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Hypoxia affects sex differentiation and development, leading to a male dominated population in fish. Rudolf Wu Centre for Coastal Pollution & Conservation City University of Hong Kong. What is “ Hypoxia ” ?. Shortage of oxygen < 2 ml /L <2.8 mg/L. Diaz & Rosenberg, 1995. Hypoxia is

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hypoxia affects sex differentiation and development leading to a male dominated population in fish
Hypoxia affects sex differentiation and development, leading to a male dominated population in fish

Rudolf Wu

Centre for Coastal Pollution & Conservation

City University of Hong Kong

slide2

What is “Hypoxia”?

  • Shortage of oxygen
  • < 2 ml /L
  • <2.8 mg/L

Diaz & Rosenberg, 1995

slide3

Hypoxia is

A Pressing Global Problem

slide4

<2.8 mgO2/L

Hypoxic area> 1 million Km2

Diaz & Rosenberg 1995

slide6

Anthropogenic activities

Organic matters & nutrients (EUTROPHICATION)

Runoff

Sewage effluent

Vessel waste discharge

Oxygen blocked

Low density

(Low salinity or high temperature)

ALGAL BLOOM

Pycnocline

Oxygen

High density

(High salinity or low temperature)

Dead algae shrink &

decomposers use upoxygen

 COD / BOD / SOD

Mortality

Organisms escape

hypoxia some trend
Decrease in DO in many coastal areas in USA, China, Norway, UK, Sweden, Germany, Denmark, the Black Sea, Adriatic Seas in the last 30-80 yearsHypoxia: Some Trend

Diaz & Rosenberg, 1995; Rabalais, 2001

current situation
Increases in nutrient concentration, algal blooms, large scale hypoxia, and change of species composition, mass mortality of fish and decline in fisheries production are found in large coastal areas all over the world Current situation

Diaz & Rosenberg, 1995; Gray & Wu, 2002

experimental set up
Experimental set up

5.8 mg/L

  • Eggs of zebrafish exposed to 0.8 and 5.8 mg O2/L for 3 months
  • Studied growth, gonad wt. gametogenesis, malformation, sex hormones, sex ratio and various genes controlling synthesis of sex hormone and apoptosis over time

0.8 mg/L

Oxygen controller

slide14

♂ Male Zebrafish

♀ Female Zebrafish

1 cm

1 cm

Testis

Ovary

2 mm

2 mm

200 µm

200 µm

hypoxia tips sex balance favors a male biased population

Hypoxia tips sex balance & favors a male biased population

***

Hypoxia

Shang, Yu & Wu, 2006

*** p < 0.001

slide18

3-HSD (-)

CYP11A (-)

CYP19A (ND)

CYP19B (-)

3-HSD (-)

CYP11A (-)

CYP19A (-)

CYP19B (-)

Aromatase (-)

Gonads differentiate into ovaries

Sex differentiation begins

Sex differentiation/ reversal is

completed

Final maturation of the gonads

Spawning

Male

3-HSD (-)

CYP11A (-)

CYP19A (+)

CYP19B (+)

T/E2 (NC)

Male

3-HSD (-)

CYP11A (-)

CYP19A (-)

CYP19B (NC)

T/E2 (NC)

Female

3-HSD (+)

CYP11A (-)

CYP19A (+)

CYP19B (+)

T/E2 (+)

Aromatase (-)

Female

3-HSD (-)

CYP11A (-)

CYP19A (+)

CYP19B (NC)

T/E2 (+)

Aromatase (-)

(A) 10 dpf

(B) 40 dpf

(C) 60 dpf

(D) 120 dpf

10-12 dpf

23-25 dpf

42 dpf

60 dpf

120 dpf

Larval

Juvenile

Adult

3 dpf

30 dpf

90 dpf

in vitro evidence
In vitro evidence
  • In vitro studies using H295R cell line
overall conclusions
Hypoxia affects very large areas and has caused major changes in aquatic ecosystems, as well as decline in fisheries production all over the world

For the first time, we found that hypoxia is an endocrine disruptor, and impairs reproduction of fish

Overall Conclusions
overall conclusions1
For the first time in science, we found that :

Hypoxia alters various genes controlling synthesis of sex hormones

Alternation of sex hormones affects sex differentiation and sex development, and favors a male-biased population in fish

A higher male to female ratio will greatly reduce the chance of fish reproduction

Overall Conclusions
overall conclusions2
Since the genes and hormones controlling sex differentiation and reproduction are highly conserved, the endocrine disrupting effects and biased sex ratio observed in fish may also occur in other vertebrates.

These are likely to be the major factors leading to decline of natural populations in hypoxic waters

The problem of hypoxia is likely to get worse in the coming years

Overall Conclusions
epilogue
Sex ratio in human depends on level of sex hormones of father and mother during conception, and high hormone level during conception favors subsequent birth of sons (James, 2004)

Patients suffering from sleeping apnea have lower sex drive and testosterone level (Saaresranta & Polo, 2003)

Epilogue
acknowledgments
Acknowledgments
  • This research was supported by the Area of Excellence Grant (AoE/P-04/04) from the University Grants Council, HK SAR government

Dr. Eva Shang

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