Fishes across the cityscape: are trait responses to urbanization similar within the city?

Background/Question/Methods

Urbanization is a global process that convert natural and rural areas into built landscapes. Such process leads to profound habitat changes that impose new selective forces for trait change that lead to adaptation. Increasing evidence shows that urban populations have traits that markedly differ from their non-urban conspecifics. However, how traits can vary within urban areas is poorly known. We use Goldfish, Carassius auratus, that invaded urban ponds in the Greater Toronto Area, Canada, to determine whether condition and life- history traits (body size and reproductive investment) change within the urban landscape. In 2021, we sampled goldfish in two urban ponds under different urban density. Each goldfish was dissected, the liver (L) and gonads (G) were retrieved and dried along with the fish carcass (C). Individual condition was estimated as the ratio L/C and reproductive investment was estimated as the ratio G/C.

Results/Conclusions

We found that condition and life-history traits of goldfish vary between urban ponds. The pond surrounded by higher urban density had larger fish than the pond with lower urban density (2±0.2 and 1.7±0.1mg, respectively) (ANCOVA, F1,212=4.2, p=0.04) which store less nutrient in their liver (6.9±0.3 and 8.6±0.2mg, respectively) (ANOVA, F1,214=11.1, p< 0.01) but invest more towards reproduction (22.6±3 and 17.9±0.9mg) (ANOVA, F1,214=5.9, p=0.02). Our results suggest that the trait response of freshwater biota to urbanization is context dependent, varying within the urban landscape. This suggest socioeconomic processes can be fundamental to shape the ecological and evolutionary response of freshwater biota to urbanization. In the future, assessing the relationship between trait response and socioeconomic differences across the urban landscape may help further understand how species adapt to persist in cities.