Male-Specific AFLP Markers Reveal Extreme Female-Biased Sex-Ratios 

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FINAL TECHNICAL SUMMARY 

STUDY TITLE: Population genetics of surfgrass (Phyllospadix torreyi) for use in 

restoration 

REPORT TITLE: Male-specific AFLP markers reveal extreme female-biased sex-ratios in 

the surfgrass Phyllospadix torreyi (Zosteraceae) 

CONTRACT NUMBER: 14-35-0001-31063 

SPONSORING OCS REGION: Pacific 

APPLICABLE PLANNING AREA(S): Southern California 

FISCAL YEAR(S) OF PROJECT FUNDING: FY 00/01, FY 01/02, FY 02/03 

COMPLETION DATE OF REPORT: June 2007 

COST(S): FY 00/01: $67,067; FY 01/02: $53,451; FY 02/03: $8,461 

CUMULATIVE PROJECT COST: $128,979

PROJECT MANAGER: Russell J. Schmitt 

ADDRESS: Coastal Research Center, Marine Science Institute, University of California, 

Santa Barbara, CA 93106-6150 

PRINCIPAL INVESTIGATORS: Douglas S. Bush1

, Daniel C. Reed2, Sally J. Holbrook1,2 

and Scott A. Hodges1* 

ADDRESSES: 1 Department of Ecology, Evolution and Marine Biology, University of 

California, Santa Barbara, CA 93106-9610; 2 Marine Science Institute, University of 

California, Santa Barbara, CA 93106-6150; *Author for correspondence

KEY WORDS: intertidal ecology, sex determination, male/female ratio, genetic markers 

BACKGROUND: The surfgrass Phyllospadix torreyi is a clonal marine angiosperm that 

occurs in dense persistent stands in the intertidal and shallow subtidal zones of moderate to 

high energy coastlines of the northern Pacific Ocean. Surfgrasses are among the most 

productive seagrass communities yet studied and their stands form the basis for a thriving 

intertidal community. Because surfgrass populations have been and may be disturbed through 

oil and gas exploration, understanding how to restore populations is an important goal. 

Complicating these efforts is the fact that surfgrass is a dioecious species consisting of 

separate male and female plants. Natural populations appear to be strongly biased towards 

females and thus replicating sex-ratios may be important in restoration efforts. 
Final Study Report – Hodges et. al. 

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OBJECTIVES: Our goal was to determine if sex determination in surfgrass was due to 

genetic factors and then to determine the actual frequency of male and female individuals. 

Because surfgrass forms dense mats it is impossible to identify genetic individuals. 

Furthermore, we sought to determine if there are microhabitat correlates with where each sex 

occurs. 

DESCRIPTION: Using a DNA fingerprinting technique, amplified fragment length 

polymorphisms (AFLP), we scanned the genome of known males and females to identify 

genetic markers associated with sex. We also used these AFLP markers to identify unique 

genetic individuals in random samples. 

STUDY RESULTS: We identified a number of genetic markers that were highly correlated 

with sex. Using a combination of these markers we were able to conclusively sex individuals 

that were non-flowering. All of the markers we identified were male-specific markers 

suggesting that surfgrass has an XY sex-determination system. The genetic markers also 

reveal that the male-determining Y region is likely accumulating transposable elements as has 

been hypothesized for the evolution of Y-chromosomes. After identifying unique genetic 

individuals from random samples across the Santa Barbara Co. coastline, we determined that 

the frequency of males was only about four percent. We did not find any correlation with the 

frequency of males and habitat. 

SIGNIFICANT CONCLUSIONS: We conclude that individual sexes in surfgrass are 

determined by an XY genetic system. Significantly, we find that males of surfgrass are 

exceptionally rare. This suggests that great care should be used to establish male plants during 

restoration to ensure that the population can sustain reproduction. 

STUDY PRODUCTS: 

Published work: 

Bush, DS, DC Reed, SJ Holbrook and SA Hodges. Male-specific AFLP markers reveal 

extreme female-biased sex-ratios in the surfgrass Phyllospadix torregyi (Zosteraceae). 

submitted, Molecular Ecology. 

Presentations: 

Bush, DS, DC Reed, SF Holbrook and SA Hodges. 2002. Sex-specific markers in surfgrass, 

Phyllospadix torreyi and extreme female-biased sex ratios. Meeting on “Sex-specific genetic 

markers”, University of Lausanne, La Sage, Switzerland.