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Adult Age and Breeding Structure of a Hawaiian Drosophila silvestris (Diptera: Drosophilidae) Population Assessed via Female Reproductive Status

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Title:Adult Age and Breeding Structure of a Hawaiian Drosophila silvestris (Diptera: Drosophilidae) Population Assessed via Female Reproductive Status
Authors:Craddock, Elysse M.
Dominey, Wallace
Date Issued:Jul 1998
Publisher:University of Hawaii Press
Citation:Craddock EM, Dominey W. 1998. Adult age and breeding structure of a Hawaiian Drosophila silvestris (Diptera: Drosophilidae) population assessed via female reproductive status. Pac Sci 52(3): 197-209.
Abstract:The Upper 'Ola'a Forest population of Drosophila silvestris, a
dipteran species endemic to the island of Hawai'i, was studied to investigate
adult age and breeding structure of this natural population. Analyses of insemination
status and ovarian developmental stage were carried out for both
laboratory-reared and field-collected females, including a sample of F1 individuals
that had been marked and released into the field population shortly
after adult eclosion. Marked females were recaptured from 7 days old to more
than 4 months after· release; this sample included representatives of all seven
ovarian developmental stages scored (from early previtellogenesis to fully
mature ovaries). The profile of female reproductive maturation in the field flies
was similar to that in laboratory-reared flies, except that developmental rates
were substantially slower and more variable in the natural population, largely
because of lower field temperatures. Using information on ages and ovarian
condition of the marked females, an independent population sample of wildcaught
adult females was estimated to include 28% young flies approximately
2 to 3 weeks old (ovaries previtellogenic), 37% maturing flies from 2 to 4 or
more weeks old (vitellogenic ovaries), and 35% reproductively mature flies from
1 to more than 4 months old. The unexpected excess of young flies in the adult
population up to 4 or 5 weeks old (65%) can be interpreted by several alternative
hypotheses (e.g., age-related dispersal, predation, location of suitable
breeding substrates, baiting effects), but further studies are required to confirm
whether this age pattern is typical. Earliest onset of female receptivity occurred
at mid vitellogenesis in both field and laboratory flies, with insemination
frequencies increasing as ovaries matured. It is surprising that field females
showed higher mating success at all competent ovarian stages than females
reared in the continuous presence of males. Further, all reproductively mature
field females, both marked and unmarked, were inseminated. In this species,
sexual selection acts primarily on males, with the lack of female mating failure
in the field providing no evidence of sexual selection among adult females.
Appears in Collections: Pacific Science Volume 52, Number 3, 1998

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