Pyrgus communis and Pyrgus albescens (Hesperiidae: Pyrginae) are separate transcontinental species with variable but diagnostic valves

Since 1906, the question of whether Pyrgus albescens Plotz is a species distinct from Pyrgus communis (Grote) or only a subspedes (or mere form) of it, has arisen repeatedly with no real resolution. Although these differentiates are superficially inseparable, highly variable features of the valves (claspers) of the male genitalia distinguish them-provided the valval variation is properly analyzed. Most workers erroneously have seen this excessive variation as more or less continuous, taken the supposed in tergrades as evidence of interbreeding, and so considered the differentiates subspecies. Since 1963, I have critically compared the genitalia of 3060 males (1910 P communis and 11:50 P albescens) to determine not only their taxonomic rank but also their geographic distribution: P communis ranges from southern Canada through most of the United States to southern Mexico; P albescens , from the southern United States to southern Mexico. Long considered a southwestern differentiate (in the USA) ranging no farther east than the Corpus Christi area of Texas, P albescens actually extends eastward along the Gulf Coast to the Atlantic Coast of Florida and currently is expanding its eastern range. Narrowly sympatric in the eastern and fur western USA, these species are broadly sympatric in the southwestern USA and montane Mexico. Though more austral than P communis, P albescens flouts conventional wisdom by occurring high in various southwestern mountains. In Mexico, it extends from coast to coast and through the entire Baja California peninsula. The rampant, ostensibly continuous genitalic variation in mixed samples of these species is clearly bimodal. Compmison of genitalia throughout each species' range shows fully as much intraspeCific genitalic variation in areas removed from interspeCific contact as in areas of overlap. The variation is inherent in each species, not a result of hybridization. J develop these points with comparative figures of the genitalia of 484 males (253 P communis and 231 P albescens) from diverse situations. Pyrgus communis is slightly larger than P albescens in average size. Additional key words: genitalia, geographic disttibution, speciation , systematics, variation. Pyrgus communis (Grote 1872) and P albescens Plotz (1884) have a checkered history, These blackand-white skipper species (Figs . 1-8) were originally described more than once; they were variously referred to different genera (Hesperia, Pyrgus , Syrichtus, Urbanus); and names applied to related, Similar-appearing species were misapplied to them. Nevertheless, by the time Lindsey et al. (1931) was published, most nomenclatural problems-which involved homonymy as well as synonymy, speCific identity, and proper generiC usage-had been solved; and these skippers were designated by the names we continue to use today. Current synonynlY may be found in Evans (1953), dos Passos (1964) , and Miller and Brown (1981, 1983). On the other hand, biological problems involving the mutual status of Pyrgus communis and albescensi.e . , whether they are completely separate species, variably hybridizing species, freely interbreeding subspecies, or one and the same taxon-surfaced early in this century and persist to its end, Knowledge of the geographic distributions of these skippers-which, early on, was unavoidably sketchy and partly erroneous-is still notably deficient. Just seven months after Skinner (1906a:96) briefly described what he called "Pyrgus occidentalis n. sp. " (=P albescens) from "the Northwest territory [an invalid source for this skipper] and . the southwest generally" (specifically "San Bernardino Ranch, Cochise Co., Arizona, , . and Brownsville, Texas"), he (Skinner 1906b:278) backtracked by declaring, "This is not a species, but only a form or geographical race of tessellata" (Scudder) (=P communis). But eleven years later, on 27 September 1917, "Williams made some interesting remarks on the genus [Pyrgus], especially regarding characters possessed by the genitalia and illustrated them by drawings. He stated that, based on the genitalic characters, occidentalis seems to be distinct from tessellata" (Cresson 1918:38). Lindsey (1921:41) treated occidentalis as a race of tessellata with the comments "California, Arizona and Texas. This form is scarcely worthy of a name, but may be regarded as a pale southwestern geographical race. I have not looked for differences in the genitalia. " However, the observation by "Williams . , regarding the apparent specific distinctness of H. occidentalis Skin. and tessellata Scud. on the baSI,S of genital structure led [Barnes & Lindsey 1921:791 to examine a long series of these races . The genitalia do undoubtedly show two very eaSily separable forms of valves, but these are connected by a great variety of intermediate forms . It is impossible to elraw a definite line between the extreme forms , so we prefer to retain the old conception of occidentalis as a. pale western race of tessellata," Independently investigating the relationship of these two entities from a greater distance, Swiss lepidopterist Reverdin (1921) took what, for that time, was the remarkable step of comparing 90 dissections of their male genitalia. He recognized, thoroughly deVOLUME 54, NUMBER 2 53