BIOGEOGRAPHY AND SPECIATION

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• BIOGEOGRAPHY AND SPECIATION
• Because of geographic barriers and thermal
  gradients the ocean can be divided into provinces
  - biogeographical regions with characteristic
  spp. Assemblages.
• Classifications of groups of spp. belonging to a
  province usually based on qualitative judgements.
• A between-locality similarity index can be
  calculated and similar locales can be grouped
  into provinces.

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• Jaccards Coefficient
• MijCij/Ni Nj - Cij
• Cij of spp. the 2 samples have in common
• Ni of spp. in sample i
• Nj of spp. in sample j

3

• Matrix of coeff. (locality spp.) can be
  clustered hierarchically
• Based on Mijs can use unweighted-pair group
  method
• 27-28 N. latitude is transition from Pacific
  equatorial water mass and colder California
  current
• 34-35 at Pt. Conception cool water from north
  and warm water from south
• Imbrie Kipp, 1961 - Factor analysis to
  construct assemblage of Atlantic planktonic
  forams - they fit very well with water mass
  distribution. - surface-thermal structure of
  oceans - same for diatoms

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• Adaptability and Biogeographical Range
• Species living in variable environments should
  also have the flexibility to occur over a broad
  biogeographical range
• Capitella capitata - worldwide
• Mulinia lateralis - New Brunswick - Yucatan
• Jackson, 1974 - Biogeographical range for
  shallow-water bivalves is much broader than for
  deep-water spp.

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• The significance of biogeographical range lies
  in its possible inverse relation to extinction
  rate
• Species over a wide area might be less prone to
  extinction
• Bivalve genera with cosmopolitan ranges go
  extinct much later
• Levinton, 1974 - cosmopolitan bivalves of the
  Paleozoic and Mesozoic have much longer
  geological time ranges than genera with more
  restricted ranges

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• Dispersal and Range Extension
• Biogeographical range can be enhanced through
  chance migration across barriers
• New colonizations of marine organisms - often
  facilitated by humans - provide insight on the
  rapidity of spread and effects

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3 Types of Colonization of Marine Organisms a)
planktonic larvae may traverse great oceanic
expanses and colonize new coasts b) attached
forms (i.e., barnacles) may raft across oceans
- logs, ships, etc. c) species introduced by
humans for culture
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• Littorina littorea - periwinkle - was noticed in
  Nova Scotia in the 19th century
• Since that time it has spread southward and
  become the dominant gastropod of New England
• Probably facilitated by shipping - down to MD,
  limited by temp., has probably displaced all
  other local spp. of Littorina
• propagule - min. of individuals that can
  establish a reproducing population

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• If colonization target is small - the absence of
  a suitable habitat or the chance of extinction
  due to predation or competition by residents will
  increase
• If immigrants of a species invade a target area
  devoid of the species at a constant rate (i), the
  expected of individuals, Nt, at time t is
• E (Nt) i/(b-d)e(b-d)t-1
• b birth on the target area
• d death on the target area

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• If b is less than or equal to d, population size
  is maintained or increased (if bd) only through
  immigration.
• If we have an exponentially growing pop. with
  initial size, a ( of propagules) - the
  probability of extinction by some time t is
• P0(t) d(eb-dt-1) / be b-dt -da(prop.)
• With b0.7, d0.2, the limiting probability of
  extinction with 1 propagule is 0.29 with 2
  propagules it is 0.08 with 4 it is only 0.006.

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• The significance of this calculation applies to
  the study of gastropods living on both sides of
  the Atlantic - many whose pelagic larvae are
  found in the open-ocean
• Thus, a is probably high (Scheltema, 1971)

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• Island Biogeography
• Schoener 1974 followed the colonization of
  marine invertebrates onto plastic mesh sponges.
  Large and small were placed near and far from an
  algal bed (a presumed source of colonists). The
  experiment was performed at Bimini Lagoon,
  Bahamas so P (spp. pool) was probably large but
  indeterminate. The following results were
  obtained

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1) A stabilization of species number did occur
with time 2) There were more species and
individuals on large than on small sponges 3)
There was no difference in species number on
near or far sponges, probably because the
source area was not the algal bed 4) Early
colonization species were suspension or
detritus feeders and other types followed
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• Origin of New Species
• Speciation - isolation of daughter pop. from
  parent pop. - genetic divergence prevents
  interbreeding
• - isolation of a pop. followed by
  allopatric, genetic divergence
• Isolation in the sea requires barriers that are
  of common occurrence
• Open sea is an effective barrier for most shelf
  benthic invertebrates

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• North-south provincial boundaries are often
  locations of between-water mass isolation
  (Mid-ocean Ridges)
• Isthmus of Panama
• Although allopatric speciation is an obvious
  explanation for speciation on either side of a
  geographic barrier, some species ranges end at
  thermal discontinuities
• Point Conception CA (N-S temp. breaks)
• Cape Hatteras, NC

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• It is possible that genetic divergence can occur
  on either side of such a discontinuity - even
  with some gene flow thus, spp. might originate
  because of strong divergent selection in two
  geographically adjacent but environmentally
  different habitats. This model of divergence and
  speciation is referred to as parapatric
  speciation.

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• Species Problems - spp. recognition morphology
  etc.
• 2 species of eel - Anguilla rostrata (Amer. Eel)
  and Anguilla anguilla (European) - species
  differences has been a subject of hot debate
• Both spp. migrate from freshwater rivers and
  brackish water to spawn in open water of Sargasso
  Sea
• Schmidt (1920s)- evidence suggesting overlapping
  but non-identical spawning grounds

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• Large difference in vertebral between the 2
  spp.
• Because vertebral in fishes is often a
  function of ambient temp. during larval stage -
  it is possible that each spp. originates as a
  single randomly mixed panmictic population in its
  spawning grounds
• Grounds may have different latitudes and hence
  different temperatures

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• Possible that all European eels do not survive
  trip to Sargasso, this would suggest that Euro.
  eels are the progeny of American eels
  reproducing in Sargasso Sea
• A difference in chromosome has been found
  between the 2 spp. - but only a large allele
  frequency difference at one biochemical enzyme
  locus was detected in an intensive investigation
  of many loci
• Furthermore - eels from Iceland have intermediate
  vertebral

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• Mussels
• M. edulis is a species with subpopulations in
  boreal and temperate waters of the N. hemisphere
  and closely related representatives in S. Amer.
  ,New Zealand, and Australia.
• Southern - M. galloprovincialia - English Channel
  and Mediterranean, but M. edulis only in the
  English Channel
• Barsotti Melluzzi, 1968 - M. gallo. - recent
  derivative of M. edulis - since geographic
  separation between Atlantic and Mediterranean.
  Speciation likely still in progress

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• Similar problem with Cardium edule (northern) and
  C. glaucum (Med.) these cockles have
  overlapping distributions in Britain and Jutland

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• Genetic Variations
• Hardy-Weinberg - ƒ(aa) - p2
• ƒ(ab) - 2pq
• ƒ(bb) - q2
• Heterozygotes might exhibit superior performance
  - overdominance
• Homozygotes might be preferred - -
  underdominance
• Genotypes with specific allele might be favored
  - - directional selection
• Assortive mating - small populations increases
  probability of chance deviations

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• Random sampling of gametes from parents to form
  offspring will on average increase with
  decreasing population size results in a random
  genetic drift of allele frequencies.
• Founder Principle States that a small isolate
  of a species migrating to a peripheral location
  is bound to have a differing genetic constitution
  than the parent population.
• Such an effect may be important when only a few
  larvae survive a trip of ca, 100 km to a site,
  originating from a parental population that
  produced several million larvae

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• Type of Variation Measurable in Marine Organisms
• Chromosome and polymorphism - some marine
  species have variable of chromosomes per
  individual among population and variation in
  morphological characteristics of a given
  chromosomes.
• In the drilling gastropod Nucella lapillus,
  variation in chrom was observed along the
  French coast. Haploid of n13 on wave-exposed
  coast, with n18 in sheltered habitats - cause is
  unknown.
• Ahmed Sparks, 1970 - Mytilus chromosomes
  differ in form, but not in .

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• Color polymorphism
• Color spot patterns - products of one of a few
  loci
• Harpacticoid copepod color spots on
  cephalothorax vary in size and shape
• Mytius edulis, brown shell phenotype co-occurs
  with more common black pheno. Crosses show that a
  simple one-locus, two allele genetic model
  governs the variation (Innes and Haley, 1977)
  Brown allele is dominant over black.

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• Genetic Polymorphism
• The amount of polymorphism maintained in a
  species is of great interest because it suggests
  the scope of variation on which selection may
  act.
• Species of Macoma living on different varieties
  of sedimentary substrate - examined for degree of
  polymorphism at 2 enzyme loci.
• No variation found at leucine aminopeptidase
  locus
• But it was more polymorphic at phosphoglucose
  isomerase locus

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• Geographic Variation
• Trends in the distribution of allele frequency
  have been commonly observed for marine species,
  particularly in protein polymorphisms. Variation
  along a geographic distance is known as a cline.
• Cline found for shell morphology, chrom , shell
  color, and protein allele frequency.

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• Johnson 1971, showed that a 2 allele lactate
  dehydrogenase locus in the intertidal crested
  blenny Anoplarchus purpurescens showed
  latitudinal clinal variation in Puget Sound, WA -
  consistent with temperature variation. The A
  allele is associated with warm temperature and
  increased from less than 0.05 from the Strait of
  Georgia southward to over 0.25 near Tacoma, WA
  (see graph in notes)
• Also for ectoproct bryozoan species - allele
  frequency correlated with temperature in Cape Cod
  - at 2 loci

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• Lactate dehydrogenase
• Powers et al. (1979) Nature 277 (240-241)
• Adaptive importance of catalytic efficiency
• In the LDH-B allozymes in Fundulus heteroclitus
• North-south cline Atlantic coast
• Temperature effect on enzymes
• Temperature effects on LDH - how it affects
  physiology.
• Growth rate at low temps, blood oxygen affinity
  etc.

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• In M. edulis, 3 common aminopeptidase alleles
• Lap94, Lap96, Lap98
• Catalytic properties of Lap94 different from
  96-98, 20 higher efficiency results in higher
  accumulation rate of free amino acids
• High temp. and salinity, show increase in
  aminopeptidase activity (increase in enzyme
  protein concentration) well understood for
  salinity not temp.
• It is where these 2 conditions (temp and
  salinity) occur that a cline with higher Lap94
  exists

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• Fluctuation of Salinity Conditions
• Higher rates of cellular protein catabolism
  (during hyperosmotic acclimation) and excretion
  of amines (during hypoosmotic acclimation)
  results in depletion of nitrogen reserves.