Hidden biodiversity in Neotropical streams: DNA barcoding uncovers high endemicity of freshwater macroinvertebrates at small spatial scales

Abstract

Aquatic macroinvertebrates play a crucial role in freshwater ecosystems, but their diversity remains poorly known, particularly in the tropics. This "taxonomic void" represents limits our understanding of biodiversity patterns and processes in freshwater ecosystems, and the scale at which they operate. We used DNA barcoding to estimate lineage diversity (and the diversity of unique haplotypes) in 224 specimens of freshwater macroinvertebrates at a small spatial scale within the Panama Canal Watershed (PCW). In addition, we compiled available barcoding data to assess macroinvertebrate diversity at a broader spatial scale spanning the Isthmus of Panama. Consistently across two species delimitation algorithms (i.e., ABGD and GMYC), we found high lineage diversity within the PCW, with ~ 100-106 molecular operational taxonomic units (MOTUs at 2% sequence divergence) across 168 unique haplotypes. We also found a high lineage diversity along the Isthmus of Panama, but this diversity peaked within the PCW. However, our rarefaction/extrapolation approach showed that this diversity remains under sampled. As expected, these results indicate that the diversity of Neotropical freshwater macroinvertebrates is higher than previously thought, with the possibility of high endemicity even at narrow spatial scales. Geographic isolation is likely a main factor shaping these patterns of diversity. However, local disturbances such as the rupture of the continental divide due to the construction of the Panama Canal might be reshaping these patterns of diversity at a local scale. Although further work is needed to better understand the processes driving diversification in freshwater macroinvertebrates, we suggest that Neotropical streams represent continental islands of diversity. Understanding these islands of diversity is crucial in the face of increasing human disturbance.