The loss of sexual size dimorphism in urban populations of a widespread reptile, the European grass snake <i>Natrix natrix</i>

Abstract

Cities represent a unique ecosystem dominated by humans and highdensity man-made infrastructure, associated with modifications or entire loss of local habitats. Thus, urbanization constitutes a considerable challenge for wildlife, and only a minority of species is able to persist in cities Species that maintain populations in cities are usually characterized by significant changes in life history characteristics, population structure, and ecological relations (Niemela et al. 2011). So far, most studies in urban ecology of vertebrates have focused on birds and mammals, whereas city-dwelling ectotherms, including reptiles, remain understudied However, considering that the worldwide decline of reptiles is largely associated with habitat deterioration Here, we investigated the impact of the urban environment on body size, as the primary fitness-relevant trait, in a widespread Eurasian reptile, the grass snake Natrix natrix, by comparing 2 replicate urban populations with sub-and non-urban sites. Due to the documented reduction of prey availability (amphibians) in cities including the studied metropolitan area In addition, a high density of roads and higher incidence of deliberate killing in cities may increase mortality mainly of larger specimens Because grass snakes express clear sexual size dimorphism (SSD) with females larger than males (Madsen and Shine 1993), we expect that the anticipated mortality will result in a skewed sex ratio with underrepresentation of females in urban sites.