Evolutionary biology 13 Flashcards
Co-evolution
the process by which two or more species evolve in tandem by exerting selection pressures on each other. Examples of coevolutionary systems include host and parasites, predators and prey, and mutualistic or symbiotic interactions.
- can also involve genetic elements within species
interspecific interactions resulting in co-evolution
1) antagonism - predation, parasitism, herbivory
2) competition
3) mutualism
examples of antagonism
Red queen dynamics - 2 species have opposite effects on each other
-constantly in arms race with each other (important in evolution of sex)
word equation for parasite evolution/fitness
Ro = bN/v+d+r
Ro = parasite fitness (number of new infections) b = probability of infecting new host N = number of hosts available v = death by parasite d= incidental death r = host recovery and death of parasite
- v+d+r = rate at which hosts are lost
predictions of parasite volution
- Correlations between virulence (v) and transmission (b) will increase virulence
- Vertically transmitted parasites will be less virulent (v+b are negatively correlated)
Examples of vertical transmission
1) Mitochondria - started off as parasite, now cant live without them
2) Aphids and their symbiotic bacteria - bacteria provide extra nutrients to the aphids, which feed on nutrient poor plant sap.
why do antagonistic- herbivore relationships develop
Herbivory behaviour is costly to the plant, has to regenerate lost plants or have less leaf area
Plant defences against herbivore behaviour
- thorns/spikes
- Toxins ( secondary metabollites)
- visual cues (e.g. mimicry)
Examples of antagonism-herbivore interactions
E.G. passiflora (passionflower)
- vines have toxins (cyanogenic compounds) in the leaves
- Counter adaptation, Heliconius caterpillars can detoxify and use these toxins for their own defence against predators.
Second example of antagonism-herbivore interactions
E.g. passiflora - Egg mimicry, deters actual ovoposition
- secrete nectar from leaves (extra floral nectaries) to attract ants and wasps that eat caterpillars.
- leaf shape variation, to avoid detection
- Counter adaptation: Heliconius butterfly’s, learn leaf shape
- leaf shape is perceived and used in ovoposition choice (drives antagonistic coevolution)
what can competition between two species lead to
- sometimes one species out-competes the other and drives them to extinction
- sometimes competition results in adaptations that reduce competition allowing species to co-exist
“Resource partitioning and niche specialization”
Resource partitioning and niche specialization
Over time, individuals within each population who are competing more heavily experience less
success. Natural selection drives each species to greater specialization and, thus, partitioning of
the resource.
example of coevolution leading to Resource partitioning and niche specialization
E.g. Heliconius and dryas caterpillars on the Passiflora plant
- when both are present larvae growth is much slower
- when they are alone they both feed on the edge of the leaf, however when they are together Heliconius feeds on shoots and Dryas feeds on the leaves
How does mutualism in plant + pollinators work, describe an example
- plant evolves flower to attract pollinator
- pollinators evolve features that beenfit the plant
E.g.
Heliconius (butterfly) - feed on pollen as well as nectar, nutritionally richer so live longer, prefer flowers that are present for duration of their lifespan.
E.g.
Psiguria plants - produce one flower daily over a period of several months (reliable food source)
What does mutalism not guarantee
that there is no conflict present,
e. g. Coffee and citrus plants have caffeine in their nectar
- alters bees behaviour (improves learning and memory)
- Bees will reject higher concentrations of caffeine.
