Fig. 2.

Phylogeny and representatives of three basic designs of female reproductive tracts. Female diving beetles have “conduit”-type reproductive tracts: sperm enter and exit storage through different ducts. (A) Large spermatheca without a distinct spermathecal duct; G. liberus. (B) Clearly defined spermathecal duct, spermatheca, and fertilization duct; Rhantus binotatus. (C) Typically narrowed and lengthened spermathecal ducts and, in some species, the addition of a receptacle; Nebrioporus rotundatus. b, bursa; c, common oviduct; fd, fertilization duct; g, gland; r, receptacle; s, spermatheca; sd, spermathecal duct. Colored branches indicate in-group taxa (see Fig. S1 for branch support). Clade 1 (red) is characterized by species with paired sperm and large sperm-storage organs (type A). Clade 2 (blue) contains species with paired sperm or larger aggregate–type conjugates and type A or B female tracts. Clade 3 (yellow) is characterized by sperm that form rouleaux and type C tracts. Dashed lines indicate species where sperm do not conjugate and stars show species with sperm dimorphism. Out-group taxa are shown in black or gray. Gray is used where sperm data are missing.