Rose Thorogood - 2025-09-15

Assigned reading

Evolution Douglas Futuyma chapters 10-13

• These chapters are about products of evolution (what has come from natural selection)
• Now we have a better understanding of how behaviour evolves, but also how behavioural traits influence evolutionary processes

How does behaviour evolve?

There are three pathways for evolution:

Natural Selection

• Individuals which are most fit for their environment and able to reproduce survive

Sexual Selection

• An adaptation which increases reproductive success, often at the expense of survival

Kin Selection

• An adaptation to favour related individuals to an organism, even at the expense of their own offspring. Altrusim in bees, ants, wasps, termites are classic examples

Natural vs Sexual Selection

An evolutionary tug of war between exagerrated sexual characteristics and their Trade-offs in survival related characteristics (resource allocation, how easy they are able to be predated on)

Example with broad-horned flour beetles

• Males with longer horns have greater reproductive success, at the trade-offof smaller adbomens
• This gene is inherited in both males and females (Intralocus sexual conflict), resulting in females with smaller abdomens who can lay fewer eggs
• In experimental conditions with no predators, larger horns are favored (and fewer eggs)
• When predators are included in the experiment, smaller horns and more eggs are favored.

Are behaviours heritable?

• Behaviour is labile meaning it changes in response to the environment
• Therefore, it is difficult to detect heritability
• Until recently there were few examples of behaviours proven to be heritable
• Now, meta-analyses have shown that behavioural trails are within the same range of heritability as other life-history and physiological traits
• This indicates that, contrary to an assumption, behavioural traits are just as heritable as other traits

How and why does behaviour evolve?

• The Four-Question Framework from Niko Tinbergen gives us a way to categorize these.

Trade-offs and fitness outcomes

• The "Darwinian Demon" is a thought experiment about imagining the "perfect organism"
• We can determine what makes an organism closer to ideal by modeling evolutionary dynamics:

Costs and benefits

• By considering the $C$osts and $B$enefits of behavioural strategies, we can: š
  • predict when a behaviour should evolve ( $B>C$ ) š
  • determine the optimal behaviour (maximize $B–C$) š
  • find the Evolutionary Stable Strategy - ESS ( $B-C$ cannot be bettered by an alternative)
• These equations are modified by environment and other organisms (population)

How does behaviour influence evolutionary processes?

Cultural inheritance

• Genes and culture are both inheritance systems that generate phenotypic change
  • Example - a bird's song has a genetic component, but is also influenced by their parent's songs in the nest and general environment
• Culture is a form of non-genetic inheritance
• Social transmission is not just inheritance - it can also be transmitted between other unrelated individuals, or even from kin to their parent.

Gene-culture co-evolution (example in Galapagos finches)

• Many other pieces of circumstantial evidence of this taking place in other contexts as well.
• Rosemary Grant has a lecture about integrating behaviour, ecology and genetics.
• Galapagos finch females are influenced by songs that they hear in their youth and prefer mates with these kinds of songs
• Variation can result in some females picking unfamiliar songs, these sorts of events eventually result in them choosing a new mate, and this kind of song will be passed on to her chicks.
• The behaviour can inhibit or allow speciation to take place in this group of birds

Parental Care

Does parental care not only change the phenotype, but alter the adaptive value of that phenotype?

• In one case, the parents bring more food to the nest, the offspring grow bigger and have more offsprings
• In another case, the adults are larger

Example: Burying beetles

Model system in Behavioural Ecology

• These breed with small animal carcasses which they bury in the ground and lay their eggs in
• They also prepare the carcass by rolling it into a ball and smear it with an anti-microbial enzyme
• There is variation in:
  • Amount of carcass preparation
  • Amount of parental care (time before leaving the larvae)
• Experimental evolution tested whether variation alters selection in offspring traits
• One control group had parents removed after making inscision in flesh, another left parents, another left no parents
  • Offspring beetles in the no-care line were more likely to make a hole in the carcass for the larva to eat
  • Larva in no-care line had larger madibles in proportion to their body mass than full-care when they were small, but older individuals had similar length mandibles

Baldwin Effect

• Phenotypic Plasticity allows populations to survive environmental change
• Individuals with higher plasticity are more likely to survive