Robert L. Minckley

A simple and distinctive microbiota associated with honey bees and bumble bees

Specialized relationships with bacteria often allow animals to exploit a new diet by providing a novel set of metabolic capabilities. Bees are a monophyletic group of Hymenoptera that transitioned to a completely herbivorous diet from the carnivorous diet of their wasp ancestors. Recent culture‐independent studies suggest that a set of distinctive bacterial species inhabits the gut of the honey bee, Apis mellifera. Here we survey the gut microbiotae of diverse bee and wasp species to test whether acquisition of these bacteria was associated with the transition to herbivory in bees generally. We found that most bee species lack phylotypes that are the same or similar to those typical of A. mellifera, rejecting the hypothesis that this dietary transition was symbiont‐dependent. The most common bacteria in solitary bee species are a widespread phylotype of Burkholderia and the pervasive insect associate, Wolbachia. In contrast, several social representatives of corbiculate bees do possess distinctive bacterial phylotypes. Samples of A. mellifera harboured the same microbiota as in previous surveys, and closely related bacterial phylotypes were identified in two Asian honey bees (Apis andreniformis and Apis dorsata) and several bumble bee (Bombus) species. Potentially, the sociality of Apis and Bombus species facilitates symbiont transmission and thus is key to the maintenance of a more consistent gut microbiota. Phylogenetic analyses provide a more refined taxonomic placement of the A. mellifera symbionts.

Complex Responses Within A Desert Bee Guild (Hymenoptera: Apiformes) To Urban Habitat Fragmentation

Urbanization within the Tucson Basin of Arizona during the past 50+ years has fragmented the original desert scrub into patches of different sizes and ages. These remnant patches and the surrounding desert are dominated by Larrea tridentata (creosote bush), a long-lived shrub whose flowers are visited by > 120 native bee species across its range. Twenty-one of these bee species restrict their pollen foraging to L. tridentata. To evaluate the response of this bee fauna to fragmentation, we compared species incidence and abundance patterns for the bee guild visiting L. tridentata at 59 habitat fragments of known size (0.002-5 ha) and age (up to 70 years), and in adjacent desert. The 62 bee species caught during this study responded to fragmentation heterogeneously and not in direct relation to their abundance or incidence in undisturbed desert. Few species found outside the city were entirely absent from urban fragments. Species of ground-nesting L. tridentata specialists were underrepresented in smaller fragments and less abundant in the smaller and older fragments. In contrast, cavity-nesting bees (including one L. tridentata specialist) were overrepresented in the habitat fragments, probably due to enhanced nesting opportunities available in the urban matrix. Small-bodied bee species were no more likely than larger bodied species to be absent from the smaller fragments. The introduced European honey bee, Apis mellifera, was a minor faunal element at > 90% of the fragments and exerted little if any influence on the response of native bee species to fragmentation. Overall, bee response to urban habitat fragmentation was best predicted by ecological traits associated with nesting and dietary breadth. Had species been treated as individual units in the analyses, or pooled together into one analysis, these response patterns may not have been apparent. Pollination interactions with this floral host are probably not adversely affected in this system because of its longevity and ability to attract diverse pollinators but will demand careful further study to understand.

Variation in Native Bee Faunas and its Implications for Detecting Community Changes

Introduction Methods Comparing studies Levels of spatial and temporal variation Effects of sampling effort and area Predictability of subsampling Results ABSTRACT Changes in flower-visiting insect populations or communities that result from human impacts can be documented by measuring spatial or temporal trends, or by comparing abundance or species composition before and after disturbance. The level of naturally occurring variation in populations and communities over space and time will dictate the sampling effort required to detect human-induced changes. We compiled a set of existing surveys of the bee faunas of natural communities from around the world to examine patterns of abundance and richness. We focused on a subset of these studies to illustrate variation in bee communities among different sites and within sites over different spatial and temporal scales. We used examples from our compilation and other published studies to illustrate sampling approaches that maximize the value of future sampling efforts. Existing studies suggest that bee faunas are locally diverse, highly variable in space and time, and often rich in rare species. All of these attributes indicate that intense sampling among sites and years will be required to differentiate changes due to specific impacts from the natural dynamics of populations and communities. Given the limits on

Spatial patterns of bee captures in North American bowl trapping surveys

Abstract.  1. Bowl and pan traps are now commonly used to capture bees (Hymenoptera: Apiformes) for research and surveys.

Detecting Insect Pollinator Declines on Regional and Global Scales

Recently there has been considerable concern about declines in bee communities in agricultural and natural habitats. The value of pollination to agriculture, provided primarily by bees, is >

Ecological niche modeling implicates climatic adaptation, competitive exclusion, and niche conservatism amongLarrea tridentatacytotypes in North American deserts 1,2

200 billion/year worldwide, and in natural ecosystems it is thought to be even greater. However, no monitoring program exists to accurately detect declines in abundance of insect pollinators; thus, it is difficult to quantify the status of bee communities or estimate the extent of declines. We used data from 11 multiyear studies of bee communities to devise a program to monitor pollinators at regional, national, or international scales. In these studies, 7 different methods for sampling bees were used and bees were sampled on 3 different continents. We estimated that a monitoring program with 200-250 sampling locations each sampled twice over 5 years would provide sufficient power to detect small (2-5%) annual declines in the number of species and in total abundance and would cost U.S.

Phylogeny and Cytogeography of the North American Creosote Bush (Larrea tridentata, Zygophyllaceae)

2,000,000. To detect declines as small as 1% annually over the same period would require >300 sampling locations. Given the role of pollinators in food security and ecosystem function, we recommend establishment of integrated regional and international monitoring programs to detect changes in pollinator communities.

Faunal composition and species richness differences of bees (Hymenoptera: Apiformes) from two north American regions

Abstract Larrea tridentata is a dominant and widespread shrub of North American warm deserts. The species comprises three “chromosomal races,” including diploids (Chihuahuan Desert), tetraploids (Sonoran Desert), hexaploids (Mojave and western Sonoran Deserts), as well as the geographically restricted tetraploid L. tridentata var. arenaria. Creosote bush is a recent arrival to the North American continent, and it is hypothesized that its geographic dispersion reflects rapid ecological divergence mediated by polyploidization. Here we use species distribution modeling to quantitatively evaluate alternate hypotheses for cytotype distributions, based on comprehensive field sampling of creosote bush populations over four years. Using ecological niche models and analyses of field-collected soils, we test whether (1) the climatic niche of the three cytotypes are differentiated; (2) there is evidence for strong climatic gradients at the distributional boundaries of the cytotypes; and (3) cytotype ranges are distinguished by edaphic features. Quantitative tests of niche equivalence indicated that distribution models for all cytotypes were significantly different from one other, suggesting that cytotype races occupy unique and distinctive habitats. However, tests of niche similarity suggest a pattern of niche conservatism, wherein cytotypes tend to occur in climatically similar regions of their respective deserts. Moreover, the modeled diploid distribution was projected to intrude into the geographic range of tetraploids, and the modeled tetraploid distribution was projected to intrude into the range of hexaploids, suggesting that intercytotype competition is a factor influencing cytotype distributions. The range boundary between the dune endemic L. tridentata var. arenaria and hexaploid L. tridentata was noteworthy for exhibiting a strong climatic gradient and striking differences in soil texture (increased sand, decreased gravel). More generally, soil texture differed statistically between sites occupied by diploid, tetraploid, and hexaploid L. tridentata, albeit with considerable overlap across the geographic ranges of the three cytotypes. Taken together, our findings suggest that multiple factors affect the distribution of creosote bush chromosome races, including but not limited to ecological divergence.

Crop domestication facilitated rapid geographical expansion of a specialist pollinator, the squash bee Peponapis pruinosa.

Abstract The North American creosote bush (Larrea tridentata, Zygophyllaceae) is a widespread and ecologically dominant taxon of North American warm deserts. The species is comprised of diploid, tetraploid, and hexaploid populations, and touted as a classical example of an autopolyploid taxonomic complex. Here we use flow cytometry and DNA sequence data (non-coding cpDNA and nuclear ribosomal DNA) to evaluate spatial and evolutionary relationships among cytotype races, as well as the origins of the species from its South American ancestors. We find the geographic distribution of North American cytotypes to be highly structured, with limited co-occurrence within populations. Diploids reside only in the Chihuahuan Desert, as reported in previous biosystematic surveys, but tetraploid and hexaploid populations interdigitate along the margins of the Sonoran and Mojave Deserts. In phylogenetic analyses, North American plants comprise a monophyletic grouping that is sister to the South American diploid species, L. divaricata. North American populations exhibit genetic signatures of rapid demographic expansion, including a star-shaped genealogy, unimodal distribution of pairwise haplotype differences, and low genetic structure. Nonetheless, polyploid cytotypes are consistently distinguished from diploid cytotypes by a cpDNA indel character, suggesting a single origin of tetraploidy in the species. These findings suggest a recent origin of the North American creosote bush via long distance dispersal, with establishment of polyploid populations accompanying its rapid spread through the Northern Hemisphere.

Resource assurance predicts specialist and generalist bee activity in drought

Host breadth and global bee species diversity are thought to be linked. Areas where bee species richness is greatest have a greater proportion of oligolectic species and fewer social species. I compared the bee faunas of two North American regions (one mesic, one xeric) and two nearby habitats (riparian and desert scrub). Species richness is greater in the xeric than in the mesic North American region. Despite strongly bimodal bloom in the xeric region and continuous bloom in the mesic region, their bee faunas were similar in the proportion of solitary oligolectic and polylectic bees. Oligolectic species of both areas have short lifespans. Social and cleptoparasitic species made up a greater percentage of the fauna in the mesic North American region. Nearby mesic and xeric habitat both had social species but xeric habitats were richer in oligolectic species. Phylogeny and historical biogeography in combination with ecology of bees and plants will be needed to understand differences of bee faunas.ZusammenfassungDie meisten Tiergruppen haben ihre höchste Artendiversität in den Tropen. Bienen sind in diesem Zusammenhang ungewöhnlich, da sie ihren größten Artenreichtum in trocken gemäßigten Regionen haben. Etliche Hypothesen wurden aufgestellt, um diese nicht eingängige Verteilung zu erklären. Eine besagt, dass mehr spezialisierte Arten in Wüstenklimaten gefunden werden, wodurch mehr Arten miteinander koexistieren können. Eine andere geht davon aus, dass durch das Fehlen von sozialen Bienenarten Solitärbienen bessere Möglichkeiten zur Diversifizierung haben. Und schließlich könnten zwei Blühperioden es ermöglichen, dass auch zwei verschiedene Bienenfaunen ein und dasselbe Wüstenhabitat besiedeln.Ich habe einige Voraussagen dieser Hypothesen geprüft, indem ich die Bienenfauna zweier gut untersuchter Regionen in Nordamerika untersuchte (eine Region mit mittlerer Feuchtigkeit, eine trockene Region) und zwei Habitate innerhalb der trockenen Region (eine Uferzone mit mittlerem Feuchtigkeitsgrad und ein trockenes Wüstenbuschland-Habitat). Der Artenreichtum ist in den trockenen Gebieten höher als in der feuchten Region Nordamerikas und lediglich zwei Arten kommen in beiden Regionen vor. Trotz der ausgeprägten bimodalen Blüte in der Trockenregion und der kontinuierlichen Blüte in der feuchten Region zeigten die Bienenfaunen in beiden Regionen ähnliche Zusammensetzungen in Bezug auf Pollenspezialisten und Pollengeneralisten. Die Pollenspezialisten in beiden Gebieten haben eine kürzere Lebensdauer als die meisten anderen Bienenarten. Soziale und kleptoparasitische Arten waren stärker in der feuchteren nordamerikanischen Region vertreten. Ein Vergleich der Bienenfaunen in Parzellen mit aneinandergrenzenden mittelfeuchten und trockenen Flächen ergab für Pollenspezialisten einen höheren Artenreichtum in dem trockenen Buschland-Habitat.Ich schließe daraus, dass Daten zur Bienenphylogenie und historische Befunde zur Biogeographie in Verbindung mit Aspekten der Bienenökologie sowie die Verteilung der Wirtspflanzen zusammen beurteilt werden müssen, um globale und lokale Unterschiede der Bienenfaunen zu verstehen.