Fluctuating asymmetry in Podarcis muralis populations from Southern Montenegro: detection of environmental stress in insular populations

We examined degree of between-sides difference in number of femoral pores (fluctuating asymmetry, FA) in Podarcis muralis populations, distributed on islands and in coastal area of Lake Skadar (Southern Montenegro). The aim of this study was to test sensitivity of fluctuating asymmetry of chosen trait to isolation effect in the absence of anthropogenic impacts. The results indicate that FA in the number of femoral pores do not vary significantly between insular populations of P. muralis. Generally, there is negative but non-significant correlation between island size and FA level. Also, overdominance hypothesis of enhanced developmental homeostasis at higher levels of heterozygosity was not confirmed in this study. The results support earlier conclusions obtained from electrophoretic studies, that analyzed insular populations from Lake Skadar archipelago still do not suffer deleterious effects as a result of isolation.

Symmetry Preference as a Cognitive By-Product in Starlings

There has been a great deal of interest in whether animals use trait symmetry as a visual cue to mediate behavioural interactions. In bilaterally symmetric traits, small asymmetries (termed fluctuating asymmetry) appear due to increased developmental stress and/or genes for poor developmental homeostasis. Hence, researchers have hypothesized that symmetry can reveal the developmental history and, perhaps, fitness of an individual and this is why symmetry preferences have been observed. However, an additional theory suggests that symmetry could be preferred merely because it represents the average expression of bilateral traits. Animals can learn to respond to signals by generalizing (or averaging) stimulus sets. As the average expression of a trait showing fluctuating asymmetry is zero asymmetry, theory predicts that animals could develop a symmetry preference as a by-product of learning. Here, we test this prediction empirically with European starlings (Sturnus vulgaris) and show that symmetry preferences can emerge as an outcome of generalized learning processes. Our results indicate that symmetry does not initially need to be associated with fitness to be an apparent cue in behavioural interactions and that symmetry preferences observed in nature could be independent of any putative fitness relationships.