Food niches of sympatric Marsh Harriers Circus aeruginosas and Hen Harriers C. cyaneus on the Dutch coast in winter

Analysis of pellets collected from adjacent communal winter roosts of Marsh Harriers Circus aeruginosus and Hen Harriers C. cyaneus on an extensive saltmarsh in the southwest Netherlands showed highly significant differences between the diets of the two species. Marsh Harrier diet showed no change throughout January, February and March. They specialized on ducks, which were about half of their prey numerically and more important by weight. Although Marsh Harriers sampled other prey, this remained at a low level and showed no seasonal response to the availability of young lagomorphs. Hen Harriers occupied the niche of a generalist predator, having a broader diet and responding to the presumed changes in availability of prey with diet shifts. In November, about half of their prey items were passerines but these declined in importance in December, and small mammals rose. The proportions of both small mammals and birds fell in February and March, due to increasing dependence on young lagomorphs. Diet overlap between the two species was greatest in January and declined in February and March.     

Scaling of Cardiovascular Physiology in Snakes

The elongate body form of snakes and the wide diversity of habitatsinto which they have radiated have affected the form and functionof the cardiovascular system. Heart position is strongly correlatedwith habitat. The heart is located 15–25% of the bodylength from the head in terrestrial and arboreal species, but25–45% in totally aquatic species. Semi-aquatic and fossorialspecies are intermediate. The viperids are exceptional, withgenerally more posterior hearts but arboreal species have heartscloser to the head. An anterior heartis favored when snakesclimb because it reduces the hydrostatic pressure of the bloodcolumn above the heart and tends to stabilize cephalic bloodpressure. In water, where hydrostatic bloodpressure is not aproblem, a more centrally located heart is favored because theheart does less work perfusing the body. In terrestrial species,head-heart distance increases linearly with body length andthe increased hydrostatic pressure is matched by higher restingarterial blood pressure in longer animals. Unlike mammals andbirds, snakes have blood pressures that increasewith body mass.The added stress on the ventricle wall in larger snakes is correlatedwith ventricles that are larger than predicted by other reptiles.Heart mass scales with body mass to the 0.95 power in snakesbut only 0.77–0.91 in other reptiles that are not as subjectto the hydrostatic effects of gravity. The spongy hearts ofreptiles do not conform well to the Principle of Laplace.     

Changes in wheat bulb fly (Delia coarctata) populations in East Anglia in relation to crop rotations, climatic data and damage forecasting

Records of wheat bulb fly egg (Delia coarctata) population densities in fields sampled throughout East Anglia in the autumns of 1953–1990 are presented. In descending order of risk, fallow, potato, pea (mainly vining), sugar beet and oilseed rape are the main crops preceding wheat or barley which attract oviposition. A declining trend of egg populations observed over the study period may be associated with climatic changes as well as with the elimination of fallow in the rotation and the dramatic increase in the use of insecticides against the pest. Negative correlations (P < 0.05) in mean annual egg numbers were found with departures from average of July temperature and January air or soil temperature; positive correlations (P<0.05) with departure from average of August raindays. Stepwise regression analysis was used to identify the most important relationships of meteorological variables with mean annual egg numbers, or the proportion of fields sampled with egg numbers in excess of the action threshold of 2.5 million eggs/ha. Up to 59% of the variation in the annual proportion of fields above threshold was accounted for in a regression equation using departures from average of July temperature, August raindays and the percentage of average of October (preceding year) rainfall. Estimated mean annual egg populations and the proportion of fields above threshold showed a good fit with the observed values. The findings are discussed and compared with previous work. The forecasting model may be readily incorporated as a regional risk-prediction component of a knowledge-based system for the management of wheat bulb fly control. Regional forecasts of wheat bulb fly oviposition from this work should be tested and modified as necessary according to experience or changing climatic or agricultural factors.     

Effects of diet and host access on fecundity and lifespan in two fruit fly species with different life‐history patterns

The reproductive ability of female tephritids can be limited and prevented by denying access to host plants and restricting the dietary precursors of vitellogenesis. The mechanisms underlying the delayed egg production in each case are initiated by different physiological processes that are anticipated to have dissimilar effects on lifespan and reproductive ability later in life. The egg‐laying abilities of laboratory‐reared females of the Mediterranean fruit fly (Ceratitis capitata Wiedmann) and melon fly (Bactrocera cucurbitae Coquillett) from Hawaii are delayed or suppressed by limiting access to host fruits and dietary protein. In each case, this is expected to prevent the loss of lifespan associated with reproduction until protein or hosts are introduced. Two trends are observed in each species: first, access to protein at eclosion leads to a greater probability of survival and a higher reproductive ability than if it is delayed and, second, delayed host access reduces lifetime reproductive ability without improving life expectancy. When host access and protein availability are delayed, the rate of reproductive senescence is reduced in the medfly, whereas the rate of reproductive senescence is generally increased in the melon fly. Overall, delaying reproduction lowers the fitness of females by constraining their fecundity for the remainder of the lifespan without extending the lifespan. © 2013 The Royal Entomological Society     

Low Temperature Treatment of Barley Plants causes Altered Gene Expression in Shoot Meristems

We have examined whether acclimation to cold may involve alteredgene expression by testing for the appearance of new mRNA, capableof in vitro translation, in shoot meristems of the temperatecereal, barley, grown at 6 ?C day/2? C night. New mRNA is foundafter only 2 d in the cold, when acclimation is detectable butnot complete. The altered pattern of gene expression persistsduring subsequent growth in the cold and is associated witha number of new mRNA molecules including a major mRNA whichencodes a polypeptide Mt 77000. Key words: Hordeum vulgare cv. Igri (barley), low temperature, acclimation, gene expression