Preface
As animals develop, they acquire a nervous system, whose properties are vital to the proximate control of behavior. Even simple observations of animals can provide important insight into the proximate properties of their neural mechanisms. E.g., the fact that male digger bees can dig up dead females buried by a researcher indicates they are very sensitive to the odors of female bees. The link to reproductive success is clear. However, what evolutionary explanation can tell us why male digger bees will try to copulate with a person's thumb? He will go and stroke a thumb just as he would a receptive female he has mounted. Obviously, the bee's nervous system has some special operating rules. When a sexually motivated male grasps an object the size of a female, the sensory signals generated by touch receptors go to other parts of the n.s., where messages are produced that ultimately get translated into a complex series of muscle commands. The behavioral result is the sequence of movements that passes for courtship in this species. - the result of neural responses (touch receptors to the brain) is a behavior that developed for other digger bees to do. Response to objects like a thumb indicates the NS of these males isn't very discriminating. - objects like a thumb or any thing similar in size does not distinct the differences between a bee and a thumb. This is not particularly unusual.
This ivy bee will attempt to mate with a mass blister beetle larvae. They jump on him, he carries them to his copulation. They jump on the female, who carries them back to her nest. The larvae feed on the provisions and offspring of the bee. Complex Responses to Simple Stimuli How can the underlying neural mechanisms be adaptive if they cause maladaptive responses? Such questions can be answered by looking at how much complex responses to simple stimuli are triggered by animal nervous systems. Tinbergen's work with gull chick begging behavior Baby gull hatchlings will peck the tip of their parents' beak.
This induces their parent to regurgitate partially digested food, which the baby eagerly eats. - gull chick will peck at their own parents own beaks to receive food from their parents mouth. one of the behaviors from neural mechanisms. Painted sticks and cardboard cutouts work just as well as the real thing in eliciting the pecking response. - painted dots on beaks and a paint brush w red paint on it has more responses than beaks without red dots. Experiments with such models show that recently hatched gulls ignore most everything except the shape of the bill and the red dot. - shape of bill and red dot are not ignored. Tinbergen proposed that when a gull chick sees a pointed object with a contrasting dot, these signals reach the brain, where other neurons generate a motor response, causing them to peck at the stimulus - whatever it may actually be. - the gull chick sees a POINTED object with a red dot. The response to this are signals reaching the brain where neurons create a motor response (pecking at the beak). pecking at the stimulus. Tinbergen and Lorenz collaborated on research with greylag goose egg rolling behavior. - this is one of the behaviors that are fixed action patterns. They are distinctive to greylag gooses. If they removed an egg from under an incubating goose, and put it about 50 cm away, the goose would retrieve it by stretching its neck forward, tucking the egg under its beak, and carefully rolling the egg back into the nest. Hence, a very complex set of behaviors elicited by a simple stimulus. Any egg-shaped object elicits the same response. Removing the egg or object as it is retrieved results in the goose completing the set of behaviors as before. - the goose will roll its egg back with the underside of its beak stretching its own neck and tucking the egg back. The behavior is performed by a simple stimulus. ANY egg shaped object like a rock will make the goose bring that object in (rolling it in w its own beak). Lorenz and Tinbergen concluded that the goose has a special perceptual mechanisms very sensitive to egg-shaped visual stimuli. - the goose has a visual stimuli related to egg shaped objects. Such stimuli elicit a fairly invariant motor program for egg retrieval. Lorenz and Tinbergen studied many similar instinctual responses. They considered the fathers of modern ethology, which focuses on proximate and ultimate causes of behavior. They were particularly interested in such instincts exhibited by wild animals in natural conditions. Instincts Instinct←a behavior pattern that appears in fully functional form the first time it is performed, even when an animal has not prior experience with the cues that elicit that behavior. - having a fixed pattern of behavior like birds building nests. Instincts are not generally determined, as they are dependent on the gene-environment actions that took place during development. - not determined but are made by gene and environment actions that took place in development. The neural network responsible for detecting the simple cue is the sign stimulus or releaser. - the simple cues are the sign stimulus or releaser This activates the instinct, or FAP (fixed action pattern), which was given the label for innate releasing behavior. - this means a FAP needs a sign stimulus (releaser); the two need a correlate with an elicitor and a behavioral event. The simple relationship between innate releasing mechanism, sign stimulus, and FAP is highlighted by the ability of some species to exploit the FAPs of other species. Sometimes referred to as "code breaking"
E.g. orchids and thyniine wasps. - code breaking bc the orchids trick the wasps by looking like the wasps. Blister beetle larvae use scents that mimic those released by receptive ivy bee females. When a male bee pounces on a pile of larvae, they swarm on him and become parasites that he may transfer to a female bee later. From a female bee, they get into the underground nest where they can move into the food producing cells. - beetle larvae will code break the male to bring these larvae to the females where the larvae will be able to eat the bees own sources of food. There, they eat the food stored for developing bee larvae. Cuckoo and Cowbird nestlings are similarly able to fool their hosts by looking and behaving in ways that stimulate their adult hosts to feed them. - the two different birds can convince a host to get fed bc they are code breaking. They are acting similar to the host bird behaviors. Earthworms respond to pounding on the soil with a stake, because similar stimuli are produced by moles moving underground near worms. - pounding of dirt is code breaking since the earth worm respond to the sign stimuli by moving around. How Moths Avoid Bats Ken Roeder's research on moths avoiding bats suggested that moths might avoid bats by diving straight down at the last minute. They might do the same if you jangle a set of keys, suggesting the role of acoustical stimuli in releasing this behavior. It turns out that the moths are responding to very high frequency sounds that humans cannot perceive. Bat echolocation sounds are between 20-80 kHz.
Roeder hypothesized that these moths are able to hear pulses of ultrasounds from bats. He began testing this idea by finding the 'ears' of noctuid moths - one on either side of the thorax. Each has a thin flexible tympanic membrane that lies over a chamber on the side of the thorax. Two neurons, A1 and A2, the auditory receptors. These are deformed when the tympanum vibrates.
These neurons work like most other neurons - they respond to stimuli by changing permeability of cell membranes to positively charged ions. These ions set up a change in membrane potential, which moves down the axon to synapses on the next neuron. This all or none response is called an action potential. Neurochemicals released at the synapse can excite or inhibit the next neuron, often an interneuron. That interneuron may reach its threshold and generate its own action potential. In the noctuid moth, the A1 and A2 receptors are linked to relay cells that may change the activity of other cells in the insect's thoracic ganglia. The ganglion is a cluster of neurons.
Certain patterns of action potentials might trigger other interneurons, whose action potentials reach the motor neurons connected to the moth wing muscles. This may cause the muscle cell to generate its own action potential and contract muscles attached to the wings. These changes can happen so fast, it gives the moth enough time to respond quickly to the right stimuli.
A1 and A2 receptors respond a bit differently to the same stimuli. 1.) A1 is sensitive to ultrasounds of low to moderate Intensity; A2 receptor only makes action potentials when an ultrasound is relatively loud. 2.) As a sound Intensity Increases, A1 fires more often with a shorter delay between stimulus and action potential.
3.) A1 fires more frequently in response to pulses of sound than steady, uninterrupted sounds.
4.) Neither receptor responds differently to sounds of different frequencies over a broad ultrasonic range. 30kHz and 50kHz elicits the same response if they are equally Intense.
5.) These receptor cells don't respond to low-frequency sounds such as we can hear.
The key property of the A1 receptor is that is very sensitive to ultrasound.
It can begin generating a response to brown bat cries up to 30 meters away (long before the bat finds it)
It provides the moth a way of determining if the bat is approaching or moving away, b/c it's response is proportionate to the loudness of the sound.
A) when a bat is to one side of the moth, the A1 receptor on the side closer to the bad fires sooner and more often than the shielded A1 receptor in the other ear.
B) when a bat is above the moth, activity in the A1 receptors fluctuates in synchrony with the moth's wingbeats.
C) When a bat is directly behind a moth, both A1 receptors fire at the same rate and time.
As signals race through the moth's nervous system, they may generate motor instructions that cause the moth to turn and fly directly away from the source of the ultrasonic signals.
When a moth moves away, it exposes less echo reflecting surface area than it would if it were at right angles.
If the bat doesn't detect the moth, and doesn't fly straight (uncommon for bats), it will lose track of the moth and find some other insect w/in its 3 meter detection range.
Moths use their A1 receptor by orienting their flight direction away from the on coming bats so that both receptors get the same activity levels.
If the bat has detected the moth, other methods are needed.
The moth has at most a second before the bat will collide with it.
In this situation, moths will employ drastic evasive maneuvers (loops and power dives).
If it successfully executes those, It may have a chance by landing in a patch of grass or on a bush, where the foliage masks the body of the moth. Other Insects have similar detection systems and employ the same kinds of evasive actions.