Activities
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Rhythmic All eukaryotic organisms have a biological clock that regulates their activities Nearly all activities mentioned in this class all quarter long have some kind of temporal pattern
Rhythm: a change with time that is repeated in a particular pattern
Endogenous rhythm: the timing actually comes form the organism itself - the organism has its own internal clock Exogenous rhythm: dictated by rhythmic phenomena outside of the organism sunrise/sunset or seasonal changes
Temporal Scales
Daily (Circadian) Monthly Rhythms Annual Rhythms
From an experimental point of view, which of these is harder to document?
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Environmental Reinforcement
What is rhythmic besides animals?
Light intensity Temperature Relative humidity Barometric pressure Cosmic radiation
All of these factors have influence on animal behaviors
Daily Rhythms
Honeybees time floral visits Experimental design
Foraging honeybees were marked and trained to visit a feeding station at specific times of day The training period lasted 6 days After training, the feeding stations were left empty and the number of bees visiting the station was recorded throughout the day
Filled with nectar substitute (sugar water)
Bees land here and collect nectar
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Results
# Bees Visiting
Time of Day
Advantages to Timing Floral Visits
Flowers have rhythm in nectar secretion Selection favors visitors that collect the most nectar
Too early: flower has not produced max amount of nectar Too late: another nectar feeder has already gotten the prize
Stabilizing Selection?
Daily Rhythms
Pheromone release of two moth species:
Hyalophora cecropia and Callosamia promethea Females of these moth species produce sex pheromones that attract both of species males However, timing of the male flights is during different times of the day
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Males approaching traps
Entrainment an endogenous clock is "reset" by outside cycles.
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The interaction between endogenous and exogenous timing
A circadian clock is set to about a 24 hour period
What Happens Without Exogenous Entrainment?
Houseflies were tested for their general activity patterns
1st week flies on a 12:12 photoperiod
Next 30 days in complete darkness
Monthly Rhythms
Less common for insects Associated with phases of the moon, not necessarily the calendar
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Ant Lions
Neuroptera: Myrmeleontidae Also called "doodlebugs" Holometabolous Larvae construct elaborate traps to capture prey Monthly variability in the size of the traps that are constructed
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The size of the funnel is larger during the full moon than during the new moon Adaptive significance?
Annual Rhythms
Very difficult to separate the effects of an actual "annual clock" from the effects of seasonal cues
Photoperiod regulates many seasonal insect behaviors
Aphids starting sexual reproduction in the fall, as the day length shortens
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Advantages of the Biological Clock
Anticipate environmental changes
Drosophila sp. flies eclose just before dawn in the desert which allows their cuticle to harden before the humidity drops
Synchronize a behavior with an event that can not be sensed directly
Honeybees timing their foraging
What Clocks Are Involved? Exogenous/Endogenous Temporal Scale
Optimal Foraging Defenses Against Predators Resource Competition Fighting and Assessment Sociality Reproduction Signals and Communication Dispersal Migration and Phase Polymorphism
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