Carbon Dioxide Effects on Carbohydrate Status and Partitioning in Rice

The atmospheric carbon dioxide (CO₂) concentration has beenrising and is predicted to reach double the present concentrationsometime during the next century. The objective of this investigationwas to determine the long-term effects of different CO₂ concentrationson carbohydrate status and partitioning in rice (Oryza sativaL cv. IR-30). Rice plants were grown season-long in outdoor,naturally sunlit, environmentally controlled growth chamberswith CO₂ concentrations of 160, 250, 330, 500, 660, and 900µmolCO₂ mol¹ air. In leaf blades, the priority between the partitioningof carbon into storage carbohydrates or into export changedwith developmental stage and CO₂ concentration. During vegetativegrowth, leaf sucrose and starch concentrations increased withincreasing CO₂ concentration but tended to level off above 500µmolmol^–1 CO₂. Similarly, photosynthesis also increased withCO2 concentrations up to 500µmol mol^–1 and thenreached a plateau at higher concentrations. The ratio of starchto sucrose concentration was positively correlated with theCO₂ concentration. At maturity, increasing CO₂ concentrationresulted in an increase in total non-structural carbohydrate(TNC) concentration in leaf blades, leaf sheaths and culms.Carbohydrates that were stored in vegetative plant parts beforeheading made a smaller contribution to grain dry weight at CO₂concentrations below 330µmol mol^–1 than for treatmentsat concentrations above ambient Increasing CO₂ concentrationhad no effect on the carbohydrate concentration in the grainat maturity Key words: CO₂ enrichment, starch, sucrose     

Nuclear Receptors in Mosquito Vitellogenesis

Vitellogenesis in insects involves the coordinated activityof the fat body, which produces large amounts of yolk proteinprecursors (YP), and oocytes, which specifically accumulatethese proteins. The expression of YP genes is achieved throughstrict sex-, tissue-, and hormone-specific control in the femalefat body. In mosquitoes, expression of YP genes is controlledby 20-hydroxyecdysone (20E). To elucidate the role of 20E inmosquito vitellogenesis, we cloned cDNAs encoding the Aedesaegypti ecdysteroid receptor (AaEcR) and two isoforms of itsheterodimeric partner, the Ultraspiracle homologue (AaUSP).The two AaUSP isoforms differ in their A/B domains and havedistinct expression patterns. The ecdysone regulation of YPgenes likely involves products of early genes. We cloned thegene of the mosquito homologue to the Drosophila early geneE75 (AaE75) belonging to the nuclear receptor superfamily. Kineticsof AaE75 expression correlate with the expression of YP genes,suggesting that AaE75 may have a regulatory role in YP geneexpression. A second nuclear receptor superfamily member, theNGFI-B homologue AaHR38 is implicated in repression of the ecdysone-signalingpathway in the fat body of the previtellogenic female mosquitoat the state-of-arrest. Finally, three isoforms of the hepatocytenuclear factor 4 (HNF-4) homologue AaHNF-4 are differentiallyexpressed in the mosquito fat body during vitellogenesis, suggestingtheir involvement in regulating vitellogenic events in thistissue.     

Dopamine influences locomotor activity in honeybee queens: implications for a behavioural change after mating

Abstract Dopamine has been suggested to be involved in physiological and/or behavioural changes triggered by mating in European honeybee (Apis mellifera) queens but its specific role remains unclear. In the present study, the amounts of dopamine (DA) and its metabolite, N‐acetyldopamine (NADA) are measured, in queens of various ages to clarify the association with locomotor activity. The effects of DA receptor agonist/antagonist drugs on locomotor activity are further investigated. Brain levels of DA and NADA are relatively constant during the period before mating when locomotor activity reportedly increases with age but decreases in 1‐year‐old laying queens with low locomotor activity. Reduced DA and NADA levels are also found in haemolymph of 1–3‐month‐old laying queens. When a DA receptor agonist or antagonist is injected into 6‐day‐old virgin queens, locomotor activity levels increase significantly with 2‐amino‐6,7‐dihydroxy‐1,2,3,4‐tetrahydronaphthalene (agonist), and decreased with cis(Z)‐flupenthixol (antagonist). These results suggest that DA systems are involved in the motor control of honeybee queens, and that the decline in DA levels reduces locomotor activity after mating but increased locomotor activity before mating may be independent of DA levels.     

Factors influencing adult emergence from soil and the vertical distribution of burrowing scarab beetles Dasylepida ishigakiensis

The present study investigates the emergence of adult white grub beetles Dasylepida ishigakiensis Niijima et Kinoshita (Coleoptera: Scrabaeidae) from soil as well as their burrowing behaviours. ‘Standby behaviour’ (i.e. adults come to the soil surface where they expose their heads) is shown in the field and, along with emergence behaviour, is entrained by LD photocycles. These 24‐h rhythms persist after transfer to continuous light conditions for 2 days. By contrast, beetles transferred from LD photocycles to continuous dark conditions fail to show standby behaviour; thus, it appears to be manifested only in the presence of illumination. Under dark conditions, beetles emerge completely from the soil directly at the time when standby behaviour is otherwise expected to occur. Emerged adults then burrow back into the soil before dawn. Virgin and mated males, as well as virgin females, which are expected to emerge from the soil for mating on later evenings, burrow to a relatively shallow depth (<2 cm), whereas mated females burrow deeper (2–10 cm). Soil properties such as moisture, grain size, topography and temperature influence the burrowing behaviour and the depths that the beetles reach.     

Niche segregation and genetic structure of Campylobacter jejuni populations from wild and agricultural host species

Bacterial populations can display high levels of genetic structuring but the forces that influence this are incompletely understood. Here, by combining modelling approaches with multilocus sequence data for the zoonotic pathogen Campylobacter, we investigated how ecological factors such as niche (host) separation relate to population structure. We analysed seven housekeeping genes from published C. jejuni and C. coli isolate collections from a range of food and wild animal sources as well as abiotic environments. By reconstructing genetic structure and the patterns of ancestry, we quantified C. jejuni host association, inferred ancestral populations, investigated genetic admixture in different hosts and determined the host origin of recombinant C. jejuni alleles found in hybrid C. coli lineages. Phylogenetically distinct C. jejuni lineages were associated with phylogenetically distinct wild birds. However, in the farm environment, phylogenetically distant host animals shared several C. jejuni lineages that could not be segregated according to host origin using these analyses. Furthermore, of the introgressed C. jejuni alleles found in C. coli lineages, 73% were attributed to genotypes associated with food animals. Our results are consistent with an evolutionary scenario where distinct Campylobacter lineages are associated with different host species but the ecological factors that maintain this are different in domestic animals such that phylogenetically distant animals can harbour closely related strains.     

Long‐term impacts of invasive species on a native top predator in a large lake system

1. Declining abundances of forage fish and the introduction and establishment of non‐indigenous species have the potential to substantially alter resource and habitat exploitation by top predators in large lakes. 2. We measured stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N) in field‐collected and archived samples of Lake Ontario lake trout (Salvelinus namaycush) and five species of prey fish and compared current trophic relationships of this top predator with historical samples. 3. Relationships between δ¹⁵N and lake trout age were temporally consistent throughout Lake Ontario and confirmed the role of lake trout as a top predator in this food web. However, δ¹³C values for age classes of lake trout collected in 2008 ranged from 1.0 to 3.9‰ higher than those reported for the population sampled in 1992. 4. Isotope mixing models predicted that these changes in resource assimilation were owing to the replacement of rainbow smelt (Osmerus mordax) by round goby (Neogobius melanostomus) in lake trout diet and increased reliance on carbon resources derived from nearshore production. This contrasts with the historical situation in Lake Ontario where δ¹³C values of the lake trout population were dominated by a reliance on offshore carbon production. 5. These results indicate a reduced capacity of the Lake Ontario offshore food web to support the energetic requirements of lake trout and that this top predator has become increasingly reliant on prey resources that are derived from nearshore carbon pathways.     

Microreticulation in Cambrian Ostracoda and its relation to similar patterns in tertiary and Recent Ostracoda

The Cambrian bradoriid ? Parahoulongdongella sp. is shown to have a microreticulate (2nd order) surface sculpture. A possible organic sheet‐like origin is proposed for this reticulation. The relation between this second order pattern and those found in tertiary to Recent Ostracoda is discussed.     

Variation in social rank acquisition influences lifetime reproductive success in black-capped chickadees

Dominance relationships structure many animal societies, yet the process of rank attainment is poorly understood. We investigated acquisition of social dominance in winter flocks and its fitness consequences in male black-capped chickadees (Poecile atricapillus) over a 10-year period. Age was the best predictor of rank, and paired comparisons showed high-ranked males to be older than their low-ranked flock-mates. When controlling for age, morphological variables did not predict male social rank, but high-ranked males were heavier, had lower fat scores and were in leaner condition than low-ranked males. Males that survived between years tended to increase in rank over time; however, the rate of rank advancement varied individually. Rank reversals between familiar contestants were rare, and changes in male social rank were associated with changes in flock membership. Average lifetime reproductive success (LRS) of males and females was variable and best predicted by lifespan. Male rank history also influenced realized reproductive success. Birds with higher average rank over their lifespan were more likely to reproduce successfully. However, among successful birds, average rank did not significantly predict LRS. Thus, birds that lived longer and attained high social rank earlier had higher fitness, but this effect was not manifested as fine-scale differences among successful individuals. Taken together, these findings demonstrate the importance of social factors influencing individual fitness.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 85–95.     

The influence of habitat management on the breeding success of the Great Bittern Botaurus stellaris in Britain

Great Bitterns Botaurus stellaris have experienced a population decline in the UK, such that in 1997 the total number of breeding males was just 11. This study aimed to identify factors affecting productivity, and how management could be used to manipulate this. An intensive study of Great Bittern breeding success was conducted between 1997 and 2001. The date that males established their booming territories was closely correlated with when females started nesting. Wetter sites with greater fish densities had males that established their booming territories earlier in the season. However, only the date that males started booming determined when females started nesting. The mean clutch size of Great Bitterns was four and the only cause of nest failure was predation. Of eight nests suspected to be second attempts the mean interval between these first and second attempts was 12.25 ± 0.88 (sd) days (range 8–15). The fate of radiotagged chicks followed to fledging revealed that the overall probability of a chick surviving to fledge was 39.1%. Daily losses of Great Bittern chicks due to starvation/exposure accounted for 76.25% and predation 21.25%. The youngest chicks in poor condition were most likely to die, particularly in periods of high rainfall. A simulated renesting model allowed estimation of Great Bittern productivity as 1.24 chicks per female and 1.52 nesting attempts per female. Habitat management, or lack of water control that resulted in sites being drier in spring, delayed nesting, although statistically there was no difference in productivity compared with wetter sites.