Evolutionary Biology

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Morphospecies concept

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Species are groups of organisms which share a common morphology and can be distinguished by some aspect of this morphology from other natural groups.

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Ecological species concept

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Species are groups of organisms (or populations) which
share a common ecological niche in the same community.

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The “Biological” Species Concept (Ernst Mayr)

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Species are groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups

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Phylogenetic species concept

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Species are the smallest
diagnosable monophyletic groups

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Sympatric

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living within breeding range of each other.

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Allopatric

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NOT living within breeding range of each other

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Parapatric

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living in immediately adjacent areas

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Sibling species (Synonym: “cryptic” species)

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Distinct species that are very similar or identical in
appearance.

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Premating mechanism: seasonal and habitat isolation

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Potential mates do not meet; eg., small-mouthed salamander breeds in ponds, but another type breeds in streams

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Premating mechanism: ethological isolation

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potential mates meet but do not mate. In pollinating systems, a pollinating insect may carry pollen but does not deposit it on the stigma

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Premating mechanism: mechanical isolation

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copulation is attempted, but no transfer of sperm takes place. Many insect genitalia require precise lock and key link for transfer of sperm

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Post mating mechanisms: gametic mortality

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sperm transfer takes place but egg is not fertilized. pseudogamy in parthenogenetic Poeceliopsis related, for example, to the Sonoran topminnow, plants, and nematodes

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Post mating mechanisms: zygotic mortality

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the egg is fertilized but the zygote dies. some leopard frogs in the Rana pipiens complex

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Post mating mechanisms: hybrid inviability

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zygote produces an F1 hybrid of reduced viability, or hybrid recombinations are less viable; eg., frogs in the genus Pseudophryne

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Post mating mechanisms: hybrid sterility

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F1 hybrid is fully viable but partially or completely sterile, or it produces a deficient F2. Crosses between horses and donkeys produce mules, which are sterile. Some hybrids in the Rana pipiens complex

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Vicariance

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division of a continuous distribution
by some (geo)physical barrier

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Dispersal

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implies the founding of an isolated population by
a small number of migrant individuals who manage to survive
and reproduce at the new location

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The Founder Effect

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A small sample of any population is almost always biased with respect to the variation of the population as a whole.
A founding population of organisms in a new habitat (e.g., an island as compared to the mainland) is therefore likely to have different gene frequencies than the original population.

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Secondary Contact

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Previously isolated populations re-establish contact
after a period of separation and divergence. They might
do this via range extension, elimination of a vicariant
barrier, etc.

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Reinforcement

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Upon secondary contact, hybrids between the two populations are of reduced fitness, and natural selection acts to reduce the frequency of hybrid formation.
It completes the process of allopatric speciation.

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Paleozoic: Cambrian

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First shelled organisms
Arthropods diversity
First chordates

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Paleozoic: Ordivician

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First bryozoans (newest animal phylum)
First vertebrates (jawless fish)
First zygomycete fungi

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Paleozoic: Silurian

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First land plants
First fish with jaws
First bony fish

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Paleozoic: Devonian

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First insects
First ferns, vascular plants, ascomycete fungi
First winged insect
First tetrapods (amphibians)
First seed plants

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Paleozoic: Carboniferous (Mississippean/ Pennsylvanian)

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First reptiles
First mammal-like reptiles

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Paleozoic: Permian

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First basidiomycete fungi
First vessels in plants

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Mesozoic: Triassic

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First dinosaurs

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Mesozoic: Jurassic

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First mammals
First bird (Archeopteryx)

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Mesozoic: Cretacious

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First placental mammals
First flowering plants

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Cenozoic: Paleocene

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First horses

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Cenozoic: Eocene

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Climate warm
Continents continue to drift apart
Collision of India with Eurasia begins
Radiation of angiosperms and pollinating insects
Ice begins to form at South pole
Australia moves north from Antarctica

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Cenozoic: Oligocene

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First apes
Oldest pollen from composite family plants
Strong drying trend in Africa and other continents; grasslands form
Alps and Himalayas begin to rise

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Cenozoic: Miocene (23.8- 5.2 Ma)

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Radiation of grazing animals
Beginning of Antarctic ice cap
Continents close to present positions
Opening of the Red Sea

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Cenozoic: Pliocene (5.2- 1.8 Ma)

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Earliest hominids
Uplift of the Sierra Nevada
North and South America joined by land bridge

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Cenozoic: Quaternary (1.8 Ma- present)

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Worldwide glaciation

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Nosocomial form

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the most virulent form of a disease found in hospitals, sanitoriums, and prisons

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Transmissibility

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rate at which new hosts can be infected

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Virulence

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rate of reproduction within a host

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Essentialism

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Species are fixed entities that never change. Often, they have been thought to embody Platonic “ideals."

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Transformationism

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Species are plastic, flexible entities that can change into other species. Most often, the mechanism of change was suggested to be hybridization, but some other mechanisms were also invoked

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Carl Linnaeus, 1707-1778

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was a distinguished botanist, zoologist, physician and professor who invented the system of binomial taxonomy that is still in use. His writings clearly show that he accepted, and apparently never questioned, the notion of fixity of species

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Georges-Louis Leclerc, Comte de Buffon (1707-1788)

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was an accomplished naturalist who openly questioned the Church’s teaching that the earth was only 6000 years old. His extensive writings include a surprisingly modern definition of species and an appreciation for the “unity of all life.” He was aware of many of the observations that later lead to evolutionary theory, but offered no mechanisms. He kept many of his ideas on evolution very private for fear of controversy with the Church.

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Erasmus Darwin (1731-1802; grandfather of Charles Darwin)

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believed that organisms changed form in response to “irritations” during their lives, and that these changes would be inherited. His ideas were similar to those of Lamarck.

His ideas were widely ridiculed, and ‘darwin-Izing” came to mean wild speculation.

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Homology

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Structural and developmental equivalence not obviously related to function

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Uniformitarianism

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the observation that, over time, relatively weak forces could have major effects. First used in Geology by Lyell.

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Pleisomorphy or pleisomorphic

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A shared character or feature
stemming from a remote ancestor. For example: all vertebrates share a basic arrangment of digits and supporting structures on their feet. We have all inherited these from a common ancestor, and they do not inform us about relationships.

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autopomorphies

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Derived features found only in a single group

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synapomorphies

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Derived or advanced features shared among two or more groups

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phylogeny

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Evolutionary history of a group

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monophyletic group

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a group containing a specific ancestral species and ALL of its descendents

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paraphyletic group

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a group that contains some, but not all, of the descendents of a specific ancestral species

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homoplasy

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noise in tree inference caused by character reversal or convergence