Organohalogen concentrations and a gross and histologic ...

Key words: polar bear, Ursus maritimus, fluctuating asymmetry, organohalogens,
DDTs, PCBs, stress, endocrine disruption.
1. Introduction
Environmental (e.g. pollution and infections) and genetic stress (e.g. bottlenecks)
may affect the ability of an individual to address developmental instability
and thereby disruption or modulation of its “true” phenotype and
fitness (Palmer and Strobeck 1986, Møller 1996, Møller and Swaddle 1997,
Rus Hoelzel et al., 2002). Often developmental instability is expressed as
asymmetry between bilateral traits, and when measured in a group of individuals
(population) the instability is called fluctuating asymmetry (FA)
(Ibid.). In it’s definition “FA refers to random differences that occur between
right and left sides in bilateral traits“ and these differences reflect ”mistakes”
in developmental processes that result from the inability of the genotype to
effectively buffer itself against environmental perturbations” (Van Valen
1962). FA is defined as the small, intermittently occurring difference between
a left and a right trait, where the side with the largest trait and the
magnitude of the difference shifts randomly. Fluctuating asymmetry is
measured as left/right metric and meristic differences. In FA the differences
observed are usually small and cannot be categorised as malformations
(Jagoe and Haines 1985, Palmer and Strobeck 1986, Jones 1989, Leary and
Allendorf 1989).
In addition to FA, directional asymmetry (DA) and antisymmetry (AS) have
also been discovered (Jagoe and Haines 1985, Palmer and Strobeck 1986,
Jones 1989, Leary and Allendorf 1989). DA occurs when the larger side is
consistent (e.g. the right testicle/ovary is larger than the left in humans). In
AS the largest side varies equally between left and right (e.g. the larger signalling
claw of male fiddler crabs is the left and right side with same frequency),
but this type of asymmetry occurs very rarely.
FA has been measured in invertebrates (e.g. flies and crabs) and vertebrates
(fish, birds and mammals) (Jagoe and Haines 1985, Palmer and Strobeck
1986, Jones 1989, Leary and Allendorf 1989) and used as an environmental
stress indicator in numerous studies of wildlife and laboratory mammals
(e.g. Palmer and Strobeck 1986, Nachman and Heller 1999). Correlations
between in utero induced FA and temperature/noise extremes, limited food
access and quality and chemical contaminants have been reported (e.g. Siegel
and Doyle 1975a-c, Doyle et al., 1977, Siegel et al., 1977a). Exposure to
anthropogenic contaminants such as PCBs (PolyChlorinatedBiphenyls),
DDTs (DichloroDiphenylTrichloroethanes), HCHs (HexaCycloHexanes),
CHLs (CHLordanes), HCB (HexaChloroBenzene), PBDEs (PolyBrominated-
DiphenylEthers) and dieldrin have been suspected as an environmental
stress factor that can lead to endocrine disruption through agonism and/or
antagonism of hormone-dependent processes in different target organs and
tissues involved in endocrine functions (Bergman and Olsson 1985, Colborn
et al., 1993, Swart et al., 1994, Feldman 1995, de March et al., 1998, Bergman
1999, Damstra et al., 2002, AMAP, 2004). Interference with receptors in the
main endocrine pathway results in endocrine disruption and stress through
the hypothalamus---hypophysis---target organ/tissue axis leading to elevated
blood corticosteroid levels (adrenocortical hyperplasia; Cushing’s
Syndrome) and may therefore also induce FA (Bergman and Olsson 1985,
Colborn et al., 1993, Feldman 1995, Borisov et al., 1997, de March et al., 1998,
Bergman 1999, Damstra et al., 2002).
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