environmental embryology

8/12/2019 Environmental Embryology

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Environmental Sex

Determination

Alba

Dingal

Eugenio

Limbago

PulancoRobles


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Sex Determination

EnvironmentGenetics

Secondary Sex Determination

Primary Sex Determination


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1. Temperature

Incubation temperature of eggs determine sex Thermosensitive Period: critical period of sex

determination. middle one-third of development

Threshold Temperature: number of individuals per sex

is even

Advantages

Not tied to 1:1 sex ratio

Adaptive habits governed by patchiness

Disadvantages

Thermal pollution could wipe out a species


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Type of Temperature-dependent SD

Type Description Examples

IA Single Transition Zone

Below temperature zone = male

Above temperature zone = female

Red-eared slider turtle

IB Single Transition Zone

Below temperature zone = female

Above temperature zone = male

II Two Transition Zones

Intermediate temperatures = maleExtreme temperatures = female

Snapping Turtle

(Macrolemys)


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Red-eared Slider Turtle

below 28 0Call male

above 31 0Call female

28 < temp. < 31both sexes


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Macrolemys(snapping turtle)

Temperature =< 22 0C and >= 280Cfemale

Temperature between 22 0C and 280Cmale


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Lizzard (Bassiana duperreyi)

Normal temperature conditions

-- sex determined by sex chromosomes Low temperature -- all the offspring are male (even

in XX chromosomes)


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European Pond Turtle (Emys obicularis)

Temperature > 30 0C

all femalesTemperature < 25 0Call males

Threshold temperature28.5 0C


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The Aromatase Hypothesis

Aromataseconverts testosterone to

estrogen

Bird and Reptiles: 10 Sex Determination is

influenced by hormones.

Reptiles: estrogen level overrides temperature

(hormone-dependent)


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Temperature-dependent aromatase

activity

Emys obicularis and diamondback terrapins

low aromatase activity at male-promotingtemperature.

Aromatase expression is activated differentlyin different species

Aromataseproteinmay be temperature

sensitive Aromatasegene activated only at high

temperatures


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Observation ConclusionGonads are taken out of

embryos and placed in

cultureovaries or

testes depending on the

incubation temperature

Sex determination is a

local activity of the

gonadal primordia and

not a global activity

directed by the pituitary

gland


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Hypotheses

Female temperatures

Activate aromatase

Activate Wnt4suppresses the formation of

testes

Male temperatures

Activate Sox9promotes testes development

Temperature is sensed by the CNS and is thentransduced to the bipotential gonads


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2. Composition of Brood

Sex of animals is not always fixed for life

Clownfish

sequential hermaphroditism

all born as males = protandrous

hermaphrodites Female dies

dominant male changes sex

Coral reef fishes

Single male fish with large

harems of females

Death of the male

dominant female becomes male (harem-keeper)


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3. Pollutants

Polychlorinated Biphenyl (PCB) binds to the minor site of estrogen receptor,mimicking its functions.

can reverse the sex of turtles decline in the reproductive capabilities of

otters, seals, and minks

Hormonal treatment Advocated by conservation biologists to

elevate the percentage of females


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DDT (Dichlorodiphenyltrichloroethane) and DDE

in pesticides

Mimics estrogen structure and inhibits

androgen effects

Feminization of fishes and increased rate of

breast cancer in mammals.

Dioxin (by-product of pesticide and paper

production)Reduced sperm count, smaller testes, fewer

male-specific sexual characteristics.


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Effect of Atrazine in Male Frogs

0.1 ppb gonadal and sexual anomalies e.g.

testicular dysgenesis

> 0.1 ppb developed ovaries in addition to testes

1 ppb vocals sacs fail to develop properly

Atrazine induces aromatase and aromatase can

convert testosterone to estrogen


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Slipper snail (Crepidula fornicata)

Young male individuals degeneration of the male

reproductive systemlability sex based on its

position in the mound

Snail is attached to a femalemale

Snail is removed from attachmentfemale


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Eels

Upper reaches of riversfemales

Estuaries

males


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5. Solutions

Higher pH

females predominate Lower pHmale predominate

Pelvichrachromis pulcher

Acid watermore males

Basic watermore females

pH 5 = 96% males

pH 6.9 = 80% females


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Bufo lentiginosus

Concentration of sugar or salt in the solution

affected sex ratio

0.252% salt or sugar before, during, or after

fertilization = excess of females

environmental embryology

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