Effects Of Urbanization On Morphological Characteristics And Age Structure Of Pelophylax Plancyi And Fejervarya Multistriata In Shanghai

Amphibians,as an important vertebrate group in forest and wetland ecosystems,the richness and abundance of amphibians have decreased significantly worldwide.Urbanization can lead to habitat loss,fragmentation,and habitat quality degradation of amphibians,which is associated with the threat of 88% of amphibian species worldwide.Urbanization is also considered to be the most important factor causing the decline of amphibian species diversity.As an easy to measure phenotypic index closely related to amphibian reproduction and movement characteristics,morphological characteristics can be used to measure the impact of habitat loss,fragmentation and habitat quality degradation on amphibians.In addition,age structure is an important life history characteristic of wildlife,which is often used to quantify amphibian population dynamics and population threat degree under the background of human activities.At present,most studies on urban amphibians focus on population dynamics and genetic structure of amphibians,but the effects of urbanization on morphological characteristics and age structure of amphibians remain unclear.In this study,two dominant frog species,Pelophylax plancyi and Fejervarya multistriata,were investigated at 38 sites along the urbanization gradient in Shanghai from May to August in2020 and from April to July in 2021.A total of 170 P.plancyi and 305 F.multistriata individuals were collected.Landscape interpretation and principal component analysis were used to define the urbanization level(urban,suburban and rural)of each study site.We measured five morphological characteristics,including snout-vent length,body mass,head width,forelimb length and hindlimb length.The response of morphological characteristics to urbanization was analyzed by combining microhabitat factors and landscape factors.Skeletochronology techniques was used to identify the age of individuals,and the differences in average age,maximum age and snout-vent length of populations of P.plancyi and F.multistriata in urban,suburban and suburban areas were compared.The main results are listed as follows:(1)The morphological characteristics of P.plancyi and F.multistriata showed a trend of large size under the influence of urbanization.The body length increased with the increase of urbanization index.The length of hind limbs,snout-vent length and head width of male and body mass of female were positively correlated with urbanization index.The morphological characteristics of the two species differed in response to urbanization,which may be related to their habitat preference and ecological niche.(2)The model was used to analyze the habitat microhabitat factors,landscape factors and population density,and it was found that the morphological characteristics were significantly correlated with population density and vegetation area.The morphological characteristics of the frog were affected by microhabitat factors,landscape factors and population density in a comprehensive way.(3)There were no significant differences in the average and maximum ages of P.plancyi populations in the urban,suburban and suburban areas of Shanghai.The average age of F.multistriata males in rural area was significantly higher than that in urban area.In urban areas,the population is threatened by habitat loss,decreased connectivity and deteriorated habitat quality which lead to the low survival rate of adult individuals.(4)Comparing the snout-vent length at age across the urbanization gradient,the snout-vent length of P.plancyi in the rural was generally smaller than that in the suburban and urban areas,and the growth rate of snout-vent length was also smaller.The snout-vent length of F.multistriata in the urban area is larger than that in the rural and suburban.It means that adult urban frogs grow faster.The results of analysis of P.plancyi and F.multistriata morphological characteristics and age structure under the urbanization background,reveals the urban amphibian populations present the trend of bigness,and accelerate the growth rate of adult in response to the adverse effects of urbanization,such as reduced population density and habitat fragmentation and loss of connectivity.