Week 13 Flashcards
(15 cards)
Recognize challenges in identifying species (and other taxonomic designations)
The distinction between species is vague and arbitrary.
Provide an example of the practical importance of defining species.
Conservation: invoking endangered species legislation requires species status
Describe/define the horizontal and vertical species concepts.
Horizontal species concept– aim to define species at an instant in time and specify which individuals belong to which species at one time.
Vertical species concept– aims to define species through time and specify which individuals belong to which species through all time
Define nominalism and realism.
Nominalism: Idea that species are artificial division of a natural continuum
Realism: idea that nature is, in fact, divided into discrete species
What is the phenetic species concept?
Defines species based on shared phenotypic attributes (e.g. morphology, behaviour, chromosome number and structure)
Phenetic = phenotypic
Most descriptive and least theoretical of the species concepts.
Describe the biological species concept.
Species are groups of actually or potentially interbreeding populations which are reproductively isolated from other groups.
- reproductive isolation
Define reproductive isolation.
Lack of gene exchange between two species due to biological (not geographic) factors
What are the pre-zygotic isolating barriers?
Pre-mating barriers: features that impede transfer of gametes to members of other species
A. Ecological isolation: potential mates (although sympatric) do not meet
- Temporal isolation (populations breed at different seasons or times of day)
- Habitat isolation (populations have propensities to breed in different habitats in the same general area, and so are spatially segregated)
- Immigrant inviability (immigrants between populations do not survive long enough to interbreed
B. Potential mates meet but do not mate
- Sexual (behavioural or ethological) isolation (in animals, differences prevent populations from mating)
- Pollinator isoaltion (in plants, pollen is transferred in different populations by different animal species or on different body parts of a single pollinator; may also be classified as ecological isolation)
What are the post-mating isolation barriers?
Post-mating, pre-zygotic barriers are when mating or gamete transfer occurs, but zygotes are not formed
A. Mechanical isolation (copulation occurs, but no transfer of male gametes taken place because of failure of mechanical fit of reproductive structures)
B. Copulatory behavioural isolation (failure of fertilization because of behaviour during copulation or because genitalia fail to stimulate properly)
C. Gamete isolation [failure of proper transfer of gametes or of fertilization, either due to competition between conspecific and heterospecific gametes {conspecific sperm precedence or pollen tube precedence) or intrinsic incompatibility]
D. Immigrant inviability after mating occurs in “alien” habitat
What are the post-zygotic isolation barriers?
Post-zygotic barriers are when hybrid zygotes are formed but have reduced fitness
A. Extrinsic (hybrid fitness depends on context)
- Ecological inviability (hybrids do not have an ecological niche in which they are competitively equal to parent species)
- Behavioural sterility (hybrids are less successful than parent species in obtaining mates)
B. Intrinsic (hybrid fitness is low because of problems that are relatively independent of environmental context)
- Hybrid inviability (developmental problems causes reduced survival)
- Hybrid sterility (usually due to reduced ability to produce viable gametes; also ‘behavioural sterility’ neurological incapacity to perform normal courtship)
True or false? Isolation barriers work independently.
False. There can be multiple isolation barriers in place
Are isolation barriers permanent?
No, isolation barriers can break down due to changes in the environment.
Ex) Coyote wolf hybrids
African cichlids, pollution of water, cannot observe colour in mate selection
Define primary and secondary hybrid zones.
Hybrid zones are regions in which genetically distinct populations come into contact and produce at least some offspring of mixed ancestry.
Primary hybrid zones– originate in situ as geographic variation in natural selection alter allele frequencies in a continuously distributed population
Secondary hybrid zones– formed when two formerly allopatric populations that have become genetically differentiated expand so that they meet and interbreed
What are the 3 stages of speciation?
(1) Population isolation– a reduction in gene flow between populations, most commonly due to geographic separation… but there are other possibilities (e.g. changes in chromosome number)
(2) Divergence– e.g. morphological traits, habitat use, mating habits
(3) Reproductive isolation– following secondary contact (when populations come back together)
What are the 4 modes of speciation?
(A) Allopatric speciation by vicariance– Population separated by barrier, different species develop, barrier is removed or new species disperse over it, re-establishing sympatry.
(B) Peripatric speciation (founder effect)– a small group is separated from the larger population and develops into a different species, through range expansion re-establishes sympatry
(C) Parapatric speciation– two subpopulations of a species evolve reproductive isolation from one another while continuing to exchange genes, range expansion leads to sympatry.
(D) Sympatric speciation– genetic differences results in reproductive isolation, there is no geographic isolation
