DEVELOPMENT (ONTOGENY) OF BEHAVIOUR (2020)_031255.pdf

Development (Ontogeny) of Behavior
(including role of nervous and endocrine systems)
Prof. John Kazgeba Mfune
Department of Biological Sciences
University of Namibia

Development (ontogeny) of Behaviour
• Nature and nurture
• Instinct and learning in their biological setting
• Maturation – development involving growth
• Hormones and early development
• Nervous system and development
• Play
• Imprinting and early experience
• Phenotypic plasticity

NATURE OR NURTURE
• Nature nurture controversy is age-old
• Does behavior develop primarily from biology
(nature), or from the environments in which
we are raised (nurture)?
• What is the influence of genetics / heredity
(Nature) and Environment (in large context
not just habitat )on development of behavior?
• What is most important, nature or
nurture?

NATURE OR NURTURE
• Is a child's athletic ability inherited, or simply a product of
training?
• Is the ability of a lion to kill prey inherited or learned?
• Is courtship in pheasants (birds) learned or inherited
• Is aggressive behaviour inherited or learned?

NATURE OR NURTURE
• Is COURTSHIP learned or inherited

NATURE OR NURTURE
• Is VIGILANCE behavior inherited or learned?

DEVELOPMENT (ONTOGENY) OF BEHAVIOUR (2020)_031255.pdf

NATURE OR NURTURE
• Animals behave in ways that allow them to eat, find shelter,
survive, mate and produce offspring.
– Are these behaviour learned (NURTURE) or inherent (NATURE) ?
• If behavior is inherited, animals respond automatically in a
certain manner i.e. instinctively. Their behaviour does not
require learning or practice. It just occurs or appears
appropriately even for the first time it is needed in response
to a stimulus
• Animals however are also able to modify their behavior due
to experience / learning / environment
e.g. Child cries for anything they want. In adulthood, we learn
not to cry anywhere anyhow
[HOW ABOUT the saying “MEN DON’T CRY”]

NATURE OR NURTURE
• Instinct (or nature) where adaptive behavior
has evolved by natural selection and is
heritable
• Learning (or Nurture) where adaptive
behavior occurs within a life time of an
individual

Nature and Nurture
READ CHAPTER 3:
BREED AND MOORE (2012)
Section 3.1-3.2: The Nature and Nurture Debate
(Photocopy scanned and posted on portal and Moodle)

EXAMPLES OF ROLE OF NATURE AND NURTURE
• Divide into two groups
Group 1. Argue for role of nature on
behavior
Group 2. Argue for role of nurture on
behavior
• Each group to support their argumentation
using specific examples

Instinct and learning in their biological setting
• Preset behavior that requires no
learning is advantageous for animals
with short life span and no parental
care.
• Shall examine two examples to
illustrate the role of :-
– INSTINCTIVE BEHAVIOUR (NATURE) and
– LEARNED BEHAVIOUR (NURTURE)

INSTINCT BEHAVIOUR:
INFLUENCE OF GENETIC MAKEUP (NATURE)
(Mason wasp (Manobia quadridenes)

Cell building in Insects
• Insects build a series of cells inside hollow stems of
plants

Cell building in Mason wasp (Manobia quadridenes
• Mason wasps build a series of cells inside hollow stems
of plants

• Mason wasps build a series of cells inside hollow stems
of plants
• Female wasp emerges from its cell and has brief
contact when she mates with male, after which she
lives alone
• She selects a hollow stem and builds a partition of
mud mixed with her saliva at the inner end
• Lays an egg which she attaches to roof of the stem
close to the partition

• She then hunts for caterpillars, kills them and puts
about 4-8 in each cell. This is future food for larva
when it hatches
• She then builds another partition sealing off the egg
with its food supply and lays a second egg beyond this,
provisions the second cell, seals it off and so on.

• She can construct as many as eight to ten cells in line
along the cavity of the stem until the female reaches
the outside end. She then plugs off this end with mud.
• She then moves to another stem and constructs more
cells.

• Female wasp lives only a few weeks but
carries out this elaborate and complex
series of behavior patterns in total
isolation.
• She could not do this if she had to acquire
everything from scratch by trial and error.
• She has to rely on pre-set unlearned
responses; INSTINCTIVE PATTERMS

Cooper (1957) observations of the
Mason wasp (Manobia quadridenes
• If examine stems where larvae have
pupated before emerging as adults one
observes the following:-
• All pupate and emerge with head facing
the open end
– Making correct choice of end
is matter of life and death
– Though an emerging adult can turn
around in the narrow strip, they do not do so.
They move ahead breaking through the partition

• The outermost pupae emerge first
• In terms of hatching and emergence,
what is the major mystery or challenge
here?

• The outermost pupae (though come from
eggs laid last in the series of cells), emerge
first, leaving a clear passage (for their
siblings from deeper the stem)

• Adults emerging from artificially reversed
pupae struggle and move inwards through
deeper cells and accumulate at the blind end
• How can a larvae, about to pupate make
correct decisions?

• Cooper’s experiments showed clearly that they
did not detect:- light, nor used gravity nor
oxygen concentrations as a cue but…
• Rely on information left behind by mothers.
• As female wasp retreats outwards, the inner
side of each is left as rough mud while the
outer side she smooths into a concave form.
• Larvae pupates with the head toward the rough
end

• Information is thus passed from one
generation to its offspring and must be
encoded genetically in a way that allows
the larvae and adult female to develop
appropriate behavior
• REMEMBER:- neither the female wasp’s
actions nor the response of the larva can
rely on experience

Learning : influence of environment
the African elephant
• Elephants live in matriarchal groups led my mature
female with her daughters and their offspring
• Offspring born in a group where individual know who
is who from long experience with each other
• Nourished and closely protected by its mother for
several years
• It slowly acquires adult repertoire of feeding
behaviour, learning how to select food and how
group migrates around its home range to match
seasonal changes in vegetation and water supply

• Elephants live in matriarchal groups
led by mature female with her
daughters and their offspring
• Offspring born in a group where
individuals know who is who from
long experience with each other
• Nourished and closely protected by
its mother for several years

• Young elephants slowly acquires adult repertoire of
feeding behavior, learning how to select food and
how group migrates around its home range to match
seasonal changes in vegetation and water supply

• Females are sexually mature
at about 20 years (for males
its even later)
• Behavior of individuals and
groups varies considerably
according to their history
• Elephants at Addo in South
Africa: abnormally nocturnal
and excessively aggressive
towards humans

• Behavior traced back to 1919
when there was an attempt to
annihilate them by shooting.
• Though very few, if any, of the
elephants that lived at that time
are still live, their descendants
have acquired and transmitted
the behavior that enables a few
to survive over 70 years.

female monkey raised in isolation
• Female monkey (her mother was killed by poachers)
raised in isolation in zoo from childhood.
• Did not experience early childhood experience of
attachment to mother, suckling (was fed milk on
bottle)
• When she grew to be an adult, could not allow her
offspring to suckle and she killed some litter.
• Issue: she did not have early childhood experience to
learn skills from mother

NATURE OR NURTURE
• Mason wasp rely on pre-set instinctive
behaviour
– Wasp must learn many things including: exact
location of each of its nests so she can return to
them after hunting

NATURE OR NURTURE
• Elephant / monkey, learn behavior by
association with others in the held.
– Must learn many things
– They also possess instinctive behavior e.g.
feeding, reproduction but these may be modified
by learning

NATURE OR NURTURE
• Most organisms show behaviors that are
influenced by both genetically inherited
abilities and the environment, i.e. learn with
experience to behave in a certain way.

Endocrine system, Nervous system and behaviour
• Endocrinology is the study of hormones, chemical messengers
that target organs and influence many processes, from growth
to reproduction.
• Hormones are secreted by ductless glands and are carried
through the body by the circulatory system
• Both the nervous system and the endocrine system act as
feedback systems
• Nervous system produces much faster results, whereas the
endocrine system is slower acting, longer lasting, and
produces more general responses

Peripheral nervous system (PNS)
• Sensory neurons running
from stimulus receptors
that inform the CNS of the
stimuli
• Motor neurons running
from the CNS to the
muscles and glands - called
effectors - that take action.
Central nervous system (CNS)
• Spinal cord and the
• Brain
Organisation of the Nervous system

Maturation: development involving growth
• Development of behaviour is associated with normal growth
process of the nervous system and the rest of the body
including the involvement of the endocrine system
(hormones)
• E.g. emergence of sexual behavior in vertebrates depends on
the growth of gonads which begin to secret hormones.
(Read Chapter 2 in Breed and Moore 2012)
• Nervous and muscular system of young animals have to
develop further and differentiate before they reach adulthood
and the term MATURATION is used to describe behavior
changes associated with such growth.

• Examples (1)
– Young birds make vigorous
flapping movements with
their wings while still in the
nest.
– Commonly thought that they
are practicing to fly??.
– However, there is no evidence
that early development of bird
flight is affected in any way by
such activities

• Examples (1)
–Spalding (1873) showed that
young swallows reared in
cages so small they could not
even stretch their wings flew
just as well as when released as
normally reared birds

• Examples (2)
– Human parents often support
their babies on their legs and
encourage them to ‘practice’
walking.
– By age of 18 months when the
majority of the children are
walking, their skills are similar
whether they first walked at 10
months or 15 months.

• In both examples, it is the :-
– maturation of the central nervous
system and the
– coordination of the muscular
development that counts.
• Practice of course helps to
sharpen and refine the skills:
young fledglings are often very
clumsy at first

Interaction between maturation & practice
• Pecking in newly hatched chicks
• Inherited tendency to peck at objects that
contrast with background.
• Their ability and accuracy at pecking is initially
poor but improves with practice
• Study by Cruze (1935)
– Hand-fed chicks in the dark on powdered food
for periods of up to five days before testing
them for accuracy on pecking.
– While in the dark, they are inactive; no chance
to practice the movement

– Measured accuracy by putting chicks individually into small
arenas with a black floor on which he scattered 2 or 3
grains of millet
– Each chick was allowed 25 pecks scored for miss or hit and
grains were replaced if the chick swallowed them.
– After accuracy tests the chicks were allowed to feed
naturally in light and the effects of practice on their
accuracy measured again after 12 hours.

Pecking accuracy of chicks at different ages
before and after 12 h of practice
Age (h) Practice (h) Average misses (25 pecks)
24 0 6.04
48 12 1.96
48 0 4.32
72 12 1.76
72 0 3.00
96 12 0.76
96 0 1.88
120 12 0.16
120 0 1.00
Describe what the results show? What conclusion can you make regarding
accuracy of pecking from data given in table? Support your answer

– There was steady
improvement with
age (bolded values)
– At each age, 12 h of
practice greatly
improves accuracy
(non bolded figures)
– Much of this
improvements arise
from maturation.
Age (h) Practice (h) Average
misses (25
pecks)
24 0 6.04
48 12 1.96
48 0 4.32
72 12 1.76
72 0 3.00
96 12 0.76
96 0 1.88
120 12 0.16
120 0 1.00

Nature of maturational changes in
nervous system and behavior
• Increasing complexity of structure of embryos is
paralleled by increasing repertoire of behavior both
spontaneous and in response to external stimuli.
• Example: development in crickets (Bently and Hoy
(1970)
– Crickets go through 9-11 larval or nymphal stages (instars)
which become more similar to adults with each successive
molt

Example: development in crickets (Bently and Hoy
(1970)
– Final molt involves biggest changes with full development
of wings and adult genitalia
– Cricket nymphs do not fly; have no wings
– But elements of flight detected as early as instar 7.

Nature of maturational changes in nervous system
and behavior
Example: development in crickets (Bentley and Hoy, 1970)
– Nymphs at this stage adopt typical flight posture when suspended in
a wind tunnel
– All muscles for flight are present at this stage but small in size
– Bentley and Hoy inserted fine wire electrodes into some of these
muscles of the thorax and recorded action potential from them.
– They detected signs of rhythmic nerve impulse characteristics of flight
from the 7th instar nymphs but it was incomplete and not sustained
– It became more complete with successive instar
• New elements could be identified as becoming active may be as
functioning synaptic contacts were established

Example: development in crickets (Bentley and Hoy
(1970)
– Although timing varied between individuals, the units
always developed in the same sequence until by the last
instar before the final molt, the entire pattern was
complete
– At this stage then the maturation of the nymph’s nervous
system is completed and it awaits only the development of
wings
• Similarly, the story is true for the cricket’s song, another
activity that require wings of an adult (they are rubbed
together rapidly tom produce sound)

Hormones and early development
How do hormones influence behaviour?

Endocrine and Sensory
systems and behavior
READ CHAPTER 2:
BREED AND MOORE (2012)
Neurobiology and Endocrinology for Animal Behavior
(Pages 25-45)
(Photocopy will be posted on Portal and Moodle)

• Hormones influence development of behavior.
• This is vividly shown in early sexual development because
hormones are involved together with clear maturational
changes to the nervous system.
• Sexual development is a case of alternative pathways along
one or the other of which an animal’s development (both
morphological and behavioral) is switched by an early ‘trigger
event’.
• In humans and some animals, to be male or female is very
distinct and pervasive difference.

• Hormones influence development of behavior.
• We should keep a broader perspective however that many
invertebrates and hermaphrodites have only one
developmental pathway to becoming male and female

• Even more strange, some fish retain the capacity to switch
paths.
• Example: Coral reef fish Anthias, (Shaipiro, 1979)
– All individuals develop into females although some transform later
into males.
– Males are brightly colored and have a conspicuous dark spot on the
pectoral fin
– Females have uniform orange-gold color

• Example: Coral reef fish Anthias, (Shaipiro,
1979)
– All individuals develop into females although
some transform later into males.
– They live in mixed groups and if a male dies,
one female changes sex.
– The change is very rapid, completed in few
days for previously female fish to develop male
features and begin to produce sperm in its
gonads instead of eggs.
– The female begins to show color change
toward male type within 3-6 days of removal
of males from the group.
– Within hours before they even produce sperm,
its behavior changes and it is treated as a male
by other females in the group

• In vertebrates, switch to male or female is
permanent
• Reptiles, sex appears to be controlled by
temperature at which egg develops

• Reptiles, sex appears to be
controlled by temperature at
which egg develops
• Bull (1980) showed that in
Mississippi alligators
– Shaded nests (lower
temperature) and longer
incubation led to a high
proportion of males
– Nests in open sunlight of the
riverside produced more females

• Birds and mammals rely on a genetic switch not
environmental one to balance the sex ratio that depends on
segregation of one pair of sex-determining chromosomes
• Fish that change sex show that they inherit potential for both
types of sexual behavior
• Similarly, in mammals and birds males and females share
almost all their genes
• Natural selection has had the “problem” somehow to make
the two sexes develop differently

• Morphologically, differentiating between sexes occurred.
Male mammals have developed functionless mammary glands
and nipples.
• For aspects of behavior and morphology where sexual
differentiation is vital, the switch is hormonal one.
• Chromosomes determine whether the gonads will develop
into an ovary or a testis but thereafter, the pattern is also
determined by hormones
• Sexual differentiation is very complex with many interesting
variations.

• In mammals, differentiation of genitalia and neural
mechanisms that initiate sexual behavior is not determined at
fertilization but later during development
• Males and females have a brain that can mediate both
masculine and feminine behavior
– Which pattern becomes dominant depends on pulse of
hormones
• Embryonic / newborn testis unlike ovary has a brief period of
activity and hormone is picked up by particular region of the
hypothalamus
• If hypothalamus picks up hormone at a certain period its
development is switched along a masculine path. If not, it
becomes feminine

• If females are given tiny quantities of hormone at the right
stage, their behavior is masculinized.
• Note that either testosterone or oestrogen will serve to
masculinize male of female embryos (they are both steroid
hormones are similar in chemical terms).
• Denying male embryos their pulse of hormone at the normal
time, removing the testes before they secrete or injecting a
chemical that inhibits the action of testosterone results in
demasculinization.
• This reveals the clear case of “critical period” because
hormone treatment earlier or later has no effect.
• E.g. a male demasculinized by early castration will not have
his masculinity restored by large dozes of testosterone given
later in life

• When they are adults, masculinised females show changed
behaviour patterns
• E.g. rats and mice
– Masculinised females will mount and thrust on receptive females
– They go on and perform the whole pattern of ejaculation
– Also show male-like aggressive behaviour
– Such females are defeminized in that their vagina fails to open, they
lack oestrus cycles and are sterile
– Female primates are readily masculinised as are rodents

Sensory-somatic nervous system
• All our conscious awareness of
the external environment and all
our motor activity to cope with it
operate through the sensory-
somatic division of the PNS
Autonomic nervous system
Peripheral nervous system (PNS)
• Responsible for monitoring
conditions in the internal
environment and bringing
about appropriate changes in
them.

• Consists of sensory neurons and motor neurons that
run between the central nervous system (especially
the hypothalamus and medulla oblongata) and
various internal organs, e.g. heart, lungs, liver etc .
• Actions of the autonomic nervous system are largely
involuntary (in contrast to those of the sensory-
somatic system)
• Subdivided into the Sympathetic and
Parasympathetic autonomous system
The Autonomic Nervous System

Sympathetic nervous system
• Stimulation of the
sympathetic branch of the
autonomic nervous system
prepares the body for
emergencies: for "fight or
flight"
• And, perhaps, enhances the
memory of the event that
triggered the response.
Parasympathetic nervous system
• Parasympathetic system
returns the body functions
to normal after they have
been altered by
sympathetic stimulation.
• In times of danger, the
sympathetic system
prepares the body for
violent activity. The
parasympathetic system
reverses these changes
when the danger is over.
The Autonomic Nervous System

Simple (Reflex Action) behaviour
• A reflex action, also known as a reflex, is an
involuntary and nearly instantaneous
movement in response to a stimulus
• The simplest reflex is a monosynaptic reflex
such as the patellar reflex when the doc
strikes your knee. its a 2 neuron pathway that
does not involve the brain just the spinal cord
at the lumbar area

Other examples of simple reflexes
• Grasp reflex
• Sudden withdrawal of a
hand in response to a
painful stimulus

The role of play in development of behavior

The role of play in development of behaviour
• It is accepted and well known that play in infancy and
childhood is important for normal development of human
(behavior)beings
• Play is observed in many animals. For instance, as kittens or
puppies grow, the most visible aspect of their behavior is play.

• Kittens and young of many animals spend long
periods of playing with each other, with objects and
even adults that play with them intermittently.
• Play however fades with age.
• It is commonly suggested that play has a role in
development of behavior in animals.

• A comparative survey across animals reveals that
apart from a few fragmented anecdotes,
– there is no evidence of play outside mammals and a few
bird species.
– Even in birds and mammals, it is not universal.
• For example young rats show chasing and wrestling behavior,
which we can reasonably describe as play but for mice, there are
very few records.

• Its amongst the ungulates, carnivores and primates
that play becomes co visible and obvious.
• We observe chases, mock fights, stalking, leaping
and all aspects of prey-catching behavior

• Adults may join in and at times, there are some postures that
indicate that an individual wants to play

• We must bear in mind that it is impossible to identify play
with certainty especially as animals grow older.
• In fact we even observe at times that even animals
themselves may have the same problem because mock fights
may change rapidly into real fights as one partner really gets
hurt

• When we discuss parental care, we accept that interchange
between mother and offspring contribute to the healthy
development of the offspring, it is difficult to identify how it
operated
• The same is true when we watch mock fights among kittens or
the amazing high speed chases and wrestling bouts of young
monkeys. We feel that such behavior must play a role in the
development of behavior

• Role / function of play
– Physical and social skills
– Gain knowledge of social group
– Exploration of the environment

IMPRINTING
• Imprinting refers to various behavioral changes whereby a
young animal becomes attached to a “mother figure” and or
future mating partner.
• Lorenz experimented with geese in which he got broods of
goslings to follow him and treat him as their other figure

IMPRINTING
• Imprinting experiments have been conducted in animals that
give birth to precocial young (those that can walk at hatching
and do not stay in the nest) e.g. geese, ducks, pheasants and
chicken
• Imprinting may be measured by the amount of attention paid
to the mother, time spent following if she moves etc

IMPRINTING
• This type of response to the mother figure is
called:-
– FILIAL IMPRINTING.
In contrast to:-
– SEXUAL IMPRINTING
• in which early experience affects the subsequent choice
of sexual partners when mature

IMPRINTING
• Imprinting usually takes place
soon after hatching or birth.
Results in very fixed attachment,
difficult to change.
• Lorenz described it as a unique
form of learning that , unlike other
forms, was irreversible and
restricted to a brief ‘sensitive’
period just after hatching or birth

IMPRINTING
• Imprinting involves a learned association between a particular
stimulus and a response. Shall refer to this again on learning.
• Imprinting plays a role in development because it occurs
before anything else has been acquired by learning. This
contributes to studies on neural basis of learning and memory

IMPRINTING
• Lorenz suggested that a wide range of objects elicits
approach and attachment in young birds
• He got broods of greylag gosling to imprint on him

IMPRINTING
• ASSIGNMENT: READ ABOUT SEXUAL IMPRINTING

Summary
Development (Ontogeny) of Behaviour
• Hormones and nervous system and early development
• Play

Development (ontogeny) of Behaviour
• Hormones and early development
• Play

Endocrine system and behaviour
• Endocrinology is the study of hormones, chemical messengers
that target organs and influence many processes, from growth
to reproduction.
• Hormones are secreted by ductless glands and are carried
through the body by the circulatory system
• Both the nervous system and the endocrine system act as
feedback systems
• Nervous system produces much faster results, whereas the
endocrine system is slower acting, longer lasting, and
produces more general responses

• Control center of vertebrate endocrine systems is the pituitary gland,
located in the brain.
• Hypothalamus funnels information into the pituitary gland
• Anterior pituitary secretes hormones, including growth, thyroid
stimulating, and follicle stimulating hormones
• Posterior pituitary acts as a storage bag for hormones. It is responsible for
oxytocin and antidiuretics, which control water balance
• Hormones secreted by the pituitary are intended for target organs, which
either produce other hormones in turn, or function in response to the
pituitary signal.

• Hormones are involved in a large array of animal
behavior, from sexual tactics to "tamability
Example: Sexual Tactics Among Midshipmen Fish
• Midshipmen fish actually have two morphologically
and behaviorally distinct types of males.
• Type I males are large, build and occupy nests
• make a droning sound that attracts females to come
and lay eggs
• The type I male then fertilizes and cares for the eggs.

Example: Sexual Tactics Among Midshipmen Fish
• Type II males are smaller and resemble the females
• They cannot sing and are too small to defend a territory
• type II males have enormous testes (approximately 20 % of
their body size).
• These "sneaker" males swim into an occupied territory,
attempt to fertilize the eggs with a "sperm bomb,“
• are aggressively chased away by type I males.
• These fish actually have three types of sex hormones rather
than the normal two, a fact that is responsible for the distinct
types of males

Phenotypic Plasticity
Definition:
• Ability of individual genotypes to produce different
phenotypes (non-heritable) when exposed to different
environmental conditions.
• Meaning that the organism's phenotype is flexible (plastic)
and can be influenced by the environment
• Genetic and Environmental influences are intricately
entangled and hence not easy to separate.

• Other definitions:
• A change in the expressed phenotype of a genotype as a
function of the environment (Scheiner 1993).
• The property of a given genotype to produce different
phenotypes in response to distinct environmental conditions
(Pigliucci 2001).
• Environment-dependent phenotype expression or the
environmentally sensitive production of alternative
phenotypes by given genotypes (Dewitt & Scheiner 2004).

• The expression of different phenotypes in a single genotype
when subjected to different environments
(Ananthakrishnan & Whitman 2005).
Phenotype
Environment
Genotype

• Environment may exert DIRECT EFFECTS on development
• Environmental variables may directly affect a development or
physiological process
• E,g. Temperature can directly influence developmental process
affecting chemical reaction kinetics and the physical properties of
membranes.
• INDIRECT EFFECTS may occur when environmental cues cause a response
that is mediated by other physiological and development events
• E.G. Photoperiod, may alter pattern of hormone secretion in insects.
In turn this may elicit a change in the developmental pathway that
leads to production of the phenotype best adapted to cope with the
coming temperature and nutritional condition
• Characterized by time delay between signal elicitation and
development response.

Phenotypic plasticity
Mustard plant seedling
grown in environment
with:-
• High carbon dioxide
levels, the new leaves
have fewer stomata
• Low carbon dioxide levels,
the new leaves have many
stomata

• Phenotypic plasticity represents a measurable variation in
which we can quantify variation in the contribution of
Genes and Environment to phenotypic variation.

• Phenotypic plasticity represents measureable
variation.
• Variance (measure of variation in statistics)
quantifies the deviation of values around a mean.
• Hence :-
• The variance of a phenotypic trait can be
partitioned as follows:
VP = VG + VE + VG ¥ E + Verror
Breakdown of variance in phenotypic expression

The variance of a phenotypic trait can be partitioned as follows:
VP = VG + VE + VG ¥ E + Verror
Where:
VP = Total phenotypic variance for a trait
VG = Genetic variance (proportion of phenotypic variation
attributable to genes)
VE = Environmental variance (proportion of variation caused by
the environment)
VG¥E = Genotype ¥ environment interaction (Genetic variation for
phenotypic plasticity)
Verror = Unexplained variance, including developmental noise,
measurement error, etc.
Breakdown of variance in phenotypic expression

• Phenotypic plasticity can be visualized by the use of
reaction norms,
• Reaction norms
• Refers to the set of phenotypes than can be produced
by an individual genotype when exposed to different
environmental conditions
• plot values for a specific phenotypic trait (e.g. wing
color) across two or more environments or treatments
• A non –plastic character is said to be Monophenic
• Polyphenism : where two or more distinct phenotypes
(without intermediates) are elicited by the environmental
cues. Hence it is a type of phenotypic plasticity
Phenotypic plasticity expression

Graphical Representation of Phenotypic plasticity
• Each color / represents different genotype
• Each genotype exhibits a different reaction norm (i.e. a
different response to environment, or different slopes)
• Reaction norms (i.e. different response to environment)
(e.g. wing color) across two or more environments or
treatments

Reaction norms for various traits in Drosophila in response to
growth temperature. Reveals great diversity in phenotypic plasticity
response. (David et al. 2004; by permission of Oxford University Press, Inc.).

• Note that each Genotype shows a different
response (non-parallel reaction norms)
• This represents genotype x environment
interaction (VG x E),
• Hence indicating genetic variation in plasticity itself

• Organisms exhibit phenotypic plasticity in different
features / characteristics in response to the
environmental conditions (temporal, spatial, abiotic,
biotic etc)
– Morphology
– Physiology
– Life history
– Behaviours
Other forms
– Acclimatization
– Learning

Wet form
Dry form
Wet and dry forms in Common evening brown butterfly Melanitis leda (©FreerkMolleman
Developmental seasonal polyphenism
?

• In Junonia (Precis) coenia
• Interaction between allelic differences
(genetic polymorphism for wing color)
and environmental conditions.
(a) Larvae exposed to a short-day
photoperiod and low temperature
regime
• Secrete low levels of a small-PTTH-like
neurohormone at the onset of the
pupal phase.
• Pupal ecdysteroid peak builds up late
and reaches threshold levels only after
the critical period (gray bar).
• This permits the expression of dark
pigments in the developing wings
which are, thus,
– adapted for higher solar absorption.
Seasonal wing color polyphenism in butterflies,
PTTH = Prothoracicotropic hormone

(b) In contrast, exposure of larvae
to a long-day photoperiod
and high temperatures
• leads to an early and
enhanced PTTH release,
• Leads to above-threshold
ecdysteroid levels during the
critical period.
• These conditions favor the
expression of the light colored,
alternative wing phenotype.
(Data by Masaki et al. (1988), Rountree and
Nijhout (1995)
Seasonal wing color polyphenism in butterflies,

The Tropical butterfly
Bicyclus anynana.
(a) The less active dry season (low
temperature) morph exhibits
small eyespots on the ventral
side of the forewings
• Mechanism
–Low ecdysteroid titer during
the critical period (shaded
bar) at the onset of pupal
development
Eyespot size polyphenism as exemplified in the tropical butterfly

(b) The forewings of the wet-season
(high temperature) morph develop
large eyespots
MECHANISM:
• An above-threshold ecdysteroid
titer during this critical period.
• In the wing discs of last instar larvae,
eyespot focal cells express the
Distal-less protein. The earlier pupal
ecdysteroid peak causes enhanced
synthesis of dark pigment from this
focal center and,
• Hence generates large eyespots in
the wet-season morph.
(Based on data and models by Brakefield and Reitsma
(1991), Kooi et al. (1994), Brakefield et al. (1996, 1998),
Koch et al. (1996, 2003),
Brunetti et al. (2001), and Beldade and Brakefield (2002
Eyespot size polyphenism as exemplified in the tropical butterfly

Discrete Seasonal polyphenisms in
Neminia arizonaria caterpillars
Summer broods
feed on oak
leaves and
resemble
an oak twig
Spring brood
feeds on and
resembles
oak catkins

Sex determined by egg temperature
Temperature dependent sex determination in Reptiles

A. L. M. Macagno, A. Pizzo, A. Roggero, A. Rolando and C. Palestrini (2009). Horn polyphenism and related
head shape variation in a single-horned dung beetle:
Onthophagus (Palaeonthophagus) fracticornis (Coleoptera: Scarabaeidae). J. Zool Syst Evol Res (2009) 47(1),
96–102. Journal compilation 2008 Blackwell Verlag, Berlin
Hornless male Horned male
Hornless female
Developmental Phenotypic Polyphenism (plasticity)

Hornless male Horned male
Developmental Phenotypic Polyphenism (plasticity)
• Larval nutrition at metamorphosis affects size of
species-specific cephalic (head) and thoracic
exoskeletal projections (‘horns’)
• Gives rise to HORNED AND HORNLESS MALES in the
same population
• Horns are male secondary sexual characteristics

Left individual was exposed to fish-predator chemicals
Right individual was not.
The long spines reduce predation (Agrawal 2001).
Predator-induced plasticity
Daphnia lumholtzi.

Caste polypenism in social insects
Termites

Caste polypenism in social insects

• From development to adulthood, individual organisms
through their genotypes produce different phenotypes
(non-heritable) when exposed to different environmental
conditions.
• Meaning that the organism's phenotype is flexible (plastic)
and can be influenced by the environment
• Genetic (Nature) and Environmental (Nurture) influences
are intricately entangled in both development and
evolution and hence not easy to separate.
• Phenotypic plasticity is an important property of
developmental systems that enable organisms to cope with
environmental unpredictability and or heterogeneities

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