Feminization in common terns (Sterna hirunda) : relationship to persistent organic contaminants
Citable URI
https://hdl.handle.net/1912/5150Location
Bird Island, Buzzards Bay, MADOI
10.1575/1912/5150Keyword
Terns; Environmental pollutionAbstract
Concern about skewed sex ratios and female-female pairings among endangered
roseate terns (Sterna dougallii) on Bird Island in Buzzards Bay, Massachusetts prompted
studies with common terns from the same site as a surrogate species. Over seventy percent
(11115) of male common tern embryos sampled from this site in 1993 had testes containing
areas of ovarian cortical tissue (ovotestes), suggesting that terns may be affected by
endocrine-disrupting contaminants. These terns are exposed to non-ortho PCBs which
bind to the aryl hydrocarbon receptor (AhR), and lower chlorinated PCBs, hydroxymetabolites
of which bind to the estrogen receptor. Our objectives were to document the
presence of ovotestes in common tern embryos from Bird Island and Nauset, a reference
site, in 1994, and to determine the relationship between environmental contaminants and
ovotestes development, as well as other health-related effects.
Pipping tern embryo gonads were examined histologically, and yolk sacs were
extracted and analyzed for PCBs and chlorinated pesticides. Extracts also were analyzed
for dioxin equivalents (TCDD-EQs) using a chick embryo hepatocyte (CEH) bioassay.
Total PCBs were significantly higher in Bird Island tern embryos (mean 114, range 17-
663 ugig lipid) than Nauset (mean 35, range 8- i 78 ugig lipid); but were variable at both
sites. Total PCBs were highly correlated with TCDD-EQs. Tern hepatic EROD activity
was relatively insensitive to induction; only when TCDD-EQs were above 82 ± 26 ng/g
lipid were EROD activities elevated. Levels of organic pesticides were below levels
thought to be of toxicological significance. The percentage of male tern embryos with
ovotestes at Nauset (60%) and Bird Island (78%) was high and not significantly different;
ovotestes in terns from both sites ranged in severity from absent (1) to intersex (4). There
was no significant relationship between ovotestes severity and any of the contaminants
measured. However, the data suggested a contaminant level threshold of 100 ug/g lipid
total PCBs and 30 ng/g lipid TCDD-EQs above which the formation of ovotestes in tern
embryos is more likely to occur. Principal component analysis of PCB isomer patterns
distinguished between Bird Island and Nauset sites, with Bird Island having relatively
higher levels of lower chlorinated PCBs; however, there was no distinction between terns
with ovotestes and those without. Common tern prefledglings and paired same-nest eggs
were collected from Bird Island in 1995 to examine the persistence of ovotestes. Gonadal
histology revealed no ovarian tissue on testes, indicating that the ovotestes do not persist
after 3 weeks posthatch.
Our data suggested that: 1) ovotestes could be related to contaminants; 2) a
background level of ovotestes may be present, but elevated by contaminant exposure; or 3)
ovotestes could be normally present in male common tern embryos at hatching.
Observations of the normal presence of persistent cortical tissue in the testes of several
avian species suggest that concern about feminizing effects of contaminants on bird
populations as measured by ovotestes development in hatching birds may be exaggerated.
Before conclusions can be made about terns from Bird Island, it is necessary to establish
whether persistent ovarian cortical areas in testes are normally present. Studies with
common terns from a pristine site are currently underway.
Description
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution January 1998
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Suggested Citation
Thesis: Hart, Constance A., "Feminization in common terns (Sterna hirunda) : relationship to persistent organic contaminants", 1998-01, DOI:10.1575/1912/5150, https://hdl.handle.net/1912/5150Related items
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