Review sheet 6
Biology 4900 – Behavior
James Adams and Kristen Sanders
Invertebrates – Arthropods -- INSECTS
Communication
Communication is absolutely necessary for any interactive (social)
behavior, and all insects must have the ability to communicate for at least one
(social) behavior -- mating. Communication may be visual, chemical, auditory
or tactile, or a combination of these signals. It may be short-range
or long-range; and may be used in sequence from long-range to short-range
(examples?). You should be aware as to which types of communication may
be either long or short range, and which are typically only short range.
Communication may be intraspecific (such as for mating, and a wide
variety of behaviors in social insects) or interspecific. Interspecific
communication can be divided into those that: 1) benefit sender (warning
signals, defensive secretions), 2) benefit recipient (predator avoidance [moth
and other insect ears, for instance]; plant chemicals attracting insects), 3)
benefit both (mutualistic, such as flower signals that result in
pollination/nectar gathering).
You will need to give examples of or recognize examples of visual,
auditory, chemical
and tactile communication in the insect world.
KEY WORDS:
Visual Communication: Aposematism, Bioluminescence
Auditory Communication: Stridulation
Chemical Communication:
Pheromones (intraspecific) -- trail, aggregation, sex, alarm
Allelochemicals (interspecific)
PREDATOR INTERACTIONS/AVOIDANCE:
First, let’s not forget all of the other arthropods (spiders, scorpions,
centipedes, etc.) that eat insects. Then, of course, there are a wide variety of
vertebrates (aquatic, terrestrial and flying) that feed on insects that are,
arguably, largely at the bottom of the animal food chain. Predatory effects on
the insects include a variety of effects on body form and coloration for
protection, and effects depend on palatability of the insects.
Palatable insects:
Cryptic coloration (pg. 194-196) and behavior includes remaining
immobile on an appropriate background and using camouflage against background,
special resemblance (twigs, flowers, bird droppings), shadow elimination
(fringes, checkering, etc.), disruptive coloration. Escape behavior in
these species is usually by dropping, jumping, or erratic flight. They may also
use eyespots/false head coloration. There are also examples of insects
whose forewings are muted, hiding brightly colored hindwings that are rapidly
flashed (pg. 195) when the insect is detected -- this is thought to
startle the vertebrate predator temporarily and allow escape. Batesian
mimicry (pgs. 198-200) of nasty insects (called models) is also
common (sometimes limited to just females [why?] -- sex-limited mimicry),
and some species may produce mimetic sounds of unpalatable species.
Unpalatable insects:
A number are brightly colored -- this may represent aposematic (warning)
coloration (pgs. 197-198), and some have additional aposematic behaviors,
including behaviors that show off bright colors, or sounds that indicate nasty
taste in nighttime active insects (Tiger Moths). Mullerian mimicry (pgs.
198-200) may also be exhibited by unpalatable species, as well as aggregation
behavior (presents a bigger signal). In addition, species may exude distasteful,
malodorous secretions. Predators must learn/be trained about these
signals.
Additionally, whether palatable or unpalatable, large gatherings can give
you some protection in numbers (see pgs.189 [puddling butterflies] and 190
[mayflies]), either by confusing your predators or overwhelming them.
Hearing and bat avoidance:
Moths and many other insects can hear bats and avoid them (pgs. 110-118).
Ears have evolved independently multiple times in the insect world.
Additionally, some moths can make sound in response to bat sound, either
indicating bad taste or mimicking those that are bad tasting. I’ll explain the
neural mechanism by which this works.
Insects eating insects:
A number of insects are feeders on other insects. These interactions fall
mainly into two catergories: 1) predator-prey and 2) parasitoids
(see below).
Predatory relationships -- some predaceous as adults, some as larvae,
many in both stages. Good eyesight is essential. Strategies can include: 1.
hunting (orient to prey at distance using visual or chemical cues; very
common for aquatic and aerial insects, though may include ground dwellers like
ants using chemicals to orient), 2. ambush (sit and wait; works in
aquatic and terrestrial environments; ambush/assassin bugs and mantids are
well-known examples), and 3. trapping (ant lions, some caddisfly larvae;
also includes species that use light to attract prey). This, of course, applies
to how most spiders capture insects as well.
FEEDING BEHAVIOR:
Predation:
See insects eating insects, above. There are a few insects that can, and
do, eat vertebrates, including predaceous diving beetles, giant water bugs,
dragonfly nymphs, large mantids, and some ants.
Parasitoids:
Parasitoids include mostly certain fly and wasp families. Cues used by
parasitoids to find hosts may include chemicals, stridulatory calls (see pg.
132, box 4.2), and visual cues.
Phoresy is transporting of one insect species by another -- this
does not specifically harm any individual (pseudoscorpion/longhorn beetle
example, pg. 225). However, adult female para-sitoids may be phoretic, hopping
off to lay her eggs on the host eggs when the host lays them.
Parasites: of vertebrates
mostly (though not aquatic vertebrates)
Parasites may be either ecto- or endoparasites.
Parasites are often attracted by carbon
dioxide produced by potential hosts. Virtually all lice and fleas are parasitic,
and some flies and beetles. Also
included in this are some blood feeding species, not only flies (including
mosquitos)/beetles, but some moths, assassin bugs and a few others. Blood is
typically ingested after a bite, accompanied by the injection of anticoagulants.
Phytophagy:
Estimates are that approximately half of all insects are phytophagous
-- plant-eating,
including a majority of the members of the six largest orders. Indeed, insects
are the most
important consumers of plants on the face of the planet.
Phytophagous insects include:
External Feeders -- leaf feeders, sap/stem feeders, fruits, seeds,
petals/flowers
External feeders are themselves exposed to predators, etc., and a
majority are
protected by chemicals and often brightly colored, as mentioned above.
Internal Feeders -- Miners inside of leaves; borers
in stems/roots, fruits/seeds; galls
Monophagy
(specialists), Oligophagy, and Polyphagy (generalists)
Many plants have developed
secondary plant compounds (poisons and other chemicals) for defense; but
some species of insects have overcome and even utilize these defensive
compounds, and use these as an attractant for feeding/oviposition.
Pollination:
The main pollinators of angiosperms (flowering plants) are
also insects, without
which we would not have most fruits, nuts, berries, etc. Plants must offer or
pretend to offer a reward -- usually nectar. The benefits for both: 1) Plants --
produce less pollen than for those that are wind-pollinated; insects numerous;
2) Insects -- guaranteed (almost) food source.
This phenomenon required plants to develop colorful targets -- brightly
colored petals (including in UV) -- and/or strong odors, especially for
attracting nighttime pollinators. Odors may be pleasant, but some species have
flesh-like odors to attract fly and beetle pollinators. Still other flowers
cheat and offer no nectar and get pollinated by mimicking other flowers or even
females of the pollinator species (both in appearance and smell; see pgs.
294-295). Though many, particularly the bees and wasps, are important
pollinators, many species will eat pollen, and others, particularly the beetles,
will eat other flower parts as well.
-lecty -- constancy of
visiting flower species;
(monolectic, oligolectic, polylectic).
Monolecty is, of course, most beneficial for plants; interestingly, monolecty
may also be at least
temporarily beneficial to the insect, especially with density of flower
availability, as the insect can form a powerful search image and learn a
specific flower "mechanism". There are plenty of
flower visitors that are oligo- or polylectic, however.
Example of complete pollinator-flower
mutualism (a coevolutionary relationship): Yucca and Yucca Moths
MATING and REPRODUCTIVE BEHAVIOR:
Intrasexual (Male-male) selection:
Combat:
Horns (pg. 97-98, dung beetles), though within species, smaller horned
individuals may invest in larger testes (pg. 319); large mandibles in many
insects, including longhorn beetles (pg. 225), stag beetles, dobsonflies, and
many others.
Sperm competition (pg. 322+) – this can occur in several ways:
Examples: 1. more ejaculate with more sperm -- fruit flies raised with rivals
ejaculate 2.5
times as many sperm than if raised in isolation in the presence of females; 2.
long mating time;
3. a copulatory plug – a sphragis in Parnassius butterflies; 4.
chemically "mark" (with a
pheromone) the female as mated; 5. remove previous males sperm with special
structures –
"scoop" in damselflies (pg. 323); 6. “toxic” semen in fruit flies (pg. 347;
“chase away” selection); 7. destructive penises (bedbugs [pg. 348]; Papaipema
moths); 8. mate guarding (damselflies/dragonflies in “tandem” [pg. 327];
crickets [pg. 357])
Intersexual selection -- mate attraction:
Female (and male) Choice – this is an obvious and driving force
for why many males seemingly have unusual, and in some cases, maladaptive
traits. Why males?
Examples: 1. Color (UV color in Colias butterflies (pg. 121);
female dance flies (females attracting males [pg. 311]). 2. Calls (katydids,
grasshoppers and crickets [pg. 125]; certain moth ultrasound [pg. 275], and many
others). 3. Gifts provided by male (scorpionflies [pgs. 319-320, 331], dance
flies [pg. 311]; Mormon cricket spermatophore [pg. 312]). 4. Flash patterns in
bioluminescent organisms (fireflies [pg. 291-292], including females that
deceive other species males). 5. Pheromonal quality and quantity . . . and many
other examples.
Reproduction: Egg-laying behavior may immediately follow mating in
many species. Some species of fruit flies have females that, once mated, and
receiving a hormone (sex peptide) from males, initiate egg laying and refuse to
mate again (pg. 172; another example of males monopolizing offspring). In
another experiment with crickets (pg. 370), male success in attracting mates is
passed to his sons, which are twice as likely to attract mates as those males
who fail to “win” mates when in competition with other males.
PARENTAL CARE:
Although not common, there is some parental (both maternal and paternal)
care (pgs. 408-426) in some insects, though we will leave this discussion for
later (with the vertebrates).
SOCIAL BEHAVIOR:
Many activities of many insects are
solitary, performed by the individual for the individual.
But almost all insects must mate, and several groups are social for more than
just mating. The obvious ones include the termites and many hymenopterans, but
also some others. Many insects are gregarious (behavior
where groups get together but not for care/rearing of young), often at food
sources, and so could be considered to exhibit some social activity. Examples
include certain beetles, tent-building moth larvae, roosting Monarchs and others
(see Zebra longwing butterflies on the website) and maggots of several fly
species. Gregarious behaviors would include lekking behavior
Subsocial Behavior
-- some parental care, but parent leaves/dies before immatures reach
adult stage. This includes a wide variety of insects, including some stinkbugs,
nine families of beetles, some roaches and mantids, and some bees/wasps.
Parasocial Behavior
-- interactions between adults of the same generation. Many wasps
and bees exhibit parasocial activity, where a nest is inhabited by several
females, some or all
of which provision their own brood cells, and may work together with others to
make more
brood cells. The benefits are added protection for all offspring in the nest.
Eusocial Behavior
(pgs. 446-447) -- characterized by the following: 1) members cooperate in caring
for the young, 2) more than one adult generation overlaps in the colony, and 3)
there is a division of reproductive labor between reproductives (queens and
kings/drones) and the non-reproductive workers. In other words, there is a
caste system (pg. 466-470). True eusocial behavior is exhibited by termites
and by a number of different hymenopteran lineages (wasps, ants, bees). In most
cases, the castes are determined largely by specific semiochemicals released by
reproductives of the colony, methylating certain genes and changing their
expression (pgs. 66-67 and chapter 12). How does this evolve? An important
concept is inclusive fitness, but there can be social/reproductive conflict
(pgs. 470-474).
In the two main insect groups, termites are hemimetabolous (no pupa), and
what hatches out of the egg is a young termite. These young termites “go to
work” immediately. Wasps/bees are
holometabolous, meaning that the young larvae are helpless and must be fed.
Additionally, termites (both males and females) are diploid and both participate
in nest/brood care, but the wasps/bees are
haplodiploid (pg. 458), with the
queens laying unfertilized eggs to make males (whose only job is to mate) and
fertilized eggs to make females (workers and queens). This is part of what leads
to social/reproductive conflict in Hymenoptera. I will explain!
The Honeybee dance: a combination of
tactile/auditory/visual/chemical communication
Worker honeybees typically exhibit
different behaviors as they get older -- initially, they are
nurses to the brood, then help build new cells inside the hive, then guard the
entrance, and finally
act as foragers for nectar and pollen (pg. 61, Fig. 3.1). These "new" foragers
learn where the best food sources are by following, and ultimately learning, the
honeybee waggle dance.
The waggle dance (pgs. 260-262) is
done on the vertical surface of a mostly dark hive (the visual communication
here is minimal, though the bees will initially learn to associate the color of
the flower with the food source, as well as learn landmarks and direction of sun
in relation to the food source). Directly up on the surface (negative
geotaxis) represents toward the sun; dancing at an angle on
the surface represents the direction to the food at the same angle away
from the sun. The dance is called the waggle dance because the bees "waggle" the
abdomen while dancing in the appropriate direction, alternating looping to the
left and then to the right, returning each time to the correct angle and
waggling again. Other bees follow the dancer, and touch the dancer with the
antennae (tactile) to get a sense of the direction to the food resource. The
followers can pick up flower odors from the dancer, and the dancer/forager may
even present a small amount nectar from her crop to the followers (chemical).
Distance to and quality of the resource is also communicated.
Distance is indicated by the duration of each waggle run (longer waggle =
farther). The quality is indicated by the overall length of time the
dance persists (longer = better). Bees can apparently even indicate changing
distance to experimental food resources (weird!). All of this will be
clarified in class; you will need to be able to interpret drawn examples of the
dance on the first test. It may be hard to imagine how such a complex behavior
could evolve, but the possible steps are characterized on pgs. 267-269 (please
READ this section).
CIRCADIAN/CIRCANNUAL RHYTHMS:
The Sun Clock and Circadian Rhythms
Most insects (indeed most organisms)
use the sun as a reference for all sorts of activities.
Different insects are active (and at rest) at different times (matinal
[dawn], diurnal, crepuscular [at dusk (or dawn)], nocturnal).
The insects may further divide their active time into foraging time at peak
resource abundance, mating time, oviposition time, molting, etc. All of these
activities will often follow a daily, or circadian, cycle.
For some activities, the cue (light)
is the complete stimulus for the behavior. However, for
several behaviors in many insects, there is an internal clock that is partly
responsible for the
behavior that is reset each day by the sun. For instance, crickets calling for
mates will continue to
do so at approximately 24-hour periods even in total light or dark (see pgs.
148-153). So, although the orientation cue is external (the sun), there is an
internal component (the clock), which will continue to run in the absence of the
external cue.
Using phototaxis as a directional reference to other resources (food, migration
to south,
etc.) requires an expectation as to where the sun should be at specific times
during the day -- in
other words, an internal clock. For example, the sun should be east in the
morning, south at noon
(if you are in the northern hemisphere), and to the west in the evening. So
migrating individuals, such as Monarch Butterflies (pgs. 122-123), trying to
maintain a constant direction will adjust their response to the sun as the
day progresses.
Migration:
Why migrate? Why do Monarchs
migrate (pgs. 248-250)?