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


What is to a male dominated population in fish “Hypoxia”?

  • Shortage of oxygen

  • < 2 ml /L

  • <2.8 mg/L

Diaz & Rosenberg, 1995


Hypoxia is to a male dominated population in fish

A Pressing Global Problem


<2.8 mgO to a male dominated population in fish 2/L

Hypoxic area> 1 million Km2

Diaz & Rosenberg 1995


150 dead zones all over the world
150 “Dead Zones” all over the world to a male dominated population in fish

UNEP, 2004


Anthropogenic activities to a male dominated population in fish

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 years

Hypoxia: 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 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

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


Endocrine disruption occurs as early as 48hpf
Endocrine disruption occurs as early as 48hpf 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

**p<0.01

Shang & Wu, 2004


Endocrine disruption occurs as early as 48hpf1
Endocrine disruption occurs as early as 48hpf 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

***p<0.005

Shang & Wu, 2004




the tail 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

the tail

Hypoxia tips sex balance & favors a male biased population

***

Hypoxia

Shang, Yu & Wu, 2006

*** p < 0.001



Expression of selected genes under hypoxia

Expression of selected genes the tailunder hypoxia


3 the tail-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 the tail 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 : changes in aquatic ecosystems, as well as decline in fisheries production all over the world

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 father and mother during conception, and high hormone level during conception favors subsequent birth of sons (James, 2004)

  • 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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