Speciation and Evolutionary Mechanisms

Flashcards covering the definitions of speciation types, reproductive isolating mechanisms (pre-zygotic and post-zygotic), and models for the pace of evolution.

Speciation

Defined as the formation of new species through evolutionary processes.

Transformation

A pathway of speciation occurring when a new species replaces the old, which does not increase the total biological diversity of species on Earth.

Divergence

Also known as Adaptive Radiation, this is speciation where one or more species arise from a parent species that continues to exist, increasing total biological diversity on Earth.

Geographical Barriers

Any geographical element of Earth, such as a river or mountain, that physically separates populations and prevents interbreeding.

Biological Barriers

Also known as Reproductive Isolating Mechanisms, these are biological or physiological attributes of a population that keep them reproductively isolated from other populations even if they exist in the same geographic area.

Pre-Zygotic Barriers

Barriers that prevent organisms from different species from mating.

Behavioral Isolation

A pre-zygotic barrier referring to species-specific signals or behaviors, such as the distinct mating calls of songbirds, that prevent interbreeding with closely related species.

Habitat Isolation

A biological barrier where different species live in the same area but use different habitats and rarely encounter each other, such as Lions in grasslands and Tigers in forests in India.

Temporal Isolation

Timing barriers such as mating or flowering at different times of day, seasons, or years, such as the blackspotted stickleback breeding later in spring than the three-spined stickleback.

Mechanical Isolation

A biological barrier where closely related species have incompatible reproductive structures, such as the species-specific genitalia of 20 different Bushbabies species across Africa.

Gametic Isolation

A biological barrier preventing eggs and sperm from different species from fusing to form a zygote, such as chemical markers on clam eggs not recognized by sperm of other species.

Post-Zygotic Barriers

Barriers that prevent hybrid zygotes from developing into viable, fertile adults after fertilization has occurred between different species.

Hybrid Inviability

A post-zygotic barrier caused by genetic incompatibility that stops the development of the hybrid zygote, such as sheep and goat hybrid embryos dying before birth.

Hybrid Sterility

A biological barrier where two species produce hybrid offspring that are sterile, such as Mules which are the offspring of a horse and a donkey.

Hybrid Breakdown

A barrier occurring when first-generation hybrids are fertile but their offspring (when mating with each other or parent species) are sterile or weak, as seen in species of cotton plants.

Coevolution

The process of reciprocal evolutionary change occurring between pairs or groups of species as they interact and apply selective pressures on each other.

Gradualism

An evolutionary model describing evolution as slow, steady, and linear, where the accumulation of many small changes produces large changes.

Punctuated Equilibrium

An evolutionary model consisting of long periods of stasis interrupted by periods of rapid change, which are often the result of mass extinctions.