Biology 112 Exam 2 Review

Taxonomy

Hierarchical system used to organize information about species.

Levels of taxonomy:

  • Domain (Archaea, Bacteria, Eukaryota)

    • Kingdom

      • Phylum

        • Class

          • Order

            • Family

              • Genus

                • Species

Domains:

  • Bacteria

    • Prokaryotic organisms, single-celled, lack a nucleus

  • Archaea

    • Prokaryotic, similar to bacteria but with unique biochemical properties

  • Eukaryota

    • Organisms with a nucleus, includes all plants, animals, fungi, and protists

Scientific name is in the format of Genus + Species

Subspecies

  • Populations within a species that are distinct but can interbreed

  • Potentially on the path to becoming separate species, but not fully divergent yet

Speciation:

  • The process by which new species arise

  • Starts with one species, something causes genetic isolation, and over time, genetic divergence occurs

    • genetic isolation occurs when groups can no longer interbreed

  • Can happen due to physical barriers and genetic mutation

Defining Species

Morphological Species Concept

Defines species based on physical characteristics

Based on physical traits or morphology

Limitations:

  • Variability withing a species (polymorphism)

  • Natural color variation

  • Sexual dimorphism

Biological Species Concept

Defines species as groups of individuals that can interbreed and produce viable, fertile offspring

Based on reproductive isolation

Limitations:

  • Does not work for asexual species

Reproductive isolation can be prezygotic or postzygotic.

Prezygotic:

  • Barriers that prevent zygote formation

    • Temporal Isolation

      • species breed at different times.

    • Habitat Isolation

      • species live in different habitats and don't meet.

    • Behavioral Isolation

      • differences in mating behaviors.

    • Other factors include mechanical barriers or gametic incompatibility.

Postzygotic:

  • Zygote forms but offspring are either unviable or sterile

Phylogenetic Species Concept

Defines species by their evolutionary history and relationships on the tree of life.

Identified through synapomorphic (shared derived) traits

Based on the concept of monophyletic groups (clades)

  • A monophyletic group includes an ancestor and all its descendants

  • A non-monophyletic group includes some but not all descendants

This method wants to recreate where the species belong on the tree of life

Limitations:

  • Limited genetic information for many species

Phylogenetic Tree

Diagrams that depict the evolutionary relationships between different species

Rooted trees indicate when species diverged from a common ancestor, while unrooted trees only show relationships

Phylogenetic trees are hypotheses about evolutionary relationships, not ultimate truths

Reading a tree

An outgroup:

  • Related to, but not as closely related to the other species

The order on the branches may differ, but the relationships remain the same

To find common ancestor

  • Where their branches intersect on the tree

Creating a tree

A data matrix is created using a set of traits to differentiate between species

Choose traits that help differentiate the species

The questions for the data table should have yes or no answers

Place traits on the tree to indicate where they appear, with everything after that point possessing the trait

Complications

The large number of possible trees for a given dataset

  • Phylogenetic inference is used to determine the most likely tree.

  • Parsimony aims for the simplest explanation, minimizing evolutionary steps

Convergent evolution = Homoplasy:

  • Independent evolution of similar traits across different branches, complicate the interpretation of evolutionary relationships

Reversal:

  • Occurs when a trait reverts back to an ancestral state, causing inaccuracies in phylogenetic interpretation

Homology vs. Convergent Evolution

Homology

  • Similarity in structure that is based on evolutionary derived traits from a common ancestor

  • Types of Homologies:

    • Structural Homologies

      • Physical features that show common ancestry

    • DNA Homologies:

      • Genetic similarities found in related species, such as differing sequences in cytochrome c.

    • Developmental Homologies

      • Shared developmental pathways observed in embryos of different species (e.g., all embryos may have tails).

Convergent Evolution (homoplasy)

  • Similar traits evolving independently in different organisms due to similar environmental pressures. Not having to do with ancestry.

Allopatric Speciation

When populations are separated by a geographic barrier

  • Geographic isolation is the first step followed by genetic divergence

  • Genetic isolation can occur through:

    • Dispersal:

      • Individuals leaving one group to colonize a new area

    • Vicariance:

      • Environmental event that splits a population

Biogeography, the past and present distribution of species, can inform allopatric speciation

Sympatric Speciation

When new species arise within the same geographic area

Can happens through:

  • Diversifying/disruptive selection where one trait is favored

  • Genetic mutations, chromosomal duplications

  • Non-random mating

Can be driven by external factors, such as ecology and the environment

Secondary Contact

When two populations that have diverged come back into contact

Outcomes:

  • Fusion:

    • Separate groups interbreed

  • Reinforcement of divergence:

    • Traits prevent interbreeding

  • Stability:

    • A geographic area where interbreeding occurs and hybrids are common

Macroevolution

Large-scale evolutionary changes, such as adaptive radiations and extinctions

Adaptive radiation

Rapid periods of diversification and speciation

Can be triggered by extrinsic factors

  • Ecological opportunity

    • Arises when a species can exploit a vacant or unutilized ecological niche

  • Intrinsic factors

    • Evolution of morphological traits

Island chains provide ideal conditions for radiation to occur because they contain a variety of ecological spaces, less competition, and allow for groups to speciate

Extinctions

Mass extinctions:

  • Large-scale events that eliminate many species

Background extinctions:

  • Normal, ongoing losses of species due to environmental changes, competition, or disease

Most species extinctions have occurred through background extinction

There have been five major mass extinctions in Earth's history

  • There is concern that the human activities are currently causing the 6th mass extinction