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5800 m in the Himalayas (Williams, 1985). Thus, bumble bees exploit a wide diversity of habitats, from alpine meadows to lowland tropical forest (Sakagami, 1976). Nonetheless, they appear similar in morphology throughout their range (Michener, 1990;

Williams, 1998), suggesting that ecological opportunity and behavioural adaptations play an important role in col- onizing diverse habitats (Sakagami, 1976;

Cameron &

Whit?eld, 1996;

Dornhaus &

Cameron, 2003;

Dorn- haus &

Chittka, 2004). For example, temperate spe- cies initiate colonies annually from a single queen, whereas the tropical species appear at least faculta- tively perennial (Sakagami, Akahira &

Zucchi, 1967;

Olesen, 1989) and even exhibit polygyny (Zucchi, 1973;

Cameron &

Jost, 1998).

162 S. A. CAMERON ET AL. ?

2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 91, 161C188 Despite the apparent constraint on structural diver- sity, bumble bees display striking inter- and intraspe- ci?c variation in colour pattern across their range (Sladen, 1912;

Skorikov, 1931;

Reinig, 1935, 1939;

Tkalc , 1968, 1974, 1989;

Williams, 1991, 1998), pur- portedly the outcome of mimetic evolution (Plowright &

Owen, 1980). Not only are Bombus predisposed to converge sympatrically on similar colour patterns (Williams, 2007), but other insects mimic the Bombus patterns (Evans &

Waldbauer, 1982), thus providing excellent opportunities to examine the in?uence of natural selection on the generation of variation among Müllerian (Plowright &

Owen, 1980) and Batesian (Waldbauer, Sternberg &

Maier, 1977;

Evans &

Wald- bauer, 1982) mimics. Elucidating the evolution of diversity requires knowledge of the historical pattern of variation, which, in turn, provides unique insights into evolutionary processes underlying the pattern of variation. A robust phylogeny of Bombus, the goal of our research, is essential for inferring the history of their wide geographical distribution and for testing hypotheses of behavioural and mimetic adaptations. CLASSIFICATION AND CURRENT STATUS OF BOMBUS PHYLOGENY Bombus comprises the monotypic tribe Bombini, which together with Apini (honey bees), Meliponini (stingless bees), and Euglossini (orchid bees), consti- tutes the corbiculate bees, distinguished by the pollen- carrying structure (corbicula) on the hindleg. Their closest relatives, estimated from DNA sequences of multiple genes, are the stingless bees (Cameron, 1993, 2003;

Mardulyn &

Cameron, 1999;

Cameron &

Mardulyn, 2001, 2003;

Lockhart &

Cameron, 2001;

Thompson &

Oldroyd, 2004), although some morpho- logical data (Roig-Alsina &

Michener, 1993;

Schultz, Engel &

Ascher, 2001) place them as sister to honey bees + stingless bees. Subsequent to Linnaeus (1758), approximately

2800 formal names, including synonyms, have been assigned to Bombus species and lower-ranking taxa (Williams, 1998). Today, we recognize approximately

250 species (Williams, 1998) assigned to

38 subgenera, primarily on the basis of male genitalia (Radosz- kowski, 1884;

Krüger, 1917;

Skorikov, 1922;

Richards, 1968). Many of the subgenera are monotypic (Rich- ards, 1968;

Williams, 1998) as a result of the distinct- ness of the male genitalia. The in?ated number of species names was often the result of distinguishing species (and later, subspecies) by colour pattern. Numerous alternative classi?cations have been pro- posed (Milliron, 1961, 1971, 1973a, b;