Management Units and Taxonomic Uncertainties

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Management Units and Taxonomic Uncertainties
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Taxonomy vs systematics
Systematics is the study ofevolutionary
relationships
Taxonomy is the science ofnaming groups of
distinct biologicalorganisms
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Negative outcomes of bad taxonomy

• Endangered species (or any species for that
  matter) go unrecognized
• Hybridization in captivity of previously
  unrecognized species
• Wasted conservation resources applied to overly
  split taxa
• Populations capable of being used for genetic
  rescue may be overlooked

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Basis for species definition (J. Hey)

• Taxonomic vs evolutionary
• Catalog or study processes?
• Theoretical vs operational
• Many theoretical concepts hard to implement in
  the real world
• Contemporaneous vs clade
• Anagenesis vs cladogenesis
• Reproductive vs cohesive
• Is ability to interbreed the determining factor
  or are other microevolutionary forces (drift,
  selection) important?

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Species concepts

• As many as 22!
• Morphological (typological, phenetic)
• Outward similarity--phenotypes works for asexual
  species
• Biological (BSC)
• Groups of interbreeding populations that are
  reproductively isolated from other such groups
  focuses on reproductive isolating mechanisms
  (Mayr)
• Similar to Isolation Species Concept (Dobzhansky)
• Recognition
• Group of individuals that recognize each other as
  potential mates pre-zygotic isolation
  (Patterson)
• Evolutionary
• a lineage of ancestor-descendant populations that
  maintains its identity from other such lineages
  and that has its own evolutionary tendencies and
  historical fate (Simpson)allows multiple species
  to occur on a single lineage through time
  (chronospecies)
• Phylogenetic
• Cladistics reveals species relationshipsmonophyly
  (autapomorphies, synapomorphies)
• Cohesion
• The most inclusive population of individuals that
  have the potential for phenotypic cohesion
  through intrinsic cohesion mechanisms
  (Templeton). An expansion of the recognition
  concept to allow for post-mating isolation.
  Allows low levels of hybridization.

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Cohesion mechanisms

• Genetic exchangability
• Factors that define the limits of spread of new
  genetic variants through gene flow
• Demographic exchangability
• Factors that define the fundamental niche and the
  limits of spread of new genetic variants through
  genetic drift and natural selection

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Units below species level

• Evolutionary Significant Unit (ESU)
• Defined (Ryder)
• A group that has undergone meaningful genetic
  divergence from other such groups
• Implies fragmentation
• Represents significant adaptation
• Implemented (Moritz)
• Populations that are reciprocally monophyletic
  for mtDNA haplotypes and that show significant
  divergence for nuclear alleles
• Management Unit
• Defined (Moritz)
• Local population dynamics are determined by birth
  and death, not immigration and emigration
• Implemented (Moritz)
• Units differ significantly in allele frequency
  distributions

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Problems (Paetkau)

• Investigators confused definition and genetic
  methods for detecting ESUs
• Ignores historic population size
• Time to reciprocal monophyly (Niegel and Avise)
• Simulation study
• Parent population still paraphyletic to daughter
  population 50 of time after N generations
• 4N generations to have 90 chance of monophyly
• Examples with a species with 10-year generations
• N 400, 50 prob of monophyly after 4000 years
• N 100,000, 10 chance of no ESU status after
  4,000,000 years
• Real example polar bears
• Evolved from brown bear lineage in Pleistocene
• No argument that it is separate species
• Yet, does not fit genetic definition of ESU
• MUs
• Demographic independence and genetic independence
  may be different due to non-equilibrium status
• Recently subdivided populations

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Exchangability (Crandall)

• Genetic and ecological exchangability
• Contemporary and historical context
• Genetic gene flow (Nm lt 1 rejected)
• Ecological fundamental niche characteristics
  (evidence of genetic drift or natural selection
  rejected)
• Temporal context distinguishes between long-term
  vs recent isolation and secondary contact

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Determining MUs

• MUs based on demographic independence
• How to delineate with genetic data?
• Estimate migrants?
• FST 1/(4Nm 1)
• Nm (1 FST)/4FST
• If FST 0.1, Nm ? 2
• Does that really tell us anything?

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Nm (1 FST)/4FST
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Problems

• Undersplitting
• Too few units recognized
• Poor statistical power of tests
• Units could go extinct
• Use assignment tests to determine of units
• Oversplitting
• Waste of resources

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Hybridization
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• Defined
• Individuals from two populations, or groups of
  populations, which are distinguishable on the
  basis of one or more heritable characters
• Becoming more widespread
• Introductions of exotics
• Habitat alteration

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Mule ? horse x ? donkey
Hinny ? donkey x ? horse
Zebroid
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New Zealand Grey Duck

• Introduced mallards
• Very common
• Native greys
• Uncommon
• Can interbreed
• Greys interbreed with mallards because they are
  easier to find as mates

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Ethiopian wolf

• One of worlds most endangered canids
• Interbreeds with domestic dog

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• Hybrid Zone
• Area of contact between genetically distinct
  population where hybridization occurs
• Geographically localized does not affect either
  parent population
• Hybrid Swarm
• Population consisting of all hybrids due to
  backcrossing with parental types and with
  breeding among hybrids
• Less localized, blurs genetic integrity of
  parental populations
• Genetic introgression
• Proportion of admixture percentage of alleles
  that come from the other population
• Not necessarily symmetric
• Mating behavior, habitat selection, etc.
• Hybrid taxon
• Independently evolving population with unique set
  of heritable traits, distinct from parental
  populations