Counting animal species with DNA barcodes: Canadian insects

Abstract

Recent estimates suggest that the global insect fauna includes fewer than six million species, but this projection is very uncertain because taxonomic work has been limited on some highly diverse groups. Validation of current estimates minimally requires the investigation of all lineages that are diverse enough to have a substantial impact on the final species count. This study represents a first step in this direction; it employs DNA barcoding to evaluate patterns of species richness in 27 orders of Canadian insects. The analysis of over one million specimens revealed species counts congruent with earlier results for most orders. However, Diptera and Hymenoptera were unexpectedly diverse, representing two-thirds of the 46 937 barcode index numbers (=species) detected. Correspondence checks between known species and barcoded taxa showed that sampling was incomplete, a result confirmed by extrapolations from the barcode results which suggest the occurrence of at least 94 000 species of insects in Canada, a near doubling from the prior estimate of 54 000 species. One dipteran family, the Cecidomyiidae, was extraordinarily diverse with an estimated 16 000 species, a 10-fold increase from its predicted diversity. If Canada possesses about 1% of the global fauna, as it does for known taxa, the results of this study suggest the presence of 10 million insect species with about 1.8 million of these taxa in the Cecidomyiidae. If so, the global species count for this fly family may exceed the combined total for all 142 beetle families. If extended to more geographical regions and to all hyperdiverse groups, DNA barcoding can rapidly resolve the current uncertainty surrounding a species count for the animal kingdom. A newly detailed understanding of species diversity may illuminate processes important in speciation, as suggested by the discovery that the most diverse insect lineages in Canada employ an unusual mode of reproduction, haplodiploidy.This article is part of the themed issue 'From DNA barcodes to biomes'.

Keywords: Cecidomyiidae; biodiversity; breeding systems; mitochondrial DNA.

Figure 1.

Heat map of sites in Canada where the one million insects analysed in this study were collected. Sites with 1–100 specimens in orange dots, 100–1000 are shown in small red dots, and 1000–10 000 are shown in larger pink dots.

Figure 2.

BIN count versus known species count for 27 orders of Canadian insects. Points above the line represent orders with more BINs than known species.

Figure 3.

The number of observed/estimated BINs versus the numbers of known/estimated species for the five largest orders of Canadian insects and the other 22 orders. The known and estimated species counts for each order are based on Danks [16], but more recent counts are available for three orders [–19]. Blue bars indicate species counts, while red bars indicate BIN counts (both in thousands). Circles indicate the number of BIN records for each order. BIN/SP is the ratio of observed BINs to known species.

Figure 4.

BIN count versus known species count for 87 families of Canadian Diptera. Points above the line represent families with more BINs than known species. Different colours indicate variation in mean nearest-neighbour (NN) distances (K2P) for the BINs in each family based on sequence divergences in the COI barcode region. n.a., data unavailable because only one BIN was analysed in this family.

Figure 5.

Lognormal abundance plots for seven families of Diptera with more than 20 000 barcode records and a composite curve for the other 91 families. B_e, expected BIN count; B_o, observed count.