Colour Patterns Do Not Diagnose Species: Quantitative Evaluation of a DNA Barcoded Cryptic Bumblebee Complex

Abstract

Cryptic diversity within bumblebees (Bombus) has the potential to undermine crucial conservation efforts designed to reverse the observed decline in many bumblebee species worldwide. Central to such efforts is the ability to correctly recognise and diagnose species. The B. lucorum complex (Bombus lucorum, B. cryptarum and B. magnus) comprises one of the most abundant and important group of wild plant and crop pollinators in northern Europe. Although the workers of these species are notoriously difficult to diagnose morphologically, it has been claimed that queens are readily diagnosable from morphological characters. Here we assess the value of colour-pattern characters in species identification of DNA-barcoded queens from the B. lucorum complex. Three distinct molecular operational taxonomic units were identified each representing one species. However, no uniquely diagnostic colour-pattern character state was found for any of these three molecular units and most colour-pattern characters showed continuous variation among the units. All characters previously deemed to be unique and diagnostic for one species were displayed by specimens molecularly identified as a different species. These results presented here raise questions on the reliability of species determinations in previous studies and highlights the benefits of implementing DNA barcoding prior to ecological, taxonomic and conservation studies of these important key pollinators.

Recognition and identification of bumblebee species in the Bombus lucorum-complex (Hymenoptera, Apidae) – A review and outlook

“…Bertsch (2009) was able to assign all but three investigated queen specimens to the correct species with the above mentioned characters, according to the biochemical evidence (n = 28). In contrast, using a larger sample from the British Isles and Denmark (n = 67), Carolan et al (2012) showed that especially the collar-characters are not reliable for species diagnosis since they show overlap (see Fig. 4: doi: 10.1371/journal.pone.0029251.…”

“…The interspecific genetic divergences of the species are considerably larger than the intraspecific divergences and these patterns are stable over wide geographic ranges of Europe. In measureable terms, the genetic divergences between the species, based on the Kimura 2-parameter model of DNA sequence evolution (Kimura 1980), from Carolan et al (2012) ranged from 0.033 to 0.044, whereas intraspecific distance was from 0.002 to 0.004. In the analysis by Murray et al (2008), which was based on Tamura-Nei (Tamura and Nei 1993), the distances are slightly smaller.…”

“…Aside from this confusing information, the work of Carolan et al (2012) strongly indicated that the collar characters are not completely reliable and should not be exclusively taken into account for species identification. In addition, the key of Rasmont (1984) uses several characters aside from the coloration of the pile, such as the form of the labrum, punctuations of several structures and the shape of the hindleg metatarsus.…”

Pollen and nectar quality drive the major and minor floral choices of bumble bees

“…Due to their high morphological similarity, individuals of B. terrestris, B. lucorum, B. cryptarum, and B. magnus were pooled into one operational taxonomic unit (OTU), B. terrestris s.l. (Carolan et al 2012;PrysJones and Corbet 2011). After the worker bees were immobilized in a marking cage with a soft plunger, the two pollen loads were gently removed using a toothpick.…”

A DNA barcoding approach in the study of tardigrades

“…DNA barcoding may be used to tackle very different issues: controlling the identity of food of animal and/or vegetal origin, e.g. fishes for sale in supermarkets (Rasmussen et al, 2009), identifying immature specimens and resolving adult and larval stages within the same species (Hebert et al, 2004a;Paquin and Hedin, 2004;Greenstone et al, 2005;Hubert et al, 2010), studying extinct species (Lambert et al, 2005) and discriminating possible cryptic species (Hebert et al, 2004a(Hebert et al, , 2004bHogg and Hebert, 2004;Barrett and Hebert, 2005;Ward et al, 2005;Lara et al, 2010;Carolan et al, 2012).…”