EVO 318: Speciation + Phylogeny

Phenetic species concept defintion

Species are distinguished by clustering individuals according to their observable characteristics (phenotypes).

ex: moon shrubs classified differently by phenotype

Phenetic species limitations

• Convergent evolution can cause different species to look alike.

• Members of the same species can look different based off of stage of life or sex.

• It is difficult to apply to fossils when distinguishing characteristics are limited.

Biological species definition

Species are groups of populations that can interbreed and are reproductively isolated from other groups

BIologial species limitations

• Bacteria reproduce asexually, so the usual interbreeding criterion does not work well for them.

• Fossil organisms cannot be tested directly for whether they could interbreed.

• It is difficult to apply to geographically isolated populations when reproductive compatibility cannot be observed directly

Ecological species definition

Species are distinguished by their ecological niches (system role), including how they use resources and function in their habitats.

Ecological species limitations

Different species may occupy similar niches, and populations within one species may use different resources or habitats. It can be difficult to determine exactly when ecological differences justify separate species.

ex: Two different bird species eat the same insects and live in the same forest.

Phylogenetic species defintion

Species are identified as distinct evolutionary lineages, often using shared derived traits to identify monophyletic groups.

Phylogenetic species limitations

The traits selected to compare organisms and distinguish lineages can affect how the species are defined. these can be subjective.

Allopatric speciation

Population separated by a physical/ geographic barrier. Cane become reproductively isolated with less sexual computability and behaviorally different.

ex: snapping shrimp. Isthmus of Panama separated shrimps and they diverged into different species over time.

Parapatric speciation

Populations occupy neighboring/adjacent areas and diverge without a physical barrier.

ex: Salamanders in California. They live across two ridges in the Central Valley and are an ex of a ring species, where compatbility decreases at the end of the ring compared to neighbors.

Sympatric speciation

Populations diverge in the same geographic area, with reproduction isolation.

ex: mountain roses. they have different behaviors such as flowering time, where could affect what organisms pollinate. would exchange fewer genes with different reproductive windows.

ex: cichlid fish: occupy the same lake but differf in morpholgy, diet, and where specifically in the lake they reside.

Would reproductive isolation occur faster in sympatry or allopatry?

Faster in sympatry since they might have to compete for resources and specialize in different niches, in which their habits and diets can change which can reduce interbreeding between them.

Adaptative radiation

Diversification of a lineage into multiple forms adapted to different ecological opportunities.

Prezygotic barriers def

Prevent mating before a zygote forms

Examples of prezygotic barriers

• Habitat isolation: Live or reproduce in different habitats

• Temporal isolation: Reproduce at different times, seasons, etc.

• Behavioral isolation: Different mating behaviors.

• Mechanical isolation: Reproductive structure incompatibility.

• Gametic isolation: Sperm and egg can’t properly fuse.

Postzygotic barriers def

After fertilization has produced a zygote

Postzygotic barriers

1. Hybrid inviability: Failure to develop

2. Hybrid sterility: Cannot reproduce in life.

3. Hybrid breakdown: Later gen descendants of hybrids have reduced fitness of fertility.

Homologous traits

Traits with shared ancestry, same origin.

ex: wings in butterflies and flies

Analogous traits

Traits with Independent evolution/origins.

ex: nectar-feeding adaptations in hummingbirds and hummingbird hawk-moths.

Convergent evolution

Similar traits evolve independently in different lineages. This often produces analogous traits

Divergent evolution

Related lineages accumulate differences after sharing a common ancestor.