why is there a difference in sex ratio between hatchery and wild steelhead? neil thompson 1, kassi...

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

Hood River steelhead

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 1.61 1.07

Hood River Sex Ratio

Hood River Sex Ratio

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

• Wild population: ALL 19 years female biasedAverage ratio - 61:39

• Hatchery population: 9 years female biasedAverage ratio - 51:49

Potential explanations1. 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

Potential explanations1. 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

Sex determination in steelhead

• Y chromosome = male• No Y chromosome = female

Mechanism of Sex Reversal

• Aromatase enzyme– Converts testosterone to estrogen

• High temperature inhibits aromatase

Mechanism of Sex Reversal

• Aromatase enzyme– Converts testosterone to estrogen

• High temperature inhibits aromatase– Expect chromosomal females develop testes

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

Research question

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

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?

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

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

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

Phenotypic gender

• Adults:– ODFW staff visually sexed fish @ powerdale

Phenotypic gender

• Adults:– ODFW staff visually sexed fish @ powerdale

• 1 year olds:– Visually sexed gonads– Male, female or unknown

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 50:50 sex ratio – Chi-square test

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

ChromosomalRun Gender % Non-concordanceWinter

Male 2.27Female 1.15

SummerMale 1.28Female 3.41

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

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

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

Potential explanations1. 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

Juvenile sex ratio at release

# Male # Female

Chromosomal 85 88

Phenotypic 87 86

*Not different from 50:50 ratio* Chi-square p-values of 0.82 & 0.94

Juvenile sex ratio at release

# Male # Female

Chromosomal 85 88

Phenotypic 87 86

*Not different from 50:50 ratio* Chi-square p-values of 0.82 & 0.94

• 50:50 at release and at return to the dam• No selection against females in hatchery or at sea!

Potential explanations1. 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

Potential explanations1. Lower rates of residency in male hatchery fish

Christie et al. 2011 Molecular Ecology

Thank You!

• Jim Gidley & Albert Santos• Parkdale fish facility

• Lyle Curtis & staff• Oak Springs hatchery

• Blouin lab