BIOSCI 109: Lecture 21 - Molecular Evolution & Phylogenetics

Characters Only Present in Living Organisms

There are some characters that we can observe only in living organisms. Most of it has to do with biological organic material

This includes:

• Comparing chromosomes

• Comparing embryology

• Comparing genetics

Comparing Chromosomes

Typically, we can’t extract chromosomes from fossils, or they tend to have very degraded genetic information. However, in living organisms, we can easily sequence entire genomes and compare it to other genomes for similarities and differences.

Embryology

Comparing embryo morphologies between organisms as well as how they develop. This may include the genetic information of development genes as well. We obviously can’t look at the embryos of fossils.

Genetic Comparisons

Branching off of chromosome comparisons, we can also focus on specific genes as well. Then, we can compare variations and similarities of these genes across living species.

Scurvy & Molecular Phylogeny

Modern day primates lack the vitamin c synthesis pathway genes that a lot of other mammals have. This means that we are more prone to developing scurvy when we lack vitamin c sources.

The L-Gulonolactone oxidase protein, which is a derivative of ascrobic acid (vitamin c), is formed from a functional 12 exon GULO gene.

Mammals lack a complete 12 exon GULO gene, with 6 of the 12 exons missing. This is likely due to how primates lived in areas with an abundance of vitamin c rich fruits. This meant that there was no functional need for this gene and that allowed mutations to accumulate in them to make them non-functional.

How Did Fly Traps Evolve?

There are two considerations to why carnivorous plants in general evolved:

1. Carnivory helped to provide nutrients in nutrient-poor environments

2. Botanical carnivory arose from the enhancement and modification of current characteristics to create varied syndromes for various straegies

There are two main types of carnivorous plants:

• Passive ones that rely on a trap or glue to passively get prey

• Active ones that rely on movements that are induced by touch to trap prey

Fly Traps & Molecular Phylogeny

By comparing the molecular composition (mainly genetics, characters, and so on), scientists were able to establish a phylogeny for venus flytraps.

Through this, it is hypothesised that venus flytraps likely evolved some morphologies, developed them, and then lost some over time.

• It is thought they started as passive glue traps, moved to active glue traps, developed their leaves, and then lost the glue

This process of gaining characters and losing them to shape specific strategies is known as scaffolding.

Geological Dates on Molecular Phylogenies

Molecular phylogenies do not have dated times on them normally/regularly as there is no dating to put it againsst. So, to put a date with them, we’d typically construct morphological phylogenies too with of the living species and related fossil species (mainly using skeletal characters)

• Then, these fossils place time constrains on the tree, allowing us to infer when splits could’ve occured

They imply minimum age. A probability distribution is also put on the node ages to determine how likely those ages fit with the phylogeny.

Biogeography & Molecular Phylogeny

Molecular & morphologies phylogenies help us to create large dated phylogenies that demonstrate biogeography, the how, what, where, and when of a lineages’ current and past locations.

It also helps us to identify location patterns of groups and where they tend to occur compared to other related groups.

• Typically, clades of taxon would all appear in a similar region. This pattern helps us to also create distinct clades as related species tend to occur close (or historically close) to each other.

Did New Zealand Completely Drown?

Using morphological & molecular phylogenies, we’ve inferred that New Zealand likely did not completely drown during the Oligocine marine transgression (OMT).

• These phylogenies show that these lineages are much older than the OMT, suggesting that they existed before the OMT, survived during it, and persisted untill today.

• If there was a complete drowning, we wouldn’t expect see lineages older than the OMT.

There was also a smooth exponential distribution of divergence times from ancient lineages to present day, which suggests proportional continual growth in lineages without disturbance,

• Even during/after the OMT, the exponential distributed continued undisturbed.