Taxonomic distribution of cryptic diversity among metazoans: not so homogeneous after all

Abstract

Cryptic diversity plagues estimates of biodiversity, conservation efforts and attempts to control diseases and invasive species. Here, we re-visit a decade-old assessment of whether or not cryptic species are homogeneously reported among higher metazoan taxa. We compiled information from an extensive survey of the literature to recover all reports of cryptic species among metazoans. After correcting for currently known species richness and research effort per taxon, we find that cryptic species are over-reported in some taxa and under-reported in others. Although several taxa showing either a lack or an excess of reported cryptic species were poorly studied invertebrate groups, we found that cryptic species were over-reported in amphibians, reptiles and crustaceans, all relatively well-studied groups. The observed heterogeneity in the distribution of reported cryptic species may reflect taxon-specific properties affecting either the propensity for cryptic species to be formed or their likelihood of being detected by conventional taxonomy. Either way, the implications of cryptic diversity may not apply equally across all taxonomic groups.

Keywords: biodiversity; cryptic species; study effort; taxonomy.

Figure 1.

Number of CSR per taxon (a) and total number of cryptic species found (b) against known extant species richness, across 34 higher taxa. Grey lines encompass the 95% CIs.

Figure 2.

Residual number of CSR per taxon (a) and residual total number of cryptic species found (b) against taxonomic study bias, across 34 higher taxa. Residuals are from the regressions in figure 1. Grey lines encompass the 95% CIs. In addition to the labelled points, those for insects (I), fish (F), birds (B) and mammals (M) are identified.