Laurence Packer

Climate change impacts on bumblebees converge across continents

Bucking the trend Responses to climate change have been observed across many species. There is a general trend for species to shift their ranges poleward or up in elevation. Not all species, however, can make such shifts, and these species might experience more rapid declines. Kerr et al. looked at data on bumblebees across North America and Europe over the past 110 years. Bumblebees have not shifted northward and are experiencing shrinking distributions in the southern ends of their range. Such failures to shift may be because of their origins in a cooler climate, and suggest an elevated susceptibility to rapid climate change. Science, this issue p. 177 Cool-adapted bumblebees are failing to shift their ranges in response to climate warming. For many species, geographical ranges are expanding toward the poles in response to climate change, while remaining stable along range edges nearest the equator. Using long-term observations across Europe and North America over 110 years, we tested for climate change–related range shifts in bumblebee species across the full extents of their latitudinal and thermal limits and movements along elevation gradients. We found cross-continentally consistent trends in failures to track warming through time at species’ northern range limits, range losses from southern range limits, and shifts to higher elevations among southern species. These effects are independent of changing land uses or pesticide applications and underscore the need to test for climate impacts at both leading and trailing latitudinal and thermal limits for species.

DNA barcoding and the mediocrity of morphology

A small but vocal community of critics has questioned the epistemological value of DNA barcoding by suggesting that either it ‘cannot work’ for the identification or discovery of species or that it ignores the ‘richness’ inherent in traditional approaches. We re‐examine these arguments through a comparison of DNA barcoding and morphological taxonomy in terms of their accuracy and diversity of characters employed. We conclude that morphology often does not work and that it is often nowhere near as ‘rich’ as has been argued. Morphology is particularly poor in numerous important situations, such as the association of larvae with adults and discrimination among cryptic species. The vehemence of some of the criticisms is surprising given that morphology alone is known to be inadequate to the task of species‐level identification in many instances.

DNA barcoding a regional bee (Hymenoptera: Apoidea) fauna and its potential for ecological studies

DNA barcoding has been evaluated for many animal taxa and is now advocated as a reliable and rapid means for species‐level identification. The coming‐to‐light of this identification tool is timely as we are now facing perhaps the greatest rate of species loss in recent millennia. This study contributes to an ever‐increasing number of published accounts of DNA barcoding successfully and accurately distinguishing animal taxa, in this instance, the bee fauna of Nova Scotia, Canada. Most members of this well‐known fauna were resolved with particular clarity; the average intraspecific divergence was less than 0.5%, and COI sequences from over 75% of the provinces species are now in the Barcodes of Life Data System. DNA barcoding also revealed some surprises within this fauna, including the possible recognition of two undescribed genetically unique species, one in the genus Ceratina (subgenus Zadontomerus), the second in the genus Andrena (subgenus Larandrena); both are presently receiving further taxonomic study. In addition, DNA barcoding has allowed sex‐associations among two pairs of cleptoparasitic species. The resulting utility of DNA barcoding for ecological studies of bee communities is discussed.

Wolbachia and DNA barcoding insects: Patterns, potential, and problems

Wolbachia is a genus of bacterial endosymbionts that impacts the breeding systems of their hosts. Wolbachia can confuse the patterns of mitochondrial variation, including DNA barcodes, because it influences the pathways through which mitochondria are inherited. We examined the extent to which these endosymbionts are detected in routine DNA barcoding, assessed their impact upon the insect sequence divergence and identification accuracy, and considered the variation present in Wolbachia COI. Using both standard PCR assays (Wolbachia surface coding protein – wsp), and bacterial COI fragments we found evidence of Wolbachia in insect total genomic extracts created for DNA barcoding library construction. When >2 million insect COI trace files were examined on the Barcode of Life Datasystem (BOLD) Wolbachia COI was present in 0.16% of the cases. It is possible to generate Wolbachia COI using standard insect primers; however, that amplicon was never confused with the COI of the host. Wolbachia alleles recovered were predominantly Supergroup A and were broadly distributed geographically and phylogenetically. We conclude that the presence of the Wolbachia DNA in total genomic extracts made from insects is unlikely to compromise the accuracy of the DNA barcode library; in fact, the ability to query this DNA library (the database and the extracts) for endosymbionts is one of the ancillary benefits of such a large scale endeavor – for which we provide several examples. It is our conclusion that regular assays for Wolbachia presence and type can, and should, be adopted by large scale insect barcoding initiatives. While COI is one of the five multi-locus sequence typing (MLST) genes used for categorizing Wolbachia, there is limited overlap with the eukaryotic DNA barcode region.

Solitary and eusocial nests in a population of Augochlorella striata (Provancher) (Hymenoptera; Halictidae) at the northern edge of its range.

SummaryAugochlorella striata was studied at the northern limit of its range. The study population contained a mixture of solitary and social nest foundresses. Eusocial foundresses produced 1 or 2 workers before switching to a male biased brood. Solitary foundresses produced males first. Cells vacated by eclosed offspring were reused late in summer. A female biased brood resulted from cell reuse in both solitary and eusocial nests. Workers were slightly smaller than their mothers and were sterile although most of them mated. In comparison to published data from a Kansas population of this species, the Nova Scotia population had i) a lower proportion of multiple foundress nests, ii) a smaller worker brood and iii) a briefer period of foraging activity but iv) comparable overall nest productivity.

Successful Biological Invasion despite a Severe Genetic Load

Understanding the factors that influence the success of ecologically and economically damaging biological invasions is of prime importance. Recent studies have shown that invasive populations typically exhibit minimal, if any, reductions in genetic diversity, suggesting that large founding populations and/or multiple introductions are required for the success of biological invasions, consistent with predictions of the propagule pressure hypothesis. Through population genetic analysis of neutral microsatellite markers and a gene experiencing balancing selection, we demonstrate that the solitary bee Lasioglossum leucozonium experienced a single and severe bottleneck during its introduction from Europe. Paradoxically, the success of L. leucozonium in its introduced range occurred despite the severe genetic load caused by single-locus complementary sex-determination that still turns 30% of female-destined eggs into sterile diploid males, thereby substantially limiting the growth potential of the introduced population. Using stochastic modeling, we show that L. leucozonium invaded North America through the introduction of a very small number of propagules, most likely a singly-mated female. Our results suggest that chance events and ecological traits of invaders are more important than propagule pressure in determining invasion success, and that the vigilance required to prevent invasions may be considerably greater than has been previously considered.

Use of diploid male frequency data as an indicator of pollinator decline

Pollination deficits in agricultural and natural systems are suggestive of large reductions in pollinator populations. However, actual declines are difficult to demonstrate using census data. Here, we show census data to be misleading because many abundant pollinators exhibit high levels of production of sterile diploid males usually found only in small inbred hymenopteran populations; Euglossa imperialis exhibits high levels of diploid male production induced by low effective population sizes (Ne ≈ 15), despite being the most abundant orchid bee in lowland tropical forests in Panama. We caution that although some pollinators appear abundant on the basis of census data, their long–term persistence may be highly tenuous based on genetic evidence. We propose the use of diploid male frequency data as a metric for assessing the sustainability of bee populations.

The evolution of social behavior and nest architecture in sweat bees of the subgenus Evylaeus (Hymenoptera : Halictidae) : a phylogenetic approach

SummaryPhylogenetic studies are required to establish the direction of evolutionary change in behavioral characters. Here I produce a phylogeny for 8 Old World species of the subgenus Evylaeus based upon cladistic analysis of 26 informative allozyme loci. By mapping behavioral character states upon the resulting cladogram, the following major conclusions could be drawn: (1) Social Evylaeus species share sociality by descent from a eusocial common ancestor which might not have been an Evylaeus species; the solitary behavior of Lasioglossum (E.) fulvicorne may be a derived condition. (2) One reversal to solitary behavior within Evylaeus is proven for a Japanese montane population of L. (E.) calceatum. (3) The perennial societies of L. (E.) marginatum are derived from an annual social cycle and do not represent an independent evolution of sociality. (4) Multiple-foundress associations are a derived condition within Evylaeus, suggesting that if social behavior evolved within the group, then the semisocial route was not the one taken by these bees. (5) The nest architectural trait of excavating a cavity around clustered brood cells is a ground plan characteristic of Evylaeus but with a reversal in L. (E.) marginatum. (6) It is likely that extended opening of brood cells during juvenile development has originated independently twice among the species considered. Another benefit of phylogenetic studies is their use in predicting which taxa are most likely to exhibit particularly interesting behavioral states. In this regard, the phylogeny suggests that close relatives of L. (E.) fulvicorne and also most of the major species groups of Evylaeus which have not received any field study should be investigated both phylogenetically and behaviorally for a full evaluation of behavioral evolution in Evylaeus.

Increased genetic differentiation in a specialist versus a generalist bee: implications for conservation

Oligolectic bees are specialists that collect pollen from one or a few closely related species of plants, while polylectic bees are generalists that collect pollen from both related and unrelated species of plants. Because of their more restricted range of floral hosts, it is expected that specialists persist in more isolated populations than do generalists. We present data on the population structure of two closely related bee species sampled from a super abundant floral host in the southern Atacama Desert. Pairwise comparisons of population subdivision over identical distances revealed that the specialist bee had significantly more differentiated populations in comparison to the generalist. Further, populations of the specialist had significantly less genetic variation, measured as observed and expected heterozgyosity, than those of the generalist. Our data support the hypothesis of decreased gene flow among populations of the specialist bee even at equivalent geographic distances. The resulting reductions in effective population size for specialists make them particularly prone to extinction due to both demographic and genetic reasons. Our findings have important implications for the conservation of bees and other specialist insects.

The potential of cleptoparasitic bees as indicator taxa for assessing bee communities

Many factors affect bee diversity and abundance, and knowledge of these is crucial for maintaining healthy bee communities. However, there are few means to fully evaluate the status of bee communities; most are based on monitoring species richness and abundance and do not consider the diverse life histories of bees. We propose that functional diversity of bee communities offers a more consistent means of evaluation and suggest that cleptoparasitic bees in particular show much promise as indicator taxa. Cleptoparasitic bees play a stabilising role within bee communities. They represent the apex of bee communities and are the first guild to respond to disturbances, are easily distinguished as such and are diverse enough to be representative of entire bee communities. The diversity and abundance of cleptoparasites in relation to all bees is indicative of the status of the total bee community, and monitoring them should form an integral part of assessing bee communities.