Speciation and Macroevolution

Hybridization

(1) Interbreeding between members of two different taxa. (2) Interbreeding between genetically dissimilar parents. (3) In molecular biology, complementary base pairing between nucleic acid (DNA or RNA) strands from different sources.

Postzygotic Reproductive Isolating Mechanisms

1) hybrid viability. Interspecific hybrid dies at early stage of embryonic development. In crosses between different species of irises (genus Iris), fertilization occurs, but the embryos in the seeds die before reaching maturity. 2) hybrid sterility. Interspecific hybrid survives to adulthood but is unable to reproduce successfully. A mule, the offspring of a female horse and a male donkey, has sterile offspring because synapsis and segregation of chromosomes do not occur properly during gamete formation. 3) hybrid breakdown. Offspring of interspecific hybrid are unable to reproduce successfully. In a cross between two sunflower species, most members of the F2 generation are defective in some way and cannot reproduce successfully. Hybrid breakdown also occurs in later generations.

Prezygotic Reproductive Isolating Mechanisms

1) temporal isolation. Similar species reproduce at different times. Two species of fruit flies of the genus Drosophila live in the same geographic area, but one is sexually active only in the afternoon and the other only in the morning. 2) habitat isolation. Similar species reproduce in different habitats. Several flycatcher species of the genus Empidonax live in the same geographic area but in different habitats; for example, the least flycatcher lives in open woods, farms, and orchards, and the acadian flycatcher lives in deciduous forests and swampy woods. 3) behavioral isolation. Similar species have distinctive courtship behaviors. The male satin bowerbird of Australia constructs an elaborate bower, dances around the female, and sings a specific courtship song that keeps closely related bowerbird species reproductively isolated from the satin bowerbird. 4) mechanical isolation. Similar species have structural differences in their reproductive organs. Black sage (genus Salvia) is pollinated by small bees, whereas white sage is pollinated by large carpenter bees. Because of differences in the flower structures, neither type of bee can successfully pollinate the other sage species. 5) gametic isolation. Gametes of similar species are chemically incompatible. In aquatic animals such as sponges that release their eggs and sperm into the water simultaneously, interspecific fertilization rarely occurs because the egg surface is compatible only with the sperm surface of the same species.

Adaptive Zones

A new ecological opportunity that was not exploited by an ancestral organism; used by evolutionary biologists to explain the ecological paths along which different taxa evolve.

Biological Species Concept

According to the biological species con- cept, one or more populations whose members are capable of interbreeding in nature to produce fertile offspring and do not interbreed with mem- bers of other species. Most widely accepted species concept.

Gene Pool

All the alleles of all the genes present in a freely interbreeding population.

Phylogenetic Species Concept

An alternative to the biological species concept in which for a popula- tion to be declared a separate species, it must have undergone evolution long enough for statistically significant differences to emerge. Also called evolu- tionary species concept.

Hybrid Zone

An area of overlap between two closely related populations, subspecies, or species in which interbreeding occurs.

Birds produce mating songs that only birds of their own species recognize. What type of isolation is this?

Behavioral

What is the mechanism of speciation for cichlids? What about the pup fish?

Behavioral. Habitat barrier.

Fusion

Cell fusion is a process by which several uninuclear cells combine to form a multinuclear cell. Mechanical isolation is a prezygotic reproductive isolating mechanism in which fusion of the gametes of two species is prevented by morphological or anatomical differences.

Speciation

Evolution of a new species. sympatric speciation is the evolution of a new species within the same geographic region as the parental species. Allopatric speciation is speciation that occurs when one population becomes geo- graphically separated from the rest of the species and subsequently evolves.

You have found a new species an you want to describe it using the biological species concept. What things would you take into consideration?

Individuals belonging to the same species tend to share com- mon features because their genes are derived from a common gene pool. Their similar characteristics, their reproductive barriers, their geographical regions, genetic makeup.

What is the relationship between mass extinction and adaptive radiation?

Large number of species within relatively short period of geological time -> catastrophic death. Vs. Adaptive radiation with is the diversification of a group of organisms into forms filling different ecological niches.

Endemic Species

Localized, native species that are not found anywhere else in the world. Compare with cosmopolitan species.

A carpenter bee is very large and cannot pollinate very small flowers. What is the isolating mechanism?

Mechanical

Prezygotic Barrier

One of several reproductive isolating mechanisms that interfere with fertiliza- tion between male and female gametes of different species, e.g., temporal isolation, habitat isolation, behavioral isolation, mechanical isolation, and gametic isolation. A prezygotic barrier prevents (a) the union of egg and sperm (b) reproductive success by an interspecific hybrid (c) the devel- opment of the zygote into an embryo (d) allopolyploidy from occurring (e) changes in allometric growth. Prezygotic barriers are reproductive isolating mechanisms that prevent fertilization from taking place.

Explain how hybridization and polyploidy can cause a new plant species to form in as little as one generation.

Polypoids have more than two sets of chromosomes and play a major role in plant evolution and hybridization through sexual reproduction between closely related organisms. The crossing of these produce new flowers.

Post zygotic Barrier

Postzygotic barriers are reproductive isolating mechanisms that prevent gene flow after fertilization has taken place. One of several reproductive isolating mechanisms that prevent gene flow between species after fertilization has taken place, e.g., hybrid inviability, hybrid sterility, and hybrid breakdown.

What are 5 geographical barriers that might lead to allopatric speciation?

Rivers shifting their courses, glaciers migrating, mountain ranges forming, and large lakes.

Sexual Selection

Sexual selection is a type of natural selection in which individu- als with reproductive advantages are selected over others of the same sex and species. Sexual selection, a type of natural selection, occurs when indi- viduals vary in their ability to compete for mates. Individuals with reproductive advantages are selected over others of the same sex and species. In intrasexual selection animals of the same sex actively compete for mates. (a) occurs mainly among animals that practice polyandry (b) occurs when animals are very similar in their abil- ity to compete for mates (c) results in animals that have lower direct fitness (d) occurs mainly among animals that practice polygyny (e) is a form of natural selection. A type of natural selection that occurs when individuals of a species vary in their ability to compete for mates; individuals with reproductive advantages are selected over others of the same sex.

Allopatric Speciation

Speciation that occurs when one population becomes geo- graphically separated from the rest of the species and subsequently evolves.

Stability

Stability is an evolutionary process in which the hybrids are more fit than either parental population. Hybrids continue to be formed, resulting in a stable hybrid zone. Stable hybrid zones often occur in ecotones, areas of transition between two dif- ferent environments. In this case, the two incipient species are adapted to two different communities, and the hybrids' com- bination of characters from both parental populations allows them to flourish in the ecotone. Eventually, a third species may form in such a hybrid zone.

What barriers prevent wood frogs and leopard frogs from interbreeding in nature?

Temporal

What if the species you found was an insect inside of a piece of amber or a plant that reproduces asexually, would this definition work? Why or why not?

The biological species concept works to show the production of fertile offspring. The ant will not be able to be classifies because it cannot reproduce (it's in amber), an asexually, there would be no gene pool to examine.

Extinction

The elimination of a species; occurs when the last individual member of a species dies; see background extinction and mass extinction.

Adaptive Radiation

The evolution of a large number of related species from an unspecialized ancestral organism.

Sympatric Speciation

The evolution of a new species within the same geographic region as the parental species.

Reinforcement

The increase in reproductive isola- tion that often occurs over time in a hybrid zone because natural selection strengthens and increases the number of prezygotic barriers between the two species.

Gene Flow

The movement of alleles between local populations due to the migration of individuals; can have significant evolutionary consequences.

Ploidy

The number of chromosome sets in a nucleus or cell.

Reproductive Isolating Mechanism

The reproductive barriers that prevent a species from interbreeding with another species; as a result, each species' gene pool is isolated from those of other species. prezygotic barrier and postzygotic barrier.

What is the morphological species concept? How do we use it today?

There are several different definitions of species, and each definition has some sort of limitation. Linnaeus was the 18th-century biologist who founded modern taxonomy: the science of naming, describing, and classifying organisms. He classified plants and other organisms into separate species based on their visible structural differences, such as feathers or number of flower parts. This method, known as the morphological species concept, is still used to help characterize species, but structural differences alone are not adequate to explain what constitutes a species.