Divergence and Reticulation among Montane Populations of a Jumping Spider ( Habronattus pugillis Griswold)

—Populations of the jumping spider Habronattus pugillis Griswold isolated on nearby mountain ranges in southern Arizona are differentiated in many features of the males (color, shape, and orientation of setae on face; shape of carapace; markings of palpi and legs; motions during courtship behavior). These features are (mostly) consistent within a range and different between ranges. The concentration of differences in male courtship behavior and body parts exposed to the female during courtship and correlations between form and courtship behavior suggest sexual selection was involved in the differentiation. A phylogenetic analysis of the populations yields a tree that for the most part groups geographic neighbors, but the history of H. pugillis populations may not be adequately described by a tree. Geographic proximity of apparent convergences suggests that populations from at least some of the mountain ranges acquired characteristics through introgression. Lowering of the woodland habitat during the last glacial period probably brought some populations into contact, but it is not clear whether the interrange woodlands would have provided corridors for extensive mixing. [Differentiation; geographic variation; homoplasy; hybridization; phylogeny; Salticidae; sexual selection; speciation; spiders. ] Phylogenetic diversications that occur rapidly and in small geographical areas may be particularly difcult to reconstruct. When phylogenetic branches are short (in time), not only might the novel characters evolving be too few to mark them, but also ancestral polymorphisms are more likely to be retained through several speciation events and then to sort to monomorphism variously in the descendants (Pamilo and Nei, 1988; Takahata, 1989). This sorting can generate character distributions that are discordant with one another and with the phylogenetic relationships of the species (Throckmorton, 1965; Arnold, 1981), leading to the “gene tree–species tree” problem (Avise et al., 1983; Pamilo and Nei, 1988; Doyle, 1992; Page, 1993; Maddison, 1997). Among closely related forms that are geographic neighbors, hybridization and introgression can also yield character discordance (Arnold, 1981; McDade, 1990, 1995; Reiseberg and Moreeld, 1995). Although discordant character distributions are usually interpreted to imply convergence or reversal, hybridization and retention of polymorphisms allow discordance to arise even when there is no convergence (i.e., when the instances of a character state are homologous to one another, for every state of every char1Author for correspondence. 2Present address: Department of Botany, Washington State University, Pullman, Washington 99164, USA. acter). The problem is that each character might have followed its own unique history of descent (de Queiroz et al., 1995). The availability of DNA sequence data has recently focused attention on the discordant character distributions that can result from hybridization (Reiseberg and Moreeld, 1995; Arnold, 1997) and the retention and sorting of ancestral polymorphisms (Avise et al., 1983; Pamilo and Nei, 1988; Takahata, 1989; Doyle, 1992). For genetic data, it is becoming well recognized that different characters may have followed different histories (Goodman et al., 1979; de Queiroz et al., 1995; Doolittle, 1999). Awareness of the phylogenetic complications of these processes is not new, however. Especially among botanical phylogeneticists, hybridization has long been a concern (Stebbins, 1950; Wagner, 1983; McDade, 1990, 1995). The phylogenetic patterns generated by retention and subsequent sorting of ancestral polymorphisms have been discussed for decades (Throckmorton, 1965; Farris, 1978; Felsenstein, 1979; Arnold, 1981) and are implicitly considered in the use of gene frequencies to reconstruct phylogeny (Cavalli-Sforza and Edwards, 1967). The concept of a gene phylogeny distinct from, and to some extent independent of, a species phylogeny is implicit in early work on polytene chromosome inversion phylogenies (Dobzhansky and Sturtevant, 1938). However, although these concerns are old,