Organohalogen concentrations and a gross and histologic ...

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Chapter 2
Fluctuating asymmetry in skulls from East
Greenland polar bears collected during
1892-2002
It can be of great importance to monitor the developmental instability in
populations of wildlife mammals from a management conservation point of
view. Threats to the health status of wildlife today are environmental factors
like infective agents (bacteria, virus, parasites), nutrition status (including
climatic oscilliations), biotoxins, pollution (heavy metals, organohalogens,
noise or other human activities), genetic limitations (bottlenecks) a.o. These
stressing factors may affect the fitness of the individual animal and thereby
influence the stability of the development of it’s “true” phenotype (e.g.
Palmer and Strobech 1986, Møller 1996, Møller and Swaddle 1997, Rus
Hoelzel et al. 2002). The developmental instability of the “true” phenotype
has been measured in several populations of wild marine mammals (e.g.
Zakharov and Yablokov 1990, Bergman et al. 1992a, Mortensen et al. 1992,
Schandorff 1997a-b, Coy and Schaeff 2001) through the use of fluctuating
asymmetry (FA). FA expresses small (not malformations) ”random differences
that occur between right and left sides in bilateral traits” (Van Valen
1962, Jagoe and Haines 1985, Palmer and Strobech 1986, Jones 1989, Leary
and Allendorf 1989) and earlier investigations have often used the skeletal
system (skull) as bilateral phenotype expression due to the relatively easy
access to large museum samples of e.g. Baltic grey (Halichoerus grypus) and
ringed seals (Phoca hispida) and Danish Kattegat harbour seal (Phoca vitulina)
(e.g. Zakharov and Yablokov 1990, Bergman et al. 1992a, Mortensen et al.
1992, Schandorff 1997a-b). The access to museum samples have not only the
force of relatively easy access to large material, but it also provides the opportunity
to investigate time trend analysis in relation to e.g. human activities
(pollution or hunt) and climatic changes.
In the present investigation it was relatively easy to obtain skull samples
(105 pcs.) from the bears from 1999 to 2002 (organohalogen analyses of adipose
tissue was only sampled 1999-2001). In addition to these, a large museum
skull sample from East Greenland (178 pcs.) was available in Copenhagen,
Denmark from 1892-1987. This gave us an opportunity to investigate
a time trend in FA in East Greenland polar bears and to relate this to
individual levels of organohalogens. The results in the present chapter is
described in details in paper II.
FA in East Greenland polar bears
Fluctuating asymmetry (FA) in 13 bilateral traits (7 in the skull and 6 in the
lower jaw) was measured in a total of 283 skulls sampled from 1892 to 2002
(Fig. 4). This was done to investigate a time trend over the entire period and
to see if there was a significantly higher FA in the supposed period with
organohalogen pollution (1961-2002) compared to the supposed period prior
to this pollution (1892-1960). The period 1892-1960 was chosen to represent a
period prior to the appearance of organohalogens (PCBs, DDTs, CHLs, dieldrin,
HCHs, HCB and PBDEs) originating from long-range transport to East
Greenland from southern latitudes. The period 1961-2002 represents the