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A Study of Hybrids in Colias (Lepidoptera, Pieridae)

Shigeru Albert Ae
Evolution
Vol. 13, No. 1 (Mar., 1959), pp. 64-88
DOI: 10.2307/2405945
Stable URL: http://www.jstor.org/stable/2405945
Page Count: 25
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A Study of Hybrids in Colias (Lepidoptera, Pieridae)
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Abstract

1. The following interspecific hybridizations among 6 species of North American Colias were attempted: a) C. eurytheme and C. philodice females × C. alexandra, C. interior, and C. scudderi males b) C. eurytheme females × C. meadii males c) C. philodice females × C. meadii males d) C. interior female × C. eurytheme and C. philodice males e) C. meadii female × C. eurytheme and C. philodice males. f) C. eurytheme × C. philodice Crosses a) and b) were tried more extensively than c), d), e), and f). 2. C. eurytheme and C. philodice females do not mate with C. alexandra, C. interior, and C. scudderi males as freely as they mate with the males of their own species. The same is true between C. eurytheme females and C. meadii males. 3. Interspecific matings between C. eurytheme and C. philodice seem to take place more readily than the pairings mentioned above. However, interspecific matability between C. eurytheme and C. philodice is definitely lower than intraspecific matability within each of the two species. 4. The following interspecific matings were obtained: a) 5 pairs between C. eurytheme orange females and C. alexandra males b) 5 pairs between C. eurytheme "alba" females and C. alexandra males c) 2 pairs between C. eurytheme orange females and C. philodice males d) 1 pair between C. eurytheme orange female and C. interior male e) 1 pair between C. eurytheme "alba" female and C. meadii male f) 1 pair between C. philodice "alba" female and C. alexandra male g) 1 pair between C. philodice yellow female and C. alexandra male All of them copulated for a period of more than one hour, and are therefore "successful" in the sense of duration. A copulation of about 5 minutes duration between C. eurytheme orange female and C. scudderi male was also obtained. 5. Fertile eggs were obtained from the following matings: a) 4 pairings between C. eurytheme "alba" females and C. alexandra males b) 2 pairings between C. eurytheme orange females and C. alexandra males c) 2 pairings between C. eurytheme orange females and C. philodice males d) 1 pairing between C. eurytheme orange female and C. interior male e) 1 pairing between C. philodice yellow female and C. alexandra male Two C. eurytheme orange females which mated with C. alexandra males laid only infertile eggs. The other 5 females did not lay any eggs. 6. The egg fertilities of the above fertile females were generally high. 7. Forty-six males and one female of F1 hybrids between C. eurytheme and C. interior, and a total of seven males and one female of F1 hybrids between C. eurytheme and C. alexandra were obtained from three broods. 8. F1 hybrid males of C. eurytheme × C. interior mated readily with C. eurytheme females. Six matings of this kind were obtained. While two of the females laid fertile eggs and one laid only infertile eggs, others did not lay any eggs. The fertilities of eggs which were laid by the above two females were high, and many offspring were obtained. 9. The matabilities and egg fertilities of the females and matabilities of the males of the above mentioned offspring were high. 10. F1, F2, and backcross to C. eurytheme from C. eurytheme × C. philodice matings were also obtained. 11. F1 hybrid males of C. eurytheme × C. interior and C. eurytheme × C. alexandra seem to have the same developmental rates as C. eurytheme at summer conditions. The developmental rates of their female sibs are very slow. F1 hybrid female larvae of C. eurytheme × C alexandra seem to have an obligatory hibernating stage, and in this they resemble C. alexandra. 12. Larvae of hybrids of C. eurytheme × C. interior stopped feeding mainly during the 3rd instar at conditions of 75⚬ F and 10 hours light a day. 13. The ground (pterine) coloration of the wings of F1 hybrids of C. eurytheme × C. interior and of C. eurytheme × C. alexandra are intermediate between the orange of C. eurytheme and the yellow of C. interior and C. alexandra. 14. Orange and intermediate ground coloration of the wings appeared among progeny from F1 hybrids of C. eurytheme × C. interior backcrossed to C. eurytheme. 15. The new data support the assumption that orange and yellow ground coloration of the wings of C. eurytheme and C. philodice are controlled by one or two pairs of genes. 16. Black wing borders of female F1 hybrid C. eurytheme × C. interior, C. eurytheme × C. alexandra, and female progeny from F1 hybrid C. eurytheme × C. interior backcrossed to C. eurytheme are as wide as the borders of one parental species, C. eurytheme, which has wider borders in the female than do other three species. 17. Colors of the wing fringes of F1 hybrid C. eurytheme × C. interior and C. eurytheme × C. alexandra somewhat resemble the fringes of C. interior and C. eurytheme, respectively. 18. The hind wing discal spot is orange on F1 hybrid C. eurytheme × C. alexandra. 19. Submarginal dark spots and the dark spot of the costa of the hind wing are present in F1 hybrid C. eurytheme × C. interior and C. eurytheme × C. alexandra. 20. The dusting of fuscous scales on the underside of the wings of F1 hybrid C. eurytheme × C. alexandra gives a somewhat grayish-green coloration, as in C. alexandra. 21. F1 hybrids, particularly males, of C. eurytheme × C. interior and C. eurytheme × C. alexandra may be produced in nature, and backcrosses of them to their parental species also may occur. However, any significant production of F2 hybrids in nature is very doubtful. 22. The broad speciation of the genus Colias in North America and the taxonomic relationship between C. eurytheme and C. philodice were discussed.

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