Animal Evolution and Innovations

• Most animal phyla originated suddenly in the Cambrian period and then diversified
• Cambrian explosion marks a major adaptive radiation of animals, beginning roughly 550 million years ago
• Approximately 1.4 million animal species have been named across 30+ phyla
• Total species count is estimated to be 3 to 10 million

What is an Animal?

• Animals are thought to have evolved from single-celled protists resembling modern choanoflagellates
• Animals are multicellular organisms lacking cell walls
• Animals are ingestive heterotrophs, they ingest food before digestion
• Animals exhibit movement at some stage of their life cycle
• Animals exclusively possess muscle and nervous tissue
• Animals predominantly have a diploid-dominant life cycle

Key Innovations in Animal Evolution

• Studying animal evolution uses fossils, comparative morphology, comparative development, and comparative genomics
• Multicellularity is a synapomorphy for animals, indicating a shared ancestry
• Multicellularity suggests animals derive from a monophyletic lineage
• The earliest animals were probably sponges, evolved from choanoflagellates
• Both sponges and choanoflagellates are sessile, and choanoflagellates can form colonies
• Both sponges and choanoflagellates are suspension feeders, capturing food from a current
• Sponge feeding cells bear a close resemblance to choanoflagellates
• Multicellularity led to key innovations, involving:
• Specialization of cell types
• Regulation of the cell cycle and growth
• Adhesion among cells
• Recognition of self and non-self, providing innate immunity
• Developmental signaling and gene regulation
• Programmed cell death, also called apoptosis

Embryonic Tissue Layers

• Tissues are structured when cells organize into similar groups in the body
• Animals are categorized by the number of tissue layers, called germ layers, that they develop as embryos
• There are three possible germ layers:
  • Ectoderm: forms the skin and nervous system
  • Endoderm: forms the linings of the digestive and respiratory systems
  • Mesoderm: forms muscles, bones, the circulatory system, and most other organs
• Animal groups differ based on number of germ layers:
  • Sponges have no true germ layers
  • Diploblasts, like jellyfish, only have ectoderm and endoderm
  • Triploblasts have all three germ layers
• Order of germ layer evolution, no germ layers -> diploblasts -> triploblasts
• The evolution of the mesoderm in triploblasts is especially significant because it allows for complex muscle tissue
• Diploblasts possess contractile cells enabling simpler motions

Symmetry, Cephalization, and Nervous Systems

• Bilateral symmetry and cephalization helped the evolutionary development of the nervous system
• Types of body symmetry:
• Asymmetry: No symmetry (e.g., sponges)
• Radial symmetry: at least two planes of symmetry (e.g., jellyfish)
• Bilateral symmetry: one plane of symmetry
• Order of body symmetry evolution, asymmetry -> radial symmetry -> bilateral symmetry
• Over 99% of animals are bilaterians which allowed the evolution of the nervous system and head
• This is possibly accountable as a driving force behind the Cambrian explosion
• Order of nervous system evolution:
• Sponges lack nerve cells
• Diploblasts have nerve cells forming a nerve net
• Since food can come from any direction, this nerve net is diffuse
• Triploblasts possess a central nervous system with:
• Nerve cells bundled into one or more projecting cords
• Other nerve cells form coordinating masses or ganglia
• Cephalization, the concentration of structures for feeding and sensing, is advantageous for bilaterally symmetrical animals

The Coelom

• The coelom only applies to triploblasts
• Tube-within-a-tube design is the basic bilaterian body plan
• The endoderm forms the inner tube - the gut with mouth and anus
• The ectoderm forms the outer tube - the skin and nervous system
• The mesoderm forms the muscles and organs in between these tubes
• Coelom is fluid-filled space between inner and outer tubes
• The coelom allows circulation of oxygen and nutrients
• The coelom enables internal organs to move independently of each other
• The coelom arose in the common ancestor of protostomes and deuterostomes
• Types of coeloms include:
• True coelom: completely lined by mesoderm; organs held in place by mesentery tissue
• Acoelom: a complete loss of the coelom, seen in flatworms, Platyhelminthes
• Pseudocoelom: where the body cavity is lined on one side by mesoderm (Nematoda)
• In soft-bodied triploblasts, the coelom functions as a hydrostatic skeleton; muscles contract against pressurized fluid

More Protostomes and Deuterostomes evolution

• A common ancestor of most animals was a bilaterally symmetrical triploblast with cephalization, a CNS & coelom
• Two major lineages diverged from this ancestral group:
  • Protostomes: include rotifers, flatworms, segmented worms, mollusks, roundworms, arthropods
  • Deuterostomes: include echinoderms and chordates
• Embryonic development differenciates protostomes and deuterostomes
• Cleavage is a rapid series of mitotic divisions
  • Starting with a zygote, it creates a 2, 4, 8, 16 cell morula (solid ball)
  • Further divisions develop a hollow ball of cells called a blastula
• Protostome and deuterostome development differentiates this further:

  • In determinate cells become determined and lose totipotency at the 2-cell stage, if it is removed the embryo will die, this is protostome development

  • In indeterminate lose later the totipotency of the cells, or they can remain at the morula stage and have twins/quadruplets, this is deuterostome development

  • 4-cell to 8-cell cleavage varies

    • protostomes  spiral cleavage

    • deuterostomes  radial cleavage

    • gastrulation  invagination of cells opening called the blastopore and the archenteron (beginning of digestive tract)

      • protostomes  blastopore develops into the mouth -deuterostomes  blastopore develops into the anus

    • Formation of the coelom also varies: -protostomes develop a schizocoelous: solid mass of mesoderm forms in blastocoel near blastopore & splits apart -deuterostomes develop a enterocoelous: mesodermal cells pinch off top of archenteron

Segmentation

• Segmentation is the presence of repeated body structures
  • Two protostome phyla, Annelida and Arthropoda, and one deuterostome phylum, Chordata, exhibit segmentation
  • Segmentation enables adaptive specialization of segments and appendages
  • Segmentation is likely homologous because genes organized in these 3 animal have been lost or not used in the same combinations in others
  • There is a conflict of how well embryology is able to predict the organisms

Themes in Animal Diversification

• animals develop a specialization in sensory
• Cephalization resulting in sensory structures concentration at the anterior has helped in the differentiation
• some senses like sight ,hearing, taste/smell and touch are found in almost all animals
• Some animals also have groups that have help with specialization like electric ,barometric fields of detection
• There are also difference related to feeding habbits -Detrivores eat deed organic matter -Herbivores eats plants and algae -Omnivores Eats both plants and meat -Carnvores eats only other animals -Parasites eat and harvest nutruents from a host
• --That can be an endo parasite or ecto parasite
• Suspension feeders used filtering to catch the food in what they eat
• Some also eat there way through a matter like Earth worms
• Fluid feeders mop or suck up fluids in the process of what they eat
• Movement has helps animals find food ,mates move up the habbitat and escape predictors
• Skelton has helped with moving the muscle system
  • Those skeletors can be :hydro static exoleton or endo exoleton
• Bilaterarian limbs helped a common ancestor that is mostly use for appendiges modified with Diversification
• Animals are know for there reproduction
  • Tremendous Diversitys were known but there know for asexually using Myosis ,which leads to a large genetic variation
  • Internal fertilization which happens usually in the females body
  • Or a external fertilization when species put semen in some out side souruce
• Some eggs develop with viviparous which helps species nourishment but the young must give birth to leave and give a chance to the next generation to be overous by dipositing it and nourishing it from its self this nourishment
  • Ovoviviparous also had female fertilization to where she nourishes herself but not the embryo
• Life cycle
  • Starts as the diploid domaint
  • Development also has variation in the system -Direct development also helps young adults to become resemble adults -indirect development helps with drastic change to develop through larva to aduld

Key Nonbilaterian Animal Lineages

• Porifera: Sponges

  • Most sponges are marine and live in the ocean bottom, this mean thay are benthic uses, in: -bath -Used as toxins against predictors for medical reasons

• Spicules provide some sort of in organic support in this process :CaCO3 and in silica

• All in al spongin has a mesh like protection Water is transported in what is called a body Incurrant cannels like :porocyte radial cannels and spongocoel which comes from all water The moraphlogy adapst to feeding in certain cases

• Asexuallity helps the cell get nourishment form where it needs -ostia that carries the nutrients Choannocytes or create the body cell, and intercellular digestion -Aembiocites help carry nutruents and cell types to carry

• Interior of the sponge is made up of mostly sponges Class calcerca has a different structure from CaCo like support But also glass sponge is made of silicon and and and bath sponge like demosopongi

• The Phylum cnidarian also have the following : has jellyfish marine marine life radially symmetrical

  • Endotherm gives rise for gastronomy
  • Extoderm gives rise to epidermis to help with body structures
  • There tissues mostly consist of mesoglea for structure

  -Extro cells have also been shown to help and allows capture to grow but that also helps the hydrostatic skeletal process to dimorphic to also help carry two body forms and to carry tents and cell for nourishment with the following reasons - - polyp is sessile cell -And medulla drifts in -In doing so the function to capture has worked in doing so to create:

  • Cnidites a capsule membrane this all happens with a the heighnternd tent
  • Some types have deadly effects to many like Austrilia and so on if its not handle correctly — Movemnts are from muscle tissue that need no cells

• Also production of external and central structures ---That all happens through the process of Hydrology

• -The class Scypha often has a medial side but takes time to fully turn

• The Anthotoza has cells which is ONLY one of the type

• It makes use of several types of cells to do so often and sometimes mutuals the side structure: -Gvc is cells and has a muitalist protists

  • They eat food and have different forms like --Anenomes to be one the ground --They often are one with limeston but can be the other

• Phylum Citerpa is the common jelly type used to create the clear jello cells - Is an predatory system -The motion works as 2”combo” --Reproduxtion is a external structure