Speciation #16

Taxonomy

• Def: the science of communicating evolutionary relationships

  • the process of naming, defining, and classifying groups of organisms

  • relies on phylogeny to help establish & define monophyletic taxa

• has a hierarchical system of classification

the science of communicating evolutionary relationships

Taxonomy

Species

• Def: metapopulations that evolve independently from other metapopulations

communicating species

Communicating species

Microevolution

• Def: the evolutionary processes and effects occurring within and between populations

  • evolution occurring below the species level

the evolutionary processes and effects occurring within and between populations

Microevolution

Macroevolution

• Def: evolutionary processes and effects occuring between metapopulations

  • evolution occuring at or above the species level

evolutionary processes and effects occuring between metapopulations

Macroevolution

Metapopulation

Speciation

• Def: the study of evolution occurring at that transition from Microevolution to Macroevolution

• the evolutionary process by which gene flow between 2 populations stops, and those populations begin diverging into independent metapopulations

• Barriers to reproduction that leads to populations diverging

  • Geographic barriers (allopatric vs parapatric vs sympatric)

  • Ecological barriers

  • Behavioral barriers

the study of evolution occuring at that transition from Microevolution to Macroevolution

Speciation

Allopatric speciation

• Def: when populations become separated by geographic barriers that interfere with gene flow and create speciation events

Allopatric speciation

What kind of speciation is this?

Parapatric

• Def: speciation that occurs when diverging populations have distributions (genes) that remain adjacent (similar) to one another without total geographic isolation

  • an environmental or selection gradient forms across the total range of populations, causing population to diverge from one another

Parapatric

what kind of speciation is this?

Sympatric

• Def: speciation that occurs even when the diverging populations are not geographically separated

  • disruptive force most often ecologically or behaviorally-based, leading to changes in niche partitioning or sexual selection pressures

Sympatric

What kind of speciation is this?

Hybridization

• if separated populations occur in the same or overlapping geographic areas, and there is a potential for gene flow, we need to compare 3 diff fitness relationships:

  • If the fitness of the hybrid offspring are the same as the fitness of the true-breeding offspring → populations will NOT speciate

  • If the fitness of the hybrid offspring is lower than the fitness of the true-breeding offspring → populations will remain reproductively isolated

the populations will remain reproductively isolated because since the fitness of the hybrid offspring is lower, natural selection favors the true-breeding offspring, reducing gene flow and reinforcing reproductive isolation

• If the fitness of the hybrid offspring is lower than the fitness of the true-breeding offspring → populations will remain reproductively isolated

• why?

Reproductive Isolation

• not good for the parent/species population to spend resources on a hybrid offspring that has a lower fitness

• so selective pressures to prevent hybridization:

  • Pre-mating barriers = ecological or behavioral separation prevents mating

  • Pre-zygotic barriers = physiological incompatibility between mates or their gametes prevents successful fertilization

  • Post-zygotic barriers = hybrid offspring is produced, but it has a fitness of 0

Polyploidy

• Def: Having three or more homologous chromosome sets

• common in flowering plants

• results from errors in cell division or hybridization between different species

• how plants readily hybridize

• hybrid offspring are fertile through self-pollination

• even if they are not fertile

  • many can propagate themselves clonally (asexual reproduction)

• a common source of diversity in plants

Having three or more homologous chromosome sets - how plants readily hybridize / a common source of diversity in plants

Polyploidy