First Week Of Incubation Research Articles

Soil nitrogen mineralization during laboratory incubation: Dynamics and model fitting

Soil nitrogen mineralization kinetics were studied for eight treatments of two soils in an aerobic long-term (30 wk) incubation experiment. Soil mineral-N (NH 4 + and NO 3 −) in the leachates was measured every week during the first 9 wk and every 2 or 3 wk thereafter. The NH 4 + percentage of the mineral-N ranged between 85 and 99% for all treatments in the first week of incubation and remained high (> 80%) in several treatments until the end of wk 4. Starting at wk 7, NH 4 + concentrations were negligible in all treatments. The net N mineralization rate was 15–24 mg N kg −1 wk −1 during the first 4–6 wk and 2–5 mg N kg −1 wk −1 from wk 8 until the end of the incubation. Four models, (i) a one-component, first-order exponential model (the single model), (ii) a two-component, first-order exponential model (the double model), (iii) a one-component, first-order exponential model including a constant term (the special model), and (iv) a hyperbolic model, were fit to the cumulative mineral-N vs time data using a non-linear regression procedure. The goodness of fit of the four models depended on the duration of incubation. With 30 wk data, the double and special models were significantly better than the other two models; with the first 15 wk data, the four models had essentially the same goodness of fit for seven out of eight treatments. The values of the regression parameters derived from each model also depended on the incubation duration. Results from this study show that the pool size and mineralization rate parameters in the different models are merely mathematically-defined quantities obtained from the kinetic analysis of the net N mineralization and do not represent any rigorously-defined pool sizes of potentially-mineralizable N and their mineralization rate constants in the soils.

The accelerating effect of aLactococcus lactis subsp.lactis lactose-utilization/proteinase-deficient strain on proteolysis and flavour development

This study describes the accelerating effect exerted on proteolysis and flavour development in cheese-curd slurries by combined application ofLactococcus lactis subsp.lactis IFPL359 and high concentrations of its Lac− Prt− derivative, (i.e. that which has reduced capacity to metabolize lactose and reduced proteolytic activity, strain T1). Cells of strain T1 partially lysed by either sonication or incubation with lysozyme, were also used to ascertain how proteolysis was affected by release of intracellular enzymes in the initial stage of incubation of the strains in cheese-curd slurries. The presence of strain T1 produced higher levels of non-protein nitrogen (NPN) and amine nitrogen (AN) during the first weeks of incubation when partially lysed cells had been added. Addition of whole cells of strain T1 produced higher values of NPN and AN at the end of incubation of slurries, accelerating proteolysis by about 2 weeks with respect to the control, which only contained the parental strain IFPL359. At the end of the experimental period higher amino acid levels were detected by HPLC in the slurry containing whole T1 cells. Volatile fractions of the different cheese-curd slurries were also analysed. The higher level of proteolysis produced by addition of high levels of strain T1 appeared to be related to release of intracellular enzymes by this strain owing to its greater capacity for autolysis.

Visibility Bias in Aerial Surveys Relating to Nest Success of Arctic Geese

We conducted annual aerial surveys of white-fronted (Anser albifrons fontalis) and Canada (Branta canadensis hutchinsii) geese during the first week of incubation over 8,000 ha near Walker Bay, Northwest Territories, from 1986 through 1992 to monitor population size and trend. Unexpectedly, population estimates of each species fluctuated widely but similarly among years (r = 0.912, P = 0.003), causing us to examine relationships with ground studies. Population estimates and nest success were negatively correlated for both species (r = −0.86, P = 0.03 for white-fronted geese; r = −0.93, P = 0.01 for Canada geese). Ground counts of nests on random 100-ha plots provided an unbiased estimate of nest density. Visibility (the probability that an object within the field of search will be seen by the observer) of nesting geese was estimated from the ratio between nest densities estimated from the air and from the ground and was related to nest success for both species. We concluded that the decrease in visibility of pairs with increasing nest success resulted from behavioral changes in birds that lost their nests. Geese that lost their nests were more conspicuous because both members of the pair were together and flushed at greater distances, whereas 1 member of a successful pair was usually incubating. Because visibility of pairs can be low in years of high nest success, variation in visibility must be accounted for when estimating densities of nesting geese by aerial survey. Failure to consider visibility could lead managers to erroneous conclusions about the status of arctic goose populations

Isoenzymes of manganese-dependent peroxidase and laccase produced by the lignin-degrading basidiomycete Ceriporiopsis subvermispora

The white-rot basidiomycete Ceriporiopsis subvermispora produces two families of ligninolytic enzymes, namely manganese-dependent peroxidases (MnPs) and laccases, when growing in liquid cultures of defined composition. In medium containing 11 p.p.m. of Mn(II), up to seven isoenzymes of MnP and four isoenzymes of laccase were resolved by isoelectrofocusing (IEF), with pI values in the range 4.10-4.60 and 3.45-3.65, respectively. Occasionally, a fifth laccase isoform of pI 4.70 was also detected. In cultures with 25 and 40 p.p.m. of Mn(II), mainly the MnPs with higher pI values are produced. The isoenzyme pattern of MnP is not altered throughout the growth period of the fungus. MnP and laccase are also produced by C. subvermispora when growing on wood chips of Pinus radiata. Highest levels of both enzymes were obtained during the first week of incubation. A second peak of MnP activity was observed during the fourth week, whereas very low levels of laccase were extracted from the chips after the second week of growth. IEF analysis showed that the pI values of these laccases are similar to those of laccases produced in liquid cultures, being in the range 3.45-3.65. In contrast, four isoforms of MnP were resolved during the first week of incubation on wood chips, with pI values of 4.40, 4.17, 4.04 and 3.53. This profile underwent a transition during the second week of growth, at the end of which isoforms of MnP with pI values of 3.53, 3.40, 3.30 and 3.20 were resolved by IEF.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of some herbicides on activities of microorganisms and enzymes in soil

Abstract Laboratory tests were conducted with eight herbicides, atrazine, butylate, ethalfluralin, imazethapyr, linuron, metolachlor, metribuzin and trifluralin, applied to a loamy sand at rate of 10 μg/g to determine if these materials caused any serious effects on microbial and enzymatic activities related to soil fertility. Some herbicides showed an effect on bacteria and fungi for the first week of incubation, but, subsequently, the populations returned to levels similar to those obtained in the controls. After several herbicide treatments there appeared to cause a slight depression of nitrification. Sulfur oxidation was better than that obtained with untreated soil in all treatments. Oxygen consumption was increased significantly after 96 hr incubation with atrazine. The soil dehydrogenase and amylase activities were inhibited by ethalfluralin treatment respectively for 1 wk and 1 day, and p‐nitrophenol liberation was inhibited for 2 hrs by all herbicide treatments. Results indicated that the herbicidal treatments at the level tested were not drastic enough to be considered deleterious to soil microbial and enzymatic activities which are important to soil fertility.

Biofilms and the survival of opportunistic pathogens in recycled water

Microorganisms are likely to develop an organic film on pipes, water reservoirs and filters used for waste water reclamation during extended missions in space. These biofilms can serve to protect and concentrate potentially pathogenic microorganisms. Our investigation has emphasized the survival strategy of opportunistic pathogenic bacteria in distilled water. Pseudomonas aeruginosa and Staphylococcus aureus were used as test organisms. Cultures were incubated at 10 °, 25 ° and 37 °C. No viable Staphylococcus cells were detected after the first week of incubation. P. aeruginosa, however, survived in distilled water up to 5 months at all three temperatures tested. The starved cells were able to form a biofilm layer on stainless steel. The cells exhibited a negative surface charge. The charge may be involved in the adhesion of this bacterium to metal substrata. We are currently investigating the importance of adhesion in the survival of this and other potential human pathogens found in water recycling systems.

Interaction of 15N-labelled ammonium nitrogen with native soil nitrogen during incubation and growth of maize ( Zea mays L.)

A laboratory incubation experiment and a pot experiment on maize ( Zea mays L.) were madee to study the interaction with native soil N of 15N-labelled ammonium applied at 25. 50. 100 or 200 μ g N g −1 soil. Incubation of soil for 4 weeks showed a significant enhancement in mineralization of native N (added nitrogen interaction. ANI) due to applied N and the effect increased with increased rate of application. The ANI occurred only during the first week of incubation and its extent was not affected significantly during the subsequent 3 weeks of incubation. The ANI was not observed in the pot experiment at any concentration of applied NH 4-N and was assumed to be due to the absence of root-driven immobilization and pool substitution in maize. Root growth showed a negative response to increased amounts of N addition. However. N uptake efficiency of plants (as revealed by total plant N) increased significantly at increasing rates of applied N but without the occurrence of ANI. Heavy losses of applied N occurred both in the incubation study (20 30%) as well as plant experiment (47–83%); the losses being more as the rate of applied N increased.

Biofilms and the survival of opportunistic pathogens in recycled water.

Microorganisms are likely to develop an organic film on pipes, water reservoirs and filters used for waste water reclamation during extended missions in space. These biofilms can serve to protect and concentrate potentially pathogenic microorganisms. Our investigation has emphasized the survival strategy of opportunistic pathogenic bacteria in distilled water. Pseudomonas aeruginosa and Staphylococcus aureus were used as test organisms. Cultures were incubated at 10 degrees, 25 degrees, and 37 degrees C. No viable Staphylococcus cells were detected after the first week of incubation. P. aeruginosa, however, survived in distilled water up to 5 months at all three temperatures tested. The starved cells were able to form a biofilm layer on stainless steel. The cells exhibited a negative surface charge. The charge may be involved in the adhesion of this bacterium to metal substrata. We are currently investigating the importance of adhesion in the survival of this and other potential human pathogens found in water recycling systems.

Impact of the BACTEC NR system in detecting Candida fungemia

As a result of the growing importance of candidemia, various techniques for the detection of Candida spp. in blood have been designed with a view to speeding up the laboratory procedure. We have performed a retrospective comparison of the efficiencies of the conventional VACUTAINER system (Becton Dickinson Vacutainer Systems) and the BACTEC NR system (Johnston Laboratories, Inc.). During a 4-year period, 88,300 blood cultures were processed, with growth of Candida species in 552. The mean times required for the detection of growth were 7.55 days with the VACUTAINER system and 4.1 days with the BACTEC NR system (P less than 0.05). During the first week of incubation, the VACUTAINER system detected 56.1% of the candidemias and the BACTEC NR detected 93.6% (P less than 0.05). Use of the BACTEC NR therefore permits reduction of the incubation period from the previously established 4 weeks to a more convenient 7 to 14 days.

Some metabolic changes during human corneal organ culture.

In order to evaluate the changes in medium composition during closed system corneal organ culture at 30 degrees C, pH, pO2, glucose and lactate was measured 1 to 7, 14 and 28 days after incubation of a total of 49 human corneas. During organ culture pO2 decreased from 17.3 kPa to 8.8 kPa at day 28. The average oxygen consumption was initially 0.16 mumole/h/cm2, but decreased rapidly to an average of 0.04 mumole/h/cm2 during the first weeks of incubation. The glucose concentration fell from 5.1 mM to 0.25 mM after 28 days, and the lactate concentration rose from 2.5 mM to 11 mM. The concentration changes were for both substances highest during the first 14 days of organ culture. The pH fell from 7.36 to 6.64 after 28 days. These findings indicate that the cultured human cornea predominantly metabolizes glucose anaerobically, and that the metabolic activity decreases during incubation. The limiting metabolic factors for prolonging the culture period seem to be development of severe acidosis and glucose depletion in the medium.

The influence of four fungicide formulations on the degradation rate and selective extractability of carbofuran in the soil

Abstract ‘Soil was incubated for 18 weeks with carbofuran alone (control) or in combination with Manate (maneb), Apron (metalaxil + mancozeb), Ridomil Special (metalaxil + maneb) and Pomarsol (TMTD) which were added to the soil at high (250 ppm) and lower (25 ppm) concentration. In the presence of fungicides the half‐life time value for carbofuran in the soil was 1.2 to 3 times higher than in the control depending on the nature of the fungicide and its concentration. The degradation rate, as reflected from the degradation ratio R measured at weekly time intervals, was greatly affected by the presence of the fungicides: at the lower concentration the R values were much lower only during the first weeks of incubation , whereas at the higher fungicide concentration this inhibitory effect on the degradation rate appeared to be very persistent. The extraction of the soil samples at the end of the incubation period has been performed using either water or a benzene‐acetone mixture as solvents. The differential extractability, which is linked to the insecticide bioavailability in the soil environment, has been shown to be influenced by the presence of the fungicides: at high application rate the carbofuran was relatively better extracted with water than at lower application rate or in the absence of fungicides.

Toxicity and distribution of 2-methyl-4-chlorophenoxyacetic acid (MCPA) in developing chick embryos

The toxicity of the herbicide Erbitox E30, a commercial formulation of 2-methyl-4-chlorophenoxyacetic acid (MCPA) containing 28% MCPA as sodium-potassium salt and 72% of unknown ingredients, was tested on chick embryos. Sterile aqueous solutions of MCPA were injected into the air chamber at doses of 0, 1.5, 3.0, 6.0, 9.0, or 10.5 mg/egg on day 0 or on day 4 of incubation. The mortality rate for the embryos treated on day 0 of incubation was high in the first 5 days, low from 5–12 days and again increased by 15 days. The 15-day LD 50 was 4.4 mg/egg (95% C.I. 3.7–5.3 mg/egg). HPLC analysis of albumen and yolk showed that concentrations of MCPA in the albumen were detectable at 5 min, highest at 7 days and markedly diminished by 14 days of incubation; a significantly lower concentration of MCPA was found in the yolk throughout the incubation period, except at 14 days when the yolk concentration was 4 times higher than the albumen concentration. At 15 days of incubation, MCPA was evenly distributed in the tissues of the embryo. MCPA was more toxic to 4-day embryos; concentrations above 6.0 mg/egg were lethal to all embryos within the first week of incubation. The 15-day LD 50 for treatment on day 4 of incubation was 2.8 mg/egg (95% C.I. 2.5–3.2 mg/egg). The liver was affected by treatment with MCPA, being green in treated embryos. However, histological examination revealed few changes in the liver parenchyma.

Effect of soybean root exudates on Bradyrhizobium japonicum

Abstract Effects of soybean root exudates on the growth and survival of Bradyrhizobium japonicum (USDA 110) in artificial medium as well as in a Chester silt loam soil were studied. Exudates were added to a yeast extract‐mannitol medium at concentrations of 0.00, 0.01, 0.02, and 0.04% (w/v). Results showed that the lowest exudate concentration did not affect the growth of B. japonicum, while the highest level (0.04%) reduced the population in the medium. Exudates at a concentration of 0.02% enhanced the. population of B. japonicum in the medium. A study of the survival of B. japonicum in soil amended with exudates at 0.0, 0.1, 0.2, and 0.4% (w/w) was also conducted. Results indicated that exudates at 0.1 and 0.2% did not affect the population of rhizobia during the first week of incubation. The 0.4% concentration exhibited a rapid reduction in the population of B. japonicum during this time. After the first week, the population of B. japonicum declined for all treatments. By the end of the study, the soil...

Reduction of inoculum of Rhizoctonia solani in soil by germlings of Trichoderma hamatum

Three- and 8-day-old inoculum of Trichoderma hamatum (TRI-4), consisting of young, actively-growing hyphae on bran, reduced survival of Rhizoctonia solani in infested beet seed by about 90% during the first week of incubation and prevented growth of the pathogen from beet seed into soil. The 3-day-old inoculum is considered a germling preparation. An older preparation (40-day-old), which did not contain growing hyphae, or conidia on bran (0-day-old) did not reduce survival or growth of R. solani even after 3 weeks of incubation. A 15-day-old preparation reduced survival about 50%. Addition of germlings to soil at a rate of 0.13% reduced pathogen survival and growth as effectively as a 1% rate after 3–6 weeks of incubation. There was nearly complete reduction (>90%) in survival when germlings were added to soil at the same time as seed infested with R. solani or 1 week later; a 50% reduction in survival when added 2 or 4 weeks after R. solani, and no reduction when added to soil 1, 2 or 4 weeks before the pathogen. Saprophytic growth was generally prevented by germlings except if they were added 2 or 4 weeks before the infested beet seed. Isolate TRI-4 rapidly grew from the bran into soil and within 2 days it penetrated and attacked R. solani embedded in beet seed so that pathogen survival dropped to about 20% and the population of TRI-4 proliferated within the seed. Germlings of TRI-4 reduced survival (>90%) and growth (>50%) of several isolates of R. solani in a loamy sand. Survival and growth of R. solani isolate R-23, was reduced more than 90% in seven different soil types within 1 week of incubation. Germlings reduced pathogen survival under all conditions of temperature, moisture and pH studied except under high moisture at 32°C. The greatest reduction (91–100%) was observed at all soil moisture levels at 15° and 23°C and at pH 5.0 and 6.4.

Comparison of mechanisms enhancing biodegradability of refractory lake water constituents1

Bacterial degradation of macromolecular DOM, aged under weakly photolytic conditions (daylight > 300 nm), was compared to that of the original compounds before and after provision of a cosubstrate. Bacteria, Pseudomonas sp., Flavobacterium sp., and Erwinia sp., and macromolecules (apparent mol wt ≥ 1,500) were isolated from the same lake water samples, one taken in winter and one in summer. Decomposition was determined by DOC measurements, since UV absorbance A200–300nm did not give an accurate indication of loss rates. Both aging and the pulse dose of nutrients enhanced the accessibility of the refractory DOM to Pseudomonas sp. and Erwinia sp., while Flavobacterium sp. utilized the original substances most effectively. The original macromolecules were decomposed 12–22%, aging increased the available portions by a further 5–10%, and provision of the cosubstrate, glutamic acid, enhanced degradation by 3–8% and by 20% (Erwinia sp. and DOM fraction, both isolated in summer). The constituents of the macromolecules in the winter sample rendered accessible by photolysis were energetically advantageous to Pseudomonas sp. and Erwinia sp. The degradable portions of the original and aged macromolecules were consumed within the first week of incubation, and the remainder was persistent. Provision of a nutrient pulse did not result in the production of enzymes that might have enabled the bacteria to assimilate the refractory remainder. Both mechanisms are thought to reduce the longevity of the refractory DOM in a stepwise manner in natural waters.

Behavior of Chloroplast Nucleus during Chloroplast Development and Degeneration in Chlamydomonas reinhardii

Changes in morphology of chloroplast nuclei (cp-nuclei), total cp-DNA content,number of cp-nuclei, oxygen-evolution activity and chlorophyll (a and b) content wereexamined during the degeneration and development of chloroplasts, usin Chlamydomonasgreinhardii cells which had been incubated on solid medium for various periods.Under 4'-6-diamidino-2-phenylindole (DAPI) epifluorescence microscopy, eachcell that had been incubated for 7 days had one cell nucleus, one cup-shaped chloroplastand abou 1t 0 small, dispersed cp-nuclei in the chloroplast. One day after incubationof these cells on fresh medium, the cell volume and cp-nuclei increased in size 2-3 fold,but rapidly decreased in size after cell division. Afte 7 days orf abou incubationt , cellsceased to divide and cp-nuclei began to associate with each other. At about 20 daysthey formed a ring-shaped structure surrounding the pyrenoid, followed by condensationinto one cp-nuclear particle near the pyrenoid. When 41-day-old cells, having only onecp-nucleus, were reinoculated on fresh solid medium, the cp-nucleus increased in size2-3 fold, divided into several cp-nuclear particles and then dispersed into the chloroplast,forming a bead-like structure, before cell division. From microscopic fluorometry,a 4-fold increase in total cp-DNA content per chloroplast, without an increase in thenumber of cp-nuclear particles per chloroplast, occurred one day after the start of theexperiment and one day after reinoculation of 41-day-old cells onto fresh medium. Theprocess of condensation of dispersed cp-nuclear particles into one cp-nucleus duringdegeneration of the chloroplast was not accompanied by any change in total cp-DNAcontent per chloroplast. A large peak of oxygen-evolution (0.6-0.9 pmoles/cell/hour)was seen one day after inoculation and reinoculation of the cells. The chlorophyllcontent (a+b) was high (1.2-2.2 pg/cell) during the first week of incubation, after whichit gradually decreased.Key words: Chlamydomonas — Chloroplast degeneration — Chloroplast development— Cp-DNA — Cp-nucleus — Oxygen evolution.

Mineralisation dans le sol de materiaux microbiens marques au carbone 14 et a l'azote 15: Quantification de l'azote de la biomasse microbienne

The mineralization of microbial material of different C-to-N ratios (5.2, 7.9, 10.2, 12.7) was followed in fumigated soil. The microbial materials used were from Aspergillus flavus cultures, grown in liquid media and labelled with [ 14C]glucose and ( 15NN4)3804. Three contrasting soils were used and the microbial materials incubated with the fumigated soils for 28 days at 28°C. The evolution of the added organic microbial C was fast: 80% of the [ 14C]CO 2 produced during the whole 28 days incubation was evolved in the first week. Microbial C mineralization was mainly related to soil type; the C-to-N ratio had small effect on the ratio (mineralized microbial carbon-to-added microbial carbon). Calculation of the K c - coefficient (the fraction of the added microbial C mineralized in 7 days) shows that K c values lie between 0.38 and 0.43 in the 3 soils. Organic N in the added microbial material also breaks down quickly: between 60 and 100% of the organic nitrogen mineralized was evolved during the first week of incubation. Mineralization kinetics are related to soil type and to the C-to-N ratio of the microbial material. The proportion of N mineralized in 7 days was lower in an acid soil than in near neutral soils and lower with high C-to-N ratio material than with low C-to-N ratio material. The ratio (mineralized microbial N-to-added microbial N) depends on soil type and is negatively correlated with the C-to-N ratio of the microbial material. The K N value (the fraction of the added microbial N mineralized in 7 days) lies between 0.22 and 0.47 for the three soils and four materials investigated. The added microbial material induced a priming effect on soil native N: materials with C-to-N ratios of 10.2 and 12.7 produced negative priming effects whereas materials with C-to-N ratios of 5.2 and 7.9 sometimes produced a positive priming action. From the relationship between the C-to-N ratio of the added material and the (mineralized microbial C-to-mineralized microbial N) ratio, the soil native microbial biomass was estimated using the fiush-C-to-flush-N ratio. Biomass nitrogen was then calculated from the formula biomass-N = biomassC/(biomass C-to-N ratio). Calculated in this way, 2–4% of the total nitrogen in the three soils was in microbial biomass.

Effect of non-Legionellaceae bacteria on the multiplication of Legionella pneumophila in potable water.

A naturally occurring suspension of Legionella pneumophila and associated microbiota contained three unidentified non-Legionellaceae bacteria which supported satellite growth of a subculture of L. pneumophila on an L-cysteine-deficient medium and another bacterium which did not support growth of the subculture. Washed suspensions containing 10(3), 10(5), 10(7), or 10(8) CFU of a mixture of isolates of these non-Legionellaceae bacteria failed to support the multiplication of an isolate of agar-grown L. pneumophila which had been washed and seeded into the suspensions. The suspensions which contained 10(3), 10(5), or 10(7) CFU of the non-Legionellaceae bacteria per ml appeared to enhance survival or cryptic growth of agar-grown L. pneumophila. A decline of 1.3 log CFU of L. pneumophila per ml occurred within the first week of incubation in the sample which contained 10(8) CFU of the non-Legionellaceae bacteria per ml. In contrast to these results, naturally occurring L. pneumophila multiplied in the presence of associated microbiota. The necessity to subculture L. pneumophila and the non-Legionellaceae bacteria on artificial medium to obtain pure cultures may have affected the multiplication of L. pneumophila in tap water. Alternatively, other microorganisms may be present in the naturally occurring suspension which support the growth of this bacterium.

Influence of egg storage on hatchability, embryonic development and vitamin status in hatching broiler chicks.

Storage of eggs for 14 d prior to incubation depressed hatchability by 10%. Most of the increase in embryonic mortality (64%) occurred during the first week of incubation, with a further 30% taking place during the third week. Chicks hatching from stored eggs did not show any increased incidence of physical abnormalities characteristic of vitamin deficiencies. Chicks from stored eggs showed haematological abnormalities characteristic of mild macrocytic anaemia. Such changes can result from deficiencies of folic acid or cobalamin. Biochemical and haematological data did not suggest impairments in the status of the chicks with respect to a range of other vitamins.

Reproductive defence priorities of male willow ptarmigan (Lagopus lagopus): enhancing mate survival or extending paternity options?

Cock willow ptarmigan (Lagopus lagopus) closely guard their mates from predators and conspecific males, and vigorously defend their nests and young. In view of potential costs and benefits of behavioural guarding descisions, I designed a test to examine if, when and how males altered defence priorities. Cock willow ptarmigan were very attentive to their mates throughout the breeding season, unaccompanied hens comprising less than 3% of the sightings of mated females. From the second week of incubation until shortly after hatch, males attempted to guard both mates and offspring. Males guarded mates preferentially over nests until the third week of incubation; they then changed their priority to defence of offspring (nest and/or chicks). The overall defence response initially was strong, but decreased after the first week of incubation. Strength of response increased again in late incubation, and declined as chicks began to fly. Consistency of defence “decisions” was highest during prenesting and egg laying and lowest during late incubation. Since males defended their mates for a longer period than required for protection of paternity, hypotheses predicting enhanced mate survival and extended paternity options through renesting were examined. Removal of males did not result in reduced survival or increased weight loss of widows during incubation. In light of heavy nest depredation and displacement pressures by conspecifics, mate guarding throughout incubation enhanced male fitness by ensuring paternity in renesting attempts.