Co-evolution: The evolutionary arms race - Topic 10 (part 2)

Co-evolution

RECIPROCAL evolutionary change in two or more species driven by their INTERACTIONS; each species acts as a SELECTIVE PRESSURE on the other

Co-evolution

• If one species evolves a new trait, the interacting species faces new WHAT, which leads to ongoing, coupled WHAT change

• WHAT selection

• Not WHAT: driven by WHAT

Co-evolution

• If one species evolves a new trait, the interacting species faces new SELECTIVE PRESSURES, which leads to ongoing, coupled EVOLUTIONARY change

• RECIPROCAL selection

• Not RANDOM: driven by SPECIFIC INTERACTIONS

• Example: Flower shape evolves to match pollinator mouthparts

Reciprocal selection

Each species selects for TRAITS in the other

Evolutionary arms Race

Cycle of CO-EVOLUTIONARY escalation; one species improves OFFENCE, other improves DEFENCE, repeat indefinitely

Red queen hypothesis

Organisms must keep evolving just to maintain FITNESS relative to co-evolving partners

Arms race and red queen

• Arms races create escalating WHAT

• WHAT based (WHAT)

• Arms races cannot escalate HWAT; WHAT and WHAT often stabilize traits

Arms race and red queen

• Arms races create escalating ADAPTATIONS

• GENETICS-based (EVOLUTION)

• Arms races cannot escalate INDEFINITELY; TRADE-OFFS and COSTS often stabilize traits

Predator-prey co-evolution

Predator strategies:

• WHAT and agility (cheetahs, peregrine falcon)

• Camouflage (polar bears)

• WHAT hunting (wolves, orcas)

• Stealth and ambush (lynx)

• WHAT specialization (sight, smell)

Predator-prey co-evolution

Predator strategies:

• SPEED and agility (cheetahs, peregrine falcon)

• Camouflage (polar bears)

• COOPERATIVE hunting (wolves, orcas)

• Stealth and ambush (lynx)

• SENSORY specialization (sight, smell)

Predator-prey co-evolution

Prey strategies:

• Speed and escape behaviours

• WHAT (stick insects, flounder)

• Armour (turtle shells, pangolin scales)

• Group vigilance, defense, coordinated escape, and visual confusion (stripes)

• WHAT and warning defences

Predator-prey co-evolution

Prey strategies:

• Speed and escape behaviours

• CAMOUFLAGE (stick insects, flounder)

• Armour (turtle shells, pangolin scales)

• Group vigilance, defense, coordinated escape, and visual confusion (stripes)

• CHEMICALS and warning defences

Arms races don’t always escalate indefinitely; WHAT and WHAT often stabilize traits

Arms races don’t always escalate indefinitely; TRADE-OFFS and COSTS often stabilize traits

Predator-prey Co-evolution: Bats and moths

Bat Adaptations:

• Echolocation to detect prey at night

• Highly maneuverable flight

Moth Counter-adaptations

• Ultrasonic ears tuned to bat calls

• Escape dives and erratic flight when bat calls detected

• Ultrasonic clicks that jam echolocation
  

Arms Race:

• Bats evolve more precise WHAT

• Moths evolve better WHAT and WHAT mechanisms

Predator-prey Co-evolution: Bats and moths

Bat Adaptations:

• Echolocation to detect prey at night

• Highly maneuverable flight

Moth Counter-adaptations

• Ultrasonic ears tuned to bat calls

• Escape dives and erratic flight when bat calls detected

• Ultrasonic clicks that jam echolocation
  

Arms Race:

• Bats evolve more precise ECHOLOCATION

• Moths evolve better DETECTION and INTERFERENCE mechanisms

Predator-prey Co-evolution: Toxins and resistance

Rough skinned Newt defence:

• Produce tetrodotoxin (TTX), one of the most potent natural toxins

• Blocks sodium channels and causes paralysis or death
  

Garter Snake Counter-Adaptation

• Genetic resistance to TTX

• Modified Na+ channels allow consumption of toxic newts

Arms race:

• Newts evolve higher WHAT levels

• Snakes evolve greater toxin WHAT

• Trade-offs constrain WHAT

• Resistance reduces snake WHAT

• Toxin production is energetically WHAT

Predator-prey Co-evolution: Toxins and resistance

Rough skinned Newt defence:

• Produce tetrodotoxin (TTX), one of the most potent natural toxins

• Blocks sodium channels and causes paralysis or death
  

Garter Snake Counter-Adaptation

• Genetic resistance to TTX

• Modified Na+ channels allow consumption of toxic newts

Arms race:

• Newts evolve higher TOXIN levels

• Snakes evolve greater toxin RESISTENCE

• Trade-offs constrain ESCALATION

• Resistance reduces snake SPEED

• Toxin production is energetically COSTLY

Predator-prey Co-evolution: Toxins and resistance

• Newt toxicity and snake resistance both vary across the landscape

• These traits WHAT each other geographically (high - high, low - low)

• Suggests a WHAT evolutionary relationship across populations

Predator-prey Co-evolution: Toxins and resistance

• Newt toxicity and snake resistance both vary across the landscape

• These traits TRACK each other geographically (high - high, low - low)

• Suggests a LINKED evolutionary relationship across populations

Visual Anti-Predatory Strategies

• WHAT

• WHAT

• WHAT

• WHAT

Visual Anti-Predatory Strategies

• Crypsis

• Aposematism

• Batesian mimicry

• Müllerian mimicry

Crypsis

Avoiding detection by BLENDING into environments; reduce visibility

Aposematism

WARNING COLOURATION; bright colours signal “I am dangerous/toxic)

Batesian mimicry

A palatable species mimics the appearance of a TOXIC species

Müllerian

Two or more TOXIC species resemble each other; both BENEFIT

Herbivory Co-evolution

• Herbivores evolve to WHAT, WHAT, and WHAT plant tissues

• Plants are not passive or defenseless; they have evolved to WHAT, WHAT, or WHAT from herbivory

• Interactions often involve WHAT, WHAT, and WHAT based strategies

• Often drives specialization on narrow set of plants that a herbivore can tolerate

Herbivory Co-evolution

• Herbivores evolve to LOCATE, CONSUME, and DIGEST plant tissues

• Plants are not passive or defenseless; they have evolved to DETER, TOLERATE, or RECOVER from herbivory

• Interactions often involve CHEMICAL, STRUCTURAL, and TIMING based strategies

• Often drives specialization on narrow set of plants that a herbivore can tolerate

Common traits shaped by herbivory

Plant defence:

• WHAT defenses (tannins)

• Structural defenses (thorns)

• WHAT defenses (after damage)

• Timing/phenology

• Mutualisms (attractive predators)

Common traits shaped by herbivory

Plant defence:

• CHEMICAL defenses (tannins)

• Structural defenses (thorns)

• INDUCIBLE defenses (after damage)

• Timing/phenology

• Mutualisms (attractive predators)

Common traits shaped by herbivory

Herbivore counter-adaptations:

• WHAT mechanisms

• Behavioral strategies (selective feeding)

• Morphological traits (dentition)

• WHAT/sequestration (store toxins)

• Timing shifts (when defenses are lower)

y herbivory

Herbivore counter-adaptations:

• DETOXIFICATION mechanisms

• Behavioral strategies (selective feeding)

• Morphological traits (dentition)

• TOLERANCE/sequestration (store toxins)

• Timing shifts (when defenses are lower)

Herbivore-Plant Co-evolution: Milkweed and Monarchs

Milkweed Defenses

• Produces toxic cardiac glycoside

• Sticky latex sap

• Tough leaves and hairs

Monarch Counter-adaptations

• Physiological resistance to cardenolides

• Sequester toxins in their tissues, making their own bodies toxic to predators !!

• Vein cutting drains latex before feeding

Co-evolution of extreme specialization:

• Monarch caterpillars feed almost WHAT on milkweed and rely on WHAT to make them unpalatable to predators (trade-off?)

Herbivore-Plant Co-evolution: Milkweed and Monarchs

Milkweed Defenses

• Produces toxic cardiac glycoside

• Sticky latex sap

• Tough leaves and hairs

Monarch Counter-adaptations

• Physiological resistance to cardenolides

• Sequester toxins in their tissues, making their own bodies toxic to predators !!

• Vein cutting drains latex before feeding

Co-evolution of extreme specialization:

• Monarch caterpillars feed almost EXCLUSIVELY on milkweed and rely on TOXINS to make them unpalatable to predators (trade-off?)

Herbivore-Plant Co-evolution: Masting Trees and Seed Eaters

Plants can evolve WHAT as an anti-predator defence; overwhelming or avoiding predators as opposed to repelling them

Herbivore-Plant Co-evolution: Masting Trees and Seed Eaters

Plants can evolve REPRODUCTIVE TIMING as an anti-predator defence; overwhelming or avoiding predators as opposed to repelling them

Herbivore-Plant Co-evolution: Masting Trees and Seed Eaters

Plant Strategy

• Synchronize heavy seed production every 2–7 years

• Overproduce = predator satiation

• Excess seeds escape predation and germinate successfully

• Low seed years keep predator populations small

Seed Predator Strategies

• Increase reproduction in mast years

• Cache seeds to survive lean years

• Rapidly track mast events with population increases
  

Temporal arms race:

• plants “WHAT” the system; consumers try to keep up; lean years WHAT the system

Herbivore-Plant Co-evolution: Masting Trees and Seed Eaters

Plant Strategy

• Synchronize heavy seed production every 2–7 years

• Overproduce = predator satiation

• Excess seeds escape predation and germinate successfully

• Low seed years keep predator populations small

Seed Predator Strategies

• Increase reproduction in mast years

• Cache seeds to survive lean years

• Rapidly track mast events with population increases
  

Temporal arms race:

• plants “FLOOD” the system; consumers try to keep up; lean years RESET the system

Parasite-Host Co-evolution

Parasites evolve to:

• WHAT hosts

• WHAT quickly

• WHAT to new hosts

Hosts evolve to:

• WHAT infection

• Limit WHAT cause by parasites

• Often involve immune response and physiological defences

• Show some of the WHAT evolutionary change in nature (SARS-CoV-2 variants)

Parasite-Host Co-evolution

Parasites evolve to:

• INFECT hosts

• REPLICATE quickly

• TRANSMIT to new hosts

Hosts evolve to:

• PREVENT infection

• Limit DAMAGE cause by parasites

• Often involve immune response and physiological defences

• Show some of the FASTEST evolutionary change in nature (SARS-CoV-2 variants)

Virulence

The harm a parasite causes to its host

Three types of virulence

• WHAT

• WHAT

• WHAT

Three types of virulence

• Low virulence

• High virulence

• Optimal virulence

Low virulence

Host survives, but LOWER transmission rate

Low virulence example the common cold

WHAT virulence x WHAT shedding x WHAT duration = WHAT

Low virulence example the common cold

LOW virulence x LOW shedding x LONG duration = STEADY

High virulence

High transmission, but short infection window

High virulence example Ebola

WHAT virulence x WHAT shedding x WHAT duration = WHAT

High virulence example Ebola

HIGH virulence x HIGH shedding x SHORT duration (host dies quickly) = CONSTRAINED

Optimal virulence

Intermediate; Maximizes transmission, not damage

Optimal virulence example Influenza

WHAT virulence x WHAT shedding x WHAT duration = WHAT

Optimal virulence example Influenza

MODERATE virulence x HIGH shedding x SHORTER duration = OPTIMAL

Myxoma Virus and Rabbits

1950s: Myxoma virus (MYXV) introduced to kill invasive rabbits
• ~99% initial mortality
• Rabbits rapidly evolved partial WHAT (only ~60% mortality)
• Rabbits became abundant again

1995: Rabbit Hemorrhagic Disease Virus (RHDV) introduced
• New virus, different physiological pathway
• WHAT the host-parasite arms race
• High rabbit mortality returns

Ongoing arms race:
• Rabbits evolving resistance again
• Myxoma virus evolving higher virulence
• Continuous back-and-forth WHAT

Myxoma Virus and Rabbits

1950s: Myxoma virus (MYXV) introduced to kill invasive rabbits
• ~99% initial mortality
• Rabbits rapidly evolved partial RESISTANCE (only ~60% mortality)
• Rabbits became abundant again

1995: Rabbit Hemorrhagic Disease Virus (RHDV) introduced
• New virus, different physiological pathway
• RESET the host-parasite arms race
• High rabbit mortality returns

Ongoing arms race:
• Rabbits evolving resistance again
• Myxoma virus evolving higher virulence
• Continuous back-and-forth ADAPTATION

Myxoma Virus and Rabbits

• Human interventions become part of the WHAT, often WHAT (rather than stopping) evolutionary dynamics.

Myxoma Virus and Rabbits

• Human interventions become part of the SELECTIVE ENVIRONMENT, often RESHAPING (rather than stopping) evolutionary dynamics.

Energy spent on defence = energy not spent on WHAT or WHAT

Energy spent on defence = energy not spent on REPRODUCTION or GROWTH

eg, heavily armoured mussels grow slower than unarmoured

Context-dependent defence

Many species only produce defences when predator cues present to save energy

eg, plankton grow neck teeth and body spines when predators are detected

Optimal defence theory

Invest in protection of most VALUABLE/VULNERABLE tissues (young, reproductive structures, head, vital organs)