Plasticity in the timing of a major life‐history transition and resulting changes in the age structure of populations of the salamander Hynobius retardatus

Variation in age and size at life‐history transitions is a reflection of the diversifying influence of biotic or abiotic environmental change. Examples abound, but it is not well understood how such environmental changes influence the age structure of a population. I experimentally investigated the effects of water temperature and food type on age and body size at metamorphosis in larvae of the salamander Hynobius retardatus. In individuals grown at a cold temperature (15 °C) or given Chironomidae as prey, the time to metamorphosis was significantly prolonged, and body size at metamorphosis was significantly enlarged, compared with individuals grown at a warmer temperature (20 °C) or fed larvae. I also examined whether larval density (a possible indicator of cannibalism in natural habitats) generated variation in the age structure of natural populations in Hokkaido, Japan, where the climate is subarctic. Natural ponds in Hokkaido may contain larvae that have overwintered for 1 or 2 years, as well as larvae of the current year, and I found that the number of age classes was related to larval density. Although cool water temperatures prolong the larval period and induce later metamorphosis, in natural ponds diet‐based enhancement of development translated into a shorter larval duration and earlier metamorphosis. Geographic variation in the frequency of cannibalism resulted in population differences in metamorphic timing in H. retardatus larvae. It is important to understand how environmental effects are ultimately transduced through individual organisms into population‐level phenomena, with the population response arising as the summation of individual responses. Without a thorough comprehension of the mechanisms through which population and individual responses to environmental conditions are mediated, we cannot interpret the relationship between population‐level and individual‐level phenomena. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 100–114.     

Geographical diversification of the genus Cicer (Leguminosae: Papilionoideae) inferred from molecular phylogenetic analyses of chloroplast and nuclear DNA sequences

Cicer L. (Leguminosae: Papilionoideae) consists of 42 species of herbaceous or semi-shrubby annuals and perennials distributed throughout the temperate zones of the Northern Hemisphere. The origin and geographical relationships of the genus are poorly understood. We studied the geographical diversification and phylogenetic relationships of Cicer using DNA sequence data sampled from two plastid regions, trnK / matK and trnS - trnG , and two nuclear regions, the internal transcribed spacer (ITS) and external transcribed spacer (ETS) regions of nuclear ribosomal DNA, from 30 species. The results from the phylogenetic analyses of combined nuclear and chloroplast sequence data revealed four well-supported geographical groups: a Middle Eastern group, a West-Central Asian group, an Aegean–Mediterranean group, and an African group. Age estimates for Cicer based on methods that do not assume a molecular clock (for example, penalized likelihood) demonstrate that the genus has a Mediterranean origin with considerable diversification in the Miocene/Pliocene epochs. Geological events, such as mountain orogenesis and environmental changes, are major factors for the dispersal of Cicer species. The early divergence of African species and their geographically distinct region in the genus suggest a broader distribution pattern of the genus in the past than at present.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 154 , 175–186.     

Structure and function of the large pronotal horn of the sand‐living anthicid beetle Mecynotarsus tenuipes

Large insect horns function as antipredator armaments, digging implements and intraspecific combat weapons. The sand‐living anthicid beetle Mecynotarsus tenuipes possesses a large horn on the pronotum. Allometric relationships between body size and horn size did not show either a slope of more than 1 or sexual dimorphism, suggesting another function of the horn other than sexual selection via combat. Behavioral observation of individuals using a microvideo camera indicated that the horn is used to dig and move forward in loose sand. Only the horned M. tenuipes could dig into sand, in contrast to the hornless anthicid beetles Stricticollis valgipes and Clavicollis fugiens, which could not dig. When moving in sand, M. tenuipes joins its pronotal horn and head to form a conical shape, with which it pierces into the sand. Then, it opens its horn and head outward to create a space in the sand for forward motion. Although it can dig deeply into sand by repeating these behaviors sequentially, digging speed tends to slow with depth, probably because the weight of the substrate increases.     

Induction and Inhibition of Meiotic Maturation in Follicle-enclosed Mouse Oocytes by Forskolin

A continuous exposure of follicle-enclosed mouse oocytes to ovine luteinizing hormone (LH, 10 μg/ml) in vitro resulted in a 3-fold elevation of CAMP levels in the follicle cells, but not the oocytes, with subsequent oocyte maturation. When follicle-enclosed oocytes were exposed to forskolin (0.01–10 μM) for 2 hr and then incubated in forskolin-free medium (transient exposure group), oocytes underwent germinal vesicle breakdown in a dose-dependent manner. In contrast, a continuous exposure of the follicles to forskolin (10 μM) for up to 10 hr failed to induce resumption of meiosis. Follicle cell cAMP levels increased within 2 hr after the initial exposure to forskolin, and thereafter decreased rapidly regardless of whether forskolin treatment was transient or continuous. A similar transient increase in oocyte cAMP levels was observed after transient or continuous treatment with forskolin. It was evident, however, that at any time examined oocyte cAMP levels were consistently higher in the continuous exposure group than in the transient exposure group. Furthermore, a continuous exposure to forskolin also blocked LH-induced meiotic maturation. These findings suggest that elevated levels of cAMP in the oocyte block meiotic maturation in mouse oocytes. The present results further suggest that an increase in follicle cell cAMP levels is essential to the LH-induced meiotic maturation.     

DNA Levels in Dividing and Developing Plastids in Expanding Primary Leaves of Avena sativa

The amounts of plastid DNA in the primary leaves of 4-d-oldlight- and dark-grown seedlings of Avena sativa were measuredby microspectrofluorometry using the DNA-fluorochrome DAPI (4',6-diamidino-2-phenylindole). In the light-grown primary leaves (40–45 mm long) therewas a marked increase in DNA level per plastid from 10.2 to18.5 ? 10^–15 g between 2.0 mm and 10 mm from the leafbase, resulting from the rate of plastid DNA synthesis beinghigher than the rate of plastid division. Beyond 30 mm the plastidDNA level was reduced to 14 ? 10^–15g due to chloroplastdivision rates being higher than the rate of plastid DNA synthesis,while from 20 mm plastid DNA levels were constant at 2.2 ? 10^–12g per cell, which corresponds to 16000 plastome copies per cell. Observations of dark-grown leaves establish that, in Avena,light is not necessary for plastid division and the dark-grownleaf cells accumulate higher amounts of plastid DNA than light-grownleaf cells. Plastid nucleoids showed a change of distribution after completionof plastid DNA synthesis in light-grown leaves. A change inthe distribution of plastid nucleoids was also observed duringthe greening of etioplasts of dark-grown leaves while plastidDNA level remained constant. Such changes in plastid nucleoiddistribution appear to be independent of plastid DNA synthesisand correlate with the formation of grana stacks. Key words: Avena sativa, microspectrofluorometry, plastid DNA     

Variation of Abscisic Acid and Batatasin Content in Yam Bulbils--Effects of Stratification and Light Exposure

Batatasin content of yam (Dioscorea batatas Decne.) bulbilsdecreased slowly during 5 month stratification at 4°C, whileit remained virtually unchanged when stored at 23°C. Abscisicacid increased considerably during the 1st month at 23°Cbut only slightly at 4°C and thereafter remained constantup to the end of the 5-month storage period. On transfer to sprouting beds at 23°C the batatasin contentof stratified bulbils decreased sharply but that of non-stratifiedbulbils showed only slight variation. Light exposure duringsprouting tests suppressed the sprouting of the non-stratifiedbulbils but promoted that of the stratified ones. The changesin batatasin contents were found when the bulbils were exposedto light and this is discussed in relation to sprouting responsesto light. A scheme for batatasin economy in bulbil dormancyis proposed.     

Effects of selective logging on the arboreal ants of a Bornean rainforest

We examined the effect of selective logging and corresponding forest canopy loss on arboreal ant diversity in a tropical rainforest. Arboreal ants were collected from an unlogged forest plot and from forest plots selectively logged 14 years and 24 years earlier in Danum Valley, Sabah, Malaysia, using a canopy fogging method. Selective logging was associated with a significant decrease in canopy cover and an increase in understory vegetation density relative to unlogged forest. Our study showed that selective logging in primary forest might not dramatically decrease total species number and overall abundance of arboreal ants; however, it may influence the species composition and dominance structure of the ant community, accompanied by an increase in abundance of shrub‐layer species and trophobiotic species. In view of the results of this study, management techniques that minimize logging impact on understory vegetation structure are likely to help maintain the conservation value of logged forests for arboreal ants. Our results also suggest that accurate assessment of the impacts on biodiversity should not be based only on measurement of species number and overall abundance, but also on analysis of species composition and community structure.     

Structural Genes of ATP-dependent Deoxyribonuclease of <Emphasis Type="Italic">Escherichia coli</Emphasis>

RECOMBINATION-deficient (Rec^?) mutants of E. coli express pleiotropic alterations of various phenotypes such as increased ultraviolet light sensitivity, altered patterns of DNA degradation after irradiation, inability to support growth of certain λ phage mutants and many others in addition to reduced recipient ability in mating with Hfr bacteria¹. Yet the primary function of any one of the genes responsible for these alterations has not been elucidated. In this paper, the characteristics of recB and recC mutants having temperature-sensitive functions are described. Particular attention is paid to the properties of the ATP-dependent deoxyribonuclease which is known to be missing in recB and recC mutants^2–5.