ENT104 - Social Behavior: Non-Classic Systems (L18)

What is simple aggregation?

When animals live in dense populations due to clustered resources

(True/False)

Simple aggregation is a form of social behavior

False

Simple aggregation results from clustered resources

Social behavior requires cooperation, not just group living

What insect performs simple aggregation?

Locusts

What insects have aggregation pheromones to facilitate aggregation?

Aphids

Roaches

Sawflies

Why do sawflies aggregate?

Group defense, feeding, and thermoregulation

Why do insects aggregate?

Selfish herd

Group defense

Group feeding

Thermoregulation

What is the selfish herd?

Individuals position themselves in the middle of the aggregation so they are less vulnerable to predators

How does aggregation help with defense?

Multiple individuals = more ways to defend against predators

How does aggregation help with feeding?

One individual might be too weak to break open food, but many individuals working together can

How does aggregation help with thermoregulation?

Aggregation creates a more favorable surface area to body ratio for heat exchange

What are the costs of aggregation?

Greater exposure to disease (diseases can spread easily)

Vulnerable to parasitoids (large clusters of hosts are easy to find)

Consume food sources faster (many mouths to feed)

What is the adaptive benefit of aggregation in sawflies?

Aggregation is indirectly beneficial for predator defense

Some sawflies sequester toxins, making large groups of them harder to feed on

Aggregation provides direct benefits in terms of group feeding and thermoregulation

(True/False)

Group size in aggregating sawflies increases survivorship against predators

False

Larger groups are just as likely to be preyed upon as small groups

(True/False)

Chemically-defended sawflies have higher survivorship rates than non-chemically-defended sawflies when faced with predators

True

Chemical defenses make the sawflies distasteful

What are the costs of aggregation in social aphids?

Galls become full of waste (dead aphids, honeydew, etc.)

Increased potential for disease transmission

Reduced feeding opportunities

Which aphids clean out the colony's galls?

Soldier aphids

Why might some social aphids parasitize other aphid galls?

Aphids that parasitize other galls do not need to produce soldiers, as the other aphids have already done that for them

What happens when P. bambucicola (aphid) parasitizes A. bamucifoliae (another aphid)? What happens when P. bambucicola nests alone?

When parasitizing other aphids, P. bambucicola does not produce any soldiers

When nesting alone, it produces soldiers to defend the gall from other aphids

(True/False)

There is an inverse relationship between the number of ant defenders and the number of soldier aphids in a colony

True

The more ant defenders there are, the fewer the soldier aphids (ants are better defenders)

What do social aphids do in response to their ant defenders being removed?

Produce more soldiers for some time, but then focus more on reproduction to try to move elsewhere

Soldier aphids are not actually that good at defending the colony, but are still useful for other tasks (such as cleaning waste) and are thus produced in smaller numbers

Bark beetles and ambrosia beetles are highly derived ______

Weevils (Curculionids)

Both bark beetles and ambrosia beetles have symbiotic (mutualistic) relationships with _____

Fungi

What do bark beetles use their fungi for?

Killing the trees they feed on (prevent the tree from defending itself)

What do ambrosia beetles use their fungi for?

Farming fungi and creating long-lived colonies (simple eusocial behavior)

How do ambrosia beetles form long-lived colonies?

Mothers start a nest in a dead/dying tree

Offspring stay and help rear fungi

Possible variation in genetics and inbreeding patterns (haplodiploidy)

What do ambrosia beetle colonies do that social Hymenopteran colonies do not?

In ambrosia beetles, males, females, AND larvae all work and show a division of labor (in Hymenoptera, only females work)

Beetle larvae are more active than Hymenoptera larvae, which likely led to the beetle larvae evolving task specialization

(True/False)

Sociality is common in spiders

False

Only 23 permanently social species of spiders out of about 50,000 species

What are the three categories of sociality in spiders?

Colonial

Subsocial

Social

What are colonial spiders?

Spiders that build individual webs side by side upon the same supports

Colonial spider webs might house how many spiders?

Up to 10,000, very large

Why do colonial spiders evolve?

Evolve in places where anchor points are rare

By sharing anchor points, spiders can occupy areas that would otherwise be unsuited for web-building

Why are colonial spiders considered to display aggregation rather than sociality?

The spiders aggregate for a clustered resource (anchor points) and do not cooperate with each other

What are subsocial spiders?

Groups of spiders composed of a mother and her pre-adult offspring (similar to alternative reproductive tactics in Hymenoptera)

What main form of social behavior do subsocial spiders fall under?

Parental care

How do subsocial spiders perform parental care?

Mothers care for young until they die

Young help maintain the nest and capture prey, and may eat the mother when they are large enough

What happens when the mother dies in subsocial spiders?

The offspring disperse

Males find mates, females set up their own families

What are social spiders?

Spiders that share one giant web, where individuals cooperate in brood care, prey capture, and other tasks

How many spiders might be in a social spider colony?

Dozens to many thousands depending on the species and stage of development of the nest

How long do social spider colonies last?

Webs can last years, spiders live about 6-12 months

(True/False)

Individuals in a social spider colony mate with other spiders in the same web, leading to significant inbreeding

True

Only _____% of spiders in a social spider colony are male

10-20%

What are the adaptive benefits of social spider colonies?

Sociality spiders can take down larger prey by attacking together, broadening their prey profile (more prey options)

Social spiders can catch prey 10x their size as opposed to solitary spiders which catch prey only 2x their size

Why did sociality evolve in spiders?

Species with parental care are more likely to form groups (eusociality evolves from parental care)

Species that produce costly webs in areas with heavy rain evolve group-living for rainproof webs (more webs = stronger webs)

Larger prey allows for the evolution of group-living