Why does the Meadowlark sing

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Tinbergens 4 Whys and causation in animal
behavior Why does the animal do that?
Why does the Meadowlark sing?
(1) In terms of the function or adaptive value
they sing to attract mates for breeding
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Tinbergens 4 Whys and causation in animal
behavior Why does the animal do that?
Why does the Meadowlark sing?
Without implying that the animal is aware of its
effects or actions - evolution produces
machines that successfully reproduce themselves
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(2) In terms of the Causation the processes
inside (endogenous) or outside (exogenous) that
produces the observed behavior. They sing b/c
increasing day length triggers hormonal changes
in the body or b/c of the way air flows across
the syrinx and creates membrane vibrations...
(3) In terms of Development they sing b/c they
learned the song from parents or neighbors
(4) In terms of the Evolutionary origins of the
behavior the evolution of complex songs arose
from simpler songs of ancestral blackbirds.
All answers are right and it is pointless to
argue about which is correct, rather it is
important to distinguish between the different
kinds of answers
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Ultimate Perspective/Causation
Proximate Perspective/Causation
Function or adaptive value

• Proximate Causation
• physiology
• environmental control
• Cognition analyzing, using,
• acquiring information
• e.g., day length

Behavior
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• Lions breed throughout the year, but females
  within a pride come into estrus
• synchronously
• Prox Chemical cues (pheromones) stimulate
  the beginning of estrus

Ultim Cubs born synchronously survive better
communal suckling of young stronger male
coalitions
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• Females come into heat for 2-4 days
• over which 600 copulations may occur
• Prox There is a high probability of
• ovulation failure and abortion

Ultim Only 13000 copulations will produce
a surviving cub devalued copulations
reduce the benefit of fighting
for access to the female
increase paternity uncertainty
to prevent males from killing young not fathered

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• After a pride takeover by new males, they will
  attempt to kill all the cubs
• under 18 mo.
• Prox Unfamiliar odor of cubs induces male
  to commit infanticide (Bruce Effect)

Ultim Induces females to come into estrus
quickly males do not invest valuable
resources raising cubs which are not their own
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What are the proximate mechanisms? Read Chapter 4

• Alternative male phenotypic strategies in tree
  lizards
• Reproductive behavior in birds

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Tree Lizard Urosaurus ornatus

• 9 recognized color-morphs
• 1 to 5 morph types per individual population
• Several behavioral correlates with dewlap color

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Differences in aggressiveness of free-living
males to a tethered random color morph male
intruder
70
Orange-blue
60
50
40
30
Orange
20
10
dewlap display
approach
face-off
charge
bite
increasing aggressiveness
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Orange
Orange-blue

• Small home range (20m2)
• Nomadic during stressful times (e.g., drought)
• Greater body mass long and lean

• Large ranges (85m2)
• Sedentary, never nomadic
• Smaller body mass, but more
• massive at a given body length

What do these represent ?
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Orange
Orange-blue

• Small home range (20m2)
• Nomadic during stressful times (e.g., drought)
• Greater body mass long and lean

• Large ranges (85m2)
• Sedentary, never nomadic
• Smaller body mass, but more
• massive at a given body length

What do these represent ?
Alternative Male Reproductive Strategies
Fixed morph types with a genetic basis in the
lab, broods are a mix of Orange and Orange-blue
phenotypes in the same ratio as seen in the
wild However, within Orange morph there is
plasticity in that individuals switch between
nomadic and territorial types depending on
environmental stress
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A model for hormonal mechanism of sexual
differentiation
male
immature
Fixed strategies
female
hormones
immature
nonbreeding
Plastic responses
breeding
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Orange-blue
territorial
immature
Fixed strategies
sneaker
hormones
Orange
Orange
immature
territorial
Plastic responses
nomadic
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Progesterone determines males reproductive
strategy

• Progesterone levels evenly split between
• 50 males 0.1-1 ng/ml
• 50 males 10-100 ng/ml

100
75
(2) Males strategy is affected by progesterone
injections at hatch day
Percentage of males
50
25
control
Progesterone
(Moore 1998)
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60
inverse relationship between TEST and CORT
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Testosterone (ng/ml)
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No patch
CORT patch
Oil patch
While the interaction between Testosterone and
Corticosterone determines males lifestyle
(nomad vs. territorial)
(Moore 1998)
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Aggressive and territorial mate with all
females in their territory
Non-aggressive, mildly territorial in good yrs
mate by sneaking into territories to steal
copulations
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General Annual Cycle Garden Warbler
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Photoperiod
i.e., sunlight, is the primary environmental
cue e.g., Dark-eyed Juncos were subjected to an
experimental increase in daylight of 5-10
minutes/day. This initiated gonadal growth and
was reversible and repeatable 3 times per year.
(Rowan 1929)
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Going from length of daylight to time of year...
The External Coincidence Model day length is
measured by greater amounts of daylight that
coincides with the photosensitivity phase of
the circadian rhythm.
of gonadal enlargement
light/dark cycle
photosensitive phase of circadian rhythm
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Testosterone and male behavior (test implanted
DEJU- Ketterson et al. 1992)
F
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(1) Feeding rate (feeds/hr)
f
m
(3) Singing rate (songs/hr)
(4) Mate choice (min w/male)
M
0
M
25
100
M
6
M
m
m
m
3
(2) Latency of defense (min)
0
0
0
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Summary
(1) Every question in Animal Behavior has a
(actually several) proximal explanations
and one (?) Ultimate explanation (2) Although
we focused on hormones, hormones are linked to
the environmental conditions, which provide a
proximal stimulus, and they must have
underlying genetic control which itself
is under molecular control ... (3) There is a
tight fit between form (proximal mechanisms) and
function (why has the trait evolved)