Can antioxidant responses be induced by habitat fragmentation process?

Animal populations are increasingly forced to live in small residual
natural or semi-natural areas due to habitat loss and fragmentation. Here,
the viability of populations is often compromised by intrinsic threat
factors typical of small and isolated populations, such as inbreeding
depression, genetic drift, and environmental and demographic
stochasticity. Under these circumstances, organisms may have low fitness
due to inadequate physiological responses needed to face environmental
challenges. However, few studies have investigated the relationship
between habitat fragmentation and stress defences. In this study, we aimed
to test whether an increase in the level of individual inbreeding produced
an increase in the antioxidant system response. To this purpose, we
genotyped 151 individuals of Fire Salamander Salamandra salamandra
(Amphibia: Urodela) within 5 sampling populations, located in forest
landscapes with different degree of fragmentation in northern Italy. For
113 individuals we also measured the glutathione-S-transferase (GST) and
catalase (CAT) enzyme activity. Results showed a significant increase in
individual GST activity for increasing levels of inbreeding, whereas no
relationship was found for CAT. We also measured acetylcholinesterase to
test the possible confounding effects of pesticides that might have
occurred in fragmented landscapes with forests interspersed with
agricultural areas. However, no difference in this enzyme activity was
found among sampling populations. We argue that high levels of GST
activity may be symptomatic of oxidative stress derived from inbreeding.
An increased frequency of homozygous deleterious alleles due to inbreeding
may cause homeostatic alterations and trigger the expression of GST for
protection against hydrogen peroxide reactive oxygen species. We suggest
using GST as a biomarker for environmental stressors with great caution
and not to underestimate that the sources of stress deriving from habitat
fragmentation could lead to an unbalance in the oxidative status, possibly
increasing population susceptibility to infectious diseases and,
potentially, spillover events and zoonoses.