chapter 27: introduction to animal diversity - BIOL 2130

fossil record

• animal evolution began 600 mya

• vary greatly in complexity

• use anatomy, morphology, evolutionary history, embryonic development, genetic makeup

• our understanding of animal evolution is constantly changing

characteristics

• obligate heterotrophs: have to obtain energy by consuming other organisms

• complex tissue structures (same as plants, but different types and function)

  • specialized cells for unique functions

• no cell wall: animals have flexible plasma membrane for movement and direct communication

• motile: can move independently at some stage of life

• diplontic life cycle: adult diploid stage (2 copies), haploid gametes

  • shared w some plants

• embryonic development follows a predetermined body plan

complex tissue structures

evolution of these structures is a result of the need to seek out food or avoid predation

• sensory structures

• movement

• digestion

• complex neurological networks

• no cell walls!

• tissues differentiate and specialize = great diversity

animal clades

no specialized tissues:

• parazoa / porifera (sponges)

• placozoa (tiny parasitic creatures resemble amoebae)

eumetazoa (true animals with tissues and symmetry):

• cnidaria (jellyfsh and relatives)

• ctenphora (comb jellies)

• bilateria (all other animals)

reproduction

most animals are diploid with haploid gametes and undergo sexually

• exceptions: asexual or mixed reproduction

  • male hymenoptera (bees, ants, wasps) rise from unfertilized eggs

  • flatworms can regenerate by splitting and each part grows a new head and tail (asexual)

  • whiptail lizards are all females due to hybridization event causing heterozygosity (inherent diff versions of alleles from each parent)

embryonic development

cleavage: mitotic cell division

• NO cell growth

• produce many small cells called blastomeres

• more division and cell rearrangement produces morula (ball of cells)

• continued arrangement to hollow balls of cells called blastula

gastrulation: cells move inward and form the digestive tube and three germ layers

germ layers

programmed to develop into specialized tissues during organogenesis

• differentiate to form body’s organs and organ systems

• ectoderm: outer body covering, skin, nervous system

• endoderm: lines digestive tract and internal organs

• mesoderm: muscles, bones, circulatory system, other internal structures between

incomplete metamorphosis

invertebrates where the young resemble small adults

• ex: grasshoppers

complete metamorphosis

invertebrates where the young look and act different from adults

• ex: caterpillar → butterfly

hox genes

the “master controlling genes” and determine the general body plan for a species

• number of body segments

• limb placement

• head/tail direction

• turn genes on/off

• encode transcription factors that control gene expression

• homologous

• contributes to body complexity and diversity

phylogeny

molecular tech has changed understanding of phylogenetic relationships from common ancestor, trees used as hypotheses

• true vs non-differentiated tissues

• embryonic development

• bilateral vs radial symmetry

• bilateral

  • deuterostomes: anus forms before the mouth

  • protostomes: mouth forms before anus

    • ecdysis: shed outer layer

    • lophotrochozoa: feeding structure/larval stage

• about 35-40 animal phyla recognized

precambrian period

early animal life thought to be evolved from protists

• no current living representatives of these species

• oldest known fossils were found in Australia 650 mya

cambrian explosion

most rapid evolution of new phyla and diversity in all of earth’s history 542-488 mya

• most animal phyla today evolved during this time

• trilobite: most dominant species

  • first animal to display sense of sight

  • none live today

diversification

can be a combination or all of these during the cambrian explosion

• environmental changes

  • atmospheric oxygen: more energy for larger, active animals

  • calcium in oceans: develop shells/skeletons

• shallow lagoons on continental shelves = habitat and niches

• changes in relationships = increased competition for resources

  • makes diverse body plans/behaviors

• genetic changes (evolution of hox genes) = increased variability in morphology

unresolved questions

how did the evolution of so many species take place all at once?

• maybe due to triggers

• exact timing and pace is unclear

why an “explosion” – animal life predates this, and other explosions occur later in evolutionary history within species 

• rapid diversification, not suddenly 

• animal life existed before

• diversification also happened later

why did the Cambrian explosion extend into the Ordovician period?

• radiation spread into new habitats/lineages

post cambrian evolution

ordovician: explosion of terrestrial plant life

• expansion of animal species

paleozoic era: temp and moisture changes from continental drift = new adaptations

• changes in environment drive evolution

• mass extinction events also lead to evolution b/c of genetic drift