Research Article |
Corresponding author: Andreas Müller ( andreas.mueller@usys.ethz.ch ) Academic editor: Jack Neff
© 2017 Andreas Müller, Volker Mauss, Rainer Prosi.
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:
Müller A, Mauss V, Prosi R (2017) Unique nest architecture in the North African osmiine bee Hoplitis (Hoplitis) mucida (Hymenoptera, Megachilidae). Journal of Hymenoptera Research 60: 99-109. https://doi.org/10.3897/jhr.60.20218
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The osmiine bee species Hoplitis mucida is considered to consist of two subspecies with H. mucida mucida (Dours, 1873) ranging from northwestern Africa to Israel and Jordan and H. mucida stecki (Frey-Gessner, 1908) occurring in southwestern Europe and Sicily. The discovery of nests of H. mucida in Morocco and Tunisia revealed striking differences in the nesting biology of the two subspecies. In North Africa, females construct fully exposed, cake-like nests of mud on the flat surface of rocks and stones containing 8–12 vertically oriented brood cells, rendering these nests unique among osmiine bees regarding both nesting site and nest architecture. In contrast, in Europe females build their few-celled mud nests inside small rock cavities. This discrepancy in the nesting biology is paralleled by considerable morphological differences between the two subspecies suggestive of a long geographical isolation. Due to these biological and morphological differences, we propose to elevate the European subspecies H. mucida stecki to species rank.
Apiformes , Echium , heat tolerance, Hoplitis adunca species group, labial glands
The osmiine bee species Hoplitis mucida (Dours, 1873) is a member of the large subgenus Hoplitis Klug, which comprises about 90 described and 50 undescribed species restricted to the Palaearctic region (
Hoplitis mucida is narrowly oligolectic, it exclusively collects pollen on flowers of Echium L. (Boraginaceae) throughout the entire species’ range (
In spring 2017, two nests of Hoplitis mucida were found in southern Morocco, which strongly differed from the nest discovered in Spain with respect to both nesting site and nest architecture. These two Moroccan nests were very similar to a nest of H. mucida found in northern Tunisia in spring 2012 indicating striking differences in the nesting biology between North African and European populations. This discrepancy in nesting behaviour is paralleled by morphological differences between populations of North Africa and the Levant on the one hand and European populations on the other hand (
In the present contribution, we describe the peculiar North African nests of Hoplitis mucida, reevaluate the morphological differences between non-European and European populations and - based on both nesting biology and morphology - propose to elevate the European subspecies H. mucida stecki to species rank.
Two nests of Hoplitis mucida were found in southern Morocco near Tlata Uonass about 4 km east of Ait Baha (30°03'42"N; 9°06'55"W) at an elevation of 610 m a.s.l. on 16 April 2017. One nest was already finalized, whereas the female of the second nest applied the last portions of mud onto its nest before she finally left the nesting site shortly after. As both nests adhered to large stones or rocks, which could not be transported back to the lab to let the bees emerge, the nests were opened with a knife to ascertain the number and arrangement of the brood cells. An additional nest of H. mucida was discovered in northern Tunisia near Sidi Mtir about 17 km southwest of El Kef (36°03'16"N; 8°36'26"E) at an elevation of 510 m a.s.l. on 28 April 2012. This nest was initially attributed to an unknown species of Megachile (Chalicodoma) but later turned out to belong to H. mucida based on the bees that emerged in the lab.
To exclude the possibility that the discrepancy in the nesting behaviour between North African and European populations of Hoplitis mucida is simply due to a misidentification, the correct determination of the female that had constructed the nest discovered in southern Spain (
To find new and reevaluate already published morphological differences (
The three nests of Hoplitis mucida found in Morocco and Tunisia had been constructed freely on horizontal to slightly sloping and almost flat surfaces of stones and rocks (Table
Characteristics of three nests of Hoplitis mucida (
Nest 1 | Nest 2 | Nest 3 | |
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(Figs |
(Figs |
(Fig. |
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Locality | near Ait Baha in southern Morocco | near Ait Baha in southern Morocco | near El Kef in northern Tunisia |
Nest substrate | middle-sized stone (28 cm × 18 cm) partly buried in the ground | rock | small stone (16 cm × 7 cm) partly buried in the ground |
Maximal length × maximal width of nest | 6.2 cm × 5.1 cm | 4.5 cm × 4 cm | 5.4 cm × 4.8 cm |
Maximal height of nest | 2.0 cm | 1.9 cm | 1.7 cm |
Sides of nest | concave | concave | convex |
Number of brood cells | 12 | 8 | 11 |
Nests of Hoplitis mucida (see Table
The three nests were all of roundish to oval shape measuring 4.5–6.2 cm in maximal length, 4.0–5.1 cm in maximal width and 1.7–2.0 cm in maximal height (Table
The nests contained 8–12 brood cells, which had been built side by side (Table
The examination of specimens of Hoplitis mucida collected throughout the species’ distribution area revealed distinct morphological differences in both sexes between individuals from North Africa and the Levant on the one hand and individuals from southwestern Europe and Sicily on the other hand (Table
Biological and morphological differences between Hoplitis mucida (Dours, 1873) and H. stecki (Frey-Gessner, 1908).
Hoplitis mucida | Hoplitis stecki | |
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Distribution | Maghreb (Morocco, Algeria, Tunisia) and Levant (Israel and Palestine, Jordan) | southwestern Europe (Iberian Peninsula, southern France, northern Italy, southern Switzerland) and Sicily |
Nesting biology | free-standing, cake-like nests constructed from mud on horizontal and flat surfaces of stones and rocks containing 8-12 brood cells | hidden nests built in small cavities of rocks containing one to possibly few brood cells constructed from mud ( |
Male characters | antennal segments 6–12 slightly shorter than wide (Fig. |
antennal segments 6–12 slightly longer than wide (Fig. |
distance between lateral ocellus and preoccipital ridge 1.5–1.65× as long as ocellar diameter | distance between lateral ocellus and preoccipital ridge 1.8–2× as long as ocellar diameter | |
pilosity of tergal discs less strongly developed, on apical half of discs 3–5 distinctly shorter than on basal half | pilosity of tergal discs more strongly developed, on apical half of discs 3–5 about as long as on basal half | |
apical rectangular plate of tergum 7 almost as long as wide (Fig. |
apical rectangular plate of tergum 7 distinctly wider than long (Fig. |
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transversal subapical swellings of sterna 2–4 more strongly developed | transversal subapical swellings of sterna 2–4 less strongly developed | |
lateral lobes of membraneous appendage of sternum 6 narrower and less diverging, separated from each other by a shorter incision and densely covered with yellowish-white pilosity (Fig. |
lateral lobes of membraneous appendage of sternum 6 wider and more diverging, separated from each other by a deeper incision and densely covered with yellowish-brown pilosity (Fig. |
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apex of gonostylus and outer margin of penis valve with distinctly longer hairs (Fig. |
apex of gonostylus and outer margin of penis valve with distinctly shorter hairs (Fig. |
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penis valve more or less parallel-sided except for its apicalmost part and apically more rounded (Fig. |
penis valve tapering towards its apex and apically more acute (Fig. |
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Female characters | distance between lateral ocellus and preoccipital ridge 1.5–1.6× as long as ocellar diameter (Fig. |
distance between lateral ocellus and preoccipital ridge 1.8–1.9x as long as ocellar diameter (Fig. |
pilosity of tergal discs shorter, on discs 3–4 less than 1.5× as long as maximal width of antennal flagellum (Fig. |
pilosity of tergal discs longer, on discs 3–4 about 2× as long as maximal width of antennal flagellum (Fig. |
Among bees, exposed nests constructed from mud and glued to the surface of stones and rocks are known only from a few taxa of megachiline and osmiine bees. Free-standing mud nests occur in numerous Megachile species of the subgenus Chalicodoma(
The nests of Hoplitis mucida were found to be extremely hard and it proved to be impossible to perforate their walls even with a strong knife. They are thus similary hard as the exposed mud nests of Megachile (Chalicodoma) species. The hardness of Megachile (Chalicodoma) nests is most probably due to the mixing of mud with secretions of the labial glands, which harden the mud and render the nests hydrophobic protecting them against the erosive effects of rain (
The two nesting sites of Hoplitis mucida in southern Morocco and northern Tunisia are exposed to average maximum daily air temperatures during July and August of more than 30°C and 40°C, respectively (https://de.climate-data.org), resulting in ground temperatures that may regularly reach far beyond 50°C during the day (
Some members of the Hoplitis adunca species group known to build exposed mud nests at the surface of rocks and stones, such as Hoplitis anthocopoides, H. benoisti, H. loti or H. ravouxi, occasionally also nest in small holes and fissures, where their brood cells are more or less hidden (
The morphological analysis revealed a distinct morphological gap between non-European and European populations of Hoplitis mucida, but morphological uniformity among specimens distributed in the Maghreb and the Levant. This finding indicates that North African and southwestern European populations were geographically and genetically isolated for a long time and suggests that the separation of the populations of the Maghreb from those of the Levant is a rather recent event, possibly taking place at the end of the greening period of the Sahara about 6000 years before present (
European populations of Hoplitis mucida substantially differ from North African populations in nesting site, nest architecture and morphology. These differences justify the recognition of the European populations as a biological species of its own. Thus, we propose to elevate the European subspecies H. mucida stecki to species rank, i.e. H. stecki (Frey-Gessner, 1908), stat. n.
C. Praz and C. Sedivy participated in an excursion to Tunisia in 2012. C. Praz bred the nest of H. mucida discovered in Tunisia in the lab. G. Le Goff provided the voucher female of the nest he found in Spain. H. Baur (Naturhistorisches Museum Bern) provided access to a digital imaging system for taking photomicrographs. Comments by V. Gonzalez, C. Praz, C. Rasmussen and J. Neff substantially improved the manuscript.