BIOL204 Cons Gen Session 6 Flashcards
how do we define a species?
Can be defined through measured differences between taxonomic units such as:
Morphology Mating mechanisms (pre-and post-zygotic isolation) Ecology/Evolutionary Significant Units Genetic distance Evolutionary distinctiveness
Although all have weaknesses and we can’t universally define a species yet
Problems with morphology for species definition? (3)
1) Most species are defined through morphology, however, some species may have polymorphisms of their colour like the Metriaclima zebra (Lake Malawi) or Asiatic golden cat which show different colours depending on their elevation.
2) Convergent evolution
3) Some species look so similar they are believed to be the same species but do not breed even when their ranges overlap e.g. Sphyrna spp. (hammerheads)
Problems with mating for species definition?
Some species can interbreed but do not occur sympatrically (occurring within the same or overlapping geographical areas.) in the wild, eg tigers and lions
What are ESU’s & Ecotypes?
(Evolutionary Significant Units) Populations or group of populations that merit separate management or priority for conservation because of high distinctiveness (both genetic and ecological)
Allendorf & Luikart (2007)
a genetically distinct geographic variety, population orracewithinspecies(or among closely related), which isadaptedto specific environmental conditions.
what does ‘pre-zygotic isolation’ and ‘post-zygotic isolation’ mean?
pre = prevents the fertilization of eggs post = prevents the formation of fertile offspring
What is convergent evolution?
independent evolution of structural or functional similarity in two or more unrelated or distantly related lineages or forms that is not based on genotypic similarity and common ancestry.
i.e. different evolutionary trajectories but look very similar .
Give an example of convergent evolution
the fish species in Lake Tanganyika and Lake Malawi evolved independently, however, have amazingly similar morphologies as they fill similar niches in their separate environments (Kocher et al., 1993).
How can we establish whether populations are actually separate?
molecular markers (e.g. microsatellites) & using Fst analysis & determining paternity.
How can we define Evolutionary Significant Units?
- Reproductive status and ecological & adaptive distinctiveness (Waples 1991)
- Reciprocal monophyly (Moritz 1994)
- All DNA lineages within a group must share a more recent common ancestor with each other than with lineages from other ESUs - Replaceability
- ‘Ecologically or genetically exchangeable’ (Crandall et al. 2000) management units within species
These all suffer with boundary limits & consistency across taxa
Give an example of an ecotype:
S. fluviatilis (marine & riverine dolphin ecotypes)
Taxonomic status uncertain
mtDNA
Freshwater species S. fluviatilis - 1st truly riverine dolphin species
Saltwater species S. guianensis – 3 ESUs – require separate management
(Cunha et al. 2005)
When using genetic distance, what DNA barcoding sequence do we use?
what are the drawbacks?
in the COI region of mtDNA, however:
In some groups COI shows too little or too much variation to usefully define species
Other groups simply do not have mitochondria
Incomplete lineage sorting
What is incomplete lineage sorting?
when an original species split to form 2 groups form either stochastic events or selection driven divergence, the neutral markers might not have had time to accumulate yet if it’s happened recently and rapidly (LeDuc et al. 2008)
Regarding the tree of life/species lineages what is the difference between cladograms and additive trees (phylograms)?
cladograms:
represent relative recency of common ancestry
additive trees:
represent the above with an indication of branch length (indicating the amount of evolutionary change). This can allow for a measure of Independent evolutionary history (IEH)
what does loss of species lead to in term of lineages?
loss of evolutionary history
What are the problems we need to consider when using genetics to solve the ‘species problem?’
- what genetic markers do we use?
- how much difference between the genetic markers do we name 2 individuals as a separate species?
- how do we ensure data recorded in public databases is accurate?