Physiological properties and tailored feeds to support aquaculture of marbled crayfish in closed systems

The marbled crayfish (Procambarus virginalis) is a recently discovered freshwater crayfish species, which reproduces by apomictic parthenogenesis, resulting in a monoclonal, all-female population. The animals have become a popular source for nutritional protein in Madagascar and are increasingly being considered for commercial aquaculture. However, their potential has remained unclear and there are also significant ecological concerns about their anthropogenic distribution. We show here that the size and weight of marbled crayfish is comparable to commonly farmed freshwater crayfish. Furthermore, chemical analysis revealed a high chitin content in the marbled crayfish exoskeleton, which is a valuable source for the synthesis of chitosan and bioplastics. To allow the further evaluation of the animals in closed aquaculture systems, we developed tailored feeds that revealed an important role of methionine supplementation for animal growth. Additional analysis revealed a feed conversion rate of 1.4, which compares favorably to leading livestock for sustainable food production. Finally, we provide a concept for ecologically safe marbled crayfish aquaculture, based on key physiological characteristics that mitigate the invasive potential of the animals.

The evolution of meiotic sex and its alternatives

Meiosis is an ancestral, highly conserved process in eukaryotic life cycles, and for all eukaryotes the shared component of sexual reproduction. The benefits and functions of meiosis, however, are still under discussion, especially considering the costs of meiotic sex. To get a novel view on this old problem, we filter out the most conserved elements of meiosis itself by reviewing the various modifications and alterations of modes of reproduction. Our rationale is that the indispensable steps of meiosis for viability of offspring would be maintained by strong selection, while dispensable steps would be variable. We review evolutionary origin and processes in normal meiosis, restitutional meiosis, polyploidization and the alterations of meiosis in forms of uniparental reproduction (apomixis, apomictic parthenogenesis, automixis, selfing) with a focus on plants and animals. This overview suggests that homologue pairing, double-strand break formation and homologous recombinational repair at prophase I are the least dispensable elements, and they are more likely optimized for repair of oxidative DNA damage rather than for recombination. Segregation, ploidy reduction and also a biparental genome contribution can be skipped for many generations. The evidence supports the theory that the primary function of meiosis is DNA restoration rather than recombination.

Apomictic parthenogenesis in a parasitoid waspMeteorus pulchricornis, uncommon in the haplodiploid order Hymenoptera

Although apomixis is the most common form of parthenogenesis in diplodiploid arthropods, it is uncommon in the haplodiploid insect order Hymenoptera. We found a new type of spontaneous apomixis in the Hymenoptera, completely lacking meiosis and the expulsion of polar bodies in egg maturation division, on the thelytokous strain of a parasitoid waspMeteorus pulchricornis(Wesmael) (Braconidae, Euphorinae) on pest lepidopteran larvaeSpodoptera litura(Fabricius) (Noctuidae). The absence of the meiotic process was consistent with a non-segregation pattern in the offspring of heterozygous females, and no positive evidence was obtained for the induction of thelytoky by any bacterial symbionts. We discuss the conditions that enable the occurrence of such rare cases of apomictic thelytoky in the Hymenoptera, suggesting the significance of fixed heterosis caused by hybridization or polyploidization, symbiosis with bacterial agents, and occasional sex. Our finding will encourage further genetic studies on parasitoid wasps to use asexual lines more wisely for biological control.

ON THE USELESSNESS OF MEN — COMPARISON OF SEXUAL AND ASEXUAL REPRODUCTION

A comparison of sexual with asexual reproduction in the Penna aging model for a single species shows the separation into males and females at a disadvantage due to the halved number of births. Also meiotic and apomictic parthenogenesis and hermaphroditism seem better than sex, even when the individuals follow the suggestion of Jan et al. to engage in sex only when their lifes are endangered by a large number of harmful mutations. In our comparison, we looked only for intrinsic effects, not for external influences like parasites or environmental catastrophes.

Fine Structure of Spermatogenesis in the Snail Tarebia Granifera (Melaniidae)

Jacob (1), citing chromosomal studies, emphasized the extreme rarity, or possible non-existence of viable males in observed Indian populations of Melanoides tuberculatus, of the same family as Tarebia granifera. The snail population, almost totally female in chromosomal count, were presumed to reproduce parthenogenetically; no sexual reproduction was in evidence (no sperm were ever reported observed). Similar findings were reported by Pace (2) in his comprehensive study of populations of T. granifera on the island of Taiwan. Pace, correlating his own findings with those of Jacob, suggested that T. granifera reproduce by apomictic parthenogenesis.A population of T. granifera is found in Brackenridge Park, San Antonio, Texas. The reproductive tract of randomly selected snails was prepared for electron microscopy. The tissue was fixed in 3% glutaraldehyde in 0.1 M sodium phosphate buffer, postfixed in buffered 1% Osmium tetroxide, dehydrated, and embedded in Spurr embedding media.