Divergent Paths: coastal vs. continental populations of Macrobrachium amazonicum (Heller, 1862) in the Amazon

The Amazon River prawn Macrobrachium amazonicum is a widely distributed species across South America, including lakes, rivers and estuarine environments. Previous studies have reported variations in both larvae and adult specimens from morphometric, morphological, and physiological data from geographically isolated populations, suggesting the existence of two distinct groups restricted to coastal and inland regions of the Amazon. In this study, we investigated the two groups using DNA and morphometric data from specimens collected over approximately 1,300 km along the Amazon River, covering both coastal and inland sites. Significant differences in length and weight were observed among samples from different localities, which were further supported by intraspecific levels of genetic differentiation. These findings reveal a separation point between coastal and inland populations of the Amazon River prawn across the Amazon region, providing valuable information for biogeographic studies and supporting the development of effective conservation policies.