fEvolution and Phylogeny:
p. 727-740, chapter 32
Evolution is the biological concept that refers to the process of change in all forms of life
over successive generations.
Adaptation refers to the mechanism by which organisms have adjusted to new environments
or to changes in their current environment. May also refer to a specific trait.
Phylogeny is the hypothetical relationship between groups of organisms being compared.
Taxonomy refers to classifying organisms into categories and providing them with a unique,
scientific name.
Rostral side End with the head
Caudal side End with the tail
Posterior side Towards the back
Anterior side Towards the front
Dorsal side Side directed upwards, from
the ground
Ventral side Side directed downwards to
the ground
All animals are heterotrophic, multicellular and
eukaryotes. Animal cells do not have a cell wall.
Animals often have muscles and nerve cells (unique to
animals), except for the earliest animals. They mostly
reproduce sexually and show characteristic
developmental stages.
The origin of animals:
The common ancestor of all animals must have lived about 770 mya and
probably resembled modern choanoflagellates (Protista; a unicellular
eukaryotic organism).
Choanoflagellates are unicellular and therefore not animals, but the
unicellular creatures form colonies. They manage to do so because of two
important mechanisms that none of the other unicellular organisms back
then had; the capacity to physically adhere to each other
(Cadherin proteins in the membrane allow for this adhesion) and the ability
to exchange signals; cell-to-cell communication. These two steps were
crucial to go from unicellular to multicellular.
There is also a morphological resemblance with choanoflagellates: collar
cells (choanocytes) in sponges (the oldest animals we know of), but also in
,higher organisms (like starfish and flatworms).
Some milestones in history of animals:
First multicellular life (770 mya)
Ediacaran biota (560 mya): Soft-bodied animals, like jellyfish, existed for millions of
years after the emergence of multicellular animals, but fossilise very poorly. There is
only one place where high diversity of these lifeforms are found: the Ediacara hills in
Australia. These are referred to as the Ediacaran Biota.
Cambrian Explosion (535-525 mya): A very quick wave of emergence of new species.
Believed to be caused by the availability of oxygen in the atmosphere, calcium
availability on the surface by volcanic activity (important element for exoskeleton
build) and the emergence of predators, which led to quick evolution to avoid/protect
against them. There’s also evidence of some parts of the genome being duplicated
around the Cambrian; this allowed the copy of the genes to create a new function.
Colonization of land (450 mya and 365 mya, respectively): Around 450 mya the first
arthropods with an exoskeleton invaded the land (centipedes, millipedes, insects).
Around 365 mya the first vertebrates colonized the land (amphibians).
Rise of the first mammals (140 mya).
Rise of the earliest hominids (5 mya).
Body plans in animals:
A collection of morphological and developmental features of a systematic group (taxon or
clade). These features can include but are not limited to:
- Symmetry (Asymmetrical, radially symmetrical, bilaterally symmetrical).
- Tissues (Diploblastic or Triploblastic).
- Early development (Protostomes or deuterostomes).
- Body cavity (Acoelomates, pseudocoelomates or coelomates).
Animal Phylogeny:
Phylogeny is the relationship between animals. There are about 35 animal phyla. Thanks to
new techniques, the view on phylogeny is subject to new insights. Phylogeny is always a
hypothesis; different sources will show different trees, depending on the set of characteristics
used to reconstruct phylogenetic relationships. There are at least 2 phylogenetic hypotheses:
- Based on morphological and developmental biological comparisons,
- Based on molecular evidence (for example, ‘whole genome’, rRNA, hox genes,
mitochondria DNA).
Metazoa: All animals (multicellular,
heterotrophic eukaryotes)
Eumetazoa: All animals with true
tissues.
Bilateria: All Eumetazoa with
bilaterial symmetry.
Deuterostomia: Bilateria in which the
mouth develops secondarily. (Divides
into Echinodermata and Chordates).
,Protostomia: Bilateria in which the mouth develops secondarily. (Divides into
Lophotrochozoa and Ecdysozoa).
In evolutionary biology, one reasons for the simplest explanation; it’s more likely that a
certain trait developed once, rather than several separate times. Therefor, a phylogenetic tree
with the least crossbars is the most plausible one. This is called the principle of Maximum
Parsimony.
If a certain feature develops multiple times in different branches, they are called analogous
features (for example wings in insects and birds).
Convergent evolution is the evolution of organisms from different ancestors with
functionally similar traits or structures. These structures appear similar in their function or
form, but they do not share a common ancestor.
Homologous structures are structures or traits that share a common evolutionary origin but
may serve different functions.
Divergent evolution is the accumulation of differences between closely related populations
within a species, sometimes leading to speciation.
p. 521-540 (chapter 22)
Unicellulas vs. Multicellular:
Life is generally divided into three domains: Eukarya, Bacteria
and Archaea. Multicellular lifeforms are only found in the
eukaryotes, in the clades of animals, land plants and fungi.
Protists is the informal, collective term for all unicellular
eukaryotic organisms. They are not animals (animals are
multicellular), but a lot of protists have animal-like features.
Protists have been here for 2 billion years, so they have had a
longer time to evolve complexity and diversity. Colony-
forming protists are believed to have led to true (multicellular)
animals.
Choanoflagellates have certain traits in order to form these colonies. They can form adhesion
by expressing proteins (cadherins) on the surface of their cells. These proteins stick out and
interact with the proteins of other individuals. They can also send and receive signals with the
help of proteins (receptors) on their surface.
There are also two other categories of signalling molecules that we find in choanoflagellates,
that we don’t find in any other unicellular organisms and those are involved in gene
regulation and in ECM (extracellular matrix formation).
Protists:
, Euglena viridis
The Euglena Viridis is a protist from the clade of Excavata with some animal features.
This organism is green because it is filled with chlorophyll (found in chloroplasts), which is a
plant like feature.
What you can also find is a light detector;
photosynthesis relies on light, so this organism has a
sensor so it can move towards the light. The eyespot
is not the light sensitive organelle but is a pigment
that shield the light detector from all directions
except one. Because of this, the sensor can sense where the light is coming from.
But aside from this, the organism also has a flagellum which is an animal like feature. Just
like a choanoflagellate, the flagella can move to help the Euglena Viridis swim. In animals,
we can find flagella in sperm cells.
The organisms live in fresh water (low salt), but the intercellular fluid is relatively rich in salt.
Because of this, it tends to absorb water by diffusion. The contractile vacuole keeps the cell
from bursting by pumping out water.
Paramecium
The paramecium is a ciliate. Ciliates have another
feature that is also seen in animals; cilia. Cilia are
many small hair-like structures that can make little
movements, by which the organisms can move or
create a current with which to move food particles
towards the mouth. The entire surface of a
paramecium is covered with cilia.
In
between the cilia you will find trichocysts.
This is an organelle that, when stimulated, can
discharge. It will shoot out another hairlike
structure, longer than the cilia, that the
organism can use to attach itself to either food
or substrate or other organisms. In animals, we can find cilia in different species. In humans
they are present in our lung tissue.
Paramecium can procreate by conjugation or via mitotic cell divisions.
Amoeba
While amoebas are unicellular,
they are quite large. Amoeba can
change shape and have many
extensions we refer to as
p. 727-740, chapter 32
Evolution is the biological concept that refers to the process of change in all forms of life
over successive generations.
Adaptation refers to the mechanism by which organisms have adjusted to new environments
or to changes in their current environment. May also refer to a specific trait.
Phylogeny is the hypothetical relationship between groups of organisms being compared.
Taxonomy refers to classifying organisms into categories and providing them with a unique,
scientific name.
Rostral side End with the head
Caudal side End with the tail
Posterior side Towards the back
Anterior side Towards the front
Dorsal side Side directed upwards, from
the ground
Ventral side Side directed downwards to
the ground
All animals are heterotrophic, multicellular and
eukaryotes. Animal cells do not have a cell wall.
Animals often have muscles and nerve cells (unique to
animals), except for the earliest animals. They mostly
reproduce sexually and show characteristic
developmental stages.
The origin of animals:
The common ancestor of all animals must have lived about 770 mya and
probably resembled modern choanoflagellates (Protista; a unicellular
eukaryotic organism).
Choanoflagellates are unicellular and therefore not animals, but the
unicellular creatures form colonies. They manage to do so because of two
important mechanisms that none of the other unicellular organisms back
then had; the capacity to physically adhere to each other
(Cadherin proteins in the membrane allow for this adhesion) and the ability
to exchange signals; cell-to-cell communication. These two steps were
crucial to go from unicellular to multicellular.
There is also a morphological resemblance with choanoflagellates: collar
cells (choanocytes) in sponges (the oldest animals we know of), but also in
,higher organisms (like starfish and flatworms).
Some milestones in history of animals:
First multicellular life (770 mya)
Ediacaran biota (560 mya): Soft-bodied animals, like jellyfish, existed for millions of
years after the emergence of multicellular animals, but fossilise very poorly. There is
only one place where high diversity of these lifeforms are found: the Ediacara hills in
Australia. These are referred to as the Ediacaran Biota.
Cambrian Explosion (535-525 mya): A very quick wave of emergence of new species.
Believed to be caused by the availability of oxygen in the atmosphere, calcium
availability on the surface by volcanic activity (important element for exoskeleton
build) and the emergence of predators, which led to quick evolution to avoid/protect
against them. There’s also evidence of some parts of the genome being duplicated
around the Cambrian; this allowed the copy of the genes to create a new function.
Colonization of land (450 mya and 365 mya, respectively): Around 450 mya the first
arthropods with an exoskeleton invaded the land (centipedes, millipedes, insects).
Around 365 mya the first vertebrates colonized the land (amphibians).
Rise of the first mammals (140 mya).
Rise of the earliest hominids (5 mya).
Body plans in animals:
A collection of morphological and developmental features of a systematic group (taxon or
clade). These features can include but are not limited to:
- Symmetry (Asymmetrical, radially symmetrical, bilaterally symmetrical).
- Tissues (Diploblastic or Triploblastic).
- Early development (Protostomes or deuterostomes).
- Body cavity (Acoelomates, pseudocoelomates or coelomates).
Animal Phylogeny:
Phylogeny is the relationship between animals. There are about 35 animal phyla. Thanks to
new techniques, the view on phylogeny is subject to new insights. Phylogeny is always a
hypothesis; different sources will show different trees, depending on the set of characteristics
used to reconstruct phylogenetic relationships. There are at least 2 phylogenetic hypotheses:
- Based on morphological and developmental biological comparisons,
- Based on molecular evidence (for example, ‘whole genome’, rRNA, hox genes,
mitochondria DNA).
Metazoa: All animals (multicellular,
heterotrophic eukaryotes)
Eumetazoa: All animals with true
tissues.
Bilateria: All Eumetazoa with
bilaterial symmetry.
Deuterostomia: Bilateria in which the
mouth develops secondarily. (Divides
into Echinodermata and Chordates).
,Protostomia: Bilateria in which the mouth develops secondarily. (Divides into
Lophotrochozoa and Ecdysozoa).
In evolutionary biology, one reasons for the simplest explanation; it’s more likely that a
certain trait developed once, rather than several separate times. Therefor, a phylogenetic tree
with the least crossbars is the most plausible one. This is called the principle of Maximum
Parsimony.
If a certain feature develops multiple times in different branches, they are called analogous
features (for example wings in insects and birds).
Convergent evolution is the evolution of organisms from different ancestors with
functionally similar traits or structures. These structures appear similar in their function or
form, but they do not share a common ancestor.
Homologous structures are structures or traits that share a common evolutionary origin but
may serve different functions.
Divergent evolution is the accumulation of differences between closely related populations
within a species, sometimes leading to speciation.
p. 521-540 (chapter 22)
Unicellulas vs. Multicellular:
Life is generally divided into three domains: Eukarya, Bacteria
and Archaea. Multicellular lifeforms are only found in the
eukaryotes, in the clades of animals, land plants and fungi.
Protists is the informal, collective term for all unicellular
eukaryotic organisms. They are not animals (animals are
multicellular), but a lot of protists have animal-like features.
Protists have been here for 2 billion years, so they have had a
longer time to evolve complexity and diversity. Colony-
forming protists are believed to have led to true (multicellular)
animals.
Choanoflagellates have certain traits in order to form these colonies. They can form adhesion
by expressing proteins (cadherins) on the surface of their cells. These proteins stick out and
interact with the proteins of other individuals. They can also send and receive signals with the
help of proteins (receptors) on their surface.
There are also two other categories of signalling molecules that we find in choanoflagellates,
that we don’t find in any other unicellular organisms and those are involved in gene
regulation and in ECM (extracellular matrix formation).
Protists:
, Euglena viridis
The Euglena Viridis is a protist from the clade of Excavata with some animal features.
This organism is green because it is filled with chlorophyll (found in chloroplasts), which is a
plant like feature.
What you can also find is a light detector;
photosynthesis relies on light, so this organism has a
sensor so it can move towards the light. The eyespot
is not the light sensitive organelle but is a pigment
that shield the light detector from all directions
except one. Because of this, the sensor can sense where the light is coming from.
But aside from this, the organism also has a flagellum which is an animal like feature. Just
like a choanoflagellate, the flagella can move to help the Euglena Viridis swim. In animals,
we can find flagella in sperm cells.
The organisms live in fresh water (low salt), but the intercellular fluid is relatively rich in salt.
Because of this, it tends to absorb water by diffusion. The contractile vacuole keeps the cell
from bursting by pumping out water.
Paramecium
The paramecium is a ciliate. Ciliates have another
feature that is also seen in animals; cilia. Cilia are
many small hair-like structures that can make little
movements, by which the organisms can move or
create a current with which to move food particles
towards the mouth. The entire surface of a
paramecium is covered with cilia.
In
between the cilia you will find trichocysts.
This is an organelle that, when stimulated, can
discharge. It will shoot out another hairlike
structure, longer than the cilia, that the
organism can use to attach itself to either food
or substrate or other organisms. In animals, we can find cilia in different species. In humans
they are present in our lung tissue.
Paramecium can procreate by conjugation or via mitotic cell divisions.
Amoeba
While amoebas are unicellular,
they are quite large. Amoeba can
change shape and have many
extensions we refer to as
