Cell Adhesion and Fusion Induced by Insemination in Zona-Free Hamster Eggs: Electrophysiological Monitoring of the Fusion Process

Cell adhesion and fusion were found to occur in zona-free hamster eggs placed in contact and then inseminated. A cytoplasmic fusion occurred in 7% of paired eggs mainly between 10 and 50 min after insemination. All other eggs that failed to fuse adhered tightly to one another within about 1 hr. Electrophysiological monitoring of the fusion process revealed that an electrical coupling (EC) suddenly appears between apposed eggs and completed within 2–15 min as the first step of cell fusion. Periodic hyperpolarizing responses (HRs), which have been found previously in fertilized hamster eggs to reflect a periodic increase in cytoplasmic Ca²⁺ ions, become gradually synchronized and completely coincide in paired eggs 10–30 min after the establishment of EC. Thus the paired eggs become an electrically single cell as the second step. Then the boundary between the eggs breaks down, resulting in formation of a single, spherical egg in several minutes. On the other hand, most of adhered eggs showed neither EC nor synchronization of HRs. Some adhered eggs showed only a low efficiency EC.     

PLASMALEMMA POTENTIAL IN NITELLA

A considerable part of the response of the vacuolar potentialof Nitella flexilis to the change of external KCl, NaCl, RbCl,LiCl, or CaCl₂ concentration is caused by the response of thecell wall (a cation exchanger) to the external medium. The potentialswere measured on the internodes whose cell sap was exchangedfor simple salt solutions. The potential difference across theplasmalemma which is the internal potential measured againstthe cell wall phase changes largely with the change in concentrationof the external KCl, but also more or less with that of theexternal NaCl, LiCl or RbCl. CaCl₂ depolarizes the plasmalemmapotential by about 50 mv when the concentration is increasedfrom 10^–5 M to 10^–3 M, and hyperpolarizes it againby about 40 mv from 10^–3 M to 10^–1 M leaving thelevel of the peak of the action potential almost unchanged. ¹This work was supported by Research Grants from the Ministryof Education of Japan     

Clonal growth of sagebrush (Artemisia tridentata) (Asteraceae) and its relationship to volatile communication

To increase systemic resistance to herbivory, some clonal plants transmit internal cues among clonal ramets to prevent widespread damage to genets. Sagebrush (Artemisia tridentata) (Asteraceae) is known to use volatile cues to induce resistance within and between plants (so‐called volatile communication). In the present study, we observed the extent and frequency of clonal growth in a natural sagebrush population in western North America to understand the influence of clonal growth on volatile communication. We used genetic analysis involving microsatellite markers and excavation of the root systems. In addition, we characterized the volatile profiles from the headspace of sagebrush ramets. Excavation of the root system of sagebrush plants revealed that sagebrush propagates clonally below ground and that daughter ramets grow near the mother stem. Volatiles were variable among genetically different ramets, although clonal ramets (genetically identical ramets) released similar volatiles, suggesting a genetic basis for volatile similarity. Sagebrush has been shown to be most responsive to volatiles released from artificially produced clones and suffers less herbivore damage as a result. Therefore, these results, taken into consideration together, imply that volatile communication may occur among genetically identical ramets under natural conditions, and that volatile similarity between the releaser and receiver may be recognized by the receiver and increase resistance against herbivory.     

Juvenile morphology of the xanthid crab Leptodius exaratus (H. Milne-Edwards, 1834) (Decapoda: Brachyura), with notes on the appearance of sexual dimorphism

Summary

The morphometrical and meristic features of the carapace, cephalic appendages (antenna, antennule), mouthparts (maxillule, maxilla, first-third maxillipeds), sternum, pereiopods, abdomen, and pleopods of juveniles and the onset of morphological sexual dimorphism were described for the xanthid crab Leptodius exaratus (H. Milne Edwards, 1834), based on laboratory-reared and wild adult specimens collected from Tateyama Bay, Japan. First instar juveniles shared some of the features of adults (e.g. gross appearance of the carapace and cheliped propodus proportions), but differed from adults on almost all other morphological parameter examined. Morphological development was still not complete at the ninth instar; extrapolation from the rate of morphological changes between instars 1–9 suggests that L. exaratus requires about 13 ecdyses to transform into adults, including development of reproductive structures. Differences in the number and morphology of pleopods and abdomen width allowed early distinction of the sexes. Thus, males formed gonopods in the first abdominal somite and lost the paired vestigial pleopods in somites 3–5 from the fourth instar; females retained the pleopods in somites 2–5, but these became biramous and had increased setation. The abdomen grew wider in females than in males from the fifth instar. Several morphological features of juveniles have phylogenetic and taxonomic implications: carapace motifs clearly place L. exaratus in the superfamily Xanthoidea, whereas the patterns of setation in the scaphognathite and first maxilliped epipod allow separation of this (xanthid) species from crabs of other Xanthoidean families.     

Mechanisms of reproductive isolation of interspecific hybridization between Trillium camschatcense and T. tschonoskii (Melanthiaceae)

Reproductive isolation plays a significant role in the prevention of gene flow between different plant species. Isolation factors can vary, acting either pre‐ or postzygotically. Trillium camschatcense and T. tschonoskii are herbaceous perennials which frequently grow together in Hokkaido, Japan. Natural hybrid formation, T. × hagae, between these species is common, and occurs asymmetrically with T. camschatcense as the maternal parent and T. tschonoskii as the paternal. Here, we examined the efficiency of each reproductive isolation factor to clarify which factor was responsible for the frequency and asymmetry of the hybridization. We found that prezygotic barriers, self fertilization and conspecific pollen precedence, are major isolation factors in both parental species, and that T. tschonoskii as a maternal parent has more effective prezygotic barriers than T. camschatcense. In addition, hybrids with T. tschonoskii as the maternal parent were not observed to reach the flowering stage. We concluded that prezygotic isolation factors in the both species act as main barriers to prevent natural hybridization, and that asymmetry of the isolating barriers between these species would promote T. camschatcense as the maternal parent of the hybrids.     

Green lacewing phylogeny, based on three nuclear genes (Chrysopidae, Neuroptera)

Abstract.  Systematic relationships among higher taxa within Chrysopidae, a large and agriculturally significant neuropteran family, are poorly understood. A molecular phylogenetic survey of Chrysopidae was performed with three nuclear genes, namely wingless (546 bp), phosphoenolpyruvate carboxykinase (483 bp), and sodium/potassium ATPase alpha subunit (410 bp). We examined 83 species in 24 genera, mainly from Japan, Eurasia and Africa. Parsimony and Bayesian analyses of combined datasets of a total of 1439 bp demonstrated that (1) monophyly of the subfamily Chrysopinae was supported but the relationship between Nothochrysinae and Apochrysinae was unclear, although the two subfamilies together may constitute the sister taxon of Chrysopinae; (2) of the three tribes examined within Chrysopinae (Ankylopterygini, Belonopterygini and Chrysopini), monophyly of Ankylopterygini and Belonopterygini was supported, but the relationships among the three remain unclear; (3) seven sub-clades in Chrysopini were indicated, namely (i) Brinckochrysa , (ii) Chrysemosa  +  Suarius , (iii) Chrysotropia  +  Nineta , (iv) Mallada  +  Chrysoperla  +  Peyerimhoffina , (v) Cunctochrysa  +  Meleoma  +  Nipponochrysa  +  Apertochrysa albolineatoides , (vi) Chrysopa  +  Plesiochrysa , and (vii) Dichochrysa  +  Apertochrysa eurydera ; and (4) most genera were monophyletic, except for Apertochrysa and Cunctochrysa , each of which was shown to have two distinct origins. Our molecular analysis allowed the assignment of several species of uncertain affinities to known genera. There was some disagreement between the molecular and previously published morphological phylogenies, but in general our results confirmed existing morphological hypotheses of evolution within the family.     

Effect of the specialist herbivore Luehdorfia puziloi on the performance of a woodland herbaceous plant, Asarum heterotropoides

Plants show many responses to herbivore damage caused by insects. We investigated the effect of the specialist leaf herbivore Luehdorfia puziloi on the performance of a deciduous forest understory perennial herb Asarum heterotropoides . We conducted artificial defoliation experiments with different levels of damage (0, 50 or 100% clipping) in the early growing period (flowering time: early May) and in the late growing period (when natural herbivory by L. puziloi larvae occurs: early June) in a natural population. Effects of the defoliation treatments on reproduction (seed-set ratio) of A. heterotropoides in the treated year and on survival and development of the plant in the subsequent year were investigated. Severe defoliation conducted in the early period resulted in less current-year seed production and increased regression to a dormant or non-reproductive stage in the following year, which would reduce the probability of future flowering. In contrast, defoliation conducted in the late period had no effect on the reproduction, survival and development of A. heterotropoides . Similarly, we found no obvious correlation between the damaged leaf area during the later period and seed set. Our results show that the specialist herbivore L. puziloi did not influence the performance of A. heterotropoides by damaging the plant later in the season when it was tolerant of damage.