L9- Tempo and Mode

  • does evolution of life on land have a big pattern (tempo and mode)?

  • does it differ between plant and animals?

Patterns of plant evolution:

Important features of land plants:

  • are very simple (40 cell types), live simple life

  • are sedentary (can’t move)→ adapted to all changes, only move vast distances when reproducing (pollen/spores/seeds), move on a generational scale

  • can react and later regenerate in times of stress

  • reproductive propagules can persist for very long (lay dormant)

  • plants readily hybridise (hybrids are generally sterile but can make them not)

  • lots of polyploidy

    • autopolyploidy→ increase in number of copies of chromosomes

    • allopolyploidy→ hybrid has both sets of chromosomes from parents

    • hybridisation + polyploidy→ get a new species

  • can reproduce asexually in lots of ways

  • very small populations can persist

  • mosaic evolution→ can adapt a single organ whilst keeping the same genetic makeup

→ these features make plants very adaptable

Mass extinctions:

  • plants aren’t affected by mass extinctions in the long term

  • mass extinctions shape animal evolution, what survives is luck, some groups survive and proliferate→ Gould’s contingency

  • the big 5:

    • End Ordovician→ glaciation→ cooling, wipes out animals in the oceans/tropics

    • End Devonian→ origin of seed plants cause oceanic/continental aquatic anoxia→ wipes out animals, only deep ocean animals survive

    • End Permian (P/T)→ outpouring of siberian traps, acid rain, super-heating→ wipes out forests and land plants, invertebrates can’t survive in water

    • End Triassic (T/J)→ heating and low oxygen

    • End Cretaceous (K/T)→ bolide impact, nuclear winter, sunlight is eliminated due to dust

  • plants aren’t affected by mass extinctions:

    • plant evolution is affected by reproductive novelty, each innovation gets an adaptive radiation, allow a new group to dominate the planet

    • gametophyte→ sporophyte→ heterospory→ seed→ flowers

    • taxonomic persistence→ few higher taxonomic groups go extinct- will just get replaced and continue living in the background, plant groups persist for long times (living fossils) e.g. bryophytes, lycopsids (not tree forms), still get ferns, equisetums, cycads, ginkgos, gymnosperms

What drives plant evolution?

  • red queen→ evolution is driven by competition, survival of the fittest

  • court jester→ organisms have to change as the environment has changed

    • red queen dominates in plants→ increasingly sophisticated reproductive strategies

    • intergenerationally migrate→ get around climate change and court jester

  • how does co-evolution affect this? is there evidence of plant-fungal-animal interactions?

  • evidence from islands→ St Helena- full of endemic plants, resemble mainland plants but are a new phylogenetic group→ plants are plastic, adapt to environmental change quickly

  • evidence from last ice age→ no evolution of vegetation, just changes habitat

Patterns of animal evolution:

Invertebrates:

  • invaded lands on multiple occasions→ marine groups invading land multiple times, some go back

  • usually marine→ freshwater→ terrestrial

Fish:

  • can switch between freshwater and marine water

  • different groups diversified at different times

  • major groups taken out at End Devonian

Tetrapods:

  • see high turnover of speciation, very early on

  • can see mass extinctions affecting them

What is driving animal evolution?

  • multiple invasions on land

  • taxonomic impersistence→ severely affected by mass extinctions, court jester drives pattern of evolution, goulds contingency

Coevolution:

  • coevolution is an important aspect of terrestrial ecosystem

  • animal evolution is linked to plant evolution→ plants are the base of terrestrial food chain

  • plant evolution is linked to animal evolution now→ flowering plants pollinated by animals

  • plant-fungal interactions

  • plant-animal interactions (herbivory, pollination, seed dispersal)