Tuesday 25th September 2018 - Evolution of Behaviour Flashcards
Fossil Records
Behaviour isn’t preserved in fossil records … but can leave us clues.
• Some things are left behind that give us clues about how animals might have behaved.
Question: what kinds of fossilised things can we get clues from?
• Physical remains.
– E.g., bones, teeth, etc.
• Evidence of animals’ presence/activity (trace fossils).
– E.g., tracks, burrows, bite marks, etc.
Fossil Records
Composition, form, and location of fossils can provide hints at behaviour. •
Dinosaurs
– Birds exhibit parental care.
– Where did it originate?
– This fossil suggests dinosaurs.
Fossil Records
Fossil records of morphology can give clues about certain behaviours.
• E.g., horses.
– Structure of teeth and feet in horses
. – Were browsers, now grazers.
Question: what else might give us clues about diet?
• Faeces/coprolites.
Fossil Records Interactions between species can sometimes be observed.
• E.g., food chain in aquatic species (Kriwet et al., 2007).
Fossil Records Predator-prey interactions can be inferred.
• E.g., probable predation (Wilson et al., 2010).
Fossil Records Predator-prey interactions can be inferred.
• E.g., probable predation (Wilson et al., 2010).
Fossil Records Information about feeding behaviour can be gleaned from coprolites.
- E.g., fossilised T. rex faecal matter (Chin et al., 1998).
- Evidence of bone crushing during feeding. • Incomplete digestion of bone fragments.
- Prey appeared to be a sub-adult dinosaur.
Fossil Records Mating behaviour may be revealed via fossils.
• E.g., intrasexual selection (male-male competition) and weaponry.
Other clues remain:
Modes of locomotion
– E.g., footprints showing if feet were wide-/closely-set.
Predation
– Scratches, holes, etc.
Habitat selection
– Dens, burrows.
Vocalisations
– Bony structures.
Comparing Species Comparative method = comparing [closely-related] species, examining behaviour patterns to determine how they evolved.
- Differences and similarities.
- Assumes that behaviour traits are heritable.
- And that behaviour traits evolved from simple → complex forms.
Fossilised footprints are excellent indicators of Animal behaviours such as locomotion.
https://www.youtube.com/watch?time_continue=58&v=jtbpusl0Vo0
Comparing Species
E.g., balloon flies (Kessel, 1955) – possible evolutionary stages.
Comparing Species
E.g., balloon flies
– questions remain.
It’s a logical arrangement, but there are limitations of this comparative method.
• Don’t know if balloon flies went through all stages during evolution.
• Is the order of stages correct?
– Traits don’t always evolve linearly, simple → complex.
– Some phenotypes are optimal for some environments (which are not static).
• Correlation ≠ causation.
– Could be additional variables.
• Knowledge of function can be useful.
– E.g., Kessel (1955) suggested nuptial feeding reduced chances of males being eaten during copulation.
– Thornhill (1976) suggested food provisioning = parental investment, females selecting on basis of quality.
Comparing Species Limitations of this comparative approach:
• Some animals remain relatively unchanged.
– E.g., horseshoe crabs.
• Not all animals are perfectly adapted to environment. Trait similarities can arise via shared ancestry, or independent evolution.
• Ancestral traits = ?
• Derived traits =?
• Ancestral traits = shared by a common ancestor.
• Derived traits = evolved more recently, not present in common ancestor.
Comparing Species Example:
Mobbing in blacked-headed gulls.
• Hypothesis: mobbing is an evolved response to predation risk to eggs in ground nests
– to distract predators
If correct, other gulls whose young are not at this risk should not display this behaviour
Comparing Species
Example: mobbing in blacked-headed gulls.
• Two potential explanations
A. Ground-nesting ancestor; kittiwakes are descended from more-recently evolved cliff-nester.
B. Original ancestors were cliff-nesting; this trait was lost and then regained. • More changes.
Comparing Species Example:
Mobbing in blacked-headed gulls.
• Simpler scenarios are more likely parsimony.
(Parsimony: extreme unwillingness to spend money or use resources.)
- Fewer predators can reach cliff nests, thus selection pressures for mobbing should be different anyway.
- The case of cliff-nesting kittiwakes, who do not mob predators …
– Kittiwakes’ different behaviour is example of divergent evolution.
– Supports original hypothesis.
Comparing Species Another comparative approach
– animals from different lineages, in same environments, may evolve similar traits due to shared selection pressures.
• Convergent evolution.
Example: burrowing behaviour in mice
Varied burrowing behaviour within one genus, Peromyscus.
- First, constructed phylogenetic tree from genetic data.
- Second, behavioural studies determined each species’ burrowing characteristics.
- Last, mapped behaviour onto phylogeny.
Variation in burrow presence/complexity.
• Results indicate:
– Ancestral trait = no burrowing.
– Derived trait = large, complex burrows.
Comparing Species
Example: swordtail fish, some males have ‘sword’ tail extensions.
Females prefer swords.
– Females in species with no natural swords – also prefer swords.
Phylogenetic analysis suggests females’ preference for swords evolved before swords.
Comparing Species Example: swordtail fish
Some males have ‘sword’ tail extensions.
• But, perhaps this trait evolved/was lost more than once over time.
– Traits evolved via sexual selection may be particularly likely to change over evolutionary time.
• Therefore, the standard comparative approach could be limited here.
