Taxonomy

The taxonomy of these butterflies is controversial regarding the delineation of both genera and species. Simonsen et al. (2006) have prepared the most recent cladistic analysis of this group based on a combination of both morphological and DNA sequence data that shows four major clades within the group. These clades may be classified into four genera or subgenera (Tuzov 2003) including Argynnis, Fabriciana, Mesoacidalia, and Speyeria based on a combination of wing pattern and genitalic characters. The first three genera are endemic to Eurasia and North Africa, while the latter genus is endemic to North America. These genera are defined as follows.

The genus Fabriciana is characterized by having black crescent-shaped or indented submarginal spots on the dorsal wings. On the ventral hindwing, the median spots are broad and square in shape, forming a somewhat continuous median band, and distinct dark postmedian spots are present. The valve of the male genitalia has a slender, finger-like process that is free above the valve. The uncus has a prominent dorsal tooth. This genus is comprised of 11 species as outlined by Tuzov (2003), with F. kamala (Moore) transitional in wing pattern towards Argynnis. Fabriciana niobe (Linnaeus) exhibits the most primitive characters in wing pattern and genitalic structure among the greater fritillaries that are shared with the lesser fritillaries of the genera Issoria, Brenthis, and Boloria (see cladogram in Simonsen et al. 2006). In general, species of Fabriciana are relatively conservative in these characters with the greatest divergence seen in such species as F. argyrospilata (Kotzsch) and F. nerippe (Felder & Felder).

The genus Argynnis is characterized by having round black submarginal spots on the dorsal wings. On the ventral hindwing, the median band is reduced to a thin median stripe, and dark postmedian spots are present. The male genitalia are similar to those of Fabriciana, but are highly variable among different species in ornamentation of the process and valve. The uncus is also highly variable, and may have multiple dorsal teeth or no teeth. This genus is comprised of 10 species as outlined by Tuzov (2003), except that we recognize A. castetsi Oberthur on the Indian subcontinent as a species fully distinct from the more common and widespread A. hyperbius (Linnaeus). The species of Argynnis are all extremely divergent in wing color pattern and genitalic structure. On the basis of this divergence, the genus has been taxonomically divided into a number of small or monotypic genera in the past, including Pandoriana, Damora, Nephargynnis, Argyronome, Childrena, and Argyreus (Tuzov 2003). Despite this great divergence among the various species, they appear to be closely related in a phylogenetic sense as shown by the cladogram of Simonsen et al. (2006).

The genus Mesoacidalia has a wing pattern identical to that of Fabriciana on the dorsal wings. However on the ventral hindwing, the median band is broken into discrete, separate median spots, and dark postmedian spots are mostly absent except for faint shadows. In the male genitalia, the dorsal process of the valve is pressed down on top of the valve, instead of being free above the valve as in Fabriciana and Argynnis. In addition, the uncus lacks the dorsal tooth of Fabriciana. Mesoacidalia is comprised of 4 species in Eurasia including M. vitatha (Moore), M. clara (Blanchard), M. aglaja (Linnaeus), and M. alexandra (Menetries). Of these species, M. vitatha has thin or narrow black median bars on the forewings, and elongate or pointed median spots and sharp, triangular submarginal spots on the ventral hindwing. By contrast, M. aglaja has variable narrow to wide black median bars, short or rounded median spots, and rounded or flat submarginal spots. Mesoacidalia clara has a more extreme wing pattern similar to that of M. vitatha, while M. alexandra has a more extreme wing pattern similar to M. aglaja.

The genus Speyeria has a wing pattern virtually identical to that of Mesoacidalia. However, the process of the male valve is relocated along the side of the valve, and is broadly expanded into a club-like structure. This contrasts with the narrow, dorsal process of Mesoacidalia. Of these, S. mormonia (Boisduval) of the Rocky Mountains has a wing color pattern virtually identical to that of M. vitatha, and only differs in smaller size. However, S. mormonia has the Speyeria-type of male genitalia, while M. vitatha retains the more primitive Mesoacidalia-type of genitalia. As shown in the cladogram of Simonsen et al. (2006), Mesoacidalia and Speyeria are closely related sister genera. On this combined basis of genitalia and wing color pattern, the genus Speyeria in North America appears to be a monophyletic group that was probably derived from the Eurasian M. vitatha.

In sharp contrast to the species of Argynnis, most species of Speyeria are extremely conservative in both wing pattern and genitalic structure, and there are often no consistent diagnostic characters for separating the various species. Only two species exhibit highly divergent wing color patterns that allow for easy taxonomic identification, S. idalia and S. diana. All other species have overlapping characters of phenotype at least to some extent, and most exhibit a tremendous amount of geographic variation in wing color pattern (Hammond 1991). This is why Grey (1961) was not able to provide a diagnostic key for the identification of most species in the genus.

We presently recognize 16 reproductively isolated species in the genus Speyeria that maintain strongly distinct identities in sympatry, and exhibit strong ecological segregation in habitat and violet resource partitioning (Hammond 1981). These may be divided into two species groups based upon differences in the male and female genitalia as outlined by Grey (1961). The callippe group including S. mormonia has a slender claw-like uncus in the male and a single bursal chamber in the female. Other species of this group include S. atlantis (Edwards), S. hollandi (Chermock & Chermock), S. sorocko Scott, Kondla, & Spomer, S. callippe (Boisduval), S. edwardsii (Reakirt), S. egleis (Behr), S. zerene (Boisduval), S. coronis (Behr), S. hydaspe (Boisduval), and S. adiaste (Edwards). By contrast, the cybele group has a thick hook-like uncus in the male and a double bursal chamber in the female, although S. nokomis does retain the more primitive single bursal chamber. Species of this group include S. aphrodite (Fabricius), S. cybele (Fabricius), S. nokomis (Edwards), S. idalia (Drury), and S. diana (Cramer).

We should note that a major taxonomic disagreement presently exists regarding the delineation of species boundaries among taxa closely related to S. atlantis. Scott, Kondla, & Spomer (1998) separated the western subspecies of S. atlantis as a distinct species, S. hesperis (Edwards), an approach recently followed by Dunford (2009). However, Grey (1951) pointed out that a broad zone of clinal intergradation exists across Canada between the eastern S. atlantis atlantis and western members of the hesperis group, beginning in the Great Lakes region and extending westward across central Manitoba and northern Saskatchewan to the Rocky Mountains of Alberta, and then south to Colorado and New Mexico. Within these regions, both S. hollandi and S. sorocko maintain separate identities as distinct, reproductively isolated species. Based upon the reproductive relationships, we suggest that the western hesperis group must be treated as geographic subspecies of S. atlantis as originally classified by dos Passos & Grey (1947), despite the superficial similarities of S. hollandi and S. sorocko to the eastern S. a. atlantis.

Hybridization Studies

Over the past ten years, we have conducted extensive hybridization experiments with most of the species within the genus Speyeria. An earlier unpublished study attempted hybrid crosses between Speyeria and some of the European species, and we report on the results of this work in the present paper. Compatibility between the genomes of different taxa may be measured at six stages of divergence as discussed by Robinson (1971).

Stage 1 shows no genetic incompatibility with completely normal male and female hybrids.

Stage 2 shows some minor Haldane effects where the heterogametic sex (females) shows some minor abnormalities due to incompatible sex chromosomes and autosomes.

Stage 3 shows major Haldane effects where the hybrid females show major abnormalities or are completely non-viable, resulting in unequal sex ratios.

Stage 4 shows normal hybrid male development, but the males are completely sterile due to a failure of disparate chromosomes to pair up during the process of meiosis.

Stage 5 shows major abnormalities in male hybrids.

Stage 6 shows no hybrid viability at all. Either fertilized eggs die in early embryonic development or no fertilization takes place.

Reproductive isolation among the various species of Speyeria appears to result from species-specific sex pheromones in both males and females that are used during courtship and mating (personal observations). Interspecies courtship is frequently observed in the field, but this almost never results in hybrid matings. In the laboratory, we have by-passed this isolating mechanism by using the hand-pairing technique of Clarke (1952) for swallowtail butterflies. Male and female genitalia are mechanically joined together, forcing the butterflies to mate whether they are inclined to do so or not. In this way, every species of Speyeria can be hybridized with every other species no matter how divergent or distantly related they might be.

Hybridization of Speyeria with European Genera. An earlier study was designed to conduct hybridization experiments between Speyeria and the three European genera, and these results are discussed as follows. For this work, three European species were selected to represent each of these genera including Fabriciana adippe (Denis & Schiffermuller), Argynnis paphia (Linnaeus), and Mesoacidalia aglaja (Linnaeus). Unfortunately, the breeding stock of F. adippe was not particularly viable and no hybrid crosses could be made. However, an extensive effort was made to hybridize A. paphia with various Speyeria species. A total of six hybrid crosses were successfully completed with A. paphia, but none of these crosses resulted in any viable progeny. This suggests a Stage 6 level of genomic divergence between Argynnis and Speyeria with virtually no genetic compatibility between these genera. This also corroborates the wide divergence between these genera shown in the cladistic study of Simonsen et al. (2006).

By contrast, two hybrid crosses were made between Speyeria and M. aglaja, and one of these made with S. nokomis nitocris (Edwards) from Arizona successfully produced a few viable male hybrids. These results indicate that some genetic compatibility still remains between the genomes of Speyeria and Mesoacidalia, and corroborates the cladistic study of Simonsen et al. (2006) that shows these genera as closely related sister genera. Unfortunately, it was not possible to backcross this hybrid to test for other measures of genetic compatibility such as fertility. The hybrid is shown in Figure 1 (1–2), and is intermediate in size and color pattern phenotype between the two parental species. On the ventral hindwing, it shows the green disc of the M. aglaja parent, and the wide yellow submarginal band and small silver median and submarginal spots of both parents. Thus in this hybrid, the green disc color of the M. aglaja parent was strongly dominant in phenotypic expression over the red-brown disc color of the S. nokomis parent.

Hybridization of Speyeria mormonia. As noted above, S. mormonia is the one North American species that is most similar to the Eurasian genus Mesoacidalia, and may be considered the most primitive for the genus Speyeria. We tested the genomic divergence of S. mormonia by crossing it with S. aphrodite. Specifically, we mated a male of S. m. erinna (Edwards) from the Oregon Cascades with a female of S. a. alcestis (Edwards) from Michigan. This hybridization combines a small species with a large species that are divergent in both male and female genitalic structure, although the adult color patterns are relatively similar.

Figure 1 (3–4) shows the phenotype of the hybrid male obtained from this cross. It was relatively small in size, only slightly larger than a normal S. mormonia, and it retained the narrow yellow submarginal band typical of S. m. erinna. Female hybrids showed a major Haldane effect and died as eggs in early embryonic development. However, male hybrids proved to be fertile in back-crosses, indicating a Stage 3 level of genomic divergence between S. mormonia and S. aphrodite.

The male hybrid was back-crossed to S. a. alcestis, and the genetic recombinants are illustrated in Figure 1 (5–8). Normal female hybrids were obtained in this back-cross (8), and butterflies segregated in phenotype between large individuals that exhibited red suffusion over the submarginal band on the ventral hindwing as in the parental S. a. alcestis (5–6), and small individuals that retained a narrow yellow submarginal band as in the parental S. m. erinna (7). Thus, the small size and yellow submarginal band of S. mormonia was somewhat dominant in phenotypic expression over the large size and red suffused submarginal band of S. aphrodite.

Fig. 1.

Hybrid crosses of Mesoacidalia and Speyeria species. Scale-bar equals 20 mm. (1) M. aglaja × S. nokomis male dorsal, (2) M. aglaja × S. nokomis male ventral, (3) S. mormonia erinna × S. aphrodite alcestis male dorsal, (4) S. m. erinna × S. a. alcestis male ventral, (5) back-cross (S. m. erinna × S. a. alcestis) × S. a. alcestis male dorsal, (6) back-cross (S. m. erinna × S. a. alcestis) × S. a. alcestis male ventral, (7) back-cross (S. m. erinna × S. a. alcestis) × S. a. alcestis male ventral, (8) back-cross (S. m. erinna × S. a. alcestis) × S. a. alcestis female dorsal, (9) S. aphrodite × S. c. cybele male dorsal, (10) S. aphrodite × S. c. cybele male ventral, (11) S. aphrodite × S. c. cybele female dorsal, (12) back-cross (S. zerene picta × S. c. cybele) × S. c. cybele male ventral, (13) S. z. picta × S. c. cybele male dorsal, (14) S. z. picta × S. c. cybele male ventral, (15) S. z. picta × S. c. cybele female dorsal, (16) back-cross (S. z. picta × S. cybele) × S. c. cybele female ventral, (17) S. edwardsii × S. aphrodite ethne male dorsal, (18) S. edwardsii × S. a. ethne male ventral, (19) S. edwardsii × S. a. ethne female dorsal, (20) back-cross (S. z. picta × S. c. cybele) × S. c. cybele female ventral.

Fig. 2.

Hybrid crosses of Speyeria species. Scale-bar equals 20mm. (1) S. zerene picta × S. callippe semivirida male dorsal, (2) S. z. picta × S. c. semivirida male ventral, (3) S. a. atlantis × S. nokomis nitocris male dorsal, (4) S. a. atlantis × S. n. nitocris male ventral, (5) S. c. cybele × S. n. nitocris male dorsal, (6) S. c. cybele × S. n. nitocris male ventral, (7) S. c. cybele × S. n. nitocris female dorsal, (8) S. c. cybele × S. n. nitocris female ventral, (9) S. c. cybele × S. n. apacheana male dorsal, (10) S. c. cybele × S. n. apacheana male ventral, (11) S. c. cybele × S. n. apacheana female dorsal, (12) S. c. cybele × S. n. apacheana female ventral, (13) S. n. nitocris × S. idalia male dorsal, (14) S. n. nitocris × S. idalia male ventral, (15) S. edwardsii × S. idalia male dorsal, (16) S. edwardsii × S. idalia male ventral, (17) S. a. atlantis × S. idalia male dorsal, (18) S. a. atlantis × S. idalia male ventral, (19) S. z. picta × S. idalia male dorsal, (20) S. z. picta × S. idalia male ventral.

Hybridization within the Central Radiation of Speyeria

Most species within the callippe species group have no constant diagnostic characters in either wing color pattern or genitalic structure as noted by Grey (1961), while S. cybele and S. aphrodite are slightly more divergent with genitalic differences in both males and females as discussed above. We conducted many hybrid crosses between various species, both within the callippe group and with both S. cybele and S. aphrodite. No adverse Haldane effects were observed in hybrid females, and all hybrids appeared to be fertile. Thus, the species of the callippe group plus S. cybele and S. aphrodite exhibited a Stage 1 level of genomic divergence among the various species with no indications of any genetic incompatibility.

These hybrid crosses provided an indication of the Mendelian phenotypic expression of the diagnostic characters that distinguish the various Speyeria taxa. A cross between a male of S. zerene picta (McDunnough) and a female of S. callippe semivirida (McDunnough) from the Washington Cascades was particularly informative as shown in Figure 2 (1–2). On the forewings, S. callippe usually has narrow black median bars, while S. zerene usually has wide median bars. On the ventral hindwing, S. callippe has a greenish brown disc, sharp pointed or elongate median spots, and sharp triangular submarginal spots. By contrast, S. zerene has a reddish brown disc, and rounded median and submarginal spots. In the hybrid, the wide median bars of S. zerene exhibited a strong dominant expression over the narrow median bars of S. callippe. However, the sharp, pointed median and submarginal spots of S. callippe showed a strong dominant expression over the rounded spots of S. zerene. Incomplete expression was exhibited by the disc colors, with some individuals having a reddish brown disc and others having green and red colors mixed together.

Figure 1 illustrates the phenotypic expression of these characters among various hybrid crosses. The primary cross between a male S. zerene picta from the Oregon Cascades with a female S. c. cybele from Michigan showed the dominance of the wide black median bars of S. zerene over the narrow median bars of S. cybele (Fig. 1, 13–15). On the ventral hindwing, the large median spots and narrow submarginal band of S. zerene were dominant over the small median spots and wide submarginal band of S. cybele. However, the pointed submarginal spots of S. cybele showed a dominant phenotypic expression over the rounded submarginal spots of S. zerene. When the primary hybrid was back-crossed to S. cybele, these characters showed recombination that indicated an independent segregation and inheritance of such traits. Thus, Figure 1 (12) shows a back-cross male with the small median spots and wide submarginal band of S. cybele, (16) shows a back-cross female with the large median spots and narrow submarginal band of S. zerene, and (20) shows a back-cross female with the large median spots of S. zerene combined with the wide submarginal band of S. cybele.

Figure 1 (9–11) shows a hybrid cross between S. aphrodite and S. cybele both from Michigan. The former species has little dark basal suffusion and thin veins in the male dorsal forewing, while the latter species has heavy dark basal suffusion and veins strongly thickened with androconial scales. On the ventral hindwing, S. aphrodite has large median spots combined with a narrow submarginal band, while S. cybele has small median spots and a wide submarginal band. The dorsal characters of the hybrid were intermediate between those of the parental species, indicating an incomplete dominance or polygenic inheritance of these traits. On the ventral hindwing of the hybrid, the larger median spots and narrow submarginal band of S. aphrodite were mostly dominant in expression over those of S. cybele. When the primary hybrid was back-crossed with S. c. cybele, these characters recombined independently in different individuals. This correlates with the dominance of similar S. zerene characters over those of S. cybele in the hybrid crosses previously discussed.

Figure 1 (17–19) shows a hybrid cross between S. edwardsii and S. aphrodite ethne (Hemming) both from Nebraska. The former species has a yellow-orange ground color on the dorsal wings, and a greenish brown disc and very large spots on the ventral hindwing. By contrast, the latter species has a reddish orange dorsal color, a red-brown disc, and smaller spots. In the hybrid, the reddish orange dorsal color of S. aphrodite and the very large spots of S. edwardsii showed a dominant expression. However, the expression of disc color was variable and intermediate, with some hybrid individuals having a pure dark brown disc and others showing a greenish brown disc (18). Similar results with mixed green and brown disc colors were seen in hybrid crosses between S. callippe and S. zerene, and between S. coronis and S. zerene. This suggests an incomplete dominance in the expression of green and brown disc colors in Speyeria. Pure green and brown colors appear to represent homozygous expressions, while greenish brown color is probably a heterozygous expression. By contrast, the green disc color of Mesoacidalia aglaja was strongly dominant over the red-brown color of S. nokomis nitocris as previously discussed.

Fig. 3.

Hybrid crosses of Speyeria species. Scale-bar equals 20 mm. (1) S. c. cybele × S. idalia male dorsal, (2) S. c. cybele × S. idalia male ventral, (3) S. c. cybele × S. idalia female dorsal, (4) superhybrid (( S. cybele pugetensis × S. c. charlottii) × S. nokomis nitocris) × S. idalia male ventral, (5) S. idalia × S. c. cybele male dorsal, (6) S. idalia × S. c. cybele male ventral, (7) S. diana × S. idalia male dorsal, (8) S. diana × S. idalia male ventral, (9) S. diana × S. n. nitocris male dorsal, (10) S. diana × S. n. nitocris male ventral, (11) S. diana × S. n. apacheana male dorsal, (12) S. diana × S. n. apacheana male ventral, (13) S. c. cybele × S. diana male dorsal, (14) S. c. cybele × S. diana male ventral, (15) S. aphrodite × S. diana male dorsal, (16) S. aphrodite × S. diana male ventral, (17) S. a. atlantis × S. diana male dorsal, (18) S. a. atlantis × S. diana male ventral, (19) S. z. picta × S. diana male dorsal, (20) S. z. picta × S. diana male ventral.

We should also mention the hybrid expression of sexual dimorphism within S. cybele. The eastern S. c. cybele and the southern Colorado S. c. carpenterii (Edwards) both lack sexual dimorphism in having orange males and females in dorsal colors. However, subspecies of the western leto complex including both S. c. pugetensis Chermock & Frechin from the Pacific Northwest and S. c. charlottii (Barnes) from northwestern Colorado show a very strong sexual dimorphism in which the females have a pale yellow dorsal ground color. A hybrid cross between S. c. pugetensis from Oregon and S. c. cybele from Michigan produced intermediate yellow-orange females. A backcross of this hybrid to S. c. cybele produced a wide range of variation from pure orange to yellow-orange female phenotypes. These laboratory results are closely similar to the natural phenotypic variation in female coloration seen in populations of S. cybele from western Colorado and eastern Utah that are intermediate between S. c. carpenterii and S. c. charlottii in a broad clinal blend zone.

Hybridization of Speyeria Nokomis

Speyeria nokomis is slightly more divergent in wing pattern and large size compared to the various species in the central radiation of Speyeria discussed above. Figure 2 (3–12) shows the results of hybrid crosses made between S. nokomis, S. cybele, and S. a. atlantis. Crosses between S. nokomis and both S. cybele and S. aphrodite showed a Stage 2 level of genomic divergence. Minor Haldane effects were evident in that female hybrids were somewhat smaller than normal. Male hybrids were fertile. However, crosses between S. nokomis and both S. atlantis and S. adiaste showed much stronger Haldane effects where few or no female hybrids survived. Thus, a Stage 3 level of genomic divergence appears to exist between S. nokomis and members of the callippe species group.

A hybrid cross between S. n. nitocris (Edwards) from Arizona and S. aphrodite from Michigan produced similar results to those seen in the aphrodite × cybele cross shown in Figure 1 (9–11), except the dorsal dark basal suffusion of the hybrid male was greatly reduced and the forewing veins were thin without androconial scales as in S. aphrodite. On the ventral hindwing, the larger median spots and narrow submarginal band of S. aphrodite were dominant over the small spots and wide submarginal band of S. nokomis just as in the aphrodite × cybele cross. A hybrid cross between S. n. nitocris and S. a. atlantis from Minnesota produced almost identical results as shown in Figure 2 (3–4), except the veins of the male dorsal forewing were thickened with androconial scales as in the S. atlantis parent.

In addition, S. nokomis exhibits a strong sexual dimorphism similar to that in the leto subspecies group of S. cybele in which the female dorsal ground color is yellow instead of orange. As with the hybrid cross between S. c. cybele and S. c. pugetensis, female hybrids of S. nokomis crossed with either S. aphrodite or S. c. cybele showed an intermediate yellow-orange ground color as shown in Figure 2 (7, 11).

Two subspecies of S. nokomis differ in the color of the disc on the ventral hindwing. In Arizona, males of S. n. nitocris have a dark reddish brown disc, while females have a reddish black disc. In Nevada and California, males of S. n. apacheana (Skinner) have a pure yellow disc and females have a green disc. The hybrid between these subspecies was intermediate with a light reddish brown disc in the male and a reddish green disc in the female. A hybrid cross between S. n. nitocris and S. c. cybele produced a dark reddish brown disc in both the male and female as shown in Figure 2 (6, 8), while a hybrid cross between S. n. apacheana and S. c. cybele produced a light reddish brown disc in the male and a dark greenish brown disc in the female as shown in Figure 2 (10, 12). The dorsal forewing veins of the hybrid males were thickened with androconial scales as in S. cybele as shown in Figure 2 (5, 9).

A hybrid cross between S. adiaste from the Coast Range of California and S. n. nitocris from Arizona combined a small butterfly with a pure yellow disc and unsilvered spots on the ventral hindwing and a large butterfly with a dark reddish brown disc and silver spots. The hybrid was intermediate in size and disc color between the two parental species, again showing the polygenic inheritance of size and disc color. As with the aphrodite and atlantis hybrid crosses described above, the large median spots and narrow submarginal band of S. adiaste were completely dominant over the small spots and wide band of S. nokomis. In addition, the unsilvered spots of the S. adiaste parent were completely dominant over the silver spots of the S. nokomis parent. As a result, the hybrid more closely resembled S. adiaste than S. nokomis. In populations of Speyeria that are polymorphic for both silver and unsilvered spots, it is not unusual to see intermediate phenotypes with partially silvered or unsilvered spots. These may represent heterozygotes with modifier genes that allow partial expression or incomplete dominance of these traits, but this was not seen in the adiaste × nokomis hybrid.

Hybridization of Speyeria idalia

Multiple hybrid crosses were made between S. idalia from Nebraska and many other species of Speyeria. This species and S. diana are both highly divergent in wing color pattern from all other species in the genus, and show completely unique diagnostic characters not found in any other species. For S. idalia, these characters include (1.) a black dorsal hindwing with white median spots and white submarginal spots in the female, (2.) a black or reddish black disc on the ventral hindwing with solid black suffusion over a narrow submarginal band, and (3.) very large pointed or elongate median spots and pointed submarginal spots on the ventral hindwing.

In the various hybrid crosses with S. idalia, major Haldane effects occurred where hybrid females were severely stunted. They usually died in the pupal stage or were unable to expand wings upon eclosion, and were rarely able to develop into a deformed adult (Fig. 3–3). In addition, male hybrids appeared to be completely sterile, and we were never able to produce a hybrid back-cross with any other species. Thus, S. idalia exhibits a Stage 4 level of genomic divergence from other species.

Figure 2 shows the results of hybrid crosses made with S. nokomis nitocris from Arizona (13–14), S. edwardsii from Nebraska (15–16), S. a. atlantis from Minnesota (17–18), and S. zerene picta from Oregon (19–20). Likewise, Figure 3 (1–3) shows a hybrid cross with a male S. c. cybele from South Dakota. Figure 3 (5–6) shows the reciprocal cross using a male S. idalia and a female S. c. cybele to check for any sex-linked or sex-limited traits. None were found. A hybrid cross with S. coronis from Oregon produced similar results to those shown with S. zerene. Figure 3 (4) shows a superhybrid cross where the primary S. cybele pugetensis × S. c. charlottii hybrid was crossed with S. nokomis nitocris, and then this secondary hybrid was crossed with S. idalia to produce a tertiary hybrid.

In all of these various hybrids, the black dorsal hindwing and white spots of S. idalia were completely recessive in phenotypic expression to the normal dorsal orange colors of other Speyeria species. On the ventral hindwing, the sharp, pointed median and submarginal spots were strongly dominant over the rounded spots of such species as S. zerene, S. coronis, S. cybele, and S. nokomis. Likewise, the narrow submarginal band covered with black to reddish suffusion of S. idalia was completely dominant over the wide yellow submarginal band of S. cybele and S. nokomis, although a few of the cybele hybrids showed a slight trace of the yellow band. However, the size of the median spots in hybrids was intermediate between the large spots of S. idalia and the small spots of S. cybele and S. nokomis. Also, the hybrid ground color of the disc on the ventral hindwing was usually a dark reddish brown as seen in the zerene, atlantis, and cybele crosses, but ranged between bright red-brown in the nokomis cross and pure black in the edwardsii cross.

Hybrids did show some unique phenotypic expressions depending on the parental species crossed with S. idalia. The cross with S. nokomis shown in Figure 2 (13–14) produced gigantic males with exceptional hybrid vigor, but they were often deformed and had difficulty with eclosion. This suggests a Stage 4 to Stage 5 level of genomic divergence between these two species. In the zerene × idalia cross (19–20), the wide black median bars of the forewing in S. zerene were strongly dominant over the narrow bars of S. idalia, duplicating similar results in other hybrid crosses made with S. zerene. In the edwardsii × idalia cross (15–16), the pale yellow-orange dorsal ground color of S. edwardsii was strangely dominant over the dark orange color of S. idalia on the forewing, which was the reverse of the edwardsii × aphrodite cross shown in Figure 1 (17–19). However, the greenish brown color of the disc on the ventral hindwing of S. edwardsii was strongly suppressed by the black color of S. idalia in the hybrid.

Hybridization of Speyeria Diana

Multiple hybrid crosses were also made between S. diana from Virginia and many other species. Unique diagnostic characters of S. diana include (1.) very large wing size, (2.) intense solid black basal suffusion that extends to the median bars of the dorsal wings, (3.) extreme suppression of the spots on the ventral hindwing, and (4.) an extreme sexual dimorphism with orange-black males and blue-black females.

Major Haldane effects were evident in these hybrid crosses where females died as eggs in early embryonic development and never produced viable larvae. Hybrid males appeared to be completely sterile and no hybrid back-crosses were possible. Thus, S. diana exhibits a Stage 4 level of genomic divergence from most other species.

Figure 3 shows the results of hybrid crosses made with S. idalia from Nebraska (7–8), S. nokomis nitocris from Arizona (9–10), S. n. apacheana from Nevada (11–12), S. cybele from Michigan (13–14), S. aphrodite from Michigan (15–16), S. atlantis atlantis from New York (17–18), and S. zerene picta from Washington (19–20). A cross made with S. coronis from Oregon produced similar results to those shown with S. zerene. The expression of dark black basal suffusion on the dorsal wings of hybrids was intermediate between that of S. diana and the various parental species. Thus, hybrids made with S. n. nitocris, S. cybele, and S. atlantis still showed very intense, dark suffusion. However, S. n. apacheana and S. aphrodite both have greatly reduced suffusion in the male, and their hybrids made with S. diana showed greatly reduced suffusion as well. Therefore, the intense solid black basal suffusion of S. diana appears to be the result of polygenic expression that has become fixated at one extreme end of a continuum.On the ventral hindwing of hybrids, the suppression of the silver basal and submarginal spots was less extreme and intermediate compared with the parental S. diana. However, the suppression of the silver median spots in hybrids was nearly as great as in S. diana for virtually all crosses, even the cross made with S. idalia. This unique character of S. diana shows a strong dominant phenotypic expression over the normal median spots of other Speyeria species. In wing size, hybrids were usually intermediate between S. diana and the respective parental species, indicating a polygenic expression for size. We could not assess the inheritance of blue and orange colors in the hybrid females because they were completely non-viable.

The hybrid cross between S. idalia and S. diana exhibited major abnormalities in the males. Larvae showed a major defect in feeding behavior, and chewed randomly on leaf surfaces instead of feeding efficiently by chewing at the leaf margins. As a result, larvae grew very slowly and were quite stunted at pupation. Most individuals died as pupae or could not expand wings upon eclosion. Although several hundred larvae were reared, only a single individual was able to expand its wings as shown in Figure 3 (7–8). These two species display a Stage 5 level of genomic compatibility and divergence as a consequence, which is concordant with their extreme morphological divergence.

Phenotypic Expression of Larval Color Patterns in Hybrid Speyeria

Most species of Speyeria have a larval color pattern that is mottled gray, black, brown, or yellow with two parallel mid-dorsal gray, yellow, or cream stripes. Such species include S. mormonia, S. hollandi, S. sorocko, S. callippe, S. edwardsii, S. egleis, S. zerene, S. coronis, S. nokomis, and S. idalia. Other species have pure black larvae that lack the pale body mottling and the pale middorsal stripes. These include S. hydaspe, S. cybele, and S. diana. Still other species are polymorphic in larval color pattern with either pale striped morphs or pure black morphs including S. atlantis, S. adiaste, and S. aphrodite. These polymorphisms represent geographic variations to a considerable extent in these species.

When we hybridized a pure black larval species such as S. cybele with a yellow-striped larval species such as S. idalia, an intermediate dusky striped and mottled phenotype was produced in the hybrid. Thus, hybrids display an incomplete dominance of larval color pattern expression in the heterozygous condition. Similar results were produced when S. cybele or black larval forms of S. aphrodite were crossed with various pale striped larval forms such as S. nokomis, S. zerene, S. coronis, and S. edwardsii. These intermediate dusky striped morphs are common in the wild within polymorphic populations of such species as S. atlantis and S. aphrodite.