Predator avoidance as a function of flocking in the sexually dichromatic Hawaii akepa

Hypotheses for joining a mixed-species bird flock consider each species as a single unit. In sexually dichromatic birds, differential conspicuousness between the sexes may result in differences in vigilance for predators. Aspects of the predator avoidance and foraging enhancement hypotheses for the selective value of joining a mixed-species flock were assessed for the strongly sexually dichromatic Hawaii akepa (Loxops coccineus coccineus). There was support for the primary predictions of the predator avoidance hypothesis: vigilance levels decreased with increasing group size, and with membership in a flock, but only for brightly colored adult males. There was little support for the hypothesis that the primary benefit of joining a mixed-species flock is to enhance foraging efficiency through local enhancement.     

Predator induced life-history shifts in a freshwater cladoceran

Summary Life-history theory predicts that maturity and resource allocation patterns are highly sensitive to selective predation. Under reduced adult survival, selection will favour genotypes capable of reproducing earlier, at a smaller size and with a higher reproductive effort. When exposed to water that previously held fish, (size selective predators which prefer larger Daphnia), individuals of Daphnia hyalina reproduced earlier, at a smaller size and had a higher reproductive investment. Hence the prey was able to switch its life history pattern in order to become less susceptible to predation by a specific predator. The cue that evokes the prey response is a chemical released by the predator.     

Host-plant effects on larval survival of a salicin-using leaf beetle Chrysomela aeneicollis Schaeffer (Coleoptera: Chrysomelidae)

Several species of willow leaf beetles use hostplant salicin to produce a defensive secretion that consists of salicylaldehyde. Generalist arthropod predators such as ants, ladybird beetles, and spiders are repelled by this secretion. The beetle larvae produce very little secretion when they feed on willows that lack salicylates, and salicin-using beetles prefer salicylate-rich willows over salicylate-poor ones. This preference may exist because the larvae are better defended against natural enemies on salicylate-rich willows. If this is true, the larvae should survive longer on those willows in nature. However, this prediction has not been tested. I determined the larval growth and survival of Chrysomela aeneicollis (Coleoptera: Chrysomelidae) on five willow species (Salix boothi, S. drummondiana, S. geyeriana, S. lutea, and S. orestera). These species differed in their salicylate chemistries and in leaf toughness but not in water content. The water content varied among the individual plants. Larval growth of C. aeneicollis did not differ among the five species in the laboratory, but it varied among the individual plants and it was related to the water content. In the field, C. aeneicollis larvae developed equally rapidly on the salicylate-poor S. lutea and on the salicylate-rich S. orestera. Larval survival was greater on S. orestera than on S. lutea in one year (1986), but there was no difference between them during three succeeding years. In another survivorship experiment, larval survival was low on the medium-salicylate S. geyeriana, but high on the salicylate-poor S. boothi and on S. orestera. Larval survival in the field was related to the larval growth and water content that had been previously measured in the laboratory. These results showed that the predicted relationship between the host plant chemistry and larval survival did not usually exist for C. aeneicollis. One possible reason for this was that the most important natural enemies were specialist predators that were unaffected by the host-derived defensive secretion. One specialist predator, Symmorphus cristatus (Hymenoptera: Eumenidae), probably caused much of the mortality observed in this study. I discuss the importance of other specialist predators to salicin-using leaf beetles.     

Predator avoidance behaviour in the buffy-headed marmoset,Callithrix flaviceps

The predator avoidance behaviour of a free-ranging group of buffy-headed marmosets,Callithrix flaviceps, was recorded in detail during the course of a long-term study of behavioural ecology at the Fazenda Montes Claros, southeastern Brazil. Four distinct patterns of predator avoidance behaviour, each with specific vocalisations, were recognised and are described here. The selection and use of sleeping sites by the study group are also described. An analysis of the records indicates that these small monkeys are generally most vulnerable to predation by aerial raptors. Variations in the frequency of alarm calls also indicate that the marmosets tend to be more vigilant at higher levels in the forest and when the leaf cover is less extensive. The implications of group size and social structure for both the evolution and the efficacy of the anti-predator behaviour of marmosets are also discussed.     

Patch-exploitation patterns in an egg parasite of elm leaf beetle

Eggs of elm beetle,Pyrrhalta luteola (Muller), normally occur in masses which can be viewed as discrete host patches in space and time. Analysis of>800 egg masses from 3 field sites in northern California revealed that the number of eggs/mass varied from 2 to>40 and that the imported egg parasiteTetrastichus gallerucae (Fonsc.) exploited a relatively large proported of the egg masses at certain times. The spatial relationship between parasitization and number of eggs/egg mass was assessed in 2 ways-i.e., for exploited masses only and for all masses combined (exploited+nonexploited). Percent parasitization was density independent in most cases for both data sets. It is suggested that both methods of analysis can provide patterns which are relevant to biological control of insect pests.      

Dynamics of leaf minerals,bdleaf area,and biomass from hardwoods intensively grown on a peat bog

Summary Water willow and grey alder were grown on a raised sphagnum bog in central Sweden. The stands were intensively treated by daily irrigation and fertilization during the growing period in order to improve site fertility. After a 2-year establishment period high production rates were achieved in willow stands, 0.8 kg stem dry weight m^–2 year^–1 on current plus one (C+1) year old shoots. In these stands the canopy was closed with a leaf area index (LAI) that peaked at approximately 7. The canopy in the alder stand did not close during the initial 3 years of growth and the measured production rate was relatively low, at approximately 0.4 kg dry weight m^–2 year ^–1 in the last year. The leaf nitrogen content was 3%–4% of dry weight during the summer and the other studied mineral elements were in almost optimal proportion to nitrogen. This was considered to be an effect of the intensive fertilization regime. Above-ground production close to maximum yield was attained in the prevailing conditions of soil, climate and biomass partitioning.     

Slow larval growth on a suboptimal willow results in high predation mortality in the leaf beetle Galerucella lineola

The slow growth/high mortality hypothesis predicts that herbivorous insects feeding on suboptimal host plants are subjected to higher predation mortality owing to the longer time spent in the vulnerable juvenile stages compared with conspecifics feeding on optimal plants. We tested this hypothesis for the willow-feeding leaf beetle Galerucella lineola raised on one suitable (Salix viminalis) and one unsuitable (S. dasyclados) willow species as well as on plants from an interspecific cross between the two species. Cohorts of larvae raised on caged plants (protected from enemies) and uncaged plants (exposed to enemies) were monitored daily throughout larval development in two consecutive years. Larvae raised on S. viminalis developed faster, grew larger and survived better than those raised on S. dasyclados. The suitability of the hybrid plants was intermediate to that of their parents. Our results strongly support the slow growth/high mortality hypothesis. In both years, total predation during the larval period was higher on S. dasyclados than on S. viminalis. Furthermore, the daily predation rate (i.e. the proportion of larvae preyed upon per day) was higher on S. dasyclados than on S. viminalis. When hybrid plants were included in the analysis total predation was positively correlated with both larval development time and daily predation rate. We suggest that high predation on beetles on low-quality plants is the combined result of their longer development time and elevated daily predation rate. The results are discussed in relation to the evolution of host plant selection and the paradox of sublethal plant defenses.     

The effects of chrysomelid beetle grazing and plant competition on the growth of Rumex obtusifolius

Summary The interaction between grazing by Gastrophysa viridula and interspecific plant competition was investigated for Rumex obtusifolius growing in the field. During an eight-month growing season non-competing R. obtusifolius grew larger than competing plants although herbivore loads (beetle productivity per unit leaf area) were similar for competing and non-competing plants. However, grazing significantly reduced the growth of R. obtusifolius only in competing plants thus demonstrating a synergism between plant competition and invertebrate herbivory. The relevance of these findings for the distribution of plant species is discussed.     

Plant stress and insect performance: cottonwood,ozone and a leaf beetle

Summary Leaf area consumption rates, development rates, survivorship, and fecundity of the imported willow leaf beetle (Plagiodera versicolora Laich) were examined on two clones of eastern cottonwood which were previously exposed to ozone or charcoal-filtered air. P. versicolora consumed more ozone treated foliage, but were more fecund when reared on charcoal-filtered air treated plants. Beetle development rates and survivorship were not significantly different on treated and control cottonwoods. We concluded that: 1) Ozone fumigation of cottonwood reduced foliage quality, and the reproductive success and overall performance of P. versicolora. 2) increased foliage consumption by beetles was probably a mechanism compensating for decreases in foliage quality. 3) Reductions in beetle fecundity were due to an initial reduction in oviposition rates. 4) Beetle feeding preference did not correlate with the suitability of foliage for beetle performance. These results are discussed in relation to the impact of air pollution on plant-insect interactions.     

Impact of epidermal leaf mining by the aspen leaf miner (Phyllocnistis populiella) on the growth, physiology, and leaf longevity of quaking aspen

The aspen leaf miner, Phyllocnistis populiella, feeds on the contents of epidermal cells on both top (adaxial) and bottom (abaxial) surfaces of quaking aspen leaves, leaving the photosynthetic tissue of the mesophyll intact. This type of feeding is taxonomically restricted to a small subset of leaf mining insects but can cause widespread plant damage during outbreaks. We studied the effect of epidermal mining on aspen growth and physiology during an outbreak of P. populiella in the boreal forest of interior Alaska. Experimental reduction of leaf miner density across two sites and 3 years significantly increased annual aspen growth rates relative to naturally mined controls. Leaf mining damage was negatively related to leaf longevity. Leaves with heavy mining damage abscised 4 weeks earlier, on average, than leaves with minimal mining damage. Mining damage to the top and bottom surfaces of leaves had different effects on physiology. Mining on the top surface of the leaf had no significant effect on photosynthesis or conductance and was unrelated to leaf stable C isotope ratio (delta(13)C). Mining damage to the bottom leaf surface, where stomata are located, had significant negative effects on net photosynthesis and water vapor conductance. Percent bottom mining was positively related to leaf delta(13)C. Taken together, the data suggest that the primary mechanism for the reduction of photosynthesis by epidermal leaf mining by P. populiella is the failure of stomata to open normally on bottom-mined leaves.     

Components of resistance of leaf rust (Melamspora laricii epitea Kleb./Melampsora ribesii-viminalis Kleb.) in Salix viminalis L.

Selection on partial resistance components, namely latent period, development rate of uredia and number and size of uredia, has been suggested as a means to achieve durable resistance. Three experiments were carried out in growth chambers to assess the impact of environmental and genetic factors on these components in the Salix-Melampsora host-pathogen system. They confirmed the environmental ability of the Melampsora-Salicaceae relationship and provided no definite answer on the possibility of attaining durable resistance through selection on partial resistance components. On the one hand, there is a large amount of heritable variation among clones for most components; on the other hand, all components were extremely sensitive to environmental conditions and isolates, making the development of standard selection methods difficult.     

Sex differentiation in postnatal growth rate: a test in a wild boar population

Summary In wild boar individual growth rate is linear between 0.5 and 6 months after birth, based on successive body weight measurements. Contrary to expectation for a dimorphic and polygynous mammal like wild boar, no sexual dimorphism in growth rate could be detected between 0.5 and 6 months. We argue that high total maternal invesment in offspring due to large litter size and/or strong selection for early reproduction in this population with a short generation time could explain this absence of early differentiation in postnatal growth rate according to offspring sex.     

The quorum-sensing system in a plant bacterium Mesorhizobium huakuii affects growth rate and symbiotic nodulation

Mesorhizobium huakuii is a free-living bacterium which is capable of establishing a specific symbiotic relationship with Astragalus sinicus, an important winter green manure widely used in Eastern Asia, allowing for nitrogen fixing during this process. Previous studies demonstrate that M.␣huakuii produces quorum-sensing molecules at high cell density and quorum sensing plays a role in biofilm formations. In this study, we isolated and characterized two quorum-sensing deficient mutants in M. huakuii. Analysis of the flanking region of transposon insertions indicated that autoinducer synthase related genes are not homologous to acyl homoserine lactone (AHL) synthase genes that are shared among many Gram-negative bacteria, but related to peptide synthesis, indicating that M. huakuii quorum-sensing signals are distinct from AHLs. Compared with the wild-type strains, these quorum-sensing deficient mutants promoted their growth rate and were defective in nodule formation on host plants, indicative of a critical role of quorum sensing in M.␣huakuii during the host–bacterium symbiotic interaction.Yijing Gao and Zengtao Zhong contributed equally to this work.     

Early spring leaf out enhances growth and survival of saplings in a temperate deciduous forest

Saplings of many canopy tree species in winter deciduous forests receive the major portion of their light budget for their growing season prior to canopy closure in the spring. This period of high light may be critical for achieving a positive carbon (C) gain, thus contributing strongly to their growth and survival. This study of saplings of Aesculus glabra and Acer saccharum in Trelease Woods, Illinois, USA, tested this hypothesis experimentally by placing tents of shade cloth over saplings during their spring period of high light prior to canopy closure in three consecutive years. Leaf senescence began 16 days (year 0) and 60 days (year 1) earlier for shaded A. glabra saplings than control saplings. No change in senescence occurred for A. saccharum. The annual absolute growth in stem diameter of both species was negligible or negative for shaded saplings, but positive for control saplings. Only 7% of the shaded A. glabra saplings were alive after 2 years, while all control saplings survived for 3 years; only 20% of the shaded A. saccharum saplings survived for 3 years, while 73% of control saplings were alive after the same period. Early spring leaf out is a critical mechanism that allows the long-term persistence of saplings of these species in this winter deciduous forest. Studies and models of C gain, growth, and survival of saplings in deciduous forests may need to take into account their spring phenology because saplings of many species are actually “sun” individuals in the spring prior to their longer period in the summer shade.     

Temperature effects on summer growth rates in the Antarctic scallop, Adamussium colbecki

Annual growth rates of Antarctic marine organisms are low compared to their relatives from warmer waters. Previous studies hypothesise that high food availability during austral spring–summer may enable Antarctic invertebrates to attain comparatively high short-term growth rates despite the low temperature. Neither a temperature-growth experiment with juvenile Adamussium colbecki (Smith 1902) nor the comparison of A. colbecki summer growth rates with an empirical scallop specific growth-to-temperature relationship could confirm this hypothesis. Hence, summer growth rates of young, immature A. colbecki are strongly affected by temperature, i.e. no uncoupling from temperature.     

Water relations of indigenous versus exotic tree species,growing at the same site in a tropical montane forest in southern Ethiopia

The objective of the study was to compare the water relations of two indigenous [Podocarpus falcatus (Thunb.) Endl., Croton macrostachys Hochst. ex. Del.] and two exotic tree species (Eucalyptus globulus Labille., Cupressus lusitanica Miller) growing in the same location in the montane Munessa State Forest, southern Ethiopia. Stem flow was measured with Granier type thermal dissipation probes. Sap flux, normalized per unit sapwood area, and the total sapwood areas of the particular trees were used to estimate daily transpiration. Maximum daily transpiration values (60 kg water) were recorded for Croton when at full foliage. After shedding most of its leaves in the dry season transpiration was reduced to 8 kg per day. Eucalyptus had the next highest transpiration (55 kg), in this case at the peak of the dry season. It transpired 4–5 times more than Podocarpus and Cupressus trees of similar size. Maximum stem flux density was tree-size dependent only in Croton. Diurnal patterns of stem flux indicated that Croton, Eucalyptus and Podocarpus, in contrast to Cupressus, responded more directly to light than to atmospheric water pressure deficit. At high VPD (>1.0 kPa) stem flux reached a plateau in Croton and Podocarpus indicating stomatal limitation. Per unit leaf area Croton had the highest and Podocarpus and Cupressus the lowest daily transpiration rates. In summary, the pioneer tree Croton had the lowest and Podocarpus the highest water use efficiency. The contribution of the study to the understanding of the role of each tree species in the hydrology of the natural forest and the plantations is discussed.     

A new MSPQC for rapid growth and detection of Mycobacterium tuberculosis

Many of the deaths caused by tuberculosis (TB) in the world are due to wrong or late diagnosis. The World Health Organization (WHO) calls for better and cheaper TB tests method for this reason. In this paper, a new multi-channel series piezoelectric quartz crystal (MSPQC) sensor system was developed for rapid growth and detection of Mycobacterium tuberculosis. It is an automatic continuous monitoring system. The system was used to detect TB based on the volatile metabolic products NH(3) and CO(2) during the growth of M. tuberculosis. The metabolic products, diffusing from the medium into the KOH absorbing solution, resulted in the conductance change of the absorbing solution detected by the MSPQC sensitively. The frequency shift versus time response curves were recorded by self-developed software. Frequency detection time (FDT) corresponding to -100Hz in frequency shift value was used as a parameter to quantitatively determine M. tuberculosis H37Ra (an avirulent strain). H37Ra and 40 strains clinic positive samples were detected by the proposed system successfully. As for H37Ra, the FDT had a linear relationship with the logarithm of its initial concentration in the range of 10(2)-10(7) colony forming units (cfu)ml(-1) (R=-0.998) and the detection limit was low to 10cfuml(-1). 4% NaOH solution that can kill contaminating microorganisms and make M. tuberculosis alive was used as pretreatment reagent to provide selectivity to this method. Comparative tests were also carried out by using BACTECtrade mark MGITtrade mark 960 and conventional Lowenstein-Jensen (L-J) slants. The results showed that the proposed system was quicker than BACTECtrade mark MGITtrade mark 960 and it is also cheaper and will be widely used in TB tests in the world.     

Patterns of water use and the tissue water relations in the dioecious shrub,Salix arctica: the physiological basis for habitat partitioning between the sexes

Summary Within the high arctic of Canada, Salix arctica, a dioecious, dwarf willow exhibits significant spatial segregation of the sexes. The overall sex ratio is female-biased and female plants are especially common in wet, higher nutrient, but lower soil temperature habitats. In contrast, male plants predominate in more xeric and lower nutrient habitats with higher soil temperatures that can be drought prone. Associated with the sex-specific habitat differences were differences in the seasonal and diurnal patterns of water use as measured by stomatal conductance to water vapor and the bulk tissue water relations of each gender. Within the wet habitats, female plants maintained higher rates of stomatal conductance (g) than males when soil and root temperatures were low (<4° C). In contrast, within the xeric habitats, male plants maintained higher g and had lower leaf water potentials _leaf at low soil water potentials and a high leaf-to-air vapor pressure gradient (w) when compared to females. Female plants had more positive carbon isotope ratios than males indicating a lower internal leaf carbon dioxide concentration and possibly higher water use efficiency relative to males. Tissue osmotic and elastic properties also differed between the sexes. Male plants demonstrated lower tissue osmotic potentials near full tissue hydration and at the turgor loss point and a lower bulk tissue elastic modulus (higher tissue elasticity) than female plants. Males also demonstrated a greater ability to osmotically adjust on a diurnal basis than females. These properties allowed male plants to maintain higher tissue turgor pressures at lower tissue water contents and _soil over the course of the day. The sex-specific distributional and ecophysiological characteristics were also correlated with greater total plant growth and higher fecundity of females in wet habitats, and males in xeric habitats respectively. The intersexual differences in physiology persisted in all habitats. These results and those obtained from growth chamber studies suggest that sex-specific differences have an underlying genetic basis. From these data we conjecture that selection maintaining the intersexual differences may be related to different costs associated with reproduction that can be most easily met through physiological specialization and spatial segregation of the sexes among habitats of differing conditions.     

Diversity and structure of shrew communities in montane forests of southeast Kenya

As a step towards setting conservation priorities for declining moist forests in southeast Kenya, we assessed for small mammal diversity and distribution. These habitats are under severe pressure due to increased demand an forests products and arable land, yet there is a dearth of information an impacts an biodiversity. Over an eight-month period, we used a combination of box and pitfall traps with drift fences to study 13 forest fragments in five geographic areas ranging between 3°28′−4°10′ S and 38°28′−39°2b′ E. We recorded 12 species including 10 soricids and two macroscelids in 31440 trap nights. Diversity estimates using rarefaction method indicate a species richness of 12, consistent with our collection. There were six unique species, each limited in distribution to one forest fragment. Our record of Crocidura cf. selina in Kyulu Hills is the first outside Mabira forest in Uganda where it is considered endemic and endangered. We also report the first record of C. fuscomurina in Kenya, white those of C. Luna and Suncus megalura are first in the southeast of the country. By providing new ranges to four species, our study is of significance to the biogeography and conservation of forest small mammals in the region.