Biology Reference
In-Depth Information
12.9.4 Congruence Between Morphology- and Molecular-Based Trees
The fossil record is incomplete, so inferences made about lineages of organisms
are based on what the scientist can observe and measure. Many scientists are
concerned about using a single method, such as sequence data
or
morphological
traits, to deduce evolutionary patterns. Often, inferences concerning phyloge-
netic relationships based on molecular data alone or morphological data alone
may not reflect the historical relationship of the taxa from which the data were
obtained, producing a “gene tree/species tree” problem (
Telford and Copley
2011
). For example,
Powell (1991)
pointed out that molecular studies on the
Drosophila pseudoobscura
group can lead to conclusions of monophyly, para-
phyly and polyphyly, depending upon the data used to construct the trees. The
different sets of data used are presumed to be accurate and thus neither tree is
“wrong,” but reflects different aspects of the history of the same taxa when dif-
ferent data are considered. Morphological and molecular data can lead to dif-
ferent conclusions in some cases, but can produce congruent results in others.
Telford and Copley (2011)
note, “To the outsider, phylogenetic debates can
seem particularly fractious. If different investigators can reach strongly sup-
ported but entirely different conclusions by analyzing the same data, how does a
consensus emerge and should it be trusted?” They conclude, “The falling cost of
DNA sequencing means that, in the near future, phylogenetic questions will be
approached with greatly expanded molecular datasets, both in terms of sampled
taxa and quantity of data.” However, much remains to be learned about how to
analyze that data. Errors in phylogeny construction can occur if we do not under-
stand how different traits evolve and accurate models of evolution are not used.
12.9.5 Genomes and Arthropod Phylogenies
Telford and Copley (2011)
review what has been done to understand the evo-
lution of animals using whole-genome sequences. They explore the following
question: Is it possible that complete-genome sequences might provide an under-
standing of what happened
≈
530 million years ago in the Cambrian explosion?
Genomes contain a vast amount of evolutionary information, but understand-
ing how genomes have evolved requires the comparisons of genomes at differ-
ent branches of the evolutionary tree. The use of genomic data is complicated
by the fact that, during evolutionary time, multiple changes can occur and con-
vergence and loss of traits can occur in genomes. Furthermore, the use of differ-
ent models of molecular evolution can result in different trees. Problems include
long-branch attraction, which is the introduction of systematic error in phylog-
eny reconstruction that results in unrelated long branches to cluster together,
which could occur if evolution in specific taxa occurred through more rapid rates
