Duration of Copulation in Poanes hobomok (Lepidoptera: Hesperiidae) and Some Broader Speculations.
Psyche 77(1):127-130, 1970.
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DURATION OF COPULATION IN
(LEPIDOPTERA : HESPERIIDAE)
AND SOME BROADER SPECULATIONS*
BY JOHN M. BURNS
Museum of Comparative Zoology, Harvard University Many aspects of diurnal lepidopteran reproductive biology are still poorly known. Duration of copulation - an awkward phrase which, for convenience, is here symbolized Ti - can readily be de- termined in various species but rarely has been. It is of interest not only as a behavioral element of possible taxonomic value but also as a highly critical time in the life cycle: copulation is, of course, required for insemination; but copulating individuals, being nlutually occupied and encumbered, must often be more vulnerable to preda- tion than separate ones are. Since the act of copulation is vital for contributing genetic material to the succeeding generation but is not performed without risk, one may ask, What fraction of adult life is, on an average, spent copulating? Answers depend on knowing such attributes as Tf and mating frequency, as well as adult longev- ity for each sex.
Progress has recently been made in gathering conlparative data on mating frequency by counting spermatophores dissected from reproductive tracts of wild females and in interpreting these data (Burns 1966, 1968; Shields 1968 ; Pliske, in prep.). On the other hand. Ti has received scant attention. Scattered observations include . ,
the following. An interspecific copulation involving pierid butterflies, Colias interior 8 X C. eurytheme 9, lasted 67 minutes (Ae 1956). Among crosses of C. eurytheme carried out to study the genetics of an intricate enzyme polymorphism (Burns and Johnson 1967), the two that were timed gave Tfs of 55 and 75 minutes. In Danaus plexippus, a nymphalid butterfly, "It is not known for what length of time the male and female remain . . . united, but on one occasion such a pair was found an hour and a half later on the same tree and in the same position" (Urquhart 1960). A related species, D, gilip-bus, copulates for a period of about one to (usually) several
hours (Brower, Brower and Cranston 1965). Indeed, timed copula- "Published with the aid of a grant from the Museum of Comparative Zoology at Harvard College.
Manuscript received by the editor December 10, 1969 Psii-he 77:127-130 119701. http:ffpsyche.cnlclub.orBf77/77- 127 html
21 24 27 30 33 36 39 42 45 48 51 54 57 60 Tf (minutes)
Frequency distribution of Tf in Poanes hobomok. 3
? 2 -
E l -
tions in this species have ranged from a low of 100 minutes to a high of 12 (å 3) hours (T. E. Pliske, personal communication). A pyrgine skipper butterfly, Erynnis tristis, copulated for a little less than one hour (Shields 1968).
Data reported below were obtained in the course of genetically analyzing sex-limited wing-color dimorphism in a hesperiine skipper, Poanes hoboinok (Burns, unpublished). All material used in this work came from southern New England: Rockfall and Portland, Middlesex County, Connecticut; vicinity of Mt. Tom, north of Holyoke, Harnpden County, Massachusetts; and Jacksonville, Wind- ham County, Vermont. Although, in nature, P. hoboi~zok is univoltine and spring-flying, a second generation was forced in late summer by laboratory rearing. On sunny days in August and September at Middletown, Connecticut, reared virgins were placed in outdoor screen cages, large enough (60" long X 28" wide X 39" high) to permit flight, and were continuously watched. Copulations were timed from beginning to end, with the result shown in Table I. The Tfs are normally distributed around a mean of 38 1/4 min- utes (fig. I). In view of their considerable length, the Tfs are remarkably consistent.
Males of P. hobomok are monomorphic but females are dimorphic: one female morph (light) is similar in facies to the male whereas the other (dark) is not. Seven experimental crosses involved light females and six, dark ones. Female color-pattern did not significantly affect Tf. Nor did the time of summer at which crosses occurred, later crosses not being significantly longer than earlier ones. In general, Tf, like so many behavioral phenomena, is best ap- proached statistically, with due regard, however, for prevailing weather conditions. Casual observations suggest that cloudiness and lower temperatures tend to prolong Tf, which is not surprising. Presunlably it cannot be shortened indefinitely because of the logistics of spermatophore production.
x = 38:
19701 Burns - Pounes hobomk 129
Taken together, the meager data assembled here from four un- related genera suggest, first, that Ty will tend to be a normally dis- tributed variable (in any particular species population and under similar environmental conditions) ; and, second, that it will vary widely from some groups of species to others. In the series Poanes : Erynnis : Colius : Dunuus, mean Trs run a gamut from 38 minutes to nearly one hour to roughly 66 minut,es to several hours. The excessively long Tf of D. gilippus may relate to the fact that individuals of this species are often distasteful to vertebrate predators that can learn to leave them alone. Similarly, it may be on this account that danaines can afford to mate so very many times (see Burns 1968; Pliske, in prep.). But inedibility does not explain why they mate so long 01- so much. Although it has been suggested that the high number of matings may partly derive from increased longevity conferred by distastefulness (Pliske, in prep.), far more than this must be involved because danaines will mate several times in what, for a butterfly, can only be considered rapid succession. For example, three pairs of D. plexippus in separate small outdoor cages at San Antonio, Texas, were seen to mate once or (usually) twice each day over a four-day period (R. 0. Kendall, personal commu- nication). The question remains open. A correlation noted, in D. gilippus, between high mating frequency and a low population density associated with great mobility (Burns 1968) hints at directions for future inquiry.
Until we have hard longevity data for these relatively long-lived danaine butterflies, we cannot be precise about the proportion of Table 1. Duration of copulation in 13 crosses of Poanes hobomok. Cross No. Date of Cross Female Morph Tf (min.) VIII-20-1963
130 Psyche [March
adult life actually given over to copulating. Unfortunately, data on longevity in the field are more laboriously got than are those on mating frequency and Ti. Yet all this information, from a variety of diurnal Lepidoptera, is needed for sound comparative analysis of evolutionarily critical features of reproductive biology. LITERATURE CITED
AE, S. A.
1956. Hybrids between Colias eurytheme and C. interior (Pieridae). Lepidopterists' News 10 : 9-14.
BROWER, I.,. P., J. V. Z. BROWER AND F. P. CRANSTON 1965. Courtship behavior of the queen butterfly, Danaus gilippus beren'.ce (Cramer). Zoologica 50: 1-39, 7 pis. BURNS, J. M.
1966. Preferential mating versus mimicry: disruptive selection and sex-limited dimorphism in Papilio glaucus. Science 153 : 551-553. 1968. Mating frequency in natural populations of skippers and butter- flies as d~etermined by spermatophore counts. Proc. Natl. Acad. Sci. 61: 852-859.
BURNS, J. M. AND F. M. JOHNSON
1967. Esterase polymorphism in natural populations of a sulfur butter- fly, Colias eurytheme. Science 156 : 93-96. PLISKE, T. E.
in prep. Mating frequencies of several species of New World butter- flies and skippers determined by spermatophore counts. SHIELDS, 0.
"1967" . Hilltopping, an ecological study of summit congregation behavior of butterflies on a southern California hill. J. Res. Lepidoptera 6 : 69-178.
URQUHART, F. A.
1960. The monarch butterfly. Toronto: Univ. Toronto Press.
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