New Observations on Gametogenesis,Fertilization, and Zygote Transformation in Plasmodium gallinaceum1

The ultrastructure of the sexual stages of Plasmodium gallinaceum during gametogenesis, fertilization, and early zygote transformation is described. New observations are made regarding the parasitophorous vacuole (PV) of gametocytes and the process of emergence in male and female gametocytes. Whereas female gametocytes readily disrupted both the PV membrane and host cell plasmalemma during emergence, male gametocytes frequently failed to break down the plasmalemma of the host cell. New observations and hypotheses are presented on the behavior of the male gamete nucleus. Following fertilization, the male nucleus appears to travel through a channel of endoplasmic reticulum in the female gamete before fusing with the female nucleus at a region in which the nuclear envelope is thrown into extensive convoluted folds. Polarization of the zygote nucleus, in association with the appearance of a perinuclear spindle of cytoplasmic microtubules, preceded all other changes in the developing zygote. After nuclear polarization becomes apparent, electron-dense material is deposited beneath the zygote pellicle, and a canopy is formed which eventually extends over the entire apical end of the developing ookinete. As the apical end begins to extend outward, polar rings, micronemes, and subpellicular microtubules become visible in this portion and a “virus-like” inclusion known as a crystalloid is formed in the posterior portion of the zygote. When female gametes are prevented from being fertilized, the cytoplasm at 24 h after gametogenesis is devoid of most of those organelles found in the developing zygote or the mature ookinete. The cell is surrounded only by a single membrane. Although at various points beneath the membrane there are deposits of electron-dense material reminiscent of those deposited in the zygote, no further development of ookinete structures takes place in the unfertilized female gamete.     

Shift from independent to dependent colony foundation and evolution of 'multi-purpose' ergatoid queens in Mystrium ants (subfamily Amblyoponinae)

Division of labour improves fitness in animal societies. In ants, queens reproduce, whereas workers perform all other tasks. However, during independent colony founding, queens live as solitary insects and must be totipotent, especially in species where they need to forage. In many ants, solitary founding has been replaced by dependent founding, where queens are continuously helped by nestmate workers. Little is known about the details of this evolutionary transition. Mystrium rogeri from Madagascar and Mystrium camillae from Southeast Asia (subfamily Amblyoponinae) have winged queens, but three congeneric species from Madagascar reproduce with permanently wingless queens instead. We show that this 'ergatoid' caste has distinct body proportions in all three species, expressing a mixture of both queen and worker traits. Ergatoid queens have functional ovaries and spermatheca, and tiny wing rudiments. They can be as numerous as workers within a colony, but only a few mate and reproduce, whereas most behave as sterile helpers. The shape of their mandibles makes them unsuited for hunting and, together with a lack of metabolic reserves (i.e. in the form of wing muscles), this means that ergatoid queens cannot be solitary foundresses. In comparison with winged queens, ergatoid queens are less costly per capita and they experience lower mortality. They remain in their natal colonies where they can either reproduce or function as helpers, making them a 'multi-purpose' caste. Within the Amblyoponinae, ergatoid queens replace winged queens in Onychomyrmex as well. However, in this genus, ergatoid queens are 'sole-purpose', few are produced each year and they reproduce but do not work. Hence, different types of ergatoid queens evolved to replace winged queens in ants.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 98 , 198–207.     

Development of Melanocyte Progenitors in Murine Steel Mutant Neural Crest Explants Cultured With Stem Cell Factor,Endothelin-3, or TPA

Stem cell factor (SCF) has been suggested to be indispensable for the development of neural crest cells into melanocytes because Steel mutant mice (i.e., Sl/Sf¹) have no pig-mented hairs. On the other hand, it has been demonstrated that the addition of endothelin 3 (ET-3) or TPA to neural crest cell cultures can induce melanocyte differentiation without addition of extrinsic SCF. In this study, we excluded the influence of intrinsic SCF by using SI/SI mouse embryos to study more precisely the effects of natural cytokines, such as extrinsic soluble SCF or ET-3, or chemical reagents, such as TPA or cholera toxin. We found that SCF is supplied within the wild-type neural crest explants and that ET-3 cannot induce melanocyte differentiation or proliferation without SCF. These results indicate that SCF plays a critical role in survival or G1/S entry of melanocyte progenitors and that SCF initially stimulates their proliferation and then ET-3 accelerates their proliferation and differentiation. TPA has the ability to elicit neural crest cell differentiation into melanocytes without exogenously added SCF but it is not as effective as SCF because many more melanocytes developed in the wild-type neural crest explants cultured with TPA.     

EFFECT OF ECDYSONE ON THE OVARIAN DEVELOPMENT OF BOMBYX SILKWORM*

From the ligation experiments, it is indicated that the secretion from prothoracic glands during early pupal period induces the ovarian development in female pupa of the silkworm, Bombyx mori. The exogenous β-ecdysone injected into isolated pupal abdomen also induces the initiation of the ovarian development.     

The Genesis and Transmission of Epidermal Potentials of Newt Embryonic Cells in Vivo and in Vitro

The genesis and transmission of action potentials in epidermal cells of a newt ( Cynops pyrrhogaster ) embryo were investigated quantitatively in vivo during development and in vitro in the absence of nerve cells. Typical action potentials, composed of a fast spike followed by a slow action potential, can be recorded from any of the epidermal cells from Stage 24/25 to 35/36. The potential is graded with current intensity, and only the slow component induces transmission to other epidermal cells. The fast spike is found in all epidermal cells from Stage 24/25 to Stage 50; it is abolished by Stage 52. The slow potential disappears at Stage 38 just before or after hatching. The cultured epithelioid explants (epithelioid aggregate) and cultured monolayer cells taken from the presumptive epidermal tissue of the ectoderm of the pregastrula, indicate that sequential changes in the genesis of the dual action potentials are similar to those of the intact embryo. In monolayer cell culture devoid of nerve cells, the epidermal cells, also generate a two-step action potential. Such two-step potentials are characteristic of both ciliated and non-ciliated epidermal cells and occur even during mitotic activity. In contrast, cultured neural plate cells isolated from the neurula generate typical spike-like action potentials.     

Co-sedimentation of Actin, Tubulin andMembranes in the Cytoskeleton Fractions from Peas and Mouse 3T3 Cells

Pea stem tissue (Pisum sativum L. var. Alaska) was homogenizedin a recently-developed cytoskeleton-stabilizing buffer, CSB,(Abeand Da vies, 1991) and homogenates electrophoresed and blottedon to membranes. Blots probed individually withantibodies toactin, alpha-tubulin, and beta-tubulin, revealed bands withapparent molecular weights of 42, 46, and 48–50 kDa,respectively.Blots probed with all three antibodies simultaneously revealedall three bands which could be distinguished in thesame lane.Homogenates of mouse 3T3 cells yielded an actin band at about42 kDa, but both alpha- and beta-tubulin appeared atabout 50kDa and thus could not be distinguished on blots probed simultaneously.This ‘triple-blotting technique’ was, therefore,suitablefor pea tissue, but not for mouse tissue. In pea tissue, sedimentabletubulin and actin were found maximally in the 4000 xg pelletand less in successive 15000 and l00000xg pellets. Both EGTAand Mg²⁺ which had been found earlier to beessential for stabilityof the actin cytoskeleton as revealed by fluorescence microscopy,were essential for co-sedimentation of actinand tubulin. Incontrast to the results with pea stems, only the actin componentof the cytoskeleton could be isolated from mouse 3T3 cells usingCSB. Pea tissue was homogenized in CSB without PTE and the resultingcytoskeletal pellets resuspended in actin- or tubulin-solubilizingbuffers with and without PTE. In the absence of PTE, the bufferssolubilized their appropriate cytoskeletal protein, but littleof the other protein, while in the presence of PTE both proteinswere quite effectively solubilized by both buffers. Incontrast,in CSB with or without PTE, both proteins remained in the sedimentablefraction. These results, taken together withother evidence,indicate that microtubules, as well as microfilaments are importantcomponents of the sedimentable cytoskeletonfraction of peasand that the membrane system is intimately involved in organizationof the cytoskeleton in peas. Key words: Actin, tubulin, membranes, detergent, Ca²⁺, Mg²⁺, cytoskeleton     

Negative genetic correlation between diapause duration and fecundity after diapause in a spider mite

Abstract.  1. Recently, the costs of diapause, i.e. the reduction of fecundity after diapause, have been examined from an evolutionary perspective.
2. The evolution of this trade-off should be clarified by quantitative genetic approaches, as theoretical studies address the evolution of multiple traits. Nevertheless, previous studies on the costs of diapause have been based on phenotypic correlations or experimental manipulations, whereas the genetic background underlying this trade-off remains unclear.
3. In the present study, a half-sib breeding design was used to examine the quantitative genetic relationships between diapause duration and post-diapause fecundity in the Kanzawa spider mite Tetranychus kanzawai Kishida (Acari: Tetranychidae).
4. The heritability of diapause duration, post-diapause total fecundity, and post-diapause early fecundity were 0.37, 0.14, and 0.11 respectively. Genetic correlations between diapause duration and post-diapause total fecundity, and between diapause duration and early fecundity were both significantly negative (–0.70 and –0.90 respectively). These results suggest that the cost of prolonging diapause duration is genetically based, and that these life-history traits respond to natural selection acting on them simultaneously.