Anthophora Latreille 1803

Anthophora subgenus Micranthophora Cockerell, 1906 Types species: Anthophora curta Provancher, 1895 (original designation) Diagnosis. The Anthophora (Micranthophora) are separable from the other Western Hemisphere subgenera by the following combination of characters: both sexes with maximum body length ~ 12 mm, usually 10 mm or smaller. T2–T4 always with at least some appressed setae, either covering terga or forming apical bands, these setae highlybranched (similar to pipe cleaners) and flatly appressed on terga (though mostly absent in male A. cockerelli; Fig. 54E). Hindleg without distinct integumental projections or spikes along anterior margin or at apex. Females with light facial maculations present (rarely absent in A. columbariae, A. phenax, A. salazariae, and A. striata). Scopa with only simple setae along posterior margin (except in A. hololeuca). Male labrum most often tridentate along rim (Fig. 49B), though rounded in some species (Fig. 49A). F1 at most as long as next 2.5 flagellomeres, more often equal to roughly next 2 flagellomeres. T7 often with lateral, gradular projections in addition to medial projection(s) (Figs. 59–63). Overall, in comparison to most other groups, they appear more compact, with broad heads, in part due to their large compound eyes, and a relatively flat frons. This compactness is further emphasized by the fact that their metasomas are only moderately longer than their mesosomas (most often true in females). Distribution. The 26 species of A. (Micranthophora), as defined here, are entirely restricted to the Western Hemisphere (Fig. 1). No records of this group are known farther east than North Dakota, farther north than Canada’s southern border provinces, or farther south than Nicaragua (Brooks 1988; Erenler et al. 2016). In terms of species per state, California clearly has the most (22 species), with high richness in Nevada (17) and Arizona (16), as well as Baja California (13), but significantly fewer farther from the arid Mojave and Sonoran Deserts (Fig. 4). Species richness is highly diminished at these limits, usually reduced to 1–4 species from their maximum species richness of 21 and 19, found in the Mojave and Sonoran Deserts ecoregions, respectively (Fig. 5; Table 2). This appears to be a consequence of this group’s general preference for xeric areas. The ecoregional distribution of specimens also strongly suggests that they prefer arid areas; the five ecoregions with the highest sampling effort (>1000 specimen records) are: Colorado Plateau shrublands, Mojave Desert, Sonoran Desert, Great Basin shrub steppe, and Chihuahuan Desert (Fig. 5). Interestingly, there are only five species found at low elevation in the Chihuahuan Desert, suggesting that a hot desert environment isn’t the only factor influencing the distribution of their species richness. There are also multiple species that seem better suited to mesic or even montane environments (usually at higher elevation in hotter regions), these detailed further in their respective species accounts and the conservation implications section of the discussion: A. albata, A. erythrothorax, A. exigua, A. flavocincta, A. maculifrons, A. peritomae, A. rhodothorax, and A. squammulosa. The species with the most unique distribution is the Mesoamerican A. squammulosa, which is present from Central Mexico into Nicaragua, south of the ranges of other A. (Micranthophora) (Orr et al. 2014). Floral biology. Almost all species of A. (Micranthophora) appear to be floral specialists to some degree, though the group uses numerous families overall. In total, species of A. (Micranthophora) specialize in pollen use on the following plant families: Asteraceae, Boraginaceae, Capparaceae, Cleomaceae, Fabaceae, Lamiaceae, Nyctaginaceae, likely Zygophyllaceae, and possibly Solanaceae. The only plausibly generalist species, each still with strong preferences, are: A. albata, A. caudata, and A. flavocincta (less likely than the other two). Alternatively, two of these species and two additional ones may be eclectic specialists, using disparate hosts exclusively in the sense of Cane & Sipes (2006): A. albata (Asteraceae and Cleomaceae), A. flavocincta (Boraginaceae and Asteraceae), A. phenax (Boraginaceae and Solanaceae), and A. striata (Zygophyllaceae and Asteraceae). Additional potential generalists include A. curta and A. petrophila, as both have been collected visiting many floral hosts, but they are primarily collected on Asteraceae (>80% of all female records) and have previously been suggested as Asteraceae specialists (Moldenke & Neff 1974). Interestingly, the majority of A. (Micranthophora) species appear to be specialized on Asteraceae (~17 species, 65%), some of which are quite selective in their hosts. For instance, among these Asteraceae specialists, A. mortuaria appears to be monolectic on Pluchea sericea and A. pachyodonta overwhelmingly visits Bebbia juncea, which several additional species likely also specialize on. Although more extensive pollen analyses will be necessary to confirm the diet breadth of some species, morphological identification of pollen below the family level may prove difficult due to the prevalence of Asteraceae specialists and the difficulty of identifying pollen from this family to lower taxonomic levels. Nesting biology. Nesting behavior has only been published for four of the 26 species of A. (Micranthophora), but these reports reveal high variation both between and within species (Hicks 1934 for A. curta; Torchio & Youssef 1968 for A. albata; Torchio 1971 and Orr et al. 2016 for A. peritomae; and Erenler et al. 2016 for A. squammulosa). Nests may be constructed with or without lateral tunnels, most often without, and either single or serial nest cells may be built within. Although most species appear to be fully solitary, it should be noted that A. peritomae has been reported as communal, with multiple females using the same entrance (Torchio 1971). This may be a consequence of the species’ use of sandstone, a much harder substrate than is typically used; communal behavior may have been selected for via reduced excavation costs through shared effort. In aggregate, these four species are known to nest horizontally in natural desert pavement (A. curta); horizontal, loose sand (A. albata), vertical, hard-packed sand banks (A. peritomae); vertical sandstone banks (A. albata, A. peritomae); and horizontal volcanic ash and tephra (A. squammulosa). At present, A. albata appears the most plastic in substrate use, reported using both horizontal loose sand and vertical sandstone. This is based on only two records for this species, however, and more work is necessary to fully understand the nesting plasticity of this group. Comments. Although this paper formally reverts all species of Western Hemisphere A. (Heliophila) to A. (Micranthophora), many of which were included in the phylogeny, additional sampling will be necessary to confirm whether any unexamined Eastern Hemisphere A. (Heliophila) also belong in A. (Micranthophora).

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