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Volume 26, Number 2
109
POLYMORPHISM IN PAP1LIO GLAUCUS L. (PAPILIONIDAE): MAINTENANCE OF THE FEMALE ANCESTRAL FORM
Sally K. Makielski
Department of Biological Sciences, Loyola University, New Orleans, Louisiana 70118
The Papilio glaucus L. female is dimorphic. One form is dark and resembles P. (Battus) philenor L.; the other resembles the yellow male. The inheritance of female color is controlled by a Y-linked gene (Clarke & Sheppard, 1962). Yellow mothers produce yellow daughters and dark mothers produce dark daughters. Consequently the two morphs are in direct competition with each other; and, heterozygote advantage cannot be the mechanism which maintains the dimorphism.
The dark form of P. glaucus is thought to belong to the mimetic assemblage which surrounds P. philenor. Other members are P. troilus L., P. polyxenes (Fabricius), Limenitis arthemis astyanax (Fabricius), and the females of Speyeria cliana (Cramer). The main evidence that the dark form of glaucus mimics P. philenor is the correspondence between the occurrence and abundance of the two. In general (Brower & Brower, 1962) the proportion of mimics is highest in the middle Atlantic States where philenor is common. This proportion decreases in a southerly and northerly direction as philenor decreases.
One hypothesis for explaining the maintenance of the dimorphic female population in P. glaucus is that the males show a mating preference for the yellow females. Burns (1966) has tested this hypothesis by counting the number of spermatophores present in the bursa copulatrix of the two morphs. He obtained data from two samples of females collected during the summer of 1965; one in the vicinity of Mountain Lake Biological Station, Giles County, Virginia, and the other in Baltimore County, Maryland. In each sample the mean number of spermatophores per female was higher in the yellow morph than in the dark morph (Mt. Lake, yellow morph-2.08 spermatophores, dark morph-1.69 spermatophores; Baltimore County, yellow morph-1.88 spermatophores, dark morphs-1.54 spermatophores).
The present study was suggested by the relatively small difference between the mean number of spermatophores per female (Mt. Lake sample, 0.39; Baltimore sample, 0.34) found by Burns. It seemed that further information about the insemination frequency in P. glaucus would be of interest.
Two hundred P. glaucus females were collected during August and
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Journal of the Lepidopterists' Society
Table 1. Observed frequency distribution, expected frequency distribution (numbers in parentheses), and mean number of spermatophores in wild-caught females of Papilio glaucus.
Number of Spermatophores Mean dumber ol
Specimens ________________________________ Spermatophores/
Morph (No.) 0 1 2 3 Female
Mimic 128 2 65 51 10 1.54
(2.56) (65.92) (51.84) (7.68)
Yellow 72 2 38 30 2 1.44
(1.44) (37.08) (29.16) (4.32)
Total 200 4 103 81 12 1.51
September of 1966, 1967 and 1968 from two valleys in Albemarle County, Virginia; one in the Blue Ridge Mountains (elevation 800'), the other approximately 24 miles east of the Blue Ridge (elevation 590'). The butterflies were found in abandoned fields in which thistle was growing. Streams and larval foodplant (Liriodendron and Prunus) were located nearby.
The females were either dissected immediately after they were caught or were frozen alive in a moist chamber and dissected later.
A comparison of the mean number of spermatophores per female (Table 1) shows that the yellow females (x = 1.44) were inseminated less frequently than the mimic females (x = 1.54). However, this difference is not significant (x(2)2 = 2.07; .50 > P > .30; categories 0 and 1 spermatophores combined). Statistical analysis also shows that there was no heterogeneity with respect to locality (x(d2 = .34; .80 > P > .70).
The results, then, show that there is no difference in the frequency of insemination between the mimetic and yellow females in the population studied. These results conflict with those of Burns (1966) and with some but not all of the data collected by Levine (1970) from females found in the vicinity of Mountain Lake, Virginia.
The reason for the discrepancy between the two sets of data is not clear. It may be related to the altitude at which the butterflies are found, the relative frequency of the model in relation to the frequency of P. glaucus, or the relative frequencies of the two female morphs. The ratio of dark to yellow morphs is 6:1 in the Mountain Lake area and 2:1 in Albemarle County, while the yellow butterflies are preferentially inseminated at Mountain Lake and are inseminated equally as frequently as the mimics in Albemarle County. Thus, it is also possible that, as in the case of Drosophila pseudoobscura (Ehrman, 1967; Spiess, 1968), female mating advantage occurs in P. glaucus. That is, that where the morph is rare
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it is inseminated more frequently. This hypothesis can be tested by obtaining data on the relative frequency of insemination of mimic females in populations where the proportion of the mimics is small.
While the mechanism which maintains the dimorphism in P. glaucus is not yet clearly understood, the evidence collected to date shows that regional differences exist in the frequency with which the two female morphs are inseminated.
Acknowledgment
This research was done while working in the laboratory of Dr. J. J. Murray, Jr., in the Department of Biology, University of Virginia, Charlottesville, Virginia. My thanks to Dr. Murray for his encouragement and for the use of his laboratory facilities.
Literature Cited
Brower, L. P. and J. VZ. Brower. 1962. The relative abundance of model and
mimic butterflies in natural populations of the Battus philenor mimicry complex.
Ecology 43: 154-158. Burns, J. M. 1966. Preferential mating versus mimicry: disruptive selection and
sex-limited dimorphism in Papilio glaucus. Science 153: 551-553. Clarke, C. A. and P. M. Sheppard. 1962. The genetics of the mimetic butterfly
Papilio glaucus. Ecology 43: 159-161. Ehrman, L. 1967. Further studies on genotype frequency and mating success in
Drosophila. Amer. Natur. 101: 415-424. Levin, M. P. 1970. The biology of Papilio glaucus L. as it relates to polymorphism
and mimicry. Doctoral dissertation, Virginia Polytechnic Institute, Blacksburg,
Virginia. Spiess, E. B. 1968. Low frequency advantage in mating of Drosophila pseudo-
obscura karyotypes. Amer. Natur. 102: 363-379.
PSEUDOPHILOTES BEURET, 1958
In a recent article of mine about Glaucopsychie piasus I called attention to the fact that Philotes sonorensis, the type species of Scudder's genus, is generically different from the rest of the genus found in North America. This requires a different name for enoptes and its allies. Such a name has been proposed. It is Pseudophilotes Beuret, 1958, with European baton as its type species. Baton is cogeneric with enoptes, et al.
The probable reasons for this generic name being overlooked by American taxono-mists are two: the Zoological Record citation made no mention of nearctic members in Pseudophilotes; the paper in which the name was proposed is in a journal rarely seen in North America. The full citation for the description of Pseudophilotes is: Beuret, H., 1958, "Zur systematischen Stellung einiger wenig bekannter Glaucopsychidi (Lep., Lycaenidae)" Mitt. ent. Ges. Basel (N.F.) 8: 61-79, 1 pi., 12 figs.; 8: 81-100, 13 pis. The original description begins on page 100.
I wish to thank Dr. Lionel G. Higgins for calling this publication to my attention.
F. Martin Brown, Fountain Valley Rural Sta., Colorado Springs, Co., 80911.