Research Article |
Corresponding author: Tamires de Oliveira Andrade ( tamiresdeoliveirandrade@gmail.com ) Academic editor: Christopher K. Starr
© 2022 Tamires de Oliveira Andrade, Kelli dos Santos Ramos, Margarita M. López-Uribe, Michael G. Branstetter, Carlos Roberto F. Brandão.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Andrade TO, Ramos KS, López-Uribe MM, Branstetter MG, Brandão CRF (2022) Integrative approach resolves the taxonomy of Eulaema cingulata (Hymenoptera, Apidae), an important pollinator in the Neotropics. Journal of Hymenoptera Research 94: 247-269. https://doi.org/10.3897/jhr.94.91001
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Species delimitation is a rich scientific field that often uses different sources of data to identify independently evolving lineages that might be recognized as species. Here, we use an integrative approach based on morphometrics, COI-barcoding, and phylogenomics using ultraconserved elements (UCEs) to investigate whether the orchid bee species Eulaema cingulata (Fabricius, 1804) and E. pseudocingulata Oliveira, 2006 represent a single variable taxon or two different species. We analyzed 126 specimens across the geographical range of these nominal species to test species hypotheses using the general lineage concept. We found substantial overlap in wing and head morphometrics, and both taxa form one phylogenetic lineage based on COI mitochondrial and UCE data. Our results support the recognition of both forms as members of the same evolutionary unit and E. pseudocingulata is herein recognized as a junior synonym of E. cingulata.
DNA barcoding, morphometrics, orchid bees, phylogenomics, species delimitation, synonymy, ultraconserved elements
Accurate species diagnosis remains a major challenge for many groups of organisms and is often described as the “taxonomic bottleneck” (
In order to circumvent some of the limitations of taxonomic classifications exclusively based on discrete qualitatively morphological characters, integrative taxonomy incorporates evidence from multiple independent datasets such as geometric morphometrics and molecular markers to inform species recognition and species boundaries (
Orchid bees (Hymenoptera: Apidae: Euglossini) are endemic to the Neotropical region. They receive their common name because males of these bees actively collect volatile compounds from orchids, and in the process pollinate the flowers (Dressler 1982). A variety of social behaviors are found among the euglossine genera, from solitary behavior to relatively complex social interactions in some species (
Eulaema (Apeulaema) cingulata (Fabricius, 1804) has a widespread distribution (from southern Brazil to southern Mexico), where it is associated mainly with wet and dry forested areas (Fig.
A, B male specimen of Eulaema cingulata from Sergipe, Brazil A body in dorsal view B velvety area in the mid tibia C geographical distribution of E. cingulata in green D, E male specimen of E. pseudocingulata from Pará, Brazil D body in dorsal view E velvety area in the mid tibia F geographical distribution of E. pseudocingulata in green.
Eulaema cingulata was initially described as Centris cingulata with no information on the number and sex of the specimens studied. The only information about these specimens is their location as “America meridionalis” (according to
Despite the distinct differences in coloration and the velvety area of the mid-leg between males of E. cingulata and E. pseudocingulata, the taxonomic status of these nominal species has not been investigated with additional datasets. A comparative phylogeographic study of E. cingulata based on mitochondrial and nuclear markers revealed a lack of structure for E. cingulata throughout the whole range of the species (
We studied 107 specimens of E. cingulata and E. pseudocingulata from across their geographic ranges. Most of the specimens were collected in the Amazon forest where both species are sympatrically distributed (Fig.
For comparisons of the overall wing and head sizes between species, we extracted the centroid size and used a generalized Procrustes analysis to capture shape variables without the effects of orientation and position of the images. A regression analysis between size and shape was performed to quantify the effect of allometry. Afterwards, we removed this allometric effect to independently quantify shape variation. The resulting landmark configurations retained only shape information (
To visually compare all individuals in multivariate trait space, we used a Principal Component Analysis (PCA) using the relative Cartesian coordinates of each landmark after alignment. The shape difference between species were tested using a Discriminant Analysis followed by a leave-one-out cross-validation test (
We extracted total genomic DNA from the hind legs or thoracic muscles of specimens using Qiagen DNeasy Kit (Qiagen) with modifications to maximize DNA yield for dry specimens as incorporated in
We amplified sequences of the cytochrome oxidase I (COI) region using universal barcoding primers LCO (5’-GGTCAACAAATCATAAAGATATTGG-3’) and HCO (5’-TAAACTTCAGGGTGACCAAAAAATCA-3’) (
To include genome-wide markers in our dataset, we sequenced 2,180 Ultra Conserved Element (UCE) loci using a recently published bait set specific to bees, ants, and other apoid wasps (“hym-v2-bee-ant-specific”;
We amplified libraries for 12 cycles, purified them using speedbeads (
For the molecular analyses, we generated DNA sequences from 19 males (less than 10 years old after collection) for the amplification of COI and UCEs. We preserved remaining body parts and associated DNA extractions for future studies (Suppl. material
For the mitochondrial data, we aligned COI sequences using the multiple sequence alignment online tool MAFFT (
For the UCE dataset, we performed most data processing steps using the software package Phyluce (
For phylogenetic reconstruction using UCE data, we inferred phylogenetic trees using Maximum Likelihood (ML), and multi-species coalescence reconstruction . We performed maximum likelihood analyses using two different strategies: single concatenated alignment and partitioned based on the best-fitting partitioning scheme. For the concatenated alignment, we obtained the substitution model (TVM+F+R2) using ModelFinder (
We also estimated a coalescent-based species tree using *Beast (
The raw UCE sequence reads have been uploaded to the NCBI Sequence Read Archive under BioProject accession PRJNA875942.
Individuals identified as E. cingulata and E. pseudocingulata formed one cluster based on the shape of the head and wings (Fig.
Cross-validated classification rates of correct group assignments between male specimens of Eulaema cingulata and Eulaema pseudocingulata based on head and wing shapes.
Head | ||||
---|---|---|---|---|
E. cingulata | E. pseudocingulata | Total | % | |
E. cingulata | 18 | 11 | 29 | 62.07 |
E. pseudocingulata | 10 | 20 | 30 | 66.67 |
Wing | ||||
E. cingulata | 33 | 17 | 50 | 66 |
E. pseudocingulata | 16 | 34 | 50 | 68 |
Shape variation of males of Eulaema species grouped considering A the shape of the head, and B the shape of the wings: The percentage explained by each Principal Components (PC) is in parenthesis. The negative and positive extremes of both PC1 and PC2 are shown below and besides of the graph (Factor scale: left -0.03, right 0.03).
The 655 bp fragment of the mitochondrial COI region resulted in an average pairwise genetic p-distance within E. cingulata of 1.3% and within E. pseudocingulata of 0.7%, while between the two species was 0.9%. The greater amount of genetic differentiation within the group of E. cingulata than between specimens from the two nominal species indicated no support for the presence of two evolutionarily independent units. The average pairwise genetic distances among E. cingulata and the outgroups (Eulaema mocsaryi, E. nigrita, and E. meriana) are greater than 5.6% (Table
Average pairwise genetic p-distance between species of Eulaema employing COI sequences with 655pb aligned.
Species | Eulaema cingulata | Eulaema pseudocingulata |
---|---|---|
Eulaema cingulata | 1.3%* | 0.9% |
Eulaema pseudocingulata | 0.9% | 0.7%* |
Eulaema mocsaryi | 5.6% | 5.3% |
Eulaema nigrita | 9.3% | 9.0% |
Eulaema meriana | 11.2% | 11.3% |
Both the COI and UCE phylogenetic reconstructions provided no support for the species differentiation of E. cingulata and E. pseudocingulata (Figs
Phylogenetic trees for Eulaema cingulata and E. pseudocingulata obtained with Ultraconserved Elements (UCE) A maximum likelihood phylogenetic tree obtained with concatenated dataset in IQ -Tree. Numbers on nodes correspond to ultrafast bootstrap B maximum likelihood phylogenetic tree obtained with partitioned dataset in IQ -Tree. Numbers on nodes correspond to ultrafast bootstrap C species delimitation analyses based on multispecies-coalescent model obtained with ASTRAL. Number on nodes corresponds to posterior probabilities D map showing the distribution of the analyzed material (ingroup).
The maximum likelihood inference of the UCEs markers recovered identical topologies from both partitioned and concatenated schemes, with most nodes showing high support (Fig.
Our results indicate that specimens identified as E. cingulata and E. pseudocingulata do not show morphological or genetic differentiation. Geometric morphometrics of the forewings has been previously used as a powerful technique to discriminate bee species (
Because the level of morphological differentiation among recently divergent lineages is sometimes insufficient to recognize species, we used mitochondrial and UCE data to test the presence of genetically distinct groups of individuals among the specimens studied. DNA barcodes are increasingly becoming a standard tool used by taxonomists and its association with morphological characters has proven useful at discriminating species in several groups of bees (
The topology obtained with genomic data also supports the monophyly and recognition of one clade that comprises E. cingulata and E. pseudocingulata. UCEs have been successfully used as a tool for species discrimination as they provide sufficient variation at shallow time scales (
Herein, we conclude that E. pseudocingulata is not an independent evolutionary lineage from E. cingulata suggesting that the morphological differences observed in the velvety area of the mid-leg of males are a species polymorphism in E. cingulata. The difference in the shape of the mid tibia velvety area, proposed as the diagnostic character between the species, can be interpreted as a variable condition: it can be narrower and farther from the rear edge in some morphs occurring in the Amazon forest, or wider and closer to the rear edge in morphs occurring throughout the species distribution. Initially, the color of the abdomen was also proposed as a diagnostic character to differentiate E. cingulata and E. pseudocingulata, but a gradient can be observed in the two morphs, varying from a yellowish tone to orange (Fig.
The mechanisms responsible for maintaining the variation of the velvety area of the mid tibia in individuals of E. cingulata in the Amazon Forest remain unknown. However, a plausible explanation for the lack of differentiation in morphological and genetic markers is that there is an ongoing speciation process driven by sexual selection in the Amazonian population of E. cingulata. Such a rapid speciation process has been described in two sympatric Euglossa species from southern Mexico: E. viridissima and E. dilemma (
Centris cingulata
Fabricius 1804: 355. Lectotype female, ‘America meridionalis’ (probably Guyana according to
Eulaema cajennensis Lepeletier 1841: 14. Lectotype male, French Guiana, Cayenne.
Eulaema fasciata Lepeletier 1841: 12. Lectotype female, French Guiana, Cayenne.
Eulaema (Apeulaema) marcii
Eulaema (Apeulaema) pseudocingulata
We recognized the taxon present in the Amazon forest under the name E. pseudocingulata as a junior synonym of E. cingulata, in light of the morphometric and phylogenetic data presented here. E. cingulata includes individuals with velvety areas of the midtibia that vary in width of the smooth area near the posterior edge (Fig.
We tested the species hypothesis of Eulaema cingulata and E. pseudocingulata by integrating multiple independent datasets: geometric morphometrics, phylogenetics using mitochondrial DNA, and phylogenomics using ultraconserved elements. All results across methods were congruent, showing no separation between morphs previously recognized as different species. Our results also suggest that the morphology of the mid tibia of E. pseudocingulata, proposed as the diagnostic character between the morphs, appears as a variable condition in some individuals of E. cingulata from the Amazon basin. Besides the variation in the mid leg, there is also color variation across samples. The evolutionary drivers of this variability are currently unknown. In the interests of nomenclatural stability, we have designated E. pseudocingulata as a junior synonym of E. cingulata. Orchid bees are important pollinators in Neotropical forests, being widely used in environmental quality studies, and they have become a good model for evolutionary genetics studies. However, as shown here, there is still a need to improve knowledge of the alpha taxonomy of these important group of Neotropical pollinators. Integration of DNA sequence analyses with geometric morphometrics of heads and wings can more rigorously test species boundaries than traditional morphological assessments alone and can ultimately improve species descriptions and identification tools.
We thank the curators and technicians of the collections for the loan of bee specimens: Elder Morato (Universidade Federal do Acre), Beatriz Coelho and Orlando Silveira (Museu Paraense Emílio Goeldi), Márcio Oliveira (Instituto Nacional de Pesquisas da Amazônia), Fernando Silveira and José Eustáquio (Universidade Federal de Minas Gerais), Maria Cristina Gaglianone (Universidade Estadual do Norte Fluminense Darcy Ribeiro). We thank José Villavicencio (Museu de Zoologia da Universidade de São Paulo -
Integrative taxonomy of Eulaema cingulata
Data type: tables (ms word file)
Explanation note: tables: Voucher ID, locality data, and institutional repositories of the male specimens of Eulaema used in Geometric Morphometric analyses; Voucher ID, locality data, and institutional repositories of the specimens used both in COI and phylogenomic analyses; Results of the Principal Component Analysis (PCA) of head analysis with their respective percentage of variance; Results of the Principal Component Analysis (PCA) of wing analysis with their respective percentage of variance.