Lecture 2 Animal Evolution

These flashcards cover key concepts regarding animal origins and diversity, focusing on early evolution, protostomes vs. deuterostomes, germ layers, and current hypotheses.

What is the primary difference between protostomes and deuterostomes regarding the blastopore?

In protostomes, the blastopore becomes the mouth; in deuterostomes, the blastopore becomes the anus.

In protostomes, what developmental fate does the blastopore typically follow?

It develops into the mouth.

In deuterostomes, what developmental fate does the blastopore typically follow?

It develops into the anus.

What term describes animals in which the first opening (blastopore) in embryonic development becomes the mouth?

Protostomes.

What term describes animals in which the first opening (blastopore) in embryonic development becomes the anus?

Deuterostomes.

What are the three germ layers in triploblastic animals?

Ectoderm, Mesoderm, and Endoderm.

What does the term 'triploblastic' mean in animal development?

Animals possessing three primary germ layers: ectoderm, mesoderm, and endoderm.

Which is the outermost germ layer in a triploblastic animal embryo?

Ectoderm.

Which is the middle germ layer found in a triploblastic animal embryo?

Mesoderm.

Which is the innermost germ layer in a triploblastic animal embryo?

Endoderm.

Which hypothesis argues that the ancestor of all animals had nerves, muscles, and a gut?

The 'Ctenophore sister' hypothesis.

According to the 'Ctenophore sister' hypothesis, what complex features were present in the last common ancestor (LCA) of all animals?

Nerves, muscles, and a gut.

What animal group does the 'Ctenophore sister' hypothesis propose as the earliest diverging lineage of animals?

Ctenophores (comb jellies).

What is a polytomy in a phylogenetic tree?

A node on a phylogeny where more than two lineages descend from a single ancestral lineage.

What does a polytomy generally indicate about the evolutionary relationships among the descendant lineages?

That the precise order of divergence is unclear or unknown, possibly due to insufficient data or rapid diversification.

What are the two main groups that arose in early animal evolution, characterized by distinct developmental patterns?

Protostomes and Deuterostomes.

What larger group of animals includes both protostomes and deuterostomes, generally characterized by bilateral symmetry?

Bilateria.

Name two examples of protostomes.

Mollusks and arthropods.

Name another major animal phylum that is classified as a protostome, besides Mollusca and Arthropoda.

Annelids (segmented worms) or Nematodes (roundworms).

What type of embryonic cleavage pattern is typically observed in protostomes?

Spiral cleavage.

What is the principle of parsimony?

The principle used to compare multiple explanations for a phenomenon by choosing the simpler explanation.

In phylogenetics, how is the principle of parsimony applied to construct evolutionary trees?

By choosing the tree that requires the fewest evolutionary changes/steps to explain the observed character states.

In what context are sponges considered a sister taxon to other animals in early evolution debate?

They are argued as either the sister taxa without nerves, muscles, or a gut.

Which animal group is hypothesized to be the earliest diverging lineage if the Last Common Ancestor (LCA) of animals was simple, lacking nerves and muscles?

Sponges (Porifera).

What key characteristics do sponges (Porifera) lack that are central to the debate about early animal evolution?

True tissues, nerves, muscles, and a gut.

Which animal groups are included in the deuterostomes?

Echinoderms, hemichordates, and vertebrates.

Name a broader animal group that encompasses vertebrates and is definitively classified as a deuterostome.

Chordates.

What type of embryonic cleavage pattern is typically observed in deuterostomes?

Radial cleavage.

What does the term 'diploblastic' refer to?

Animals, like jellyfish, having two cell layers: ectoderm and endoderm.

Which two germ layers are present in diploblastic animals?

Ectoderm and Endoderm.

Which germ layer is absent in diploblastic animals compared to triploblastic animals?

Mesoderm.

Name a broad group of animals that are typically diploblastic.

Cnidarians (e.g., jellyfish, corals, sea anemones) or Ctenophores.

What is the main point of contention in early animal evolution research?

Whether sponges or ctenophores are the sister taxa to all other animals.

What tissue layers arise from the ectoderm germ layer?

Skin and nervous system.

From which germ layer do external coverings like skin (epidermis) and sensory organs develop?

Ectoderm.

From which germ layer does the central nervous system, including the brain and spinal cord, develop?

Ectoderm.

What are the roles of the mesoderm germ layer in triploblastic animals?

It gives rise to muscles and bones.

Besides muscles and bones, what other major body systems develop from the mesoderm in triploblastic animals?

Circulatory system, reproductive organs, excretory system, and the lining of the coelom.

Which germ layer forms the circulatory system, including the heart and blood vessels?

Mesoderm.

Which germ layer gives rise to the skeletal system, including cartilage and bone?

Mesoderm.

Which germ layer is responsible for forming the muscular system?

Mesoderm.

What tissue structures primarily develop from the endoderm germ layer?

The lining of the digestive tract and its associated glands (e.g., liver, pancreas), and also the respiratory system.

From which germ layer does the lining of the gut and all associated digestive organs originate?

Endoderm.

Which germ layer forms the respiratory system, including the trachea and lungs?

Endoderm.

What is the term for the developmental process in protostomes where the coelom forms from solid blocks of mesoderm that split?

Schizocoely.

What is the term for the developmental process in deuterostomes where the coelom forms from outpocketings of the archenteron (primitive gut)?

Enterocoely.

What is an animal body plan characterized by the absence of a body cavity?

Acoelomate (e.g., flatworms).

What is an animal body plan characterized by a body cavity that is not entirely lined by mesoderm?

Pseudocoelomate (e.g., nematodes).

What is an animal body plan characterized by a true coelom, which is a body cavity completely lined by mesoderm?

Eucoelomate (or Coelomate).

What is the general term for the ancestor of all animals, often central to debates about early animal evolution?

The Last Common Ancestor (LCA) of animals.

What does the term 'bilateral symmetry' imply for an animal body plan, typically found in Bilateria?

The body can be divided into two mirror-image halves along only one plane.

What is the primary function of a coelom in an animal body?

It provides space for organ development, protects internal organs, and can act as a hydrostatic skeleton.

What is the scientific field dedicated to studying evolutionary relationships among biological entities?

Phylogenetics.

What is represented by each branch point (node) on a phylogenetic tree?

A common ancestor and a speciation event (the divergence of two or more new lineages from a single ancestral one).