Speciation and Reproductive Isolation Mechanisms

Species

A group of interbreeding natural populations.

Speciation

The process by which new species form.

Biological Species Concept

Species defined by reproductive isolation.

Pre-zygotic mechanisms

Prevent mating or fertilization before zygote forms.

Post-zygotic mechanisms

Prevent hybrid offspring from developing or reproducing.

Geographic isolation

Physical barriers separate populations.

Ecological isolation

Different habitats prevent species from mating.

Temporal isolation

Species breed at different times.

Behavioral isolation

Differences in mating behaviors prevent interbreeding.

Mechanical isolation

Morphological differences prevent successful mating.

Prevention of gamete fusion

Sperm and egg proteins must match.

Hybrid zygote dies

Zygote fails to develop after fertilization.

Hybrid individual dies

Hybrid survives briefly but does not reproduce.

Hybrid sterility

Hybrid offspring are unable to reproduce.

Allopatric speciation

Speciation due to geographic separation.

Sympatric speciation

Speciation occurs within the same geographic area.

Polyploidization

Increase in chromosome number leading to speciation.

Microevolutionary forces

Mutation, drift, and selection drive divergence.

Reinforcement of reproductive isolation

Natural selection strengthens isolating mechanisms.

Carduelis pinus

Example of a species within the finch family.

Carduelis flammea

Common redpoll, another finch species.

Carduelis tristis

American goldfinch, distinct species.

Ernst Mayr

Proposed the Biological Species Concept.

Gene flow

Movement of genes between populations.

Discrete units

Distinct species recognized in nature.

Mule

Hybrid of donkey and horse, sterile.

Murres

Example of species with hybridization issues.

Canids

Wolves and coyotes, can interbreed.

Mussels

Example of species that hybridize frequently.

Lactuca canadensis

Wild lettuce species flowering in summer.

Lactuca graminifolia

Wild lettuce species flowering in early spring.

S. arcticus

Species with disjunct distribution.

S. maritimensis

Another species with geographic isolation.

Tiglon

Hybrid between tiger and lion.

Liger

Hybrid between lion and tiger.

Hybrid embryos

Embryos resulting from interspecies mating.

Spontaneous abortion

Natural termination of a pregnancy.

Morphological variation

Differences in physical form among species.

Birds of Paradise

Example of behavioral isolation in mating.

Secondary contact

When previously separated species meet again.

Extinction of intermediate populations

Loss of populations that connect two species.