1. The environment regulates animal development in several ways, such as requiring certain substrates to trigger metamorphosis or relying on symbiotic bacteria for proper organ development. 2. Environmental conditions can influence development through phenotypic plasticity, inducing different phenotypes from the same genotype. Some species exhibit polyphenisms where the environment determines distinctly different phenotypes. 3. Factors like seasonality, temperature, food availability, and presence of predators can alter development to increase fitness. Temperature also determines sex in some species.

1. Environmental Regulation of
Animal Development
SUMMARY:
Regulation of Normal Development
Disruption of Normal Development

2. Environmental Regulation in Animal
Development
•Larval Settlement-Red abalone- must bind coralline red algae to
begin metamorphosis
•Mosquito- blood meal triggers egg production
**In Aedes aegypti , the digested product of blood meal
stimulate the brain to secrete EGG DEV'T
NEUROSECRETORY HORMONE (EDNH)
1. Many examples of environmental regulation exist
•Developmental symbiosis
•A bacterium multiplies only in leaf hopper CYTOPLASM
•No bacterium= embryonic death due to lack of
abdomen development

4. 1. environmental regulation (cont.)
•Seasonality and sex in Aphids- hatch only
reproducing females in the spring, but male and
female are hatched in the autumn (mechanism
unknown)
•Many insects use diapause- a suspension of development
due to harsh conditions (e.g winter condition)
•Nitrogen fixing bacteria provide nitrogen to legumous
plants (e.g. bean plants)
•Diapause is not triggered by harsh conditions, but
before the harsh conditions arrive
•Gravity/pressure
•affects development of bones in chicken

8. 2. Phenotypic plasticity- (cont.)
c. Environment-dependant sex determination
Crocodiles- extremes temperature result in female
Moderate temperature result in Male
Advantage- increase sexual reproduction if 10
females to each male ratio/ male:female ratio
Disadvantage- less adaptable to slight
environment change (e.g. Pollution)
• Blue headed Wrassse (reef fish) -depends on other fish it
encounters
•If wrasse reaches reef with males, it develops into Female
•If wrasse reaches reef without males, it develops into male
•If male dies, largest female becomes male within a day

10. d. PREDATOR -induced polyphenism
a. Organisms change shape in response to soluble
factors released by predators

11. •The immune system “destroy ” its foreign invaders
3. Predator-induced polyphenism (cont.)
b. Mammalian immunity
•A foreign object (antigen) is recognized by a one B-
lymphocyte (B-cells)

12. The basis for the immune response is summarized in the five
major postulates of the clonal selection hypothesis (Burnett 1959)
1. Each B lymphocyte (B cell) can make one, and only one, type of
antibody. It is specific for one shape of antigen only
2. Each B cell places the antibodies it makes into its cell membrane with
the specificity-bearing side outward.
3. Antigens are presented (usually by macrophages) to the antibodies on
the B cell membranes.
4. Only those B cells that bind to the antigen can complete their
development into antibodysecreting plasma cells. These B cells divide
repeatedly, produce an extensive rough endoplasmic reticulum, and
synthesize enormous amounts of antibody molecules. These antibodies
are secreted into the blood.
5. The specificity of the antibody madeby the plasma cell is exactly the
same as that which was on the cell surface of the B cells.

14. 4. Learning is an environmentally induced system
a. New neurons are produced
– in male songbirds/juvenile females learning a song
b. Visual pathway development is affected by experience
• A flash of light seen by a cortical neuron right
eye is also “seen” by the corresponding cortical
neuron in the left eye
•If sew right eye of newborn closed for 3 months,
they were functionally blind in right eye
•Kitten experiments
•If sew both eyes of newborn closed for 3 months,
vision remains (though weak) in one eye or the
other.

16. 4. Learning is an environmentally induced system
•Critical window of development is 4 weeks to 3
months
Thus, not all development is encoded in the Genome
Some is the result of learning
•Thus, synapses have been stabilized by 3 months
2. experience plays key role in determining whether neuronal
connections remain
Two key principles:
1.neuronal connections are made prior to when the animal sees
Also, the adult functions phenomenon is due to learning

17. 5. Environmental disruptions to development
•About One-half/two-thirds of human conceptions survive to term
•About 5 percent of human babies have a recognizable
deformation (normally in limbs, lungs or face)
•Abnormalities caused by exogenous agents are called DISRUPTIONS
Examples
Skunk cabbage induced Sonic hedgehog in sheep
In Humans
likely to have infants that are smaller than those born
to women who do not smoke
•Quinine cause deafness
•Smoking (>20/day)
•Alcohol (>2oz/day) cause physical and mental retardation in the infant
•Abnormalities caused by genetic mutations agents are called
MALFORMATIONS (e.g Down’s syndrome, aniridia (Pax6 mutation))

19. Experimental Evidence
 Mutations in normal developmental
pathways lead to malformations in
embryonic development

21. a. Retinoic acid as a teratogen
Accutane-for treating severe cystic acne
About 160,000women of childbearing age have used Accutane
1985 study of pregnant Accutane users
26“ normal”
12aborted spontaneously
21with anomalies- absent ears, small
jaws, cleft palate, and/or CNS problems
5. Disruptions (cont.)

22. FAS children have mean IQ of 68; at 16.5
yrs, they have vocabulary of 6.5 yrs
Estimated that 30 to 40 percent of
children born to alcoholic mothers
will have FAS
b. Alcohol is a teratogen
Fetal alcohol syndrome (FAS) is 3rd
most prevalent type of mental
retardation (behind fragile X and
Down Syndrome) affects 1 out of
every 500 750 children born children in
USA
CH3CH2OH
Fetal Alcohol Syndrome
Huge problem in South Africa due to alcohol-based economy
Misshapen eyes, flat nose,
long upper lip

23. c. Pathogens as teratogens
. Rubella (German measles) can cause deafness, heart malformations
. Herpes simplex and cytomegalovirus can cause
deafness, blindness, mental retardation
. Treponema pallidum, the cause of Syphilis can cause deafness or
death
d. Chemicals as teratogens
lead, mercury, and zinc are common ones
In Kazakhstan (former Soviet Union) nearly half of
population have extensive chromosome breakage
due to “industrial production at all costs”

24. Other teratogens
• Radiation (fallout)
• Infectious agents- Herpes simplex II,
cytomegalovirus
• Drugs- alcohol, aminopterin, chlorophenyls,
tetracyclines, thalidomide
• Other possible teratogens- heat fron high
fever and zinc deficiency

25. e. Estrogen
DDT is a banned insecticide that
can act like estrogenic compound
DDT is linked to increased incidence of
breast cancers, and decreased alligator
populations in Florida and the worldwide
decline of human sperm counts

26. e. Estrogen (cont.)
•p-nonylphenol(used to harden plastics
used in plumbing and milk/orange juice
containers)- replaces role of estrogen to
induce certain cultured cell to divide
•PCBs (previously used as refrigerants);
banned in 1970 due to cancer-causing
ability in rats; yet remain in environment
•Blamed for reduced reproductive capacities in
seals, mink and fish
Dramatic increase in deformed frogs in US- Due to toxins
in water?

28. Summary: The Environmental Regulation of Development
1. The environment can affect development in several ways. Development
is sometimes cued to normal circumstances that the organism can expect
to find in its environment. The larvae of many species will not begin
metamorphosis until they find a suitable substrate. In other instances,
symbiotic relationships between two or more species are necessary for
the complete development of one or more of the species.
2. Developmental plasticity makes it possible for environmental
circumstances to elicit different
phenotypes from the same genotype. Many species have a broad reaction
norm, wherein the genotype can respond in a graded way to
environmental conditions.
3. Some species exhibit polyphenisms, in which distinctly different
phenotypes are evoked by different
environmental cues.
4. Seasonal cues such as photoperiod, temperature, or type of food can
alter development in ways that make the organism more fit. Changes in
temperature also are responsible for determining sex in several
organisms, including many types of reptiles and insects.

29. 5. Predator-induced polyphenisms have evolved such that the prey
species can respond morphologically to the presence of a specific
predator. In some instances, this induced adaptation can be transmitted to
the progeny of the prey.
6. The differentiation of immunocompetent cells and the formation of
synapses in the visual system are examples where experience influences
the phenotype.
7. Compounds found in the environment (teratogens) can disrupt normal
development. Teratogens can be naturally occurring substances or
synthetic ones.
8. Alcohol and retinoic acid are two of the most intensively studied human
teratogens. They may produce their teratogenic effects through more than
one pathway.
9. It is possible that numerous compounds may be acting as hormone
mimics or antagonists disrupt normal development by interfering with the
endocrine system.
10. Genetic differences can predispose individuals to being affected by
teratogens.

30. THE END....