24 Speciation Flashcards
Species
an evolutionary independent population or group of populations; generally distinct from other species in appearance, behaviour, habitat, ecology, genetic characteristics etc.
What are the four criteria for identifying species?
(1) biological species concept (2) morphospecies concept (3) ecological species concept (4) phylogenetic species concept
Biological species concept
a species as a population or group of populations that are reproductively isolated from other groups (no gene flow occurs between them); members of a species can potentially interbreed in nature to produce viable, fertile offspring but cannot interbreed successfully with members of other species
Prezygotic isolation
prevents individuals of different species from mating successfully
Postzygotic isolation
the hybrid offspring of matings between members of different species either do not survive or cannot reproduce
What are the mechanisms of prezygotic isolation?
temporal, habitat, behavioural, gametic barrier, and mechanical
Temporal mechanism
populations are isolated because they breed at different times
Habitat mechanism
populations are isolated because they breed in different habitats
Behavioural mechanism
populations do not interbreed because their courtship displays differ
Gametic barrier
matings fail because eggs and sperm are incompatible
Mechanical mechanism
matings fail because male and female reproductive structures are incompatible
What are the mechanisms of postzygotic isolation?
hybrid viability and hybrid sterility
Hybrid viability
hybrid offspring do not develop normally and die as embryos
Hybrid sterility
hybrid offspring mature but are sterile as adults
Morphospecies “form species” concept
a species as a population or group of populations that have measurably different anatomical features from other groups
Ecological species concept
a species as a set of organisms exploiting a single set of resources, having the same range of environmental tolerances, and facing the same predators and parasites
Phylogenetic species concept
a species as the smallest monophyletic group in a phylogenetic tree
What are phylogenetic species made up of?
populations that share one or more unique synapomorphies
What are the advantages and disadvantages of the biological species concept?
Advantage: reproductive isolation = evolutionary independence; Disadvantages: not applicable to asexual or fossil species, difficult to assess if populations do not overlap geographically
What are the advantages and disadvantages of morphospecies concept?
Advantage: widely applicable; Disadvantages: subjective, misidentifies polymorphic species, misses cryptic species
What are the advantages and disadvantages of ecological species concept?
Advantage: applicable to sexual species; Disadvantage: different species may have similar ecological roles
What are the advantages and disadvantages of phylogenetic species concept?
Advantages: widely applicable, based on testable criteria; Disadvantage: relatively few well-estimated phylogenies currently available
Cryptic species
a species that cannot be distinguished from similar species by easily identifiable morphological traits
Polymorphic species
a species that has two or more distinct phenotypes in the same interbreeding population at the same time
What are the ways geographical isolation can occur?
dispersal and vicariance
Vicariance
the physical splitting of a population into smaller, isolated populations by a geographic barrier
Dispersal
colonists establish a new population in a novel location
Allopatric “different homeland” speciation
speciation that occurs when populations of the same species become geographically isolated, often due to dispersal or vicariance
Allopatry
condition in which two or more populations live in different geographic areas
Sympatry
condition in which two or more populations live in the same geographic area, or close enough to permit interbreeding
Sympatric speciation “together homeland’
divergence of populations living within the same geographic area into different species as the result of their genetic (not physical) isolation
What types of events can initiate the process of sympatric speciation?
external events like disruptive selection and internal events like chromosomal mutations
Niche
range of resources that a species can use and the range of conditions that it can tolerate i.e. the role that a species plays in its ecosystem
Sympatric speciation by disruptive selection
sympatric populations may become reproductively isolated by adapting to different ecological niches
Reinforcement of divergence
If hybrid offspring have low fitness, natural selection favors the evolution of traits that prevent interbreeding between the populations
Hybrid Zone
a geographic area where interbreeding occurs between two species, sometimes producing fertile hybrid offspring; may move over time or be stable
What are the possible outcomes of secondary contact between populations?
fusion of the populations, reinforcement of divergence, hybrid zone formation, extinction of one population, creation of new species
Fusion of the populations
the two populations freely interbreed; occurs whenever populations of the same species come into contact
Extinction of one population
if one population or species is a better competitor for shared resources, then the poorer competitor may be driven to extinction
Creation of new species
if the combination of genes in hybrid offspring allows them to occupy distinct habitats or use novel resources, they may form a new species
