Vert zoology quiz 1 study set

Early vertebrate with 4 eyes

Early fossils thought the extra eyes were pineal organs, but melanin evidence suggests the pineal eyes likely functioned as camera-type eyes

Metazoans

Multicellular heterotrophs that can be motile (at least as larvae)

Endoderm

Forms linings of the gut and lung

Mesoderm

Forms muscles, bones, cartilage, heart, kidneys, and notochord

Ectoderm

Forms nervous system, epidermis, and sensory organs

Bilaterians

Animals with two sides

Protostomia

~90% of bilaterian phyla; “mouth first” development

Deuterostomia

“Mouth second” development

Blastopore

Opening that forms first during development; becomes the anus in deuterostomes

“We all start as an anus”

In deuterostomes, the blastopore becomes the anus first

Embryogenesis

Development from fertilization to hatching

Basal deuterostome body plan

Shown by sea urchin and tunicate development

Sea urchin cleavage type

Radial holoblastic cleavage

Vegetal pole/plate (sea urchin)

Region where mesenchymal cells detach and where invagination begins

Micromeres (sea urchin)

Undergo epithelial-mesenchymal transition and migrate into the blastocoel

Sea urchin gastrulation

Vegetal cells invaginate to form the gut which elongates toward the animal pole

Tunicate cleavage type

Bilateral holoblastic cleavage

Tunicate early cleavage pattern

Vegetal half divides before the animal half

Tunicate gastrulation

Involution of endoderm and spreading over of ectoderm

Tunicate neurulation

Notochord forms and extends down a tail bud

Vertebrates

Allow study of development of notochord and vertebrae

Xenopus blastula division

Animal side divides faster; divisions become asynchronous between animal and vegetal sides

Xenopus gastrulation

Vegetal middle region invaginates, forming the blastopore lip and blastopore (anus forms first)

Xenopus neurulation

Strong head-to-tail neurulation with notochord extension and neural tube formation

Xenopus tailbud stage

Whole body elongates; tadpole stage ~37, adult stage ~66

Zebrafish cleavage

Discoidal cleavage

Zebrafish blastula formation

Cleavage happens at the top; yolk forms the bottom

Zebrafish gastrulation

Involution occurs atop yolk and cells move down sides of yolk

Primary neurulation

Most vertebrates use primary neurulation (like Xenopus)

Secondary neurulation

Zebrafish use secondary neurulation (some vertebrates use it only in the tail)

Amniotes

Group where development involves importance of the amnion

Avian gastrulation structure

Primitive streak

Primary hypoblast formation

Hypoblast islands form primary hypoblast with congregation around Koller’s sickle

Secondary hypoblast formation

Primary hypoblast connects to posterior marginal zone (PMZ) to form secondary hypoblast cells

Primitive streak function

Cells migrate through the streak to form mesoderm and endoderm

Primitive streak equivalent to blastopore lip

The streak is equivalent to the blastopore lip

Primitive groove equivalent to blastopore

The groove is equivalent to the blastopore

Primitive groove timing

Appears ~18–20 hours after egg is laid

Notochord and somite formation timing (birds)

~20–22 hours after egg is laid

Primitive streak regression timing

~23–25 hours after egg is laid

Somites

Paired structures forming vertebral column, ribs, occipital bone, skeletal muscle, cartilage, tendons, and skin

Why primitive streak exists

Blastopore is circular but streak defines body axes and separates embryo from yolk

Animals with a primitive streak

Birds, reptiles, and mammals

Haeckel’s law

“Ontogeny recapitulates phylogeny”

Problem with Haeckel’s embryo drawings

Accidental printing of the exact same woodcut three times

What was missing in Haeckel embryo comparisons

Yolks or placenta

Issue with drawings vs photographs

Bias and Missing structures may be less obvious in drawings

Why Haeckel was wrong

Biogenetic law (embryos pass through adult ancestral stages) is not true

Von Baer’s Laws of Divergence

General traits appear early; specialized traits appear later

Embryological diversity

Shown across fish, amphibians, reptiles, birds, and mammals

Phylogeny (phylogenetic tree)

Branching diagram showing evolutionary relationships among species

Tips/taxa (taxon singular)

The endpoints of a phylogeny representing species/groups

Nodes

Branch points on a phylogeny

MRCA

Most recent common ancestor

Closest relative (on a tree)

Taxon that shares the most recent MRCA

Phylogenetic systematics

Classifying organisms based on evolutionary relationships

Clade

A monophyletic group including an ancestor and all descendants

Monophyletic

Includes an ancestor and all its descendants

Paraphyletic

Does not include all descendants (not a clade)

Molecular scaffolding

Combine molecular data for extant taxa with morphology to place fossils on tree

Extinct taxa on phylogenies

Can be shown with daggers (†)

Chronogram

Phylogeny where branch lengths represent time since divergence

Divergence times estimated using

Fossil ages, molecular clocks, and geological events

Molecular clock concept

Genetic differences accumulate at a known rate to estimate divergence time

Character states on phylogenies

Traits can be mapped on tips, nodes, and branches

Tick marks on branches

Show when a character state change likely occurred

Ancestral vs derived states

Ancestral = original state; derived = changed state

Homology

Trait similarity due to shared ancestry

Homoplasy

Trait similarity not due to shared ancestry (convergent evolution)

Apomorphy

A trait that has changed from its ancestral form

Plesiomorphy

An ancestral trait

Synapomorphy

A shared derived trait inferred to be in the MRCA of a group

Misconception (most evolved taxon)

Tip order does not mean “most evolved/advanced/derived”

Reality (phylogeny rotation)

Tip order can rotate; only branching pattern matters

Misconception (basal = primitive)

First branching taxon is not the ancestor or “most primitive”

Reality (sister taxa)

Early-branching taxa are sister to the rest; no extant taxon is ancestral

Misconception (species branch from species)

Extant species do not evolve from other extant species

Correct view of evolution

Humans did not evolve from chimps; humans and chimps share a common ancestor

Human classification summary

Animal → bilaterian → deuterostome → vertebrate → jawed vertebrate → bony fish → tetrapod → amniote → mammal → primate → Homo sapiens

Heterochrony

Changes in timing of gene expression or development

Heterotopy

Changes in location/position of gene expression

Heterometry

Changes in the degree/amount of gene expression