Phylogenetic relationships and host‐plant evolution within the basal clade of Halictidae (Hymenoptera, Apoidea)

Abstract

Bees are among the most important pollinators of angiosperm plants. Many bee species show narrow host-plant preferences, reflected both in behavioral and morphological adaptations to particular attributes of host-plant pollen or floral morphology. Whether bee host-plant associations reflect co-cladogenesis of bees and their host plants or host-switches to unrelated host plants is not clear. Rophitinae is a basal subfamily of Halictidae in which most species show narrow host-plant preferences (oligolecty). We reconstructed the phylogenetic relationships among the rophitine genera using a combination of adult morphology (24 characters) and DNA sequence data (EF-1a, LW rhodopsin, wingless; 2700 bp total). The data set was analyzed by parsimony, maximum likelihood and Bayesian methods. All methods yielded highly congruent results. Using the phylogeny, we investigated the pattern of host-plant association as well as the historical biogeography of Rophitinae. Our biogeographical analysis suggests a number of dispersal ⁄ vicariance events: (1) a basal split between North America and South America (most likely a dispersal from South America to North America), and (2) at least two subsequent interchanges between North America and Eurasia (presumably via the northern hemisphere land bridges). Our analysis of host-plant associations indicates that Rophitinae specialized on a closely related group of angiosperm orders in the Euasterid I clade (mainly Gentianales, Lamiales and Solanales). However, there is little evidence of cocladogenesis between bees and plants and strong evidence of host switches to unrelated host plants. Based on our phylogenetic results we describe two new tribes of Rophitinae: Conanthalictini new tribe (including the genus Conanthalictus) and Xeralictini new tribe (including Xeralictus and Protodufourea).Ó The Willi Hennig Society 2007.Bees constitute a monophyletic group of > 16 000 described species feeding exclusively on the pollen and nectar of flowers (Michener, 2000). Like many groups of herbivorous insects (Schoonhoven et al., 1998), they show enormous variation in host-plant breadth. Some species, such as Apis mellifera and Halictus ligatus, are widespread and visit many different host plants. Many other species show much narrower host-plant associations. These oligoleges (host-plant specialists) tend to restrict their pollen foraging to phylogenetically closely related host plants (within the same family, tribe, or genus) (Robertson, 1925;Cane and Sipes, 2006).Bee species restricted to a single host-plant species are rare, but some examples exist (e.g., Andrena florea on Bryonia dioica) (Cane et al., 1996;Cane and Sipes, 2006;Schlindwein and Medeiros, 2006).Oligolecty in bees appears to be driven by several factors and is most common in solitary bees with short life cycles. On the contrary, eusocial species tend to be polylectic. Resource abundance is likewise closely related with the evolution of host-plant specificity in bees. Abundant and widespread plants [e.g., Larrea (Zygophyllaceae); Min...

Phylogeny and host-plant evolution in Melittidaes.l.(Hymenoptera: Apoidea)

“…Most cases of host-plant variation involve shifts in the host-plant visited with little change in diet breadth. This pattern is consistent with previous studies on the evolution of host-plant associations in bees (Müller, 1996a;Sipes and Tepedino, 2005;Patiny et al, 2007;Larkin et al, 2008).…”

“…Host switches based on morphological similarity among host-plants has been demonstrated in some previous studies. For example, several genera within the subfamily Rophitinae (Halictidae) (Penapis, Protodufourea and Xeralictus; reviewed by Patiny et al, 2007), Diadasia (Apidae; Sipes and Wolf, 2001;Sipes and Tepedino, 2005) and Macrotera (Andrenidae; Danforth, 1996) present equivalent shifts to unrelated, but morphologically similar, host-plants.…”

“…Other oligolectic bee genera associated with multiple, unrelated plant families include Colletes (species group of C. succintus; Kuhlmann et al, 2007); Dufourea (Ebmer, 1984;Patiny et al, 2007), Micralictoides (Bohart and Griswold, 1987) and Rophites (Ebmer and Schwammberger, 1986). Note that the presence of closely-related bee species on distantly related host-plants could also be explained by extinction of bee lineages on intermediate host-plant families.…”

“…However, specialist bumblebees (Bombus consobrinus and B. gerstaeckeri; Ponchau et al, 2006) are known to forage exclusively on pollen of Aconitum sp. Specialist bees are particularly common in some lineages, such as Andrenidae, non-social Apinae, Lithurgini, Melittidae s.l., Paracolletini and Rophitinae (Linsley, 1958;Wcislo and Cane, 1996;Michener, 2000;Patiny et al, 2007;Larkin et al, 2008).…”

Bee-flower association in the Neotropics: implications to bee conservation and plant pollination

“…According to the current theoretical framework, such generalist species are important to maintain the cohesion and stability of plant-bee networks (Memmott et al 2004). On the other hand, relationships between plants and bees may exhibit phylogenetic components that drive the preferences of a group of bees to a given group of plants (Müller 1996;Patiny et al 2008). Thus, certain bee taxa preferentially visit certain plant families or genera.…”