Turning Up the Heat on a Hotspot: DNA Barcodes Reveal 80% More Species of Geometrid Moths along an Andean Elevational Gradient

Abstract

We sampled 14,603 geometrid moths along a forested elevational gradient from 1020-3021 m in the southern Ecuadorian Andes, and then employed DNA barcoding to refine decisions on species boundaries initially made by morphology. We compared the results with those from an earlier study on the same but slightly shorter gradient that relied solely on morphological criteria to discriminate species. The present analysis revealed 1857 putative species, an 80% increase in species richness from the earlier study that detected only 1010 species. Measures of species richness and diversity that are less dependent on sample size were more than twice as high as in the earlier study, even when analysis was restricted to an identical elevational range. The estimated total number of geometrid species (new dataset) in the sampled area is 2350. Species richness at single sites was 32-43% higher, and the beta diversity component rose by 43-51%. These impacts of DNA barcoding on measures of richness reflect its capacity to reveal cryptic species that were overlooked in the first study. The overall results confirmed unique diversity patterns reported in the first investigation. Species diversity was uniformly high along the gradient, declining only slightly above 2800 m. Species turnover also showed little variation along the gradient, reinforcing the lack of evidence for discrete faunal zones. By confirming these major biodiversity patterns, the present study establishes that incomplete species delineation does not necessarily conceal trends of biodiversity along ecological gradients, but it impedes determination of the true magnitude of diversity and species turnover.

Fig 1. Study area with all sampling sites (first and second studies) in southern Ecuador.

See S1 Table for detailed information on all sites. “+” indicates that samples from these sites were pooled for analysis.

Fig 2. Rarefaction / extrapolation curves for regional diversity of geometrid moths in southern Ecuador.

Symbols in each curve refer to observed total sample size. The grey vertical line indicates a rarefaction level of 10,306 specimens.

Fig 3. Partitioning of multiplicative gamma diversity of geometrid moths into its mean alpha and beta fractions, based on either observed species richness or exponential Shannon diversity, for the first and second studies.

For both data sets, the local alpha component is, on average, smaller for species richness than for Shannon diversity. In the second data set, with far more observed species and far more species recorded as singletons, the relative contribution of the beta component is substantially larger than in the first data set, which was based on morphospecies delimitations only.

Fig 4. Richness and diversity patterns of geometrid moths along an elevational gradient (1000–3000 m a.s.l.) in southern Ecuador with data from the first study (blue diamonds) and the second study (green circles).

The slopes of all regression lines (fitted by ordinary least squares regression) are not significantly different from zero, indicating that geometrid moth diversity is not related to elevation. Sites that were sampled in both studies are outlined in black. a) expected species richness (at coverage 0.8), b) exponential Shannon diversity, exp (H’), c) Fisher’s alpha.

Fig 5. Ordination plots (by non-metric two-dimensional scaling) of species composition along an elevational gradient in southern Ecuador.

Sites were largely located in the ordination according to their elevation, along dimension 1. a) first study (blue diamonds), b) second study (green circles). Sites that were sampled in both studies are outlined in black.