SPECIES CONCEPTS Flashcards
Latin for “kind” or “appearance”
organisms belonging to the same “kind”
Species
Estimate ranges from 3.6-111 million species * Normally used working figure is often 10-15 million
True
concept that each species remains unchanged since its creation
Species Fixity
supported Species Fixity
Theory of Forms * Perfect vs imperfect forms; variations are imperfections
Plato (428-348 BC)
supported Species Fixity
Theory of Types Species reflect existence of unchanging, ideal form, the “universal” or “type” variations are imperfections
Reinforced by Aristotle (384-322 BC)
supported Species Fixity
Adhered to the Aristotelian fixity of species “In the beginning were created only germs or causes of the forms of life which were afterwards to be developed in gradual course”
St. Augustine (AD 345-430)
design in nature is evidence of benevolence, omnipotence, and existence of God as Creator of the existing order (Argument from design)
Thomas Aquinas (1225-1274)
Species as Evolving Entities
Origin of Species* (1859) 2000+ years of certainty in fixed species ended * But the ‘Species Problem’ was born
- Charles Darwin (1809-1882)
supported Species Fixity
an entire species could be represented by one type specimen (holotype)
TYPOLOGICAL SPECIES CONCEPT = Morphological Species Concept
Carolus Linnaeus (1707-1778)
Said that
A species is a set of organisms that resemble one another and is distinct from other sets”
Species are groups of individuals that are morphologically similar and clearly distinguishable from individuals of other groups”
Carolus Linnaeus (1707-1778)
The Modern Species Problem components (4)
- Biological Species Concept
- Paleontological Species Concept
- Ecological Species Concept
- Phylogenetic Species Concept
defines species as… “…groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups.”
In short: members of a population mate with each other and produce fertile offspring
Biological Species Concept
who made the biological species concept
Ernst Mayr’s
populations whose members do not mate with each other or who cannot produce fertile offspring
Reproductively isolated
barriers to successful reproduction
Reproductive isolating mechanisms
Reproductive isolating mechanisms (7)
Geographic - Behavioral - Mechanical - Ecological - Temporal - - Gamete fusion - Postzygotic
tiger and lion Reproductive isolating mechanisms
Geographic
Ecological
species differ in their mating rituals
Behavioral isolation
fireflies recognize signals of their own species
frogs have calls that only attract their own species
birds have songs that only attract their own species
Behavioral isolation
PREZYGOTIC ISOLATING MECHANISMS (6)
Geographic
Behavioral
Mechanical
Ecological
Temporal
Gamete fusion
species reproduce in different seasons or at different times of the day e.g. frog species mate at different seasons
Temporal isolation:
structural differences between species prevent mating
Mechanical isolation:
Example:
- Flowers of varied nature of corolla are likely visited by dissimilar pollinators
- insects whose copulatory organs may not fit together, so no sperm would be transferred
Mechanical isolation:
gametes of one species functions poorly with the gametes of another species or within the reproductive tract of another species
Prevention of gamete fusion (Gametic/gametophytic isolation):
Postzygotic barriers
- Reduced Hybrid Viability
- Reduced hybrid fertility
- Hybrid Breakdown
Does not reach sexual maturity
Reduced Hybrid Viability
Even if hybrids are vigorous, they may be sterile
Reduced hybrid fertility
offspring of hybrids have reduced viability or fertility
Hybrid Breakdown
Limitations of biological species concept: (4)
-Interspecific hybridization among animals
-10% of bird species have hybridized in nature
- many plants naturally hybridize
- concept applies to sexual species only, excludes fossils and asexual organisms such as prokaryotes
OTHER SPECIES CONCEPTS
Paleontological Species Concept
Phylogenetic Species Concept
Ecological Species Concept
focuses on morphologically discrete species known only from the fossil record.
Paleontological Species Concept
defines a species as a set of organisms with a unique genetic history-that is, as one branch on the tree of life
Phylogenetic Species Concept
views a species in terms of its ecological niche, its role in a biological community
Ecological Species Concept
Real species problems
Asexual populations
Prokaryotes
Interspecific hybrids
Endosymbionts
Are all organisms assignable to species?
the process by which new species arise, either by - transformation of one species into another, or by the splitting of one ancestral species into two descendant species
Speciation
transformation of one species into another
ANAGENESIS
or by the splitting of one ancestral species into two descendant species
leads to diversity
CLADOGENESIS
PATTERNS OF SPECIATION
CLADOGENESIS
ANAGENESIS
Modes of speciation
Allopatric speciation
Sympatric speciation
Parapatric Speciation
speciation that takes place in populations with geographically separate ranges. Gene flow is interrupted and new species evolve.
Allopatric speciation
speciation that takes place in geographically overlapping populations. Chromosomal changes and nonrandom mating reduce gene flow.
Sympatric speciation
Adjacent populations evolve into distinct species while maintaining contact along a common border
Parapatric Speciation
This can occur by chromosomal changes and nonrandom mating. Both can reduce gene flow between organisms and cause populations to evolve to new species.
common in plants
Sympatric speciation
the heritable condition of possessing more than two complete sets of chromosomes.
common in plants
Polyploidy
the heritable condition of possessing more than two complete sets of chromosomes in own species
autopolyploidy
offspring with polypoid karyotyope may be viable and self-fertile
true
Causes of genome duplication:
a) meiotic non-reduction of gametes (both in egg and sperm)
b) genome duplication w/o cytokinesis (after fertilization)
are fertile because each chromosome has a partner with which it can pair during meiosis, the process in which gametes are produced.
Duplicated genomes are tetraploid when the cell contains 4 copies of each chromosome. It is diploid when it contains only 2 copies of each.
Autopolyploids
in some plants can result in cells with more than a hundred chromosomes.
Autopolyploidy
occurs when an organism has more than two sets of chromosomes from different species.
allopolyploidy
arises from hybridization plus
genome duplication
homologous pairing is predominant
may lead to speciation
allopolyploidy
does not lead to speciation
Autopolyploidy
theory about the evolution and relationships among the members of the plant genus brassica
the triangle of u
