Large proportions of nonhybrid progeny result from controlled crosses between Palmer amaranth and common waterhemp, both dioecious weeds. Agamospermy was proposed as an explanation for this phenomenon, and here we provide evidence in support of this hypothesis. We evaluated 60 nonhybrid offspring from two interspecific crosses, and all plants were females and had DNA content values similar to the female (Palmer amaranth) parent. Among nine hybrids resulting from these crosses, eight were nonviable (lethal or neuter), and only one hybrid allowed for continued gene movement. Cytogenetic evaluation of this hybrid revealed triploidy, further supporting the occurrence of unreduced gametes in these species. In light of this new evidence, we examine earlier data regarding Palmer amaranth by common waterhemp hybridization and suggest some prior conclusions may be premature.

A method of geometric morphometrics was used to characterize body shape variation inmeiotic gynogenetic and triploid sea bass in comparison with diploid controls. A total of13 coordinate landmark data were recorded on the profile of 34-month-old control(n = 81), gynogenetic (n = 117) and triploid(n = 131) siblings generated from two females (A and B). Three mainaxes of morphometric variation were consistent, and these accounted for 60.8 and 57.6% ofthe total variability in females A and B, respectively. There were significant shapedeviations of triploid and gynogenetic fish relative to the controls, and differences wereparticularly evident in the progeny of one female. Overall, triploids displayed a moreslender shape than diploids, whereas gynogenetic fish were deeper bodied and had flexedcaudal peduncles and cranial features. The results are discussed especially in relation tothe characterization of triploid fish for commercial purposes.

Karyotyping of Fasciola hepatica samples from Britain and Ireland has identified a triploid isolate which is effectively aspermic, rendering it necessarily asexually reproducing. Considering the extensive presence of asexually reproducing diploid and triploid Fasciola in Asia it is suggested that facultative gynogenesis is widespread in this parasite. This has important implications for the population genetics and evolution of Fasciola, especially in relation to the development and spread of drug resistance, and must be considered in the mathematical modelling of this process.

Retention of the second polar body for the production of triploid Arctic charr (Salvelinus alpinus) was induced by 65 MPa (650 bar) pressure shocks applied 30, 40 or 50 min after fertilization, each shock lasting 5 min. Triploid yield (percentage of relative survival to control × percent triploidy) varied from 55 to 100 % and it was generally superior to 80. Despite increased mortality and decreased growth in diploid charrs during the spawning period, growth and survival did not differ between diploid and triploid Arctic charr up to and during their third year of life. Most of the triploid males had developed testis, but they did not render milt; few triploid females had developed ovaries. Fecundity of triploid females was low and fertilized eggs from triploid females did not hatch.

The aquaculture production of all-female triploid (sterile) populations is recognized as being of potential advantage for many species of fish where sexual maturation is not desired. All-female triploids have been produced by inducing triploidy in eggs that had been fertilized with monosex female sperm. However, monosex stocks to produce this type of sperm are currently available only for a limited number of economically important species. To circumvent this problem, an alternative method would be the direct fertilization of tripoid embryos. In Pacific salmon, pressure shocks applied shortly after fertilization have consistently resulted in high yields of tripoids, and feminization by direct estrogen treatment has also been shown to be highly effective if applied shortly after hatching. In this study, coho salmon eggs were made triploid by a pressure shock of 633 kg/cm2 for 4 min, applied 20 min after fertilization and incubation at 10 °C. Some of the resulting embryos were then feminized with estradiol-17β in single 2-hour immersion treatments at 400 μg/liter, administered 1 and 8 days after hatching. Six months later, when the fish were juveniles, analysis of the DNA content of erythrocytes by flow cytometry revealed a 100% induction of triploidy, while histological examination of the gonads showed 82% females, which were completely devoid of oocyte development and thus genetically sterile. These manipulations reduced survival during early stages of development but survival became stable later. Together, these results suggest that the production of sterile fish by direct feminization of induced triploids could be of particular advantage for those species in which all-female stocks are yet not available or difficult to obtain.

Triploid hybrids between female rainbow trout (Oncorhynchus mykiss) and male arctic char (Salvelinus alpinus), together with triploid and diploid rainbow trout controls from the same dams, were tested in freshwater farming from fry stage up to the age of 3 years. When farming was operated in cold water, the survival rate of the hybrids was as good as those of the diploid and triploid rainbow trout. Hybrid growth was noticeably hindered relative to that of diploid controls at the beginning of the juvenile period, but this was partly tempered later on by the effect of diploid sexual maturation; at 3 years of age, the hybrid weighed 20% less than the diploid rainbow trout and did not differentiate significantly from the triploid rainbow trout. The impairment of sexual maturation was very much the same in the hybrid as in the triploid rainbow trout, and dressing traits were therefore quite similar, despite a slight difference in perivisceral fat losses of immature individuals, to the advantage of the hybrid. These results allow one to consider the suitability of this hybrid for large-sized fish production in cold water farming.

Heat shocks effective for the production of triploid brown trout (Salmo trutta) were optimized: 28 °C shocks lasting 10 to 15 minutes and applied 5 minutes after fertilization induce very high rates of triploidy (close to 100%) without causing much mortality; they can therefore be proposed for mass production of triploid brown trout. Female homogamety in that species is also demonstrated from analysis of gynogenetic progenies and progenies of sex-inverted females. Although the efficiency of masculinizing hormonal treatments requires further improvement, production of all-female sterile populations is now possible in this species promising for European sea-farming.

An effective treatment using cytochalasin B (1 mg CB/ml dimethylsulfoxyde in 1 litre of sea water) was developed to induce triploidy in the Manila clam Ruditapes philippinarum (Adams and Reeve). The percentage of induced triploidy was assessed by karyological examination of embryos and spat. The treatment was found to be optimal beween 20 to 35 minutes post-insemination exposure to CB, at 25 °C, and produced 75.8 ± 5.7% triploid embryos on the average over four experiments. Growth and survival of larvae to metamorphosis were recorded for two different rearings each split into two replicates. Both larval rearings showed similar survival up to settlement: 19.3 and 27.0%, on average over two replicates, in the treated batches relative to the controls. Mean shell length of treated larvae was significantly smaller than that of the controls in one of the larval rearings, where mortality of triploids relative to diploids within the treated group was low (21.0%). No significant differences in shell length were observed in the other trial where a high rate of differential mortality (64.5%) was recorded.

Survival and growth performances of autotriploids in rainbow trout (Salmo gairdneri) and three types of triploid hybrids between female rainbow trout and brown trout males (Salmo trutta,) coho salmon males (Oncorhynchus kisutch) and brook trout males (Salvelinus fontinalis) were analysed relatively to the parental species in freshwater farming conditions. At the end of the immature period, autotriploids exhibit moderate but significant depression relative to the control for both survival (about 25% depression) and growth (10 to 15% depression). Most of this depression is established during the first three months of life, triploids appearing very similar to the control later on. At the onset of sexual maturation at 2 years old, relative value of triploids becomes higher than that of the control, for both survival and growth. Long term evaluation (2+ or 3+) balances in favor of triploids with particular advantage for triploid females. Triploid hybrids exhibit much more important depression in early survival (up to 60%). Later on, their survival remains always lower than those of parental controls. Their growth performances are intermediate between their two parental species. Despite a relative advantage for these groups during the onset of sexual maturation in control groups, especially for growth, long tem evaluation is in favor of diploid rainbow trout, but in some specific cases.