The Collection of Spermatozoa from the Domestic Fowl and Turkey

When mixtures of semen containing an equal number of spermatozoa from two males are inseminated, the males usually sire disproportionate numbers of the offspring. In this study, when a mixture of equal numbers of spermatozoa from a Columbian (C) and a Leghorn (L1) cock was inseminated, the C male sired 34% of the offspring. The proportion of offspring was constant regardless of age of males, season, total number of spermatozoa, breed of hen or the interval from insemination to the time of egg-lay over a 15-day period after insemination. The proportion of C offspring observed from inseminating nine different ratios of spermatozoa arranged progressively from 1C :9L, 2C:8L and so on, was 10%, 20%, 23%, 34%, 38%, 44%, 58%, 74% and 82%. These results were in close agreement with mathematically derived estimates. It appears that the relationship between sperm ratios and the proportions of offspring sired by two males competing heterospermically is dependent on the ratio of the number of competing spermatozoa but not on total number, season, breed of hen or the interval from insemination to fertilization.

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The effect of ratios and numbers of spermatozoa mixed from two males on proportions of offspring

1.

In three experiments on the effects of mating order, wild-type male deer mice, Peromyscus maniculatus bairdi were tested in competition with brown recessive, wide-band agouti, and blonde mutant males. Females of the homozygous recessive genotype received two ejaculatory series from a male of each genotype; mating order was varied. There were no significant effects of mating order on litter composition. In a parallel experiment wild-type and albino male prairie voles, Microtus ochrogaster, mated for one ejaculation each with albino females. There was a significant advantage with respect to litter composition for the male ejaculating last. Together with data from other species, these results suggest that effects of mating order are highly species-specific and must be evaluated for each species before speculations are made regarding the effects of multiple matings.




2.

Males of various genotypes differed with respect to differential fertilizing capacity. Wild-type male deer mice outcompeted both brown recessive and wideband agouti males. The combinations of blonde and wild-type deer mice and albino and wild-type prairie voles yielded strain differences in litter composition in one mating order but not in the other. Counts of the numbers of sperm from males of different genotypes in the uteri of females revealed no sigificant strain differences. Thus, strain differences are not simply a function of sperm numbers. 3. Female deer mice mated or exposed to more than one male had a lower probability of pregnancy than those mated for comparable numbers of ejaculations with one male in previous studies. Additional data on pregnancy initiation in females of the brown-recessive genotype mated with one male revealed them to be only slightly less likely to become pregnant than wild-type females. Strain of male had little effect. 4. No significant effects on litter composition were attributable to the length of the delay between matings by successive males. This was established both via correlational analyses of the data from the mating order studies and in an additional experiment in deer mice in which delays of 2 h were imposed between the last ejaculation by the first male and introduction of a second male. 5. Litter composition in deer mice reflects the number of ejaculations attained by each of two males. In one experiment, female deer mice mated first with a blonde male and then with a wild-type male. The blonde male delivered three ejaculations and the wild-type male one ejaculation in one condition and the wild-type male three ejaculations and the blonde male one in the other. Litter composition was significantly affected.

Studies of sperm competition in two species of muroid rodents

The effectof time after insemination on fertility and embryonic loss has been studied for each day’s egg production (60-150 eggs per day) by direct observation of chicken eggs after 18 days of incubation, The resultsshowed a significantinitialincrease in fertilitywith sperm storage from day I (firstday of fertileeggs) to day 3, followed by a few days of high fertility which was then followed by a linear decline through 18 days. Embryonic death was higher initially,reduced to a minimum when fertility was maximum, and increased linearly with increasing age of spermatozoa until fertilitywas reduced to a low level. The effect on fertilityand embryonic loss was influenced significantlyby both the male and female as well as time after insemination, and embryonic loss was negatively related to fertilitylevel of the male. That embryos die at an earlierage due to fertilizationby aged sperm wa s not conclusively confirmed in this study.

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L. C. Dunn

Papers

Selective Fertilization in Fowls