Geographic and developmental variation in expression of the circadian rhythm gene, timeless, in the pitcher-plant mosquito, Wyeomyia smithii

Expression of the circadian rhythm gene timeless was investigated in the pitcher-plant mosquito, Wyeomyia smithii (Coq.), and was found to vary with time of day, instar of diapause, and latitude of origin. The temporal pattern of timeless expression differed between the two diapausing instars and was significantly higher in southern (38-40 degrees N) than in northern (50 degrees N) populations, when diapausing instar was held constant. Expression of timeless is therefore both developmentally and evolutionarily variable. This result provides the first example of a latitudinal difference in the expression of timeless, suggesting that, along with evidence from other insects, timeless has the potential to affect photoperiodic response and its adaptive evolution in temperate seasonal environments.     

Non-invasive Measurement of Brown Fat Metabolism Based on Optoacoustic Imaging of Hemoglobin Gradients

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Environmental warming increases invasion potential of alpine lake communities by imported species

Global warming increasingly pressures species to show adaptive migratory responses. We hypothesized that warming increases invasion of alpine lakes by low-elevation montane zooplankton by suppressing native competitors and predators. This hypothesis was tested by conducting a two-factor experiment, consisting of a warming treatment (13 vs. 20°C) crossed with three invasion levels (alpine only, alpine+montane, montane only), in growth chambers over a 28-day period. Warming significantly reduced total consumer biomass owing to the decline of large alpine species, resulting in greater autotrophic abundance. Significant temperature-invasion interactions occurred as warming suppressed alpine zooplankton, while stimulating certain imported species. Herbivorous invaders suppressed functionally similar alpine species while larger native omnivores reduced invasion by smaller taxa. Warming did not affect total invader biomass because imported species thrived under ambient and warmed alpine conditions. Our findings suggest that the adaptability of remote alpine lake communities to global warming is limited by species dispersal from lower valleys, or possibly nearby warmer alpine ponds.     

Bacteriocin production by Enterococcus faecium NA01 from 'wara'—a fermented skimmed cow milk product from West Africa

An Enterococcus faecium strain from Nigerian fermented skimmed cow milk ('wara') produced bacteriocin inhibitory towards Lactobacillus, Enterococcus and Listeria strains. The bacteriocin (designated enterocin 01) was inactivated by proteases, heat-stable at 100°C and active at pH 2.0–6.0. The Ent. faecium isolate harboured plasmids of ca 36.3 and 23.1 kb. Curing experiments with ethidium bromide resulted in a bacteriocin-negative mutant which had not lost immunity to the bacteriocin. Slight differences in plasmid profiles between wild-type and mutant indicated a possible plasmid-coded bacteriocin production.     

Pāteke (Anas chlorotis) population trends in response to predator control on Great Barrier Island and Northland,New Zealand

Pāteke, brown teal (Anas chlorotis) were until recently restricted to two key strongholds in northern New Zealand: Great Barrier Island and eastern Northland. In 2000, we applied predator control at two sites within the strongholds. We analysed three decades of summer pāteke flock count data collected at ‘trapped’ and ‘untrapped’ locations to assess numerical pāteke response to predator control. Using piecewise regression, we found that Northland pāteke at trapped sites increased from 130 individuals before predator control, to 341 by 2015. Conversely, pāteke in untrapped areas in Northland remain low. Compared with the Northland trapped site, there was a slower rate of population increase in the predator treated site at Okiwi on Great Barrier Island; 286 individuals at trapped sites before predator control and 390 individuals in 2015. Pāteke numbers at untrapped sites on Great Barrier Island also increased, from 214 to 316 individuals. Cause of death analyses confirm that predation is a significant factor at trapped sites in Northland (87% of pāteke deaths) and Okiwi (56% of deaths), with starvation accounting for an additional 16% of identified causes of death at Okiwi. Access to sufficient food sources may be limiting at Okiwi, but overall the provision of predator control has benefitted pāteke populations.     

Radiation resistance of lactobacilli isolated from radurized meat relative to growth and environment.

Of 113 lactobacilli isolated from radurized (5 kGy) minced meat, 7 Lactobacillus sake strains, 1 L. curvatus strain, and 1 L. farciminis strain were used for radiation resistance studies in a semisynthetic substrate (i.e., modified MRS broth). Five reference Lactobacillus spp., one Staphylococcus aureus strain, and one Salmonella typhimurium strain were used for comparative purposes. All L. sake isolates exhibited the phenomenon of being more resistant to gamma-irradiation in the exponential (log) phase than in the stationary phase of their growth cycles by a factor of 28%. Four references strains also exhibited this phenomenon, with L. sake (DSM 20017) showing a 68% increase in resistance in the log phase over the stationary phase. This phenomenon was not common to all bacteria tested and is not common to all strains with high radiation resistance. Four L. sake isolates and three reference strains were used in radiation sensitivity testing in a natural food system (i.e., meat). The bacteria were irradiated in minced meat and packaged under four different conditions (air, vacuum, CO2, and N2). Organisms exhibited the highest death rate (lowest D10 values [doses required to reduce the logarithm of the bacterial population by 1] ) under CO2 packaging conditions, but resistance to irradiation was increased under N2. The D10 values of the isolates were generally greater than those of the reference strains. The D10 values were also higher (approximately two times) in meat than in semisynthetic growth medium.     

Interaction between photoperiod, temperature, and chilling in dormant larvae of the tree-hole mosquito, Toxorhynchites rutilus Coq.

1. Unchilled, diapausing larvae of Toxorhynchites rutilus rely on photoperiod for the maintenance of diapause. The photoperiodic clock is temperature-compensated between 16.5 degrees and 25 degrees C, maintaining both a similar set-joint and inherent accuracy over this range. The rates of development among larvae terminating diapause are dependent upon both temperature and photoperiod. 2. Chilling of dormant Toxorhynchites rutilus can promote response to progressively shorter daylengths, thus decreasing the critical photoperiod. Chilling can also accelerate response to long days, thereby decreasing the depth of diapause and, after prolonged exposure, can eventually terminate diapause directly, leaving subsequent morphogenesis independent of photoperiod. 3. The optimal temperature for these effects of chilling is above 4 degrees C, below 16.5 degrees C, and may lie around 7 degrees C. 4. Temperatures between 5 degrees and 15 degrees C are vernal and autumnal rather than hibernal. The interaction between chilling and photoperiod may then represent an adaptive compromise between selection due to long-term climatic trends and the vagaries of spring weather.     

Rhythmic components of photoperiodic time measurement in the pitcher-plant mosquito, Wyeomyia smithii

Photoperiodic time measurement regulating larval diapause in the pitcher-plant mosquito, Wyeomyia smithii, varies in a close relationship with latitude. The critical photoperiod mediating the maintenance and termination of diapause is positively correlated with latitude (r ² = 0.977) among six populations from southern (30–31° N), intermediate (40° N), and northern (46–49° N) latitudes in North America. The developmental response to unnaturally short and to unnaturally long photoperiods declines with increasing latitude, so that longer critical photoperiods are associated with a downward rather than a lateral shift in the photoperiodic response curve. Exotic light and dark cycles of varying period (T) with a short (10 h) photophase and a scotophase ranging from 14 (T = 24) to 62 (T = 72) h, reveal two geographic patterns: a decline in perturbability of the photoperiodic clock with increasing latitude, and no change with latitude in the 21-h period of rising and falling development with increasing T. These results show (1) that there is a rhythmic component to photoperiodic time measurement in W. smithii, (2) that the period of this rhythm is about 21 h in all populations, and (3) that more northern populations show decreasing responsiveness to photoperiod and increasing stability against perturbation by exotic period lengths (T > 24). Previous studies on W.␣smithii indicate that this single temperate species of a tropical and subtropical genus has evolved from south to north. We therefore conclude that the evolution of increasing critical photoperiod in W. smithii during its adaptive radiation into North America has more likely involved the amplitude and not the period of the underlying circadian pacemaker. Received: 22 July 1996 / Accepted: 30 September 1996