Effects of biotic and abiotic stressors on asymmetries and head size in two sympatric lizard species

Organisms face numerous environmental stressors, which can affect
developmental precision. Developmental instability can be used as an
efficient and reliable bioindicator of environmental stressors and
individual health. However, little information is available about effects
of interspecific interactions on occurrence of developmental instability.
We analyzed fluctuating asymmetry in two sympatric lizard species
(Iberolacerta horvathi and Podarcis muralis), which exhibit a competitive
interaction, to determine potential effects of altitude, interspecific
competition and urbanization on a set of physical characteristics. We
sampled 16 syntopic and allotopic populations and used methods of
geometric morphometrics to analyze head morphology. We detected
significant effect of altitude, but the trend was not linear: lizards had
most asymmetrical heads at mid altitudes, which could be related to lower
availability of favorable lizard habitats (open areas) at this altitude
and therefore higher competition. We observed that lizards from allotopic
populations attained larger head sizes compared to lizards in syntopy that
experienced interspecific competition. This could suggest that in sites
where competing species is absent, individuals can invest more energy in
the development of the body. Moreover, head shape of Iberolacerta horvathi
was more asymmetric compared to Podarcis muralis, which could indicate
difference between species in the vulnerability to stress effects. We did
not detect any statistically significant effect of urbanization, which
could relate to relatively low degree of pollution and habitat degradation
in our study area. Our results highlight the possibility of using lizards
and developmental instability for bioindication of environmental
stressors.