Ent 104 Midterm 2

dendrite

dendrite

receives information from sensory structure, tissue, or another neuron

Axons

Send info away from neuron

can send info to:

• another neuron

• glandular structure

• effector

Synapses

where axons and dendrites meet

neurotransmitters trigger the next neuron to fire

neuromodulators change the likelihood of the neuron firing

can be simple (one to one) or complex (one to many)

Effector

receives input and does something

muscle or gland changes function in response to a signal from a brain center

types of insect gaits

Simple (classic tripod gait)

Complex

• roaches can sprint on hind legs alone and gallop like a horse

• when legs are surgically removed new stereotyped pattern can be immediately used

Stereotyped behaviors

• flight

• digging

• eating

• reproduction

• predation

• anti-predation

• signaling

in some sense nearly all insect behaviors are sterotyped as cyclical or one time cue responses

Central pattern generators

nerves organized into fixed circuits that control stereotyped periodic behavior like walking

can function independent of sensory inputs

Physical models

physical models can be useful compared to mathematical or computer models because they show actual responses and physical representations

reflexes

fixed neuronal circuit that links external info to an immediate fixed response

distributed nervous system

insects have distributed nervous system

knee jerk response

ganglia function as mini brains and can handle more tasks than in vertebrates with bigger brains

evolution of decisions

decisions evolved from reflexes

1- information received by sensory structures

2- information is filtered, only useful info is kept

3- signal is sent to the brain, again filtered and integrated

4- signal sent out to effectors to change behavior

neuroethology (colony mate recognition)

hypothesis 1: individual compares smell of another to template in the brain (central nervous system)

hypothesis 2: individual is habituated to odor of nestmates and is alerted when they smell something different (peripheral nervous system)

4 classes of sensory information

• mechanical stimuli

• thermal stimuli

• chemical stimuli

• visual stimuli

trichoid sensilla

basic insect tactile structure

hair connected to a neuron

movement of the hair squeezes the dendrite of the sensory neuron causing it to fire

trichoid sensilla are very sensitive and can sense air currents and touch easily

proprioceptors

structures that measure the position of one body segment relative to another

important for balance

come in two forms: hairs and cuticle structures

types of proprioceptors

• hair (most basic)

• campaniform (senses stress on cuticle)

• chordotonal (highly derived; sense substrate vibrations)

sound receptors

sound receptors are modified proprioceptors

substrate vibrations are sensed with the subgenual organ

Johnstons organ

simple hearing

located on antenna

sense air speed via antenna deflection

tympanic organ

elaborate ears

thin membrane connected to an air sac that vibrates when sound hits it (eardrum)

can be anywhere on the insect

most insects dont have this, only ones that need it (eg moths and insects that sing to find mates)

Jamming (moths and bats)

bats use echolocation to locate prey in the dark; moths have evolved ears to know when they are being hunted

some moths can send back ‘jamming’ noises to make echolocation less effective

moths often also use other strategies like irregular flight pattern or dropping to the ground

thermosensors and thermoregulation in insects

poorly understood in insects

receptor is in antenna in most insects

insects lose heat fast because of small body size

can heat themselves up with flight muscles immediately before taking off

honey bee thermoregulation

create a warm cluster to keep warm through winter

bees in the center of the cluster generate heat

bees at the edge of the cluster provide insulation

bees rotate between edge and center

allows bees to start foraging earlier in the spring

How do asian honey bees use thermoregulation to kill hornets

asian honey bees form a cluster around a hornet that has invaded the nest and heat themselves up in order to kill the hornet

this works because the bees have a higher heat tolerance than the hornet

only asian honey bees can do this

chemoreception

includes both taste and smell

1- molecules are trapped in viscous substance

2- odorant binding proteins carry molecules to odorant receptor proteins on sensory neurons which trigger neuron firing

types of sensory structures

• antennae (smell and taste)

• mouthparts (taste)

• feet, ovipositor, etc (taste)

*chemosensory structures can be in many places on the body depending on what the species needs

Types of eyes

Larva:

• stemmata— good at detecting light, poor at resolving

• mainly used for detecting light and dark

Adults:

• Ocelli— 3 on top of the head; very sensitive to light

• ocelli may be horizon detectors used in flight

• Compound eyes— main source of vision

Insect Vision

Poor resolution (vision is pixelated)

Good ability to sense movement (higher fusion flicker rate)

Insects can see UV and polarized light

Most cannot see in the dark

cues

information left passively in the environment by an animal

can be used by anyone

eg tracks, odors, sounds

Signals

Information intentionally sent by one animal to another (usually within species)

can be used by others (eavesdropping)

How do signals evolve from cues

signals= exaggerated cues

For example, threat signals evolve from the moment preceding an attack

selection works to increase both the production of the cue and the sensitivity of the receiver

How do we tell what a signal means?

observe the context in which it is produced (is a predator present?)

Observe the receiver and what is their response (prey of that predator responds by running)

How did the waggle dance evolve

In a hypothetical ancestor, inactive workers can use nest activity as a cue for how much foraging is occurring. Over time, workers learn to exaggerate the cue after finding food

Example of a complex signal (birds)

Bird mating signals can have different meanings for males and females

For males, it may indicate territoriality

for females, it may act as a mating call

Complex signal

a signal that can have multiple meanings for different individuals

this is common in social insects

Types of honey bee communication signals

Chemical (pheromones):

• fertility

• alarm

• flower visitation

• colony membership

• mate attraction

Mechanical / acoustical:

• dances

• other buzzing/shaking/vibrating type signals

What two types of signals do foragers produce

• signals with info about food sources (received by other foragers; telling them to go collect nectar)

• signals to coordinate activity (received by middle age bees; telling them to help process nectar)

Bee vision

Bees can see a lower wavelength of light than us, they see UV but not red

Distance experimental design (Von Frisch)

Food source was moved different distances in the same direction. As the food source got farther away, the “waggle” part of the dance got longer

Direction Experimental design (Von Frisch)

Food source was moved the same distance but in different directions. As the angle of the feeder changed, the angle of the dance changed.

How do bees communicate the quality of a food patch?

The number of waggle dances the bee performs correlates to the quality of the food

How do bees determine site quality?

Bees use energy gain as metric for site quality

a combination of distance from nest and nectar concentration

via what sensory modalities is the waggle dance communicated?

• releasing pheromones (a blend of hydrocarbons)

• send sound, motion, and vibrations

How do bees measure distance?

optic flow: the rate of image flow across the retina

Optic flow experiment

make foragers fly down a narrow tube to a feeder

narrow tube increases optic flow, but not time or energy used

Results: recruits of bees that flew down tunnel flew significantly further, indicating the original bee communicated a farther distance

pheromones

chemicals secreted by an animal that elicit a response from another animal (usually a member of the same species)

often used for sexual, territorial, and social behavior

volatile pheromones

can be smelled from a distance

travels quickly but does not last long

contact pheromones

must be contacted in order to be sensed

short range but lasts a long time

How do pheromones evolve?

They evolve from other chemical compounds produced for other reasons

eg ant trail pheromones come from modified sting gland components

stridulation

type of sound production

Two components:

• scraper/plectrum (rigid structure like guitar pick)

• file (ridged structure that plecturm scrapes against)

can be many places on the insect depending on need

Cricket stridulatory organ is modified from wings

most grasshoppers have it between their legs and abdomen

Buzzing

type of sound production: modified wing beat frequencies

modified by individual species to contain information

mosquitos use wings in mate attraction

bees use buzzes in dances

Tymbals

type of sound production (functions like drum)

air sac is connected to a flexible cuticle that makes a click, the air sac resonates at the frequency of the clicks and amplifies the sound

found in male cicadas

Pigments

differentially absorb light wavelengths

stable colors

can be extracted and used as dyes

structural colors

more intense, often metallic colors

produced by scattering of light waves

color is only visible from certain angles

How does Lepidoptera mate attraction work?

• female releases a volatile mate attraction pheromone

• male follows odor plume upwind using zigzag pattern

Artificial pheromone dispensers can cause males to get lost and disrupt mate finding

Pheromone mimic example

Bola Spider— mimics moth pheromone to draw in male moths, then catches them using silk lasso

pheromone mimicry is a common strategy used by predators

Ant foraging trails

Ant trails are a blend of contact and volatile pheromones

When the scout find food, she lays a volatile pheromone trail on her way back to the nest, which other ants can then follow to food

The scout also lays a contact pheromone which can be followed again later by the scout to see if old food sources will produce new food. because it is a contact pheromone, the ant must walk slowly with her antennae to the ground

Recruitment mechanisms in ants and bees

Tandem running— one ant guides others to food

Piloting— bees point other bees in the direction of food

How do bark beetles use aggregation pheromones?

bark beetles feed on ponderosa pines, but they cannot overcome the sap defense unless there are many beetles

when a suitable tree is found a beetle releases a pheromone to attract other beetles

The beetles aggregate and overcome the tree defenses, laying eggs inside alongside the help of a symbiotic fungus

When the tree is at capacity the beetles stop releasing the aggregation pheromone and start releasing a “spacing” pheromone to stop other beetles from arriving

Cicada songs

cicadas have long larva stage and short adult stage

adult males have a chorusing song that is very loud to attract females

females approach and give a clicking sound to indicate receptiveness

males then switch to courtship signaling, then mate

process is not well understood

Warning sounds

many insects hiss or make sudden sounds when disturbed, which is meant to startle the predator and allow the insect to escape

bullet ants click while orienting to potential predators

Aposematic coloration

bright coloration to indicate danger/ toxicity

Predator either learns to avoid these colors or instincively avoids them

Mullerian mimicry

All toxic animals in an area are similarly colored

predator can learn from one species and they all benefit

common in butterflies and hymenoptera

Batesian Mimicry

palatable animal mimic toxic animal to avoid predation

mimic is usually rare relative to the animal they mimic (otherwise predator will not get enough negative reinforcement)

Ant mimicry

ants are often feared, so pretending to be an ant is adaptive

ants are often mimicked by spiders

Founders of chemical ecology

Thomas Eisner- animal behaviorist

Jerry Meinwald- chemist

Worked together at cornell

Formed under the basis that chemicals are central to much of animal behavior

Bombadier Beetle study

The bombadier beetle can spray scalding water into the face of a predator when captured

Two components are involved:

• Quinone (repellent)

• Hot water vapor

Quinone is stored in inactive components, then created and sprayed out when needed

Uthesia sexual selection (mating pheromone study)

Study 1: mating pheromone

• male moths separated into two groups; One fed crolataria beans which contain toxins and the other fed pinto beans with no toxin

• showed that the brushes males use during mating store a pheromone directly derived from the toxic chemicals they consume as caterpillars

Uthesia sexual selection (Mating gifts)

Study 2: Mating gifts

• both males and females contribute defensive chemicals to the eggs

• Study designed in which groups were matched with mates that did not have the sequestered toxin, then measured how much each egg received from each parent

• found that female gives nearly all of the toxins in her body while males give only 15%

• Males with the most defensive compound sequestered are more likely to be chosen

________ is the context in which chemical communication is the most complex.

Social behavior

Nestmate recognition

• labels= cues or signals produced by individuals

• each individual has a template (set of labels)

• labels of other bee are compared to personal template

• if template matches, individual is accepted

• template made up of different hydrocarbon chains which vary in length and side groups

Footprint pheromone

Bees mark flowers which they have foraged on. The next bee to arrive smells the pheromone and knows it has recently been foraged, so it is most likely empty

Nasonov pheromone

Essentially a homing beacon

used to guide bees to a location

Examples of species manipulating others

Cuckoos

orchids and wasps

slave making ants

Two types of slave making ants

Type 1: larva stealer

• slave making ants steal larva from other ant colonies; colony pheromone makes them believe that they belong

• some species are totally dependent on slaves as they are only specialized for fighting

Type 2: Social parasite

• One ant takes over the queen from another nest by killing host queen and using her pheromone

• parasite queen raises parasite eggs alongside her own

Purpose of mosquito hum

specific mate attraction call

allows mosquitos to recognize members of their own species

How was the Johnstons organ verified in mosquito mate recognition

In the 1948 study by Roth, males were “called” with tuning forks and behavior was recorded

When the tuning fork was struck males flew toward the sound and began mating behaviors

Ablation experiments were conducted in which certain structures were removed and response was recorded. Those with removed antenna showed no response

Important to note that this was a lab study, not a field study

How was mate finding in mosquitos investigated?

Mosquito buzzing cannot be heard from very far away, so there must be some way for mosquitos to congregate and find mates

in the 1970 study by Hartberg, mosquitos were caught before and after biting people

they discovered that both males and females are attracted to humans, and mating is occurring near the host

Sexual selection in crickets

The 1994 study by Hedrick looked at female preference for different types of male calls

They found that females prefer males with long trills over males with short trills

Presumably trill length is an indicator of male quality

Sympatric speciation

reproductive isolation without geographic isolation

two species form from one population in one place

Allopatric speciation

Two populations are isolated geographically

Species diverge over time

Pre-reproductive barriers

Factors causing males and females to not mate

can be behavioral or physical

Post-reproductive isolation

animals of two different species can mate but the offspring have reduced fitness

mules are a common example

Rhagoletis fly case study (sympatric speciation)

Rhagoletis larva develop on fruits and nuts, overwintering as pupae and emerging before fruits are ready, then mating occurs on fruits

Rhagoletis pomonella flies historically used hawthorne as a host, but when apples were introduced some switched to apples

100 years later the apple vs hawthorne flies differ in many ways including body size and emergence time

Each fly morph is shown to prefer the fruit in which they hatched

male male competition (sexual selection)

males fight over access to females

often involves evolution of elaborate weapons in males and sexual dimorphism

Female choice (sexual selection)

Females choose the best male based on elaborate mating displays

Best can mean many things:

• best provider (good territory, best gifts, etc

• most healthy

• best genes

Two dung beetle morphs

Alpha male (dominant)

• large size, large horns

• bonds and mates with female

• helps build and guard nest

Sneaker male

• much smaller, looks like female

• sneaks into nest to mate with female

• often have larger and more sperm than alpha male in order to promote his own fitness

Sperm competition

male competition within reproductive tracts

often occurs in multiply mated societies

males compete to make more sperm and larger sperm so that their sperm is more likely to succeed

Often produce substances (eg sperm plug) that interfere with other male sperm

Dung beetle ecological role

Dung beetles break down dung that would otherwise harden and cover the landscape

Unremoved dung can block plant growth and breed flies

Dung beetles in Australia

When large amounts of ungulates were introduced to australia as livestock, dung began to pile up because there were no beetles to break it down

The dung beetles in australia were not specialized for sheep and cow dung and did not clean it up

Dung beetles were brought in from South Africa and France to remove the dung with some success

Leks

Places where males congregate to participate in mating rituals and advertise themselves

usually 99% of matings go to one male

Females perform all parental care after mating

Orchid bees

tropical bees which collect scents from orchid to use in mating

males with the most complex odors are most often chosen by females

odor complexity corresponds with age which indicates greater fitness because they lived a long time