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Chapter 7

LIFESCI 2D03 Chapter Notes - Chapter 7: Olfaction

Life Sciences
Course Code
Rashid Khan

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Chapter 7: Foraging Behaviour
7.1 Animals Find Food Using A Variety Of Sensory Modalities
1. Natural selection favours modalities that most efficiently and accurately provide
information about the location of food, but the efficiently of a modality can vary
with environmental conditions.
1. Mechanoreceptors: sensory sensitive to changes in pressure.
2. Lateral line system: in fish, mechanoreceptors that provide hydrodynamic
3. Chemoreception: the process by which an animal detects chemical stimuli.
4. Olfaction: the detection of airborne chemical stimuli.
5. Gustation: The detection of dissolved chemicals, often within the mouth.
1. Some fish, such as minnows, have well-developed chemoreception systems
that allow them to recognize conspecific predation events and then respond
accordingly with antipredator behaviours. Other fish, such as bullhead
catfish, use the chemoreceptors on their barbel-the slender, whisker like
organs near the mouth- to locate stationary food.
1. Pohlmann and colleagues investigated how nocturnal piscivorous (fish eating)
catfish fins food in the dark. The research team used guppies as prey fish because
they create a swimming wake that has been well described.
1. Pohlmanns team aimed to determine whether catfish could use cues
provided only from the wake of individual fish to stalk and attack their prey.
2. The researchers designed an infrared video system to track the movement
path of both the predator and the prey in an environment of complete
3. They used four catfish and observed each one stalking up to ten individual
guppies. Each catfish was allowed to acclimate to the experimental tank for
one hour in the dark, after which the first guppy was added to the tank.
4. After a guppy was consumed, another was added every 20 mins to replace the
one that had been eaten. The researchers ended a trial when ten guppies had
been consumed or when no guppy had been consumed in 20 mins.
5. They used computer software to digitize the movement behaviour sequence of
both the catfish and the guppies and classified them in one of three ways.
1. Path following (the catfish followed the guppy wake)
2. Head one encounters (the catfish encountered the guppy head-on without
a previous encounter)
3. Attack on a stationary guppy/
6. Found that 80% of the attacks occurred on moving guppies. In the majority of
all attacks, the catfish were following the same path as the guppy before the
attack. The researchers concluded that the catfish appeared to be following
the wake of the guppies to find and attack their prey in the dark.

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7. Pohlmanns team conducted a second experiment using the same setup. In this
experiment, they manipulated either the lateral line or the external gustation
system of the catfish and compared to their behaviour to that controls.
8. The lateral line provides hydrodynamic information and can be rendered
temporarily non-functional by immersing a fish in a CoCl2 (cobalt chloride)
solution for six hours prior to the experiment.
9. The external gustation system, which provides chemical information, was
manipulated by surgically removing an area of the dorsal medulla oblongata
that controls this system.
10. The researchers found that individuals with a non-functioning lateral line
attacked guppies head-on 88% of the time. Most of the gustation-ablated fish
also attacked guppies head-on, though less often (58% of attacks); only 27%
of attacks were characterized as path following.
1. The capture success rates also differed across treatments. Control and
gustation-abalted fish exhibited similar; relatively high capture success
(approximately 60%).
11. Pohlmann and colleagues concluded that the lateral line is a very important
factor in catfishs ability to track the wake of their prey; in contrast, the
external gustation system does not appear to be as important in facilitating
this mode of attack behaviour.
1. The lateral line system may be key not only because it provides feedback
to the predator about the movement of the prey but also
because it provides feedback to the predator about its
own movements and position.
7.2 Visual Predators Find Cryptic Prey More Effectively By Learning A
Search Image
1. Many predators, especially birds and mammals like the gray mouse lemur, rely
heavily on vision to find prey.
2. Evolutionary arm race: the back-and-fourth process of adaption in one species
favouring counter adaption in another.

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3. Search image: the visual distinctive features of a single prey type that, once
learned, can enhance prey detection.
4. Pietrewicz and Kamil studied visual prey detection in blue jays, to determine
whether they use a search image to find cryptic prey.
1. They trained individual birds to search for images of moths that were
displayed as video images on tree trunks.
2. They designed a very clever apparatus to examine whether blue jays use
search images to find prey. They used two different species of bark-like
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