1. radiation because it introduced many new species

1.    
In
order to hypothesize the last common ancestor of Metazoans, data regarding the
Protozoans is needed to construct a timeline of origin and compare the
differences between these unicellular animals and the transition to
multicellularity, which is found in the metazoans. Fossil records would be
needed to analyze physical structures of unicellular species and make
inferences about the behavior and morphological evolution of multicellular eukaryotes
such as metazoans. Data collected from cellular processes and machinery in
choanoflagellates, the closest living relative to animals, including information
about cell division and divisions of labor has been useful in hypothesizing
their relationship to metazoans and linking them to their last common ancestor.
Specialized feeding cells only found in the choanoflagellates and the metazoan uphold
this hypothesis as well as analysis of protein sequences backed by statistical
support. The last common ancestor of metazoans would have also most likely been
aquatic and unicellular, similar to choanoflagellates. Recreating the
phylogenetic tree to show their similarities also places choanoflagellates as a
monophyletic group, and despite ambiguity of exact placement from a small
amount of nonchoanoflagellate protozoa showing no clear similarities to
metazoan cells, it is sufficient enough to claim they have a closer relationship
to the metazoan than with other groups. The uncertainty of placement is partly
due to the possibility that choanoflagellates may be degenerate porifera,
meaning that metazoans last common ancestor would actually be the sponges. To
determine this, one would need to examine whether choanoflagellates diverged
before animals originated or if they instead evolved from the porifera. In
depth studies of these relationships can be supported through mitochondrial
genome sequencing.

 

2.    
            Adaptive radiation describes an
event in which a lineage diversifies quickly and evolves different adaptations
in the new lineages that are formed. This diversification and evolution of new
adaptations allows for new niches to be taken up by new organisms. In well
preserved fossil records, morphologies and the numerous new varieties of species
that develop from adaptive radiation events can be examined. The Cambrian
explosions is an adaptive radiation because it introduced many new species and
niches that were not seen before it occurred. During this time, new body plans,
types of symmetry, patterns, and ecological opportunity evolved. This includes adaptations
such as coelomate bodies, bilatarian symmetry, triploblasty, and new
predator/prey interactions. These innovations show how animal evolution was
able to become increasingly complex and grow in diversity through coevolution.
In living animals today, these adaptations are still seen which illustrates the
importance of evolution post-Cambrian explosion. Pre-Cambrian animals lacked
obvious body parts such as heads and mouths, and did not have complete
digestive tracts that were found in post-Cambrian animals. They also were most
likely soft-bodied and fed through filtering processes as opposed to active
predation. These differences in animals pre- and post- Cambrian explosion depict
how drastic the adaptations in animals can be in response to rapid environmental
change, and how complex they can become over a short period of time.

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3.    
            The success of a phylum depends on their
species diversity, abundancy, ability to take up various niches, and their capacity
to inhabit as many environments as possible. The phylum Arthropoda fits these
criteria because it consists of over one million species, is considered the
most diverse, and have adapted to survive successfully in land, water, and air
environments. The show a great amount of resilience to extreme environments due
to the development of exoskeletons supporting an overall large size range, and
have exploited a vast number of niches with a minimal amount of competition for
the same resources because of their ability to grow through distinctive
development stages. Their high rates of reproduction and motility allow them to
have an immense survival advantage over other phyla. Their fossil record shows
their acquisition of flight to be dated about 300 million years ago, meaning
their success has be ongoing for a long time. This adaptation alone as an
extremely efficient means of transportation has given them the ability to
escape predators, expand to different habitats, and make use of new resources,
all necessary to maintain their position of biological dominance over other phyla.

 

4.    
            Parasites have a large diversity and
are able to evolve rapidly partly due to their short generation periods and
large populations. Animals that evolve to parasites are thought to have come
from originally free-living and mutualistic organisms but later became
degenerate. The concept of parasitism lies in the fact that these organisms occupy
a narrow niche, gaining nutrients from their host while causing them harm, but
not necessarily always killing them. Mutations in what used to be benign forms
may have led them to becoming disease-causing, resulting in counter-adaptations
from their host, which in response increased their resistance as well. This adaptive
genetic change is known as host-parasite coevolution, which is the
reciprocation of selective pressures on one another leading to rapid
adaptation. The Red Queen hypothesis sums this up to the constant change in
both host and parasite in order to counter each other’s adaptations and ensure
the survival of their own population. Benefits of parasitism are that they have
complex life cycles that allow them to have multiple methods of transmission
and they reproduction potential is much greater than their hosts. Parasites can
also modify their host and act as an extended phenotype to increase
transmission rate, increase their growth, and make reproduction more effective
for them. Counter adaptations from the host can reduce the fitness costs of
parasites and parasitic infection can alter resource allocation for the host’s
other bodily processes.

 

5.    
            Cephalopods of the Mollusca phylum
are considered among the most intelligent invertebrates due to the advanced
cognitive abilities they have evolved. Intelligence in this case is measured by
skills such as spatial learning, navigational capacities, and predation techniques
which are widely studied in cephalopods. Octopuses are the most acknowledged in
terms of cephalopod intelligence, which can be tested through a series of
cognitive tasks that require advanced thought processes such as dexterity, the
ability to use tools, and the capability to communicate or learn. In an
octopus, one could observe the ability to grasp and manipulate objects for locomotion
or attaining food. The ability to communicate can be tested by placing
different backgrounds against its body to calculate the speed of changes in
skin color controlled by nervous control of chromatophores, which has been done
with cuttlefish. Observational learning of basic tasks such as placing objects or
evasion tactics such as escape from enclosures can be studied to examine
learning capacities. It is difficult to compare invertebrate intelligence to
vertebrate animals because their nervous systems are so different and
intelligence in mainly attributed to vertebrates. Intelligence in invertebrates
is also thought to be environment-dependent rather than social-dependent, which
makes it difficult to know whether they can be tested the same way.

 

 

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