Species and Speciation

Vocabulary practice flashcards covering species concepts, reproductive isolation mechanisms, allopatric and sympatric speciation, and secondary contact outcomes.

Species (Evolutionary Definition)

An evolutionarily independent population or group of populations.

Biological Species Concept

A concept defining species as groups of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups, with evolutionary independence maintained by a lack of gene flow.

Gene Flow

The movement of alleles between populations, which reduces population distinctiveness by blending their genetic composition.

Prezygotic Isolation

Reproductive isolation mechanisms that prevent individuals of different species from mating or prevent fertilization from occurring.

Temporal Isolation

A form of prezygotic isolation where populations do not interbreed because they breed at different times of the day, seasons, or years (e.g., distinct spawning times past sunset in the corals M. franksi and M. annularis).

Habitat Isolation

A prezygotic barrier where populations are physically isolated by breeding in different habitats or geographic spaces (e.g., parasites on different host species, or elk and red deer separated by changes in sea level).

Behavioral Isolation

A prezygotic barrier where populations exhibit different courtship rituals, displays, or signals that prevent interbreeding (e.g., distinct flash sequences in fireflies).

Gametic Isolation

A prezygotic barrier that occurs when individuals mate, but their egg and sperm are incompatible, preventing successful fertilization.

Mechanical Isolation

A prezygotic barrier occurring when male and female reproductive organs are physically incompatible, preventing successful copulation.

Postzygotic Isolation

Reproductive isolation occurring after mating and fertilization, wherein the resulting hybrid offspring have low fitness, fail to survive, or are sterile.

Hybrid Inviability

A postzygotic barrier where hybrid zygotes or embryos fail to develop properly or survive (e.g., interbreeding between ring neck dove Streptopelia capicola and rock dove Columba livia results in only ~$6\%$ of eggs hatching).

Hybrid Sterility

A postzygotic barrier where hybrid offspring develop normally into adulthood but cannot produce viable gametes (e.g., crosses between Western meadowlark Sturnella neglecta and Eastern meadowlark Sturnella magna).

Morphospecies Concept

A species concept that identifies evolutionarily independent lineages by distinguishable phenotypic and morphological features.

Cryptic Species

Species that are morphologically indistinguishable or extremely similar yet remain reproductively isolated from one another (e.g., Australian field crickets Teleogryllus commodus and Teleogryllus oceanicus).

Phylogenetic Species Concept

A species concept that defines a species as the smallest aggregation of sexual populations or asexual lineages diagnosable by a unique combination of character states (synapomorphies) on a cladogram.

Monophyletic Group

An evolutionary lineage consisting of an ancestral population and all of its descendants.

Synapomorphy

A homologous trait or character state that is unique to and shared by members of a monophyletic group.

Speciation

The evolutionary process involving the splitting of a single ancestral population into two or more distinct species, driven first by genetic isolation (loss of gene flow) and subsequently by genetic divergence (via selection, drift, or mutation).

Allopatric Speciation

Speciation that begins when populations become geographically and physically separated from one another.

Dispersal (Speciation)

An allopatric speciation process where a small portion of a population moves across a geographic barrier to colonize a new, isolated habitat.

Vicariance

An allopatric speciation process where an existing population is physically split into geographically isolated subgroups by the emergence of a new physical barrier (e.g., continental breakup of Gondwana isolating ratite birds).

Ring Species

A series of geographically adjacent populations that can interbreed with neighbors, but whose terminal populations wrap around a geographic barrier and cannot interbreed where their ranges overlap (e.g., the Ensatina eschscholtzii salamander complex).

Sympatric Speciation

The divergence of populations and formation of new species occurring within the same geographical area, often driven by natural selection overcoming gene flow or by polyploidy.

Polyploidy

A genetic condition involving more than two complete sets of chromosomes, typically caused by meiotic non-disjunction producing diploid gametes, enabling rapid sympatric speciation in plants.

Reinforcement

Natural selection that strengthens prezygotic reproductive barriers against interbreeding when diverging populations come into secondary contact, driven by the low fitness of hybrid offspring.

Hybrid Zone

A geographic area where divergent populations meet, interbreed, and produce hybrid offspring (e.g., the hybrid zone between Townsend's warblers and hermit warblers in the Pacific Northwest).