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Darwinian: selection & behavior
Fig 1.13 from Animal Behaviour Copyright Sinauer Press (from original Gary Larson cartoon)
Darwinian Selection and the Biological Environment: The creation of biodiversity
Host Cuckoo Model From: Brooke & Davies (1988) Nature 335:630
Cuckoos are social parasites which lay their eggs in other species of birds and never care for
their young. Each cuckoo race specializes on a different host where it lays its eggs to look like
the host’s eggs. Hosts are good at discriminating against parasite eggs. The more incubation
costs are the better the host is at discriminating against parasite eggs and the higher the cuckoo
eggs matching the host eggs! Low cost of incubation is reason why Dunnocks not evolve to
discriminate against parasite eggs.
No flexibility in what hosts to lay eggs in (each race specialized) + phenotypic differences
between the races. But have gene flow between the races e because males can mate with females
from any race.
Microsatellites: repeating sequences of 1-6 base pairs of DNA. -> No host specific differences.
Mitochondria DNA: maternally transmitted, has strong host species differences. Mum ->
daughter -> granddaughter. Males inherit but not pass.
Hypothesis 1: markers of divergence.
Hypothesis 2: same females were same from both places. Not supported because large
distances between each sample field.
But genome (not mitochondrial DNA) codes for egg colour!
Hypotheses for how host-race adaptations remain distinct. W is where coding for host specific
egg is. Assumptions: no Z W recombination.
• (Birds have a ZW=female, ZZ=male sex chromosome system)
Sympatric speciation is the process through which new species evolve from a single ancestral
species while inhabiting the same geographic region. Eg) 1 fruit fly lays eggs on apples other on
other type of fruit. Separated by time and place.
Allopatric speciation or geographic speciation is speciation that occurs when biological
populations of the same species become isolated due to geographical changes
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