BIO A01 Lecture 9: Phylogeny & the Species Concept

Vocabulary practice flashcards covering cladistics, phylogenetic tree construction, molecular clocks, and species concepts from BIO A01 Lecture 9.

Principle of Parsimony (Occam’s razor)

The phylogenetic principle stating that the simplest explanation is most likely correct; it assumes that evolutionary changes and homoplasies should be minimized, making trees with derived characters appearing once the most favored.

Synapomorphy

A shared, derived trait present in an ancestral lineage and all its descendants that is used to infer evolutionary relationships.

Homoplasy

A trait or character state independently gained or lost in two or more separate taxa rather than being inherited from a recent shared common ancestor.

Morphological Traits (in Phylogenetics)

Anatomical features (such as skeletal systems in vertebrates, floral structures in plants, or insect exoskeletons) used to describe species, limited by environmental variation, distant relations, or cryptic species.

Developmental Traits

Similarities observed during embryogenesis and early growth—such as the presence of a notochord in both sea squirt larvae and vertebrate embryos—that reveal evolutionary affinities within the phylum Chordata.

Paleontological Traits

Morphological information obtained from fossil records providing evidence of past organisms, divergence times, and ancestral versus derived states, though often limited by a fragmentary record.

Behavioural Traits (in Phylogenetics)

Heritable behavioral characteristics used in phylogenies, such as genetically determined frog calls, which can be distinguished from culturally learned behaviors like some bird songs.

Molecular Characters

DNA, RNA, or amino acid sequences reflecting evolutionary lineages; they provide abundant data unaffected directly by the environment, but are limited by having only 4 nucleotide or 20 amino acid character states.

Molecular Clock

The hypothesis that genetic mutations accumulate at a relatively constant rate over evolutionary time, allowing researchers to estimate the time of divergence between species based on sequence differences.

Mosaic Evolution

The phenomenon in which different DNA sequences, genes, or traits evolve and tick at differing evolutionary rates.

Unrooted Tree

A phylogenetic tree diagram specifying the relationships among taxa without denoting a common ancestor or temporal direction.

Rooted Tree

A phylogenetic tree that includes an ancestral node at the base, establishing the order of lineage divergence and the direction of evolutionary time.

Outgroup

A distantly related reference taxon (such as a bird or turtle relative to a mammal tree) incorporated into phylogenetic analysis to root the tree and integrate evolutionary time.

Combinatorial Explosion

The rapid mathematical growth in the number of potential phylogenetic topologies as taxa are added, increasing from 3 unrooted trees for 4 taxa to $105$ for 6 taxa, and approximately $6.02 \times 10^{23}$ for 20 taxa.

Species (General Definition)

The smallest independently evolving biological unit, containing populations that follow independent evolutionary trajectories.

Morphological Species Concept

A classification concept originated by Carl Linnaeus that categorizes organisms into species according to shared anatomical traits and appearance.

Biological Species Concept

A species concept that defines a species as a group of organisms capable of interbreeding in nature and producing viable, fertile offspring.

Hybrid Sterility (Limitation of BSC)

An evolutionary phenomenon exemplified by mules (offspring of a horse and a donkey) being infertile due to an uneven set of chromosomes, posing a limitation to simple biological classification.

Androdioecious Species

A reproductive system characterized by the coexistence of distinct male individuals alongside hermaphrodites, as found in certain killifish.

Gynogenetic Species

An asexual reproductive system where an embryo inherits purely maternal chromosomes because egg development is triggered by sperm that subsequently degenerates without nuclear fusion (exemplified by the Amazonian Molly).

Ecological Species Concept

A definition of species stating that a species is a set of organisms adapted to and sharing a distinct ecological niche through specific resource use and behavioral isolation.

Phylogenetic Species Concept

A species concept defining a species as a group of organisms united by a unique, shared lineage and evolutionary ancestry.

Introgression

The transfer of genetic information between distinct species via hybridization followed by repeated backcrossing, observed between Common Raven lineages and Chihuahuan Ravens.