PS 48-234 - It's about time: The effects of urbanization on phenotypic traits in a Tropical city

Abstract: Urban ecosystems are good testbeds to study eco-evolutionary dynamics because they alter the pace of evolution of natural populations. Urbanization promotes habitat fragmentation and isolation, reduces gene flow, and creates small populations more prone to genetic drift. Consequently, maladapted phenotypes may be fixed, decreasing fitness. However, the effects of urbanization on species with low dispersal ability are expected to be more pronounced. Yet, little is known about eco-evolutionary responses of organisms with low dispersal ability to urbanization, especially in the Global South. Here, we tested how urbanization affects phenotypic traits associated with dispersal and performance (i.e., body size and leg length) in a treefrog (Dendropsophus nanus) using a space-for-time substitution approach. We tested for spatial autocorrelation in traits and estimated the adaptive landscape of leg length using body condition index as a fitness proxy. We sampled 767 male frogs in 21 ponds along an urbanization gradient and measured snout-vent length, length of tight, tibia, and foot with a digital calliper; and body mass with a hand Pesola (to the nearest 0.1 g) to calculate the Scaled Mass Index. We also calculated urbanization rate for each pond using satellite images showing land cover change from 1985 to 2019 in a 1-Km buffer. Our results shows that mean body size and leg length do not change consistently along the urbanization gradient. However, the variance in less urbanized is greater than in more urbanized sites. Additionally, there is no clear, linear spatial pattern in either body size or leg length. Moreover, fitness was slightly enhanced when body size was bigger, suggesting it might be under directional selection. Urban evolutionary dynamics is a burgeoning field, and more effort is needed to understand how cities affect the evolutionary trajectories of species, especially in the Global South. In conclusion, our study suggests a different pattern in phenotypic responses to urbanization for frogs in a city in the Global South, which contrasts with recent studies in the Global North that detected significant phenotypic changes between rural and urban frog populations. Our results can contribute to building urban ecological theory that explicitly includes city age, their development, growth rate, and history. Furthermore, changes associated with urbanization can affect populations in different ways in tropical environments, due to their climate conditions, eliciting different strategies in animals compared to temperate environments.