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

Abstract

23 Aquatic macroinvertebrates play a crucial role in freshwater ecosystems, but their diversity 24 remains poorly known, particularly in the tropics. This "taxonomic void" represents limits our 25 understanding of biodiversity patterns and processes in freshwater ecosystems, and the scale at 26 which they operate. We used DNA barcoding to estimate lineage diversity (and the diversity of 27 unique haplotypes) in 224 specimens of freshwater macroinvertebrates at a small spatial scale 28 within the Panama Canal Watershed (PCW). In addition, we compiled available barcoding data 29 to assess macroinvertebrate diversity at a broader spatial scale spanning the Isthmus of Panama.30 Consistently across two species delimitation algorithms (i.e., ABGD and GMYC), we found high 31 lineage diversity within the PCW, with ~ 100-106 molecular operational taxonomic units 32 (MOTUs at 2% sequence divergence) across 168 unique haplotypes. We also found a high 33 lineage diversity along the Isthmus of Panama, but this diversity peaked within the PCW. 34 However, our rarefaction/extrapolation approach showed that this diversity remains under 35 sampled. As expected, these results indicate that the diversity of Neotropical freshwater 36 macroinvertebrates is higher than previously thought, with the possibility of high endemicity 37 even at narrow spatial scales. Geographic isolation is likely a main factor shaping these patterns 38 of diversity. However, local disturbances such as the rupture of the continental divide due to the 39 construction of the Panama Canal might be reshaping these patterns of diversity at a local scale.40 Although further work is needed to better understand the processes driving diversification in 41 freshwater macroinvertebrates, we suggest that Neotropical streams represent continental islands 42 of diversity. Understanding these islands of diversity is crucial in the face of increasing human 43 disturbance. 3 44 Introduction 45 Aquatic macroinvertebrates are a fundamental component of Neotropical freshwater 46 environments. They mediate important processes such as food web dynamics, energy flow and 47 nutrient cycling, and therefore play a central role in sustaining the biodiversity and functioning 48 of freshwater ecosystems [1-3]. However, the diversity of Neotropical freshwater 49 macroinvertebrates remains poorly described, and even less is known about the processes that 50 drive their diversity, and the scale at which they operate [4]. For instance, despite considerable 51 efforts by local taxonomists [e.g., 5-8], only a limited number of species are recognized (e.g. , 52 [9,10], and most of the published literature use genus and family as a standard taxonomic unit for 53 Neotropical macroinvertebrates [9,[11][12][13][14][15]. This is partially due to the complexity of these 54 communities, which are often composed of multiple life-stages existing at the interface between 55 the terrestrial and aquatic environment [16,17]. Another limitation is the low accuracy and 56 precision of traditional morpholo...

Evolutionary mismatch along salinity gradients in a Neotropical water strider

“…was obtained from De León et al. (2020) (GenBank accession number: ).…”

A survey of aquatic macroinvertebrates in a river from the dry corridor of Nicaragua using biological indices and DNA barcoding

“…This high diversity is derived from the early migratory settlement of dry forest, as this was the first to colonize Central America from Mexico around 2.5 Mya (Willis et al, 2014). Large endemicity of aquatic macroinvertebrates at a small spatial scale has been documented in this type of environment (de León et al, 2020). Spatial isolation, biological function, and habitat variability are all important drivers of macroinvertebrate diversity in the Neotropics (Múrria et al, 2015).…”

“…Furthermore, BOLD systems identified 39 unique BINs, which represented a considerable percentage (42%) of sequences from our dataset. The limited identification to species level (14) using nucleotide databases compared with OTUs (69–73), from species delimitation methods, indicates that the diversity of aquatic macroinvertebrates in neotropical environments is largely understudied, as suggested by previous studies from Panama (de León et al, 2020; Múrria et al, 2015). Description and identification of species will help to create accurate libraries of neotropical diversity.…”

“…In the Neotropics, Costa Rica has developed an initiative to create a DNA barcode database focused on Lepidoptera taxa (Hajibabaei et al, 2006; Janzen & Hallwachs, 2011). However, a recent study in Panama showed that aquatic macroinvertebrate identification using nucleotide databases matches less than 50% of sequences and only to genus and family level (de León et al, 2020). This indicates that more work is needed to strengthen this region's macroinvertebrate knowledge.…”