2nd half Lecture 2
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• Adaptation: A trait that increases the f itness of it’s bearer and that evolved for that specific role
• The biological environment (natural enemies in other species (parasites), conspecific rivals &
potential mates) represents a set of constantly changing (evolving) selection pressures
• This has led to host-race formation in some species -> can lead to speciation. But did not
happen in cuckoos because males can mate with female from any race.
• Behavioural and other adaptations in different populations can lead to population divergence
even in sympatric populations
• Given the social biology of cuckoos, however, sympatric speciation is unlikely
Parasites Manipulating Hosts Hypothesis Testing & the Culture of Science
Parasite wasp larvae live inside caterpillar which then acts maternally! Caterpillar not care for
Flukes make ants go to top of vegetation where the ant gets eaten by a cow!
Malaria: mosquito -> human (some parasites go through different hosts)
Horsehair worm infects aquatic insect which then dies and gets eaten by another insect which
then gets infected the retur n to the water to die. Final host is cricket. Wor m comes out of the
dying cricket then mates in the water.
Hypo 1: worm makes cricket jump into water.
The prevalence of infection (by wor ms) was very different between (crickets) collected in the
forest (15%) and t hose collected around the swimming pool (95%).
Hypo 2: cricket is sick (thirsty). Not supported bec found chemicals in crickets.
Cr icket manipulation theor y is true for the cricket because worm releases chemicals to control
Thor ny-headed wor m (Acanthocephala)
• Lives in guts of (intermediate host) sowbugs Armadillium. Sowbugs are eaten by definitive host
bird. Eggs shed in bird feces and eaten by sowbugs (2 hosts)
• Parasitized sowbugs are found more frequently away from cover, in less humid areas and on
Infected rats went near cat urine more than non-infected rats!
Alternative hypothesis: animal is simply sick
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