Geographic patterns of Darwinian shortfall and implications for fish conservation in the Tocantins-Araguaia River basin

Abstract To understand biodiversity patterns at distinct geographic scales, it is important to consider the impacts of lack of knowledge (shortfalls) on such patterns. Our aim here is to evaluate the spatial patterns in the lack of phylogenetic knowledge (i.e., Darwinian shortfall) among fish species in the Tocantins-Araguaia River Basin and to correlate it with key conservation metrics and patterns, including the difference between protected and non-protected areas. We used linear models to test these relationships, considering the spatial structure of the basin. We highlight a high level of Darwinian shortfall for the basin, where 35% of the evolutionary history is unknown, which is more pronounced in the Tocantins drainage. Also, we found that endemism, phylogenetic diversity, rarity, and species richness are predictors of the shortfall. This study underscores a critical knowledge shortfall in the Tocantins-Araguaia River basin, a region of national and global significance due to its remarkable biodiversity. The positive correlations found between the Darwinian shortfall with endemism, phylogenetic diversity, and rarity imply that the basin's distinctive evolutionary history remains underappreciated. Consequently, we highlight key regions within the basin that are imperative for future aquatic research.