A window on remarkable cryptic diversity of the Merodon planifacies subgroup (Diptera: Syrphidae) in the Afrotropical Region

Abstract

The genus Merodon Meigen (Diptera: Syrphidae) is one of the most species-rich hoverfly genera distributed across the Palaearctic and Afrotropical regions. In the Palaearctic, the genus Merodon boasts 195 described species, while its Afrotropical region pales in comparison, with a mere 17 species documented thus far. As a result of 8 years of fieldwork conducted in the Republic of South Africa, in this paper, we present the description of 11 new species for science with a description of immature stages for 2 species, which increases the diversity of this genus in the Afrotropical region by remarkable 39%. These revelations are based on integrating morphology, molecular analysis (COI gene and 28S rRNA) and geometric morphometry. All described species belong to the Merodon planifacies subgroup, the Merodon desuturinus lineage and, within that, to the Afrotropical Merodon melanocerus group. Additionally, we provide an illustrated key to 15 species belonging to the subgroup, a detailed discussion on relevant taxonomic characters, a morphological diagnosis, a distribution map and clarification of the association between M. capi complex and host plants from the genus Merwilla.

Keywords: integrative taxonomy; new species; new synonym; preimaginal stage; sub-Saharan Africa.

Graphical Abstract

Fig. 1.

Fieldwork; collecting larvae.

Fig. 2.

Merodon autumnalis sp. n. A) head, frontal view; B) metaleg, lateral view; C and D) head, dorsal view; A and C) male; D) female. Scale bar A), C), and D) = 0.5 mm, B) = 1.5 mm.

Fig. 3.

Face of male, lateral view. A) Merodon autumnalis sp. n.; B) M. herbaceus sp. n.; C) M. jugosus sp. n.; D) M. maritimus sp. n.; E) M. natalensis sp. n.; F) M. paulodumus sp. n.; G) M. planifacies; H) M. pratum sp. n.; I) M. stevensoni; J) M. tenebrosus sp. n. Scale bar = 1 mm.

Fig. 4.

Male genitalia of Merodon maritimus sp. n. A) epandrium, lateral view; B) epandrium, ventral view; C) hypandrium, lateral view; Abbreviations: al, anterior surstylar lobe; c, cercus; ea, ejaculatory apodeme; p, aedeagus; pl, posterior surstylar lobe; s, lateral sclerite of aedeagus. Scale bar = 0.5 mm.

Fig. 5.

Antenna of male, lateral view. A) Merodon natalensis sp. n.; B) M. herbaceus sp. n.; C) M. autumnalis sp. n.; Scale bar = 1 mm.

Fig. 6.

Male genitalia of Merodon autumnalis sp. n. A) epandrium, lateral view; B) epandrium, ventral view; C) hypandrium, lateral view; Scale bar = 0.5 mm.

Fig. 7.

Antenna of female, lateral view. A) Merodon autumnalis sp. n.; B) M. levis sp. n., C) M. natalensis sp. n.; D) M. roni. Scale bar = 1 mm.

Fig. 8.

ML trees of Merodon planifacies subgroup based on A) COI gene sequence analysis and B) concatenated dataset comprising COI and 28S rRNA genes. Bootstrap values ≥ 50 are presented near nodes.

Fig. 9.

Strict consensus MP trees based on A) COI gene sequence analysis and B) concatenated dataset comprising COI and 28S rRNA genes of Merodon planifacies subgroup. Filled circles stand for unique changes, and open circles stand for nonunique changes.

Fig. 10.

Distribution map of the species from the Merodon planifacies subgroup (except species from M. capi complex presented in Fig. 53). Scale bar = 1,500 km.

Fig. 11.

Habitat of Merodon autumnalis sp. n.

Fig. 12.

Merodon herbaceus sp. n. male. A) head, frontal view, scale bar = 0.5 mm; B) metaleg, lateral view, scale bar = 1 mm; C) head, dorsal view, scale bar = 0.5 mm.

Fig. 13.

Male genitalia of Merodon herbaceus sp. n. A) epandrium, lateral view; B) epandrium, ventral view; C) hypandrium, lateral view. Scale bar = 0.5 mm.

Fig. 14.

Merodon jugosus sp. n., male. A) head, frontal view, scale bar = 0.5 mm; B) metaleg, lateral view, scale bar = 1 mm; C) apical part of metatibia, lateral view, scale bar = 0.5 mm.

Fig. 15.

Male genitalia of Merodon jugosus sp. n. A) epandrium, lateral view; B) epandrium, ventral view; C) hypandrium, lateral view. Scale bar = 0.5 mm.

Fig. 16.

Merodon maritimus sp. n., male. A) head, frontal view, scale bar = 0.5 mm; B) metaleg, lateral view, scale bar = 1 mm.

Fig. 17.

Antenna of male, lateral view. A) Merodon stevensoni sp. n.; B) M. maritimus sp. n.; C) M. tenebrosus sp. n.; Scale bar = 0.5 mm.

Fig. 18.

Merodon natalensis sp. n. A) head, frontal view, scale bar = 0.5 mm; B) metaleg, lateral view, scale bar = 1 mm; C) head, frontal view, scale bar = 0.5 mm; D) metatibia, lateral view, scale bar = 1 mm; A), B), and D), male; C), female.

Fig. 19.

Male genitalia of Merodon natalensis sp. n. A) epandrium, lateral view; B) posterior surstylar lobe, lateral view; C) epandrium, ventral view; D) hypandrium, lateral view. Scale bar = 0.5 mm.

Fig. 20.

Habitat of Merodon natalensis sp. n. A) Sunday Falls; B) Mount Currie; C and D) Coleford Nature Reserve.

Fig. 21.

Merodon paulodumus sp. n. A and C) head, frontal view, scale bar = 0.5 mm; B and D) metaleg, lateral view, scale bar = 1 mm; A) and B) male; C) and D) female.

Fig. 22.

Antenna of male, lateral view. A) Merodon planifacies; B) M. pratum sp. n.; C) M. paulodumus sp. n.; Scale bar = 0.5 mm.

Fig. 23.

Male genitalia of Merodon paulodumus sp. n. A) epandrium, lateral view; B) epandrium, ventral view; C) hypandrium, lateral view; Scale bar = 0.5 mm.

Fig. 24.

Merodon paulodumus sp. n. A) habitat; B and C) Ledebouria sp.

Fig. 25.

Merodon planifacies, male. A) head, frontal view, scale bar = 0.5 mm; B) head, lateral view, scale bar = 0.5 mm; C) metaleg, lateral view, scale bar = 1 mm.

Fig. 26.

Male genitalia, epandrium. A, B, and E) Merodon capi; C and D) M. planifacies; A, B, and C) lateral view; D and E) ventral view; Scale bar = 0.2 mm.

Fig. 27.

Male genitalia, hypandrium. A, B and, D) M. capi; C) M. planifacies; A, B, and C) lateral view; D) anterior view. Scale bar = 0.2 mm.

Fig. 28.

Habitat of Merodon planifacies. A and B) Van Reenen.

Fig. 29.

Merodon pratum sp. n., male. A) head, frontal view; B) metaleg, lateral view; Scale bar = 1 mm.

Fig. 30.

Male genitalia of Merodon pratum sp. n. A) epandrium, lateral view; B) posterior surstylar lobe, lateral view; C) epandrium, ventral view; D) hypandrium, lateral view; Scale bar = 0.5 mm.

Fig. 31.

Habitat of Merodon pratum sp. n.

Fig. 32.

Merodon stevensoni, male. A) head, frontal view; B) metaleg, lateral view, scale bars = 1 mm; C) metatibia, dorsolateral view, scale bar = 0.5 mm.

Fig. 33.

Male genitalia of Merodon stevensoni. A) epandrium, lateral view; B) epandrium, ventral view; C) hypandrium, lateral view; Scale bar = 1 mm.

Fig. 34.

Merodon stevensoni, female. A) antenna, lateral view; B) head, dorsal view; C) thorax, dorsal view; D) thorax, lateral view; E) apex of abdomen, dorsal view; F) metaleg, lateral view; G) body, lateral view; Scale bars A = 2 mm, B), D), and F) = 1 mm, C), E), and G) = 1.5 mm.

Fig. 35.

Merodon tenebrosus sp. n. male. A) head, frontal view; B) metaleg, lateral view; Scale bar = 1 mm.

Fig. 36.

Male genitalia of Merodon tenebrosus sp. n. A) epandrium, lateral view; B) epandrium, ventral view; C) hypandrium, lateral view; Scale bar = 0.5 mm.

Fig. 37.

Head of male, lateral view. A) Merodon capi; B) M. levis sp. n.; C) M. planus sp. n.; D) M. roni; E) M. reenensis sp. n.; F) M. melanocerus; Scale bar = 1 mm.

Fig. 38.

Antenna of male, lateral view. A) Merodon roni; B) M. capi; C) M. reenensis sp. n.; D) M. levis sp. n.; E) M. planus sp. n.; Scale bar = 1 mm.

Fig. 39.

Merodon capi, male. A) head, frontal view, scale bar = 0.5 mm; B) metaleg, lateral view, scale bar = 1 mm.

Fig. 40.

Habitat of Merodon capi. A and B) Cathedral Peak; C) habitat of Merwilla plumbea; D) flower of Merwilla plumbea.

Fig. 41.

Merodon levis sp. n., male. A) head, frontal view, scale bar = 0.5 mm; B) metaleg, lateral view, scale bar = 1 mm.

Fig. 42.

Male genitalia of Merodon levis sp. n. A) epandrium, lateral view; B) epandrium, ventral view; C) hypandrium, lateral view; Scale bar = 0.5 mm.

Fig. 43.

Habitat of Merodon levis sp. n. A, B, and C) Cynthia Letty Nature reserve; D) Merwilla sp.

Fig. 44.

Merodon planus sp. n., male. A) head, frontal view; B) metaleg, lateral view, scale bars = 1 mm; C) metatibia, lateral view, scale bar = 0.5 mm.

Fig. 45.

Male genitalia of Merodon planus sp. n. A) epandrium, lateral view; B) epandrium, ventral view; C) anterior part of the theca of the hypandrium, lateral view; D) aedeagus, lateral view; Scale bar = 0.5 mm.

Fig. 46.

Habitat of Merodon planus sp. n. A) a lowland habitat in KwaZulu-Natal; B) Merwilla plumbea.

Fig. 47.

Merodon reenensis sp. n., male. A) head, frontal view, scale bar = 1 mm; B) metaleg, lateral view, scale bar = 0.75 mm; C) metatarsus, dorsal view; D) metatibia, lateral view, scale bars = 0.5 mm.

Fig. 48.

Male genitalia of Merodon reenensis sp. n. A) epandrium, lateral view; B) epandrium, ventral view; C) hypandrium, lateral view; Scale bar = 0.5 mm.

Fig. 49.

Habitat of Merodon reenensis sp. n. A) Van Reenen; B and C) bulb of Merwilla plumbea; D) flower of Merwilla plumbea.

Fig. 50.

Merodon roni, male. A) head, frontal view, scale bar = 0.5 mm; B) metaleg, lateral view, scale bar = 1 mm.

Fig. 51.

Distribution map of the species from Merodon capi complex.

Fig. 52.

Habitat of Merodon roni, Royal Natal National Park.

Fig. 53.

Merwilla plumbea in the type locality of M. roni.

Fig. 54.

Immature stage. A and B) third-instar larvae, dorsal view, scale bar = 2 mm; C and D) Head skeletons, lateral view, scale bar = 250 µm; A and C) Merodon levis sp. n.; B and D) M. reenensis sp. n. Abbreviations: arp, anterior respiratory process; dc, dorsal cornu; m, mouthhooks; prp, posterior respiratory process; vc, ventral cornu.

Fig. 55.

Immature stage. A and B) anterior respiratory process, scale bar = 100 µm; C, D, E, and F) posterior respiratory process; A, C, and E) Merodon levis sp. n.; B, D, and F) M. reenensis sp. n.; C and D) dorsal view, scale bar = 500 µm; E and F) vertical view, scale bar = 250 µm.

Fig. 56.

Immature stage. A and B) puparium, dorsal view; C and D) third-instar larvae, anal segment, ventral view; A and C) Merodon levis sp. n.; B and D) M. reenensis sp. n. Abbreviations: Sn 6, sensilla 6; the dotted lines show the outline of the central lobe. A) Scale bar = 3.5 mm. B) Scale bar = 2.5 mm. C and D) Scale bar = 500 µm.

Fig. 57.

Immature stage. A and B) pupal spiracles, scale bar = 250 µm; C, D, and E) detail of spiracular tubercles; A, C, and E) Merodon levis sp. n.; B and D) M. reenensis sp. n. E) ventral view; C) and D) Scale bar = 100 µm; E) Scale bar = 200 µm.

Fig. 58.

Spiracular opening shape variability among Merodon capi, M. roni and M. reenensis sp. n. A) a scatter plot of individual scores of CV1 and CV2; B) UPGMA phenogram constructed using squared Mahalanobis distances.