Why is there a difference in sex ratio between hatchery and wild steelhead?

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Why is there a difference in sex ratio between
hatchery and wild steelhead?

• Neil Thompson1, Kassi Cole2, Laura McMahon1,
  Melanie Marine1, Lyle Curtis and Mike Blouin1
• 1 Department of Zoology, Oregon State University
• 2 Department of Zoology, University of Hawaii

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Hood River steelhead

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Hood River Sex Ratio
Wild Wild Wild sex ratio Hatchery Hatchery Hatchery sex ratio
Run Year Male Female (Females per male) Male Female (Females per male)
1991 290 434 1.50   182 111 0.61
1992 159 260 1.64 99 133 1.34
1993 132 264 2.00 99 85 0.86
1994 100 104 1.04 56 57 1.02
1995 112 167 1.49 172 106 0.62
1996 118 175 1.48 334 301 0.90
1997 88 137 1.56 172 220 1.28
1998 112 188 1.68 156 166 1.06
1999 355 567 1.60 151 150 0.99
2000 372 645 1.73 533 415 0.78
2001 406 648 1.60 670 527 0.79
2002 260 485 1.87 231 366 1.58
2003 245 386 1.58 506 497 0.98
2004 160 208 1.30 238 297 1.25
2005 208 300 1.44 461 396 0.86
2006 186 313 1.68 186 267 1.44
2007 116 235 2.03 72 122 1.69
2008 81 140 1.73 202 190 0.94
2009 255 411 1.61   772 1076 1.39

Average sex ratio over all run years Average sex ratio over all run years Average sex ratio over all run years 1.61 1.07
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Hood River Sex Ratio

• Wild population ALL 19 years female biased
• Average ratio - 6139
• Hatchery population 9 years female biased
• Average ratio - 5149

Question Why is there a difference in sex ratio
between wild and hatchery populations?
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Potential explanations

1. Lower rates of residency in male hatchery fish
2. Selection against hatchery females, in the
   hatchery or at sea
3. Sex reversal of chromosomally XX females into
   phenotypic males

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Potential explanations

1. Lower rates of residency in male hatchery fish
2. Selection against hatchery females, in the
   hatchery or at sea
3. Sex reversal of chromosomally XX females into
   phenotypic males

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Sex determination in steelhead

• Y chromosome male
• No Y chromosome female

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Mechanism of Sex Reversal

• Aromatase enzyme
• Converts testosterone to estrogen
• High temperature inhibits aromatase

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Mechanism of Sex Reversal

• Aromatase enzyme
• Converts testosterone to estrogen
• High temperature inhibits aromatase
• Expect chromosomal females develop testes

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Why Aromatase?

• Spawned in Parkdale, Oregon
• Reared at Oak Springs on Deschutes R.
• Deschutes warmer than Hood River

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Research question

• Does the chromosomal gender match the phenotypic
  gender in Hood River steelhead?
• If not, what is non-matching?
• What direction is mismatch?

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Research question

• Does the chromosomal gender match the phenotypic
  gender in Hood River steelhead?
• If not, what is non-matching?
• What direction is mismatch?
• Does the sex ratio in the hatchery population
  change from juvenile release to adult return?

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Methods - Adults

• Adults sampled at Powerdale dam (1991-2009)
• Gender, origin, fin clip taken by ODFW
• Random 96 individuals per run type sex
• Total 384 adult samples
• Wild and Hatchery origin

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Methods - Juveniles

• Juveniles produced following Hood River
  Production Program protocols
• Sampled at 1 year of age
• Fin clip floy tagged
• Bodies preserved in formalin
• Gonad inspected by stereomicroscopy
• Fish type, family, spawn date

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Chromosomal gender

• OmyY1 marker - gender marker
• 4 non-concordance rate
• Male band
• Positive reaction band

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Phenotypic gender

• Adults
• ODFW staff visually sexed fish _at_ powerdale

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Phenotypic gender

• Adults
• ODFW staff visually sexed fish _at_ powerdale
• 1 year olds
• Visually sexed gonads
• Male, female or unknown

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Research question

• Does the chromosomal gender match the phenotypic
  gender in Hood River steelhead?
• If not, what is non-matching?
• Mismatch sex reversal
• Test for non 5050 sex ratio
• Chi-square test

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Results - Adults

• 341 successful reactions
• 7 fish mismatched (2.1 non-concordance)
• Male-to-female and female-to-male mismatch

Chromosomal
Run Gender Non-concordance
Winter
Male 2.27
Female 1.15
Summer
Male 1.28
Female 3.41
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Results - Juveniles

• 173 successful reactions
• 6 fish mismatched (3.5 non-concordance)
• Male-to-female and female-to-male mismatch

Juvenile ID Spawn Date Family ID Fish Type
2 4/20/2010 2821x2796 HH
3 5/24/2010 382x477 WW
29 5/10/2010 2764x2783 HH
44 5/10/2010 2812x2761 HH
62 5/17/2010 458x2804 WH
223 5/24/2010 2774x383 HW
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Overall Results

• Adults
• No evidence for sex reversal
• Mismatches in both directions
• Rate not above published non-concordance rate
• ODFW staff VERY good at visually identifying
  gender both run types

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Overall Results

• Adults
• Juveniles
• No evidence for sex reversal
• Mismatches in both directions
• Non-concordance rate below published rate
• Mismatches from 6 different families, 4 spawn
  dates and 4 fish types

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Potential explanations

1. Lower rates of residency in male hatchery fish
2. Selection against hatchery females, in the
   hatchery or at sea
3. Sex reversal of chromosomally XX females into
   phenotypic males

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Juvenile sex ratio at release
Male Female
Chromosomal 85 88
Phenotypic 87 86
Not different from 5050 ratio Chi-square
p-values of 0.82 0.94
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Juvenile sex ratio at release
Male Female
Chromosomal 85 88
Phenotypic 87 86
Not different from 5050 ratio Chi-square
p-values of 0.82 0.94

• 5050 at release and at return to the dam
• No selection against females in hatchery or at
  sea!

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Potential explanations

1. Lower rates of residency in male hatchery fish
2. Selection against hatchery females, in the
   hatchery or at sea
3. Sex reversal of chromosomally XX females into
   phenotypic males

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Potential explanations

• Lower rates of residency in male hatchery fish

Christie et al. 2011 Molecular Ecology
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Thank You!

• Jim Gidley Albert Santos
• Parkdale fish facility
• Lyle Curtis staff
• Oak Springs hatchery
• Blouin lab