All-male Progeny Research Articles

Search for genes involved in the temperature-induced gonadal sex differentiation in the tilapia, Oreochromis niloticus.

In the tilapia, Oreochromis niloticus, sex is determined by genetic factors (XX/XY) but temperature can also influence the gonadal sex differentiation. Elevated temperatures of 35 degrees C can generate functional male phenotypes if applied before and during sexual differentiation. The genes and mechanisms by which temperature acts on the cascade leading to sex differentiation have been investigated. Two strategies have been followed: 1) Search for novel genes by differential display, and 2) Expression studies of candidate genes. Genetically all-female and all-male progenies were reared at 27 degrees C (natural temperature) and at 35 degrees C (masculinizing treatment) and gonads dissected. Using differential display, we isolated a 300 bp cDNA (MM20C) from temperature-masculinized females. Virtual northern analysis revealed a 1.2 kb transcript in 35 degrees C treated females and males, but hardly any expression in natural females (27 degrees C). Semi-quantitative RT-PCR established a several-fold increase in MM20C expression in 35 degrees C masculinized fry. Elevated expression was observed in natural males (27 degrees C) with higher levels detected in those reared at 35 degrees C. Furthermore, we have analyzed as a candidate gene the P450 11beta-hydroxylase, an important androgen steroidogenic enzyme. Low levels of expression were found in natural males. This coincides with low concentrations of 11 ketotestosterone in the gonads before and during gonadal sex differentiation. Higher expression levels of 11beta-hydroxylase were detected in male gonads at 35 degrees C but levels in phenotypic males were similar to those found for natural females. Previous results reported that expression of aromatase is repressed by masculinizing treatments. Our study demonstrated that masculinizing-temperature can also stimulate the expression of other gene(s).

The Nature of Heterosis and Methods of Enhancing and Fixing It in a Series of Generations without Hybridization

The long-standing studies into the problem of heterosis on the silkworm and other objects are reviewed. Silkworms are divided by sex for hybridization using the genetic marking of the eggs by sex, an improved method of ameiotic parthenogenesis providing all-female progeny, or the method of obtaining all-male progeny as a result of the death of eggs with female embryos under the influence of two non-allele embryonic lethals balances in the Z-chromosome. The experimental data suggest that heterosis is determined by the heterozygosity of lethals and semilethals, rather than depending on the heterozygosity of all gene types. The number of modifier genes that control viability plays a big role in the vigor of heterosis. An effective method is proposed to enhance the vigor of heterosis through the selection of one or two parents of a hybrid for viability, both of which received a strong semilethal. In hybrids, this semilethal is suppressed by the normal allele, and then a more unbalanced complex of modifier genes initiates a heterosis two to three times more vigorous than in standard hybrids. A method is developed to fix heterosis through the backcrosses of females of the high-heterosis hybrids to the absolutely homozygous males of androgenetic origin obtained from these females. These crosses preserve the main genotype of the hybrid and eliminate lethals and semilethals, and, as a result, heterosis is not damped during standard intrahybrid reproduction.

Growth performance trials of genetically male tilapia (GMT) derived from YY-males in Oreochromis niloticus L.: On station comparisons with mixed sex and sex reversed male populations

Genetic manipulation of predominantly monofactorial sex determining mechanisms in the Nile tilapia Oreochromis niloticus is proposed as a technology for the mass production of all-male progeny for culture. Existing alternative methods for producing all-male tilapia, principally direct hormonal masculinization, have produced inconsistent results and are largely the preserve of scientists and developed country aquaculturists. Successful adoption of these techniques in developing countries is seriously limited by the number and complexity of factors involved in their effectiveness. Novel YY-male genotypes have been shown to be viable and to produce all- or nearly all-male (XY) progeny in crosses with normal XX females. This paper presents the results from a series of on-station growth performance trials of these genetically male tilapia (GMT) in three environments. Two comprehensive and replicated trials in extensively managed earthen ponds, compared the performance of GMT with sex reversed male (SRT) and normal mixed sex tilapia (MST). Three further, smaller experiments, compared the growth of GMT with that of MST populations in rice-cum-fish culture and under intensive culture in closed recirculating systems. These comparisons were made within the ‘Egypt-UCS’ strain of O. niloticus. Results indicate that culture of GMT populations can improve marketable yields under all environments. In the first experiment in ponds, GMT had significantly ( P = 0.003) higher yields than both MST (+ 58.8%) and SRT (+ 31.03%). The second experiment, following the same design, showed a similar trend, although differences were smaller and not significant. GMT produced yields 11.9% greater than MST in rice-cum-fish culture and 33.6–47.0% greater in recirculating systems. There was no recruitment in GMT pond populations whereas recruits were present in MST and SRT populations. Coefficient of variance for individual weight in ponds was significantly ( P < 0.05) lower for GMT than for MST for both pond experiments. GMT produced from novel YY-males in this strain has considerable potential for increasing yields from tilapia culture.

Production of ZZ females in the female-heterogametic black molly, Poecilia sphenops, by endocrine sex reversal and progeny testing

Feminization was achieved in the female-heterogametic viviparous P. sphenops by administering 200 mg β-estradiol or diethylstilbestrol per kg diet to newly born fry for 30 days. Treatment with the optimum dose of β-estradiol led to the production of a single homogametic (ZZ) female, which when crossed with a normal male, sired an all-male progeny. A comparison between production of P. reticulata homogametic males and homogametic P. sphenops females indicated that the treatment with the optimum dose of β-estradiol enhanced survival and production of ‘supermale’ (YY) in P. reticulata or ‘superfemale’ (ZZ) in P. sphenops. Hence, amenability of female-heterogametic viviparous fish to induced sex reversal is comparable with other species. However, P. sphenops suffered higher mortality and lower fecundity than P. reticulata.

Parthenogenesis-inducing microorganisms in Aphytis (Hymenoptera: Aphelinidae).

Production of males in uniparental lines of two species in the parasitic wasp genus Aphytis was induced by rifampicin, and male sexual functioning was determined. Wolbachia-specific 16S rDNA primers were used in a PCR in order to: (1) assess correlation between thelytokous reproduction and the presence of Wolbachia; (2) detect the loss of Wolbachia DNA in uniparental A. lingnanensis following antibiotic treatments, with or without the presence of a host; and (3) clone and sequence part of the Wolbachia 16S rDNA from the uniparental Aphytis species for phylogenetic studies. Males produced viable sperm that was transferred to the female spermatheca following mating. However, sperm failure to effect egg fertilization resulted in all-male progeny. Wolbachia were found in the two uniparental (A. lingnanensis and A. diaspidis) but not in the two biparental (A. lingnanensis and A. melinus) Aphytis lines tested. They can be detected in wasps up to 7 days following antibiotic treatments, regardless of the presence of host. The 16S rDNA for the symbionts in the two Aphytis species is virtually identical, and is most closely related to the Wolbachia found in Muscidifurax uniraptor (Pteromalidae).

Production of a high percentage of male offspring with 17α-ethynylestradiol sex-reversed Oreochromis aureus. I. Estrogen sex-reversal and production of F2 pseudofemales

This study aims at developing a production process of male monosex populations of tilapia without the use of steroids. The sex-reversal of O. aureus (male genotype, ZZ; female genotype, ZW) with an estrogen treatment produces pseudofemales with a male genotype (ZZ). Crossing these fish with normal males (ZZ) gives, in theory, 100% male offspring. The objective of this study was to develop this technique for mass production of pseudofemale O. aureus producing a high percentage of male offspring. Batches of 250 O. aureus fry were submitted during a 40-day period to 17α-ethynylestradiol treatments of 100, 150 and 200 mg · kg −1 of food. We obtained 93 to 98% females in the treated groups in comparison with 53% females in the control group. Females randomly taken from the treated groups were crossed with normal males. Out of 64 fish tested, 30 gave progenies with a high percentage of males (68 to 100%) and were considered as pseudofemales. Crosses were repeated ( n = 2–5) to test the sex ratio stability in successive progenies (variation from 0 to 16.4% of the male ratio). Fry from pseudofemales producing only 100% male progenies were submitted to a 17α-ethynylestradiol treatment of 150 mg · kg −1 of food to obtain F2 pseudofemales. The results of the sex-reversal were variable and fluctuated between 18 and 95% of females. After the elimination of the males, we obtained 725 sexually mature F2 pseudofemales. Tests of the progeny of 6 F2 pseudofemales gave 97.5 to 100% of males and showed the heritability of the high percentage male offspring feature of the selected fish. These results confirm the possibility of multiplication of the pseudofemale stock (F2) to obtain, on a large scale, all-male progenies. Although it would be difficult to obtain only 100% male offspring, this method has the advantage, when compared to the classical sex-reversal process with 17α-methyltestosterone, of producing high percentage male progenies without the use of steroid treatment.

Possible ecological consequences of heterospecific mating behavior in two tetranychid mites

Interspecific mating between the two-spotted spider mite,Tetranychus urticae Koch, and the Banks grass mite,Oligonychus pratensis (Banks), was documented using laboratory populations. The incidence of mating betweenT. urticae males andO. pratensis females was 26.0%, while that for the reciprocal mating was 18.8%. The incidence of mating was affected by both male and female species. Such matings may have several important ecological consequences. Interspecific matings resulted in all-male progenies. Thus, progeny sex ratios may be distorted by misdirected mating behavior. In addition, heterospecific mating resulted in lower fecundity than conspecific matings in the two-spotted spider mite, although not in the Banks grass mite. Aerial dispersal behavior of the two-spotted spider mite was also affected. Under crowded conditions and deteriorating resource quality, female mites exhibit an aerial dispersal posture that helps them to become airborne, and allows them to disperse long distances. Forty-two percent ofT. urticae females that mated with conspecific males exhibited this dispersal behavior, compared to only 3.6% for virgin females. The incidence of aerial dispersal behavior for females that mated with heterospecific males was intermediate (27.3%). The effects of these behavioral alterations on male and female fitness may depend on the population structure and resource distribution.

The heredity of sex determination in tilapias

Evidence for the genetic mechanism of sex determination in tilapias has been generated from interspecific hybridization, chromosome manipulations, sex inversion and intraspecific investigations. In some interspecific hybrids and hybrid derivatives, Mendelian segregations are found in sex ratio, i.e., 0 : 1, 1 : 1 and 1 : 3 segregations. Attempts were made to explain these ratios by a dual system of sex chromosomes whereby, in some species, the female is homogametic and the male heterogametic, while in another group of species the opposite is the case. This model, alone, is not capable of explaining further sets of empirical data, since in other crosses and gynogenetic broods sex ratios are variable and non-Mendelian. Series of single-pair, intraspecific spawns showed that sex ratio is a continuously variable trait, with a mean of about 50% and, in at least one species, a range of 0–100%. Sex ratio was also shown to be a stable trait and to respond to selection, behaving like a quantitative trait. Based on these facts, we hypothesize that some sex-determining factors are concentrated on one pair of chromosomes which thereby become the sex chromosomes. Presumably crossing-over takes place between these sex chromosomes, as demonstrated in other fish species. Further genetic determinants of sex are situated on other chromosomes, the autosomes. Segregation of sex chromosomes brings about Mendelian sex segretions in the absence of variation in autosomally carried sex determinants. Non-Mendelian sex segregations, continuous variation in sex ratios and response to selection could result from variation in autosomal sex determinants and crossing-over between sex chromosomes. We suggest that the genetic mechanism of sex determination in tilapias is analogous to that in platyfish, depending on variation in both sex chromosome and autosomally carried factors. Empirical evidence for this is not available for tilapias, due to the absence of sex-linked markers. In such a complex system, the chances of producing “super males”, which generate all-male broods with any female, in either interor intraspecific combination, appear small. We suggest that intraspecific investigations have a better chance than interspecific ones of advancing our knowledge of sex determination in tilapias, as well as producing stable broodstocks generating sex ratios tending to all-male progenies.

Progeny-testing selection of tilapia broodstocks producing all-male hybrid progenies — Preliminary results

Prolific and uncontrolled reproduction of tilapias in production ponds is one of the most serious limitations in tilapia culture. Monosex culture by manual sexing is a practical method to overcome this problem, but requires skilled manpower and is time consuming and wasteful. The early promise of a genetic solution by the use of interspecific all-male hybrids has not been realized on a commercial scale due to broodstock management problems. None of the existing genetic models for sex determination is capable of serving as a breeding tool. Furthermore, intrapopulation variation for sex determination was demonstrated in Israeli populations of Sarotherodon aureus and S. niloticus. In order to obtain reliable broodstocks for commercial production of all-male S. niloticus × S. aureus hybrids, single pairs consisting of a female from one species and a male from the other are progeny-tested. The selection criterion used is the sex ratio in the hybrid progenies of these interspecific crosses. In crosses involving a S. niloticus female and a S. aureus male, all-male progenies are required for selecting the parents. In the reciprocal crosses the required sex ratio is 1 female: 3 males. Preliminary results confirm that some, but not all, S. niloticus × S. aureus pairs yield all-male progenies.

House Fly (Diptera: Muscidae) Genetics: Field Studies of Males from a Male-Producing Strain1

Male house flies (Musca domestica L.), which produced only male progeny when mated with wild-type females were released on a dairy farm in Minnesota during the fly breeding seasons of 1978 and 1979. The progress and mating interactions of the released flies (designated as the PM strain) were monitored by recording sampling frequencies of 1) allozyme variants at an enzymatic marker locus, 2) all-male progenies produced by females fertilized in the field, and 3) all male progenies resulting from matings between field-sampled males and laboratory-reared wild-type females. Also, sex-ratios were recorded from all individual cultures produced by field-collected females. Mortality of the PM males was measured in cages placed at the test location. In addition, PM males marked with fluorescent pigments were released on two occasions during 1978 to determine recapture frequencies. Mark-release-recapture experiments using field-collected flies were used to estimate population sizes. The combined data indicated that the PM males failed to compete for mates during 1978. However, there was significantly higher number of all-male cultures produced by field-collected females during 1979. Mating competitiveness values of 0.21 and 0.12 were calculated for the PM males during 1978 using two methods of calculation. Corresponding values for 1979 were 0.45 and 0.42, respectively.

The ‘White-clubbed’ form ofSyntomosphyrum(Hym., Eulophidae) parasitic on tsetse flies

Cross-mating experiments are reported between adults of the typical, darkclubbed form ofSyntomosphyrum glossinaeWtstn., obtained from pupae ofGlossina pallidipesAust. from Kenya and ofG. palpalis(R.-D.) andG. morsitans submorsitansNewst. from Northern Nigeria, and the ‘white-clubbed’ form ofSyntomosphyrum, originally reported by Waterston from Nyasaland, obtained from pupae ofG. morsitansWestw. from Tanganyika.Fertilised eggs, giving rise to offspring of both sexes, were produced only by crosses between the strains of typicalS. glossinae. Crosses in either direction between the ‘white-clubbed’ form and typicalS. glossinaeresulted in all-male progeny, presumed to develop from unfertilised eggs. It is considered that this is evidence of a physiological barrier to reproduction between the two forms. The ‘white-clubbed’ form is therefore regarded as a distinct species.