inhabiting the Amazon Basin region.
Their colourful patterns would look at first glance to be identical, however further examination would
reveal them to be morphologically distinct. Moreover, one species of Heliconius (erato) would exhibit a
very distasteful aftertaste as form of avoidance to predators, while the other species (melpomene)
would be quite tasty to possible predators.
-But because the delectable butterflies are utilizing a form of colourful mimicry (known as Batesian
mimicry) they fool predators into believing that they taste disgusting. By observing the phylogenies of
these two incipient species (racial groups), we see that there is incredible concordance the evolutionary
branching patterns. So, in examining phylogenies, we provide evidence for coevolution due to the
mimicry of unpalatable forms.
(THE ORIGIN OF LIFE)
The 5 Kingdoms:
-This is an old method of conveying the evolutionary relationships among the once-proposed main
groups of life on Earth. For example, Monera was kingdom consisting of only bacteria (lacking a
membrane-bound nucleus), while Protista consisted of only single-celled organisms. As you can already
see, the polytomy present at the most recent ancestor of all eukaryotes creates a challenge, as in this
model the eukaryote classification contains unresolved evolutionary relationships. Inferring The Universal Phylogeny:
-When attempting to deduce a better outcome for the universal phylogeny, it is essential that the most
appropriate loci is selected for comparison among the various species. Small-subunit ribosomal RNA
would be the best possible loci as it has the slowest mutation rate, which means it has been retained for
billions of years and is present in all cellular life. To summarize, it is conserved and critical to life (protein
translational machinery), much more valuable than using microsatellite DNA for example (which mutate
to fast to track across evolutionary time).
The 3 Domains:
-In the most recently deduced version of the universal phylogeny, organisms are classified under three
mains Domains of life: Prokarya, Archaea and Eukarya. As you can see, many of the former problematic
evolutionary relationships have been resolved in Eukarya whereby Fungi now occur as a paraphyletic
group (with slime molds) and the same occurs with paraphyletic relationship occurs with Protista (with
ciliates and flagellates).
Different Universal Phylogenies:
-Depending on the loci that are chosen for observation, different universal phyl