Showing papers on "Incubation published in 1990"

Field measurement of nitrogen mineralization using soil core incubation and acetylene inhibition of nitrification

Abstract: A technique for measuring net rates of mineralization under field conditions is described. Soil cores were incubated in the field in sealed containers with acetylene to inhibit nitrification and thereby minimize losses of N through denitrification. Mineralization was estimated as the difference between the mineral N content after a 14-d incubation and that determined from soil samples taken at the start of incubation. Mineralization in the spring and summer in unfertilized plots in the field amounted to 90 and 70 kg N ha−1 in S.E. England under grass and grass/clover swards, respectively, and 40 kg N ha−1 under a grass sward in S.W. England. Daily rates of mineralization ranged from 0.02 to 1.90 kg N ha−1, with peak values related to re-wetting of the soil after dry weather. Laboratory incubation of soil showed that neither the low concentration of acetylene (2% v/v) adopted for field incubation, nor the accumulation of mineral N during incubation was likely to affect the total measurement, but that frequent and regular soil sampling was necessary to minimize the effects of changes in soil water content. Estimates for mineralization over the whole growing season (180 d) were obtained for two years from extrapolation of the early season field measurements and were, on average, 50% higher than predictions based on a chemical extraction index of potentially mineralizable N.

Analysis of linkage between scrapie incubation period and the prion protein gene in mice.

Abstract: A single gene is known to have a predominant influence on scrapie incubation period in mice. In crosses between strains that give a short incubation period, such as NZW mice, and those which give a long incubation period, such as I/LnJ mice, long incubation period was dominant using a Chandler scrapie agent isolate. Recently a close linkage was found between the incubation period gene and the prion protein (PrP) structural gene in I/LnJ mice crossed to NZW mice. Because this linkage suggested an important role for PrP in the pathogenesis of scrapie we sought to verify the linkage between these genes and extended the analysis to three additional mouse strains. All four of the mouse strains that we evaluated, I/LnJ, P/J, MA/MyJ, and RIIIS/J, had incubation periods longer than those of the NZW mice to which they were crossed. In addition, all four strains shared an XbaI restriction enzyme polymorphism, which suggested that all four strains might also exhibit linkage between the incubation period and the PrP structural gene. Very strong linkage between PrP and incubation period was found in I/LnJ and P/J mice crossed to NZW mice, whereas less obvious linkage was demonstrated for MA/MyJ mice crossed to NZW mice. In MA/MyJ mice genes other than PrP also had an obvious influence on incubation period. In RIIIS/J mice no linkage was shown. Although linkage between PrP and incubation period was very significant in I/LnJ and P/J mice, a few animals were identified in both crosses that represented potential recombinants in which PrP and incubation period did not segregate together. Therefore, although these phenotypes are certainly linked in I/LnJ and P/J mice, it is possible that PrP and incubation period are controlled by separate genes.

Incubation as a Reproductive Cost in Female Wood Ducks

Abstract: -We investigated the effects of body mass of incubating female Wood Ducks (Aix sponsa) on aspects of their current and future reproduction, and we examined factors that affect length of the incubation period. During three breeding seasons, body mass of female Wood Ducks averaged 578.0 g early and 553.3 g late in the incubation period. Body mass at the start of incubation was not related to either hatching success or length of the incubation period. In one of three years, females that were heavy at the end of incubation survived better to the next breeding season than those that were light. Reduced survival of light females in one year coincided with a greater loss of body mass in that year relative to other years, which indicates that incubation can be an important reproductive cost to female Wood Ducks. There were no relationships between body mass at the end of incubation and date of nesting or clutch size in the next breeding season. Partial correlations between clutch mass and length of incubation that controlled for date of nesting indicated a positive association between clutch mass and incubation length in every year. This relationship was evident only for parasitic nests (i.e. nests in which more than one female was laying eggs). Increased length of the incubation period associated with larger clutch mass represents a potential cost of intraspecific nest parasitism not previously recognized. Received 26 December 1989, accepted 17 June 1990. INCUBATING birds must provide the proper thermal environment for embryonic development. Simultaneously they must maintain their body condition so that survival and subsequent reproduction are not affected adversely. Time for feeding is restricted during incubation, which often makes it difficult for incubating individuals to meet daily metabolic costs (see Drent et al. 1985). Some avian species have adjusted to the demands of incubation by having biparental incubation (Eisner 1960, Feare 1984). In other species, males provide incubating females with food (Lyon and Montgomerie 1985, Nilsson and Smith 1988). In waterfowl (Anatidae), females of large-bodied species generally begin incubation with large energy reserves and are more attentive during incubation than females of small-bodied species, because largebodied females spend less time feeding (review in Afton and Paulus 1990). Small anatids depend on exogenous foods to meet most metabolic demands during incubation and take two 2 Present address: Maryland Department of Natural Resources, P.O. Box. 68, Wye Mills, Maryland 21679 USA. to three recesses each day to forage (Afton 1980, Hohman 1986). Successful development of bird eggs occurs within a relatively narrow range of incubation temperatures (White and Kinney 1974). Cooling of eggs increases as ambient temperature decreases, and as time away from the nest by incubating individuals increases (Caldwell and Cornwell 1975, Afton 1979). Short-term declines in egg temperature, however, apparently have little effect on hatching success (Vleck 1981, Haftorn 1988). Nevertheless, a decrease in average egg temperature may lengthen the incubation period, which exposes the nest to greater risk of predation and increases the energy expended by developing embryos (Vleck et al. 1980, Booth 1987). Greater amounts of energy used by embryos of precocial species before hatching may decrease the size of residual yolk reserves that are important to newly hatched chicks for maintenance and growth (Peach and Thomas 1986). Many species of birds modify activity patterns during incubation in response to variation in weather and food availability (Caldwell and Cornwell 1975, Cartar and Montgomerie 1985, 756 The Auk 107: 756-764. October 1990 This content downloaded from 157.55.39.124 on Mon, 16 Jan 2017 18:11:55 UTC All use subject to http://about.jstor.org/terms October 1990] Incubation Costs of Wood Ducks 757 Drent et al. 1985). Large-bodied species are affected less by environmental factors than smallbodied species (Afton 1980). Flexibility of incubation patterns within and among species suggests there is a tradeoff between maintaining body condition during incubation and providing eggs with a suitable environment for development. If time and energy constraints are important during incubation, then attentiveness at the nest should increase as body condition or food availability increases, assuming that greater attentiveness shortens the incubation period and increases hatching success (Martin 1987). Several studies support this idea. Aldrich and Raveling (1983) reported that female Canada Geese (Branta canadensis moffitti) that began incubation in good condition spent more time on the nest and had shorter incubation periods than females in poor condition. In years when food was abundant, European Starlings (Sturnus vulgaris) spent less time feeding, and some females were able to incubate without assistance from their mates (Drent et al. 1985). Female Blue Tits (Parus caeruleus) that were given a food supplement during incubation had shorter incubation periods and greater hatching success than females that were not provisioned (Nilsson and Smith 1988). Loss of body mass during incubation may reflect the need to provide constant care for developing embryos (Sherry et al. 1980), or it may enable females to reduce wingloading and to conserve energy during brood rearing (Freed 1981). However, a critical body mass certainly exists for individuals during incubation. Below that threshold, birds either spend more time feeding (Aldrich and Raveling 1983) or they abandon the nest (Drent 1975, Ankney and MacInnes 1978, Jones 1987). Body mass of female waterfowl during the annual cycle typically is lowest at the end of incubation (Afton and Paulus 1990). Ability of individuals to balance the conflicting demands of incubation may influence current and future reproductive suc-

Incubation of eggs of tuatara, Sphenodon punctatus

Abstract: Eggs of the tuatara, Sphenodon punctatus, were incubated either buried or half buried in vermiculite at constant temperatures of 15, 18, 20, 22 and 25 °C and constant water potentials between —90 and —400 kPa. Many clutches failed completely, possibly because they had been taken from females prior to proper shell development. Failed eggs were significantly smaller than successful eggs. Incubation is unsuccessful at 15 °C. Hatching success is high between 18 and 22 °C but low at 25 °C, but equally successful between 18 and 22°C. Incubation is strongly influenced by temperature, with mean incubation periods of 328 days at 18 °C, 259 days at 20 °C, 169 days at 22 °C and 150 days at 25 °C. Water potential generally has little influence on incubation time at a given temperature. Buried eggs hatch sooner than partially buried eggs at 20 °C but the large range makes significance dubious. Eggs on the driest substrata at 18 and 20 °C lose water initially but then gain water through the rest of incubation. Eggs in all other conditions gain water throughout incubation, with the rate of i water absorption being maintained or increasing late in incubation. The suggestion that increasing rate of water absorption late in incubation facilitates explosive hatching is not supported. Egg mass at the time of hatching varies from 132 to 398% of initial values, depending on incubation conditions. Final egg mass is not affected significantly by incubation temperature. Hence, rates of absorption increase with temperature. Water potential has no influence on hatchling size. However, hatchlings from buried eggs generally are significantly larger than those from partially buried eggs.

Effects of Temperature and Oxygen on the Growth of Listeria monocytogenes at pH 4.5

Abstract: Growth effects were studied using tryptose phosphate broth adjusted with hydrochloric acid. The microorganism survived for extended periods at low incubation temperatures (5 and 10°C), and grew at intermediate temperatures (19 and 28°C). Aerobic incubation at 37°C resulted in relatively rapid inactivation of the organism; however, when oxygen was restricted the organism recovered and survived for extended periods. Oxygen restriction enhanced the growth rate at 19°C. Results demonstrated temperature and oxygen availability interacted to influence survival of L. monocytogenes in low pH environment.

Particles in "Particle-free" Seawater: Growth of Ultraphytoplankton and Implications for Dilution Experiments

Abstract: Ultraphytoplankton cells were detected by flow cytometry in seawater that passed through filters of the finest pore size commonly used in aquatic research (0.22-μm Millipore®, 0.45-μm Millipore®, 0.2-μm Nuclepore®, Whatman® GF/F). Although the relative number of cells in freshly prepared filtrate was very small (generally less than 1% of the intact assemblage), the number of such cells increased rapidly during incubation. The implication of this apparent growth was investigated in dilution experiments where diluent was mixed with unfiltered seawater in varying proportions. Plots of apparent rate of change versus dilution factor were generally hyperbolic, with high rates at high dilutions. Simple calculations indicated that fluorometric measurements of bulk chlorophyll a would not have been able to detect these changes.

Ethylene, ethanol, acetaldehyde and carbon dioxide released by Prunus avium shoot cultures.

Abstract: Wild cherry (Prunus avium L.) shoots were cultured in closed vessels on a proliferation medium and the volatile substances released during incubation at photosynthetic photon flux density of 30 μmol m–2 S–1 were determined. Ethylene and CO2 started forming at the beginning of the incubation period and a linear relationship between their formation was observed even at high CO2 concentrations. After 30 days of culture, CO2 reached a concentration of 30%. Shoots released elhanol and acetaldehyde after several days of incubation.

Hydroxyapatite assay to measure epidermal growth factor receptor in human primary breast tumours

Abstract: FIGURE 1. Scatchard analysis of usI-EGF binding to membrane preparations of five different human breast tumours. membrane preparations, after addition of BSA to a final concentration of 0·1%, were incubated in a final volume of 130ilL for 16 h at 20°C with increasing concentrations of 123I-EGF (specific activity: 400 Ci/mmol; mouse EGF, receptor grade, Sigma, St Louis, USA; iodinated using Pro tag 125, Baker Fine Chemicals, Philipsburg, USA) ranging from 50 to 2500 pM in the absence and presence of a 100-fold excess nonlabeled EGF to correct for non-specific binding. For separation of free and receptor-bound ligand after the incubation of membrane preparations with 12sI_EGF, lOOIJL of the HAPsuspension at 4°C is added to each assay tube and incubation is performed for 30min at 4°C. During the incubation with HAP the tubes are shaken twice. Following this incubation, O'5mL of ice-cold buffer B (= buffer A, containing 0·1% bovine serum albumin: BSA, purified, Behringwerke AG, Marburg, West Germany) is Additional key phrases: breast tumour recurrence; tumour membranes; endocrine therapy; oestrogen receptors

Changes in the lipid and fatty acid composition of the yolk during embryonic development of the alligator (Alligator mississipiensis)

Abstract: 1. 1. Changes in absolute and relative amounts of the yolk lipid fractions and their fatty acids were determined for alligator embryos at various stages during incubation. 2. 2. Lipid absorption was particularly active after day 56 of incubation. 3. 3. The major lipid components at the start of incubation were triacylglyceride and phosphoglyceride. The levels of both these fractions decreased considerably during incubation whilst cholesterol ester increased to become a major lipid component of the yolk at hatching. 4. 4. All lipid fractions displayed high levels of palmitoleic acid in the phosphoglyceride there were high levels of C20 and C22 polyunsaturated fatty acids. 5. 5. The fatty acid composition of the triacylglyceride and phosphoglyceride remained relatively unchanged during incubation but there was extensive esterification of cholesterol with oleic acid

Modulation of mammalian sperm motility by quercetin.

Abstract: The flavonoid quercetin inhibits collective motility of ejaculated ram spermatozoa in the first 2 hr of incubation; during the next 3–4 hr motility is stimulated. To explain this interesting effect, we followed the influence of quercetin on sperm glycolysis, extracellular pH, ATP content, mitochondrial respiration, and lipid peroxidation. The collective motility of untreated cells is decreased to about 40% of the original motility during two hours of incubation. During this time, the rate of glycolysis is constant, respiration rate is increasing, there is no change in ATP content, the rate of lipid peroxidation is very slow, and the extracellular pH became very acidic (pH 5.5). It is concluded that motility is decreased due to this acidification. This acidification is prevented to some extent by quercetin, which indirectly inhibits glycolysis. Quercetin inhibits motility due to the inhibition of the plasma membrane calcium pump, as we showed previously (Breitbart et al., J Biol Chem 260:11548–11553, 1985). The motility of untreated cells is arrested after 3.5 hr of incubation, whereas quercetin-treated cells show high motility, which continues for additional 2–3 hr. After 3.5 hr, the control cells show no glycolytic activity, ATP content and respiration rates are decreased, and rate of lipid peroxidation is highly increased. At this time, quercetin-treated cells show no glycolytic activity, only a small decrease in ATP content and respiratory rate, and a very low rate of lipid peroxidation. Based on these data it is concluded that sperm motility after 3.5 hr of incubation is dependent mainly on mitochondrial respiration. It is also concluded that lipid peroxidation activity has a major role in loss of sperm motility during time of incubation.

Importance of albumen content in whole-body protein synthesis of the chicken embryo during incubation.

Abstract: The importance of egg albumen content in whole‐body protein synthesis was investigated in developing chicken embryos by using lines genetically selected for high and low albumen contents and by removing albumen from eggs before incubation. 2. Whole‐body protein synthesis was estimated by injecting l‐[15N]‐phenylalanine intravenously on day 12 of incubation. 3. Embryos from high albumen eggs had higher whole‐body protein synthesis rates than those from low albumen eggs. 4. Whole‐body protein synthesis was reduced by the removal of albumen from eggs before incubation. 5. It was concluded that albumen content per se was of crucial importance in regulating whole‐body protein synthesis in chicken embryos during incubation.

Impairment by glycation of immunoglobulin G Fc fragment function.

Abstract: Incubation of human immunoglobulin G (IgG) with glucose in vitro leads to the formation of glycated IgG concomitant with marked changes in functional properties of the Fc fragment. After 22 days of incubation in the absence and presence of 13.9, 27.7 and 55.5 mmol/l glucose, respectively, protein A binding was reduced by 42, 66 and 83%, depending on the glucose concentration employed. Binding of complement by IgG was abolished after incubation of the immunoglobulins for 13 days at 13.9 mmol/l glucose. In contrast, functional properties of the Fab region were unaffected upon glycation, as revealed by determination of antigen-binding capacity, antibody affinity and antibody concentration. The functional changes of the Fc fragment were observed at glycation levels comparable to those found in diabetics.

The dose-response curves for IAA induced elongation growth and acidification of the incubation medium of Zea mays coleoptile segments

Abstract: The initial dose-response curves for auxin-induced elongation growth of Zea mays L. coleoptile segments and simultaneously measured changes of pH of the incubation medium were studied. It was found that these curves are bell-shaped on all occasions and that at all IAA concentrations studied acidification of the incubation medium took place. The optimum response for IAA-induced elongation growth and acidification of the incubation medium was 10−5 and 10−4M IAA, respectively. The regression curves and correlation coefficients between magnitude of the growth response and acidification of the incubation medium indicated a close relationship between these sets of data over a wide range of IAA concentrations.

Sex-determining potencies vary among female incubation temperatures in a turtle.

Abstract: Reptiles whose sex is determined by incubation temperature typically exhibit all- male or all-female sex ratios over a wide range of incubation temperatures. The question arises as to whether the various all-female temperatures (or the various all-male temperatures) are equiva- lent in their "potency," or capacity to effect female determination. In map turtles, warm incubation temperatures produce all females and cool ones produce all males. We compared sex determining potencies of two all-female temperatures, 31°C and 32.5"C, by incubating eggs first at a male- producing temperature (26°C) and then shifting them to the warm temperatures. The resulting sex ratio was significantly more male biased in the 26"C+3loC shift than in the 26"C-+32.5"C shift, indicating that 325°C has the greater female potency. These results point to the possibility that sex determination depends on a quantitative rather than qualitative level of gene expression. Incubation temperature of the embryo deter- mines sex in many reptiles (reviewed in Bull, '80; Raynaud and Pieau, '85). Yet despite documenta- tion of a temperature effect on sex determination in many species, details of how temperature de- termines sex are still scant. In many species, a range of incubation temperature produces only males and another range produces only females. However, while warm temperatures produce males and cool temperatures produce females in some lizards and crocodiles, the reverse pattern occurs in many turtles; in yet other species, fe- males are produced at both high and low ex- tremes, with males developing at intermediate temperatures (see reviews cited above). One ques- tion that arises from these observations is whether all temperatures producing the same sex are equivalent. That is, if two temperatures each produce 100% females, are they equally potent in their female determining effect? This question is the focus of our study. METHODS AND MATERIALS

The role of prolactin in parental care in a monogamous and a polyandrous shorebird.

Abstract: -We compared circulating prolactin levels in two species of shorebirds which have very different social systems, and which breed sympatrically at La Perouse Bay, 40 km east of Churchill, Manitoba. Semipalmated Sandpipers (Calidris pusilla) are monogamous and share incubation equally, although females normally desert broods earlier than males. Rednecked Phalaropes (Phalaropus lobatus) are facultatively polyandrous, and only males care for eggs and young. High prolactin values were correlated with persistent incubation behavior in male Rednecked Phalaropes, and male and female Semipalmated Sandpipers. Prolactin levels in Semipalmated Sandpipers increased dramatically at the onset of incubation, and were not different between the sexes. Incubating male phalaropes had greater prolactin values than the nonincubating males and females. Changes in prolactin levels, however, did not explain the early brood desertion of female Semipalmated Sandpipers. Prolactin levels did not decline with age of brood in either sex of this species. Received 16 October 1989, accepted 29 April 1990. PROLACTIN is involved in a wide variety of physiological and behavioral events in vertebrates (Bentley 1982). However, controversy continues regarding prolactin's role in initiation and maintenance of incubation in birds. Early studies by Riddle and others (e.g. Riddle et al. 1935, Riddle and Lahr 1944) showed that injections of mammalian prolactin induced incubation behavior in female domestic fowl (Gallus gallus) and Ringed Turtle-Doves (Streptopelia risoria). Subsequent studies (Saeki and Tanabe 1955, Lehrman and Brody 1961, Opel and Proudman 1980, Hohn 1981) did not yield the same result, although incubation behavior was induced by prolactin in ovariectomized female Wild Turkeys (Meleagris gallopavo), after the birds were "primed" with injections of estradiol and progesterone (El Halawani et al. 1986). Recent development of radioimmunoassays to measure avian prolactin has allowed researchers to follow changes in plasma levels throughout the breeding season, and relate these changes to behavior. The fact that plasma prolactin levels often are elevated before persistent 4Present address: Prairie and Northern Wildlife Centre, Canadian Wildlife Service, 115 Perimeter Road, Saskatoon, Saskatchewan S7N OX4, Canada. incubation has led some authors to suggest that prolactin induces incubation behavior (e.g. Lea et al. 1981). Others have concluded (from eggremoval studies and studies that involve anesthetization or denervation of brood patches) that either tactile or visual presence of the nest and eggs stimulates incubation and results in elevated plasma prolactin, which in turn maintains incubation behavior (e.g. Hall and Goldsmith 1983). Still others propose a combination of these processes (El Halawani et al. 1986). Other studies of turkeys, bantam hens, and Pied Flycatchers (Ficedula hypoleuca) have shown that incubation can persist for at least a short time in the absence of high circulating levels of prolactin (Lea et al. 1981, El Halawani et al. 1980, Silverin and Goldsmith 1984). The issue is further complicated by the fact that some researchers have found seasonal increases in prolactin levels in the absence of incubation or nestling-feeding behavior. In some instances such increases have been linked to onset of photorefractoriness (e.g. European Starlings [Sturnus vulgaris], Dawson and Goldsmith 1983, Goldsmith and Williams 1984; White-crowned Sparrows [Zonotrichia leucophrys], Hiatt et al. 1987). Our primary objective was to examine the pattern of circulating levels of prolactin at dif718 The Auk 107: 718-729. October 1990 October 1990] Prolactin and Parental Care 719 ferent stages of the reproductive cycle in two species of shorebirds with very different breeding systems. In the Red-necked Phalarope (Phalaropus lobatus), only males incubate (Hilden and Vuolanto 1972). Females desert their males as soon as the clutch is completed, and then attempt to obtain subsequent mates (Reynolds 1987). Semipalmated Sandpipers (Calidris pusilla) are monogamous, with incubation shared equally by both members of the pair (Ashkenazie and Safriel 1979a, b). If changes in circulating levels of prolactin are primarily related to incubation behavior, prolactin levels should be similar in both sexes of the Semipalmated Sandpiper, and greater in incubating male phalaropes than in females and nonincubating males. In both species plasma prolactin should increase substantially at the onset of incubation behavior. However, if prolactin levels increase seasonally-without a change in behavior-in males and females of both species, its function may primarily relate to photorefractoriness. The gradual decline of plasma prolactin levels of attending parents of altricial and semialtricial young after hatch has been related to a decrease in feeding or brooding with increased age of nestlings (e.g. Silverin and Goldsmith 1984, Hector and Goldsmith 1985). In contrast to species with altricial young, prolactin levels decline dramatically at hatch (or within two days afterwards) in virtually all species examined with precocial young (Dittami 1981, Goldsmith 1982a, Goldsmith and Williams 1980, Hall and Goldsmith 1983, Wentworth et al. 1983). Spotted Sandpipers (Actitis macularia) appear to be an exception, because prolactin levels did not decline in the first two days after hatch (Oring et al. 1986a). In addition, prolactin levels in Wilson's Phalaropes (Phalaropus tricolor) declined gradually and reached basal levels by nine days posthatch (Oring et al. 1988). These authors suggested that the gradual decrease is related to the decline in brooding behavior with age of chicks, as found in other shorebirds. In view of the proposed relationship between prolactin levels and brood-care behavior, particularly in shorebirds, a second objective of this study was to examine hormonal control of brood care in the Red-necked Phalarope and Semipalmated Sandpiper, both of which have precocial young. In phalaropes, however, only males participate in brood care (Hilden and Vuolanto 1972, Reynolds 1987). Almost all female Semipalmated Sandpipers gradually desert their broods to the care of the male soon after hatch (Ashkenazie and Safriel 1979a, b; Gratto and Cooke 1987). Therefore we predicted that prolactin levels of females would decline at rates faster than those of males.

Strain differences in whole-body protein turnover in the chicken embryo.

Abstract: 1. Whether or not there is a strain difference in embryonic whole‐body protein turnover rates was tested using the chicken embryos of Rhode Island Red carrying a sex‐linked dwarf gene (dwarf), White Leghorn (layer), and White Cornish x White Plymouth Rock (broiler) strains on day 12 of incubation. 2. Whole‐body protein synthesis was estimated by injecting l‐[15N]‐phenylalanine either intraperitoneally or intravenously on day 12 of incubation in order to investigate the effect of the route of isotope administration. The results showed that the values for fractional and absolute synthesis rates were approximately 13% higher by intravenous injection than by intraperitoneal injection. 3. Whole‐body protein turnover, both in terms of fractional and absolute rates, was significantly faster in dwarf than in broiler embryos, with intermediate values in layer embryos, although no growth differences were observed on day 12. 4. Difference in egg weight, measured before incubation, did not affect protein tur...

The effect of incubation media on the water exchange of snapping turtle ( Chelydra serpentina ) eggs and hatchlings

Abstract: The effect of two different incubation media, sand and vermiculite, on the water exchange of eggs and the mass of hatchlings of snapping turtles (Chelydra serpentina) was assessed. The eggs were incubated fully buried in either sand or vermiculite at 30 °C and egg mass was measured periodically throughout incubation. The wet and dry masses of each hatchling and its residual yolk were measured at the end of incubation. The media had similar water potentials (Ψ) but their thermal conductivities differed 2.8-fold. The eggs experienced a net water gain during incubation. The rates of water uptake between treatments were not statistically different throught the first 36 days of incubation but were statistically different thereafter, with eggs incubating in sand taking up water at about twice the rate of eggs incubating in vermiculite. Hatchling masses were similar to both media but hatchling water contents were significantly different. Hatchlings incubated in sand had lower water contents than hatchlings incubated in vermiculite even though the eggs in sand took up more water. Hatchling mass was correlated with egg water exchange for eggs incubated in vermiculite but not for eggs incubated in sand. The difference in egg water exchange in the two media appears to be attributable to differences in the thermal conductivity of the media. The presence of such a thermal effect supports the hypothesis that the eggs exchanged water with the media as water vapor. Egg water exchange was limited by the shell and shell membranes and not by the media. The shell and shell membranes appear to present an effective barrier to water uptake.

A method for assessing resistance to the snow molds Typhula incarnata and Microdochium nivale in winter wheat incubated at the optimum growth temperature ranges of the fungi

Abstract: Studies were carried out to determine whether incubation of wheat plants at the temperatures optimum for growth of fungi could reduce the time normally required for determination of resistance to Typhula incarnata and Microdochium nivale in wheat, comparing with conventional under-snow incubation methods in field plots. Typhula incarnata produced greater damage to the winter wheat plants at temperatures of 5 and 10 °C than M. nivale. At 15 and 18 °C, there existed little difference in virulence and we could complete incubation in a period of weeks. Incubation of the plants for varying periods of time was of use for quantitative determination of the degree of resistance expressed as LI50 (the number of incubation days when 50% of the plants are killed) values. The relative order of resistance among cultivars of wheat was consistent with that obtained from an under-snow incubation method. The new technique permitted wheat breeders to screen genotypes of wheat for resistance to snow mold pathogens in a short...