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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.

SUBMITTER: Carolan JC

PROVIDER: S-EPMC3253071 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature

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Colour patterns do not diagnose species: quantitative evaluation of a DNA barcoded cryptic bumblebee complex.

Carolan James C JC Murray Tomás E TE Fitzpatrick Úna Ú Crossley John J Schmidt Hans H Cederberg Björn B McNally Luke L Paxton Robert J RJ Williams Paul H PH Brown Mark J F MJ

PloS one 20120106 1

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 d ...[more]

PMID: 22238595

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Project description:Our grasp of biodiversity is fine-tuned through the process of revisionary taxonomy. If species do exist in nature and can be discovered with available techniques, then we expect these revisions to converge on broadly shared interpretations of species. But for the primarily arctic bumblebees of the subgenus Alpinobombus of the genus Bombus, revisions by some of the most experienced specialists are unusual for bumblebees in that they have all reached different conclusions on the number of species present. Recent revisions based on skeletal morphology have concluded that there are from four to six species, while variation in colour pattern of the hair raised questions as to whether at least seven species might be present. Even more species are supported if we accept the recent move away from viewing species as morphotypes to viewing them instead as evolutionarily independent lineages (EILs) using data from genes. EILs are recognised here in practice from the gene coalescents that provide direct evidence for their evolutionary independence. We show from fitting both general mixed Yule/coalescent (GMYC) models and Poisson-tree-process (PTP) models to data for the mitochondrial COI gene that there is support for nine species in the subgenus Alpinobombus. Examination of the more slowly evolving nuclear PEPCK gene shows further support for a previously unrecognised taxon as a new species in northwestern North America. The three pairs of the most morphologically similar sister species are separated allopatrically and prevented from interbreeding by oceans. We also find that most of the species show multiple shared colour patterns, giving the appearance of mimicry among parts of the different species. However, reconstructing ancestral colour-pattern states shows that speciation is likely to have cut across widespread ancestral polymorphisms, without or largely without convergence. In the particular case of Alpinobombus, morphological, colour-pattern, and genetic groups show little agreement, which may help to explain the lack of agreement among previous taxonomic revisions.

Project description:Competition theory states that multiple species should not be able to occupy the same niche indefinitely. Morphologically, similar species are expected to be ecologically alike and exhibit little niche differentiation, which makes it difficult to explain the co-occurrence of cryptic species. Here, we investigated interspecific niche differentiation within a complex of cryptic bumblebee species that co-occur extensively in the United Kingdom. We compared the interspecific variation along different niche dimensions, to determine how they partition a niche to avoid competitive exclusion. We studied the species B. cryptarum, B. lucorum, and B. magnus at a single location in the northwest of Scotland throughout the flight season. Using mitochondrial DNA for species identification, we investigated differences in phenology, response to weather variables and forage use. We also estimated niche region and niche overlap between different castes of the three species. Our results show varying levels of niche partitioning between the bumblebee species along three niche dimensions. The species had contrasting phenologies: The phenology of B. magnus was delayed relative to the other two species, while B. cryptarum had a relatively extended phenology, with workers and males more common than B. lucorum early and late in the season. We found divergent thermal specialisation: In contrast to B. cryptarum and B. magnus, B. lucorum worker activity was skewed toward warmer, sunnier conditions, leading to interspecific temporal variation. Furthermore, the three species differentially exploited the available forage plants: In particular, unlike the other two species, B. magnus fed predominantly on species of heather. The results suggest that ecological divergence in different niche dimensions and spatio-temporal heterogeneity in the environment may contribute to the persistence of cryptic species in sympatry. Furthermore, our study suggests that cryptic species provide distinct and unique ecosystem services, demonstrating that morphological similarity does not necessarily equate to ecological equivalence.

Dataset Information

Colour patterns do not diagnose species: quantitative evaluation of a DNA barcoded cryptic bumblebee complex.

Publications

Colour patterns do not diagnose species: quantitative evaluation of a DNA barcoded cryptic bumblebee complex.

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