Showing papers by "University of California, Davis published in 1979"
TL;DR: Data indicate the following sequence for the pathway of ethylene biosynthesis in apple tissue: methionine --> S-adenosylmethionine ― ACC ― ethylene --> methylthioadenosine --> ACC --> ethylene.
Abstract: L-[U-14C]Methionine fed to apple tissue was efficiently converted to ethylene when the tissue was incubated in air. In nitrogen, however, it was not metabolized to ethylene but was instead converted to 1-aminocyclopropane-1-carboxylic acid (ACC). When apple tissues were fed with L-[methyl-14C]methionine or L-[35S]methionine and incubated in nitrogen, radioactivity was found subsequently in methylthioribose. This suggests that methionine is first converted to S-adenosylmethionine which is in turn fragmented to ACC and methylthioadenosine. Methylthioadenosine is then hydrolyzed to methylthioribose. The conclusion that ACC is an intermediate in the conversion of methionine to ethylene is based on the following observations: Labeled ACC was efficiently converted to ethylene by apple tissue incubated in air; the conversion of labeled methionine to ethylene was greatly decreased in the presence of unlabeled ACC, but the conversion of labeled ACC to ethylene was little affected by the presence of unlabeled methionine; and 2-amino-4-(2′-aminoethoxy)trans-3-butenoic acid, a potent inhibitor of pyridoxal phosphate-mediated enzyme reactions, greatly inhibited the conversion of methionine to ethylene but did not inhibit conversion of ACC to ethylene. These data indicate the following sequence for the pathway of ethylene biosynthesis in apple tissue: methionine → S-adenosylmethionine → ACC → ethylene. A possible mechanism accounting for these reactions is presented.
1,254 citations
TL;DR: The method is quite specific and can detect as little as 5 pmol of ACC, the immediate precursor of ethylene in plant tissues, which is normally 80% and can be determined by internal standards.
987 citations
TL;DR: In this paper, a more general stochastic specification is proposed, free of these a priori restrictions, and the proposed functional form estimation is discussed and demonstrated with nitrogen response data and common log-linear production functions.
Abstract: There has been considerable interest in estimations of input effects on the probability distribution of output. Most empirical and theoretical analyses utilize multiplicative stochastic specifications which are analyzed and found unduly restrictive, particularly since inputs that marginally reduce risk are not allowed. A more general stochastic specification is proposed, free of these a priori restrictions. The proposed functional form estimation is discussed and demonstrated with nitrogen‐response data and common log‐linear production functions. Though nitrogen is risk‐increasing, the marginal variance contribution is smaller when compared to estimates based upon multiplicative specification. Finally, stochastic specification error effects are analyzed.
573 citations
TL;DR: In this paper, a semi-empirical formula is developed for estimating the total amount of surface material moving in eolian saltation, surface traction, and suspension on the surface of Mars, and the ratio of final particle speed to the particle threshold friction speed is found to be several times that of saltation on earth.
Abstract: Results of low-pressure wind tunnel testing and theoretical considerations are used to estimate the eolian transport of surface material on Mars Saltation on Mars, equations of particle motion, computational results, and analytical determination of surface material movement are considered A semiempirical formula is developed for estimating the total amount of surface material moving in eolian saltation, surface traction, and suspension Numerical solutions of the equations of motion for particle trajectories on the surface of Mars are presented The ratio of final particle speed to the particle threshold friction speed is found to be several times that of saltation on earth
449 citations
TL;DR: It is suggested that in the ethylene biosynthetic pathway, IAA stimulates C(2)H(4) production by inducing the synthesis or activation of ACC synthase, which catalyzes the conversion of SAM to ACC, and Co(2+) exerts its effect by inhibiting the Conversion of ACC to ethylene.
Abstract: Auxin is known to stimulate greatly both C2H4 production and the conversion of methionine to ethylene in vegetative tissues, while amino-ethoxyvinylglycine (AVG) or Co2+ ion effectively block these processes. To identify the step in the ethylene biosynthetic pathway at which indoleacetic acid (IAA) and AVG exert their effects, [3-14C]methionine was administered to IAA or IAA-plus-AVG-treated mung bean hypocotyls, and the conversion of methionine to S-adenosylmethionine (SAM), 1-amino-cyclopropane-1-carboxylic acid (ACC), and C2H4 was studied. The conversion of methionine to SAM was unaffected by treatment with IAA or IAA plus AVG, but active conversion of methionine to ACC was found only in tissues which were treated with IAA and which were actively producing ethylene. AVG treatment abolished both the conversion of methionine to ACC and ethylene production. These results suggest that in the ethylene biosynthetic pathway (methionine → SAM → ACC → C2H4) IAA stimulates C2H4 production by inducing the synthesis or activation of ACC synthase, which catalyzes the conversion of SAM to ACC. Indeed, ACC synthase activity was detected only in IAA-treated tissues and its activity was completely inhibited by AVG. This conclusion was supported by the observation that endogenous ACC accumulated after IAA treatment, and that this accumulation was completely eliminated by AVG treatment. The characteristics of Co2+ inhibition of IAA-dependent and ACC-dependent ethylene production were similar. The data indicate that Co2+ exerts its effect by inhibiting the conversion of ACC to ethylene. This conclusion was further supported by the observation that when Co2+ was administered to IAA-treated tissues, endogenous ACC accumulated while ethylene production declined.
411 citations
TL;DR: The proximate mechanism causing cessation of egg laying appears to be depletion of some essential material(s) stored during the spring weight gain, probably protein.
Abstract: --Fluctuations in weight, lipid, and protein content of the body, breast muscles, and liver and changes in the size of leg muscles, gizzard, and intestines of adult Cackling Geese (Branta canadensis minima) were determined for specimens collected during autumn migration, winter, spring migration, arrival at nesting areas, egg laying, incubation, and molting time periods. Both sexes lost most of their lipid stores in winter. Larger-sized races of Canada Geese maintain a store of fat during winter even though they lose as much or more weight as Cackling Geese. Differences in amounts of fat storage in relation to body size, climate severity, and the frequency with which food shortages may occur may limit the northern boundaries of the winter range in this and other species that conform to Bergmann's Rule. At the time of their arrival on nesting grounds, body weights of males and females had increased 25.8% and 45.9%, respectively, over their weights in April. Females gained 1.8 times more weight, 2.4 times more fat, and 1.4 times more protein than did males. By the onset of incubation, 17 days after their arrival on nesting grounds, both sexes had lost weight nearly equivalent to amounts gained prior to their arrival. Lipid reserves of males were used by the onset of incubation, but were sufficient in females to maintain them until the end of their 26-day incubation period. Total protein in males was nearly maintained from the time of their arrival to the end of incubation, whereas it declined 22.7% in females between the time of arrival and the onset of incubation. At the time of hatching of their eggs, females had lost 42.1% of their peak spring weight, and they were emaciated. The reserves stored by geese during spring migration allow them to initiate nesting before food supplies become abundant and are critical in controlling clutch size. The proximate mechanism causing cessation of egg laying appears to be depletion of some essential material(s) stored during the spring weight gain, probably protein. Gizzard, intestines, and liver are probably major sources of labile protein for egg production, and decline in weight of these organs lowers the metabolic cost of their maintenance while they are little used because of fasting during the period of repro-
366 citations
TL;DR: It is found that at least half of the 300-nucleotide duplex regions in inverted repeated sequences also have a cleavage site for the restriction enzyme Alu I, implying that the interspersion pattern of repeated and single copy sequences in human DNA is largely dominated by one family of repeated sequences.
362 citations
TL;DR: Results support the view that ACC synthase is a pyridoxal enzyme, which catalyzes the conversion of S -adenosylmethionine to ACC and methylthioadenosine in tomato extract.
324 citations
TL;DR: A new family of unitary transforms is introduced and it is shown that the well-known discrete Fourier, cosine, sine, and the Karhunen-Loeve (KL) (for first-order stationary Markov processes) transforms are members of this family.
Abstract: A new family of unitary transforms is introduced. It is shown that the well-known discrete Fourier, cosine, sine, and the Karhunen-Loeve (KL) (for first-order stationary Markov processes) transforms are members of this family. All the member transforms of this family are sinusoidal sequences that are asymptotically equivalent. For finite-length data, these transforms provide different approximations to the KL transform of the said data. From the theory of these transforms some well-known facts about orthogonal transforms are easily explained and some widely misunderstood concepts are brought to light. For example, the near-optimal behavior of the even discrete cosine transform to the KL transform of first-order Markov processes is explained and, at the same time, it is shown that this transform is not always such a good (or near-optimal) approximation to the above-mentioned KL transform. It is also shown that each member of the sinusoidal family is the KL transform of a unique, first-order, non-stationary (in general), Markov process. Asymptotic equivalence and other interesting properties of these transforms can be studied by analyzing the underlying Markov processes.
314 citations
TL;DR: It is demonstrated that all de novo fatty acid biosynthesis in spinach leaf cells requires acyl carrier protein (ACP) and occurs specifically in the chloroplasts, and the presence of ACP in a compartment of the spinach leaf cell would serve as a marker for de noovo fatty acids synthesis.
Abstract: This communication demonstrates that all de novo fatty acid biosynthesis in spinach leaf cells requires acyl carrier protein (ACP) and occurs specifically in the chloroplasts. Antibodies raised to purified spinach ACP inhibited at least 98% of malonyl CoA-dependent fatty acid synthesis by spinach leaf homogenates. Therefore, the presence of ACP in a compartment of the spinach leaf cell would serve as a marker for de novo fatty acid biosynthesis. A radioimmunoassay capable of detecting 10(15) mol (10(-11) g) of spinach ACP was developed to measure the levels of ACP in leaf cell components isolated by sucrose gradient centrifugation of a gentle lysate of spinach leaf protoplasts. All of the ACP of the leaf cell could be attributed to the chloroplast. Less than 1% of the ACP associated with chloroplasts resulted from binding of free ACP to chloroplasts. Of interest, ACP from Escherichia coli, soybean, and sunflower showed only partial crossreactivity with spinach ACP by the radioimmunoassay. These results strongly suggest that, in the leaf cell, chloroplasts are the sole site for the de novo synthesis of C16 and C18 fatty acids. These fatty acids are then transported into the cytoplasm for further modification and are either inserted into extrachloroplastic membrane lipids or returned to the chloroplast for insertion into lamellar membrane lipids.
298 citations
TL;DR: A rapid sensitive method has been developed for the detection of protein bands in sodiumdodecyl sulfate-polyacrylamide gels that is suitable for the recovery of individual polypeptides on a preparative scale and allows for the complete recovery of unmodified protein from preparative gels.
TL;DR: Two-dimensional echocardiography provided better separation of normals from right ventricular volume overload patients than did M-mode techniques, and enables accurate visualization of the right atrium and ventricle in almost all patients.
Abstract: No data are available on determining right atrial and right ventricular size by two-dimensional echocardiography. We performed two-dimensional echocardiograms on eight human right-heart casts obtained at autopsy and on 50 patients who underwent complete left- and right-heart catheterization. Measurement of individual dimensions of the long and short axes of the right atrium and ventricle from right heart casts closely correlated with the volume of these structures as determined by water displacement. Further, individual dimensions by cross-sectional echo correlated well with actual casts dimensions. Subsequently, echocardiographic measurements of right atrial and ventricular long and short axes were obtained in the apical four-chambered view in a group of normals and compared with a group of patients with right ventricular volume overload states. Mean values for right atrial short-axis and long-axis measurements were greater in right ventricular volume overload patients than in normals: 6.5 +/- 0.3 vs 3.6 +/- 0.1 cm, and 6.0 +/- 0.3 vs 4.2 +/- 0.1 cm, respectively (both p less than 0.001). In addition, measurements of both individual dimensions as well as planed area of the right ventricle were greater in right ventricular volume overload patients than in normals: maximal short axis 6.1 +/- 0.3 vs 3.5 +/- 0.2 cm, mid-short axis 6.1 %/- 0.4 vs 2.8 +/- 0.2 cm, and area 40 +/- 2.6 vs 18 +/- 1.2 cm2 (all p less than 0.001). There were no differences in right ventricular long-axis measurement. Two-dimensional echocardiography provided better separation of normals from right ventricular volume overload patients than did M-mode techniques. Thus, two-dimensional echocardiography, with the apical four-chambered view, enables accurate visualization of the right atrium and ventricle in almost all patients. Futher, measurements of right atrial and right ventricular size by two-dimensional echocardiography readily distinguish normal patients from those with right ventricular volume overload.
TL;DR: It is argued that defendability depends on the ability of an animal to monitor the boundaries of its range in order to detect potential intruders and introduces an index of defendability (D) which is the ratio of observed daily path length to an area equal to the diameter of a circle with areaequal to home range area of the animal.
Abstract: 1.
Existing theory suggests that territoriality will evolve when resources are limited and defendable, but defendability has seldom been analyzed quantitatively.
2.
Here we argue that defendability depends on the ability of an animal to monitor the boundaries of its range in order to detect potential intruders and introduce an index of defendability (D) which is the ratio of observed daily path length (d) to an area equal to the diameter (d′) of a circle with area equal to home range area of the animal. This index is sensitive only to extreme deviation from circular shape.
3.
Review of the literature on primate ranging reveals that all territorial groups for which data are available have an index of 1.0 or greater, and that few nonterritorial species have an index of 1.0 or greater.
4.
Regression analysis of the relationship of daily path length to feeding group weight and foliage in the diet reveals that both feeding group weight and foliage in the diet account for a large proportion of the variance in daily path length, and that territorial and nonterritorial groups do not differ in day range for a given group weight and diet.
TL;DR: α-Tomatine, an alkaloid in tomato plants, is toxic to an endoparasite of a major lepidopterous pest of tomatoes, creating a potential dilemma to controlling herbivorous pests through chemical antibiosis in plants.
Abstract: alpha-Tomatine, an alkaloid in tomato plants, is toxic to an endoparasite of a major lepidopterous pest of tomatoes. The parasite acquires the alkaloid from its host after the host ingests the alkaloid. This form of interaction creates a potential dilemma to controlling herbivorous pests through chemical antibiosis in plants.
TL;DR: The equation of continuity shows the importance of including both growth velocity, u, and growth rate, ▽ ·u in estimates of local biosynthesis and transport rates in expanding tissue, although the classical continuity equation must be modified to accommodate the compartmentalized distributions characteristic of plant tissue.
TL;DR: In this paper, the concept of social world is given greater analytical power by categorizing differential participation through a typology of social types (strangers, tourists, regulars, and insiders).
Abstract: The concept of social world is given greater analytical power by categorizing differential participation through a typology of social types—strangers, tourists, regulars, and insiders. These trans-situational social types are examined in terms of their commitment, relationships, experiences, and orientation to social worlds. Social worlds are also discussed in terms of three qualities of interaction—relevance, accessibility, and receptivity.
TL;DR: The standard metabolic rate of birds correlates broadly with climate of origin, and tends to be higher in birds from cold climates and lower in tropical forms than would be expected from the bird's mass.
Abstract: The standard metabolic rate (SMR) of birds correlates broadly with climate of origin. SMR tends to be higher in birds from cold climates and lower in tropical forms than would be expected from the bird's mass. SMR changes, on the average, 1% per degree change in latitude. The influence of climate on SMR is, however, subject to modification by other aspects of the bird's life history. For example, in tropical species adaptive modifications in SMR correlate with thermal microhabitat. Tropical birds which forage in the sun have SMR's averaging 25% lower than expected, while SMR of species which forage in the shade is normal. Species of penguins which undergo prolonged fasts during the breeding season do not show elevated SMR's typical of high latitude birds.
TL;DR: Six triploid individuals were found in a full-sib family of 11 adult rainbow trout (Salmo gairdneri) from a domesticated hatchery stock, suggesting that the Y chromosome is male determining in trout.
Abstract: Six triploid individuals were found in a full-sib family of 11 adult rainbow trout (Salmo gairdneri) from a domesticated hatchery stock. The triploid individuals were normal in size and external appearance, had underdeveloped gonads, and showed no evidence of 3n/2n chimerism or mosaicism. XXY triploids were males, suggesting that the Y chromosome is male determining in trout. Because they may avoid production losses associated with sexual maturation in normal fish, triploid trout and salmon could potentially be useful in fish culture.
TL;DR: This report describes a multiple mutant of T4 that displays the property of generalised transduction, and transfers E. coli genes with frequencies that, in general, are higher than those observed for other transducing phages.
Abstract: GENERALISED transduction—the transfer of bacterial genes from one cell to another via bacteriophages—is one of a small number of processes by which bacteria can acquire exogenous genetic information. Transduction was first demonstrated in Salmonella typhimurium with the phage P22 by Zinder and Lederberg1,2 and subsequently in Escherichia coli with the phages P13 and T14. Bacteriophage T4 is the largest, and one of the most thoroughly studied of the virulent coliphages but has never been observed to mediate generalised transduction. In this report we describe a multiple mutant of T4 that displays the property of generalised transduction, and transfers E. coli genes with frequencies that, in general, are higher than those observed for other transducing phages.
TL;DR: The numbering systems for mammalian ribosomal proteins used in several laboratories have been correlated and a proposal for a standard system is presented.
Abstract: The numbering systems for mammalian ribosomal proteins used in several laboratories have been correlated and a proposal for a standard system is presented.
TL;DR: It is proposed that the tumors are composed principally of cells derived from a subset of the many infected cells in a mammary gland, supported by the finding that Eco RI digestion of DNA from several transplants of a primary tumor yields the pattern characteristic of the primary tumor.
TL;DR: The daily cycle of leaf elongation rate, water potential, and solute potential of maize and sorghum, as well as temperature, were monitored in the field, showing evidence that the decrease in psi.
Abstract: The daily cycle of leaf elongation rate, water potential, and solute potential of maize and sorghum, as well as temperature, were monitored in the field. Major climatic features were high radiation and a minimum air temperature of about 12 C. Leaf elongation of both crops was slowest at night, presumably because of low temperature. Peak elongation rates were in daytime when leaf water potential (Psi) was low. Solute potential also decreased during daylight, thus permitting the maintenance of appreciable turgor pressure, a critical parameter for cell expansion.Leaf Psi versus relative water content (RWC) curves were developed by sampling detached leaves at intervals as they dried quickly in the laboratory. At a given RWC, Psi was lower in leaves at midday than early in the morning, which is evidence that the decrease in psi. at midday was caused by an increase in the amount of solute in the tissue. Estimates of psi. at 100% RWC were 4 bars lower at midday than early in the morning in both crops. Soluble sugars, mainly nonreducing, accounted for most of the observed psi. decrease in sorghum leaves. Shading the leaves from light eliminated most of the solute buildup.
TL;DR: The separation of dhurrin and its catabolic enzymes in different tissues prevents its large scale hydrolysis under normal physiological conditions, which would be expected to proceed when the contents of the ruptured epidermal and mesophyll cells are allowed to mix.
Abstract: The tissue distributions of dhurrin [p-hydroxy-(S)-mandelonitrile-β-d-glucoside] and of enzymes involved in its metabolism have been investigated in leaf blades of light-grown Sorghum bicolor seedlings. Enzymic digestion of these leaves using cellulase has enabled preparations of epidermal and mesophyll protoplasts and bundle sheath strands to be isolated with only minor cross-contamination. Dhurrin was located entirely in the epidermal layers of the leaf blade, whereas the two enzymes responsible for its catabolism, namely dhurrin β-glucosidase and hydroxynitrile lyase, resided almost exclusively in the mesophyll tissue. The final enzyme of dhurrin biosynthesis, uridine diphosphate glucose:p-hydroxymandelonitrile glucosyltransferase, was found in both mesophyll (32% of the total activity of the leaf blade) and epidermal (68%) tissues. The bundle sheath strands did not contain significant amounts of dhurrin or of these enzymes. It was concluded that the separation of dhurrin and its catabolic enzymes in different tissues prevents its large scale hydrolysis under normal physiological conditions. The well documented production of HCN (cyanogenesis), which occurs rapidly on crushing Sorghum leaves, would be expected to proceed when the contents of the ruptured epidermal and mesophyll cells are allowed to mix.
TL;DR: Candida lusitaniae associated with infection in a patient with acute myelogenous leukemia developed resistance to amphotericin B during systemic treatment of the patient, and required 100 and 50 μg/ml, respectively, for complete inhibition at 48 h.
Abstract: Candida lusitaniae associated with infection in a patient with acute myelogenous leukemia developed resistance to amphotericin B during systemic treatment of the patient. The organism, when isolated initially, was inhibited by 0.31 μg of amphotericin B per ml in yeast nitrogen base agar, but when isolated (20 days later) just antemortem and postmortem, required 100 and 50 μg/ml, respectively, for complete inhibition at 48 h.
TL;DR: The data indicate that cardiac size is significantly affected by alterations in heart rate, and guidelines by which to account for alterations inHeart rate in the measurement of echocardiographic variables of cardiac size and performance are provided.
Abstract: No systematic correlation is available regarding the effect of heart rate on cardiac size and performance in man. Thus echocardiograms were performed in 25 normal subjects at 10 beat increments of heart rate from 50 to 150 beats/min during atrial pacing. Blood pressure as obtained with sphygmomanometer did not change significantly during pacing (group mean systolic 125, diastolic 81 and mean 96 mm Hg). Left ventricular end-diastolic dimension and end-systolic dimension decreased with increasing heart rate from a group mean of 4.8 and 3.0 cm, respectively, at a rate of 70/min to 3.0 and 2.3 cm at a rate of 150/min. The percent reduction in left ventricular dimensions was linear and was related to heart rate as end-diastolic dimension = −0.0027 heart rate + 1.26, r = 0.90 and end-systolic dimension = −0.0026 heart rate + 1.24, r = 0.72. Mean fiber shortening velocity increased with a greater heart rate from 1.09 at a rate of 70/min to 1.63 circumference/sec at a rate of 150 beats/min, and the percent increase was also linearly related to rate as velocity = 0.0047 heart rate + 0.56, r = 0.67. Echocardiographic shortening fraction did not change during pacing (mean 0.38). Interventricular septal and posterobasal wall thickness measured at end-diastole increased with accelerated pacing rates from 9.2 and 8.7 mm, respectively, at a rate of 70/min to 11.3 and 10.2 mm at a rate of 150/min. The percent increase in septal and posterobasal wall thickness was linearly related to rate as septal thickness = 0.0036 heart rate + 0.66, r = 0.82 and posterobasal thickness = 0.0027 heart rate + 0.75, r = 0.70, respectively. Left atrial dimension diminished with increased pacing rate to a rate of 120/min but reached a plateau at rates of greater than 120/min. These data indicate that cardiac size is significantly affected by alterations in heart rate. Although velocity of circumferential fiber shortening is augmented by accelerated heart rate, shortening fraction is not influenced by changes in heart rate. These data provide guidelines by which to account for alterations in heart rate in the measurement of echocardiographic variables of cardiac size and performance.
TL;DR: In this paper, the design and fabrication of small air-core inductors of sufficiently high inductance and Q for integrated-circuit applications is discussed along with experimental results on their inductance.
Abstract: It is extremely difficult to fabricate small air-core inductors of sufficiently high inductance and Q for integrated-circuit applications due to the large number of turns required. Although the need for passive inductors can be circumvented by means of active filters at lower frequencies, such substitutes are difficult to realize at frequencies above 100 MHz. To drastically reduce the number of turns required thus rendering the fabrication of IC inductors feasible, we used anisotropic magnetic film cores of permeability as high as 104. In this paper, the design and fabrication of such inductors are discussed along with experimental results on their inductance.
TL;DR: Here I compare estimates of instantaneous birth rates using the Edmondson-Paloheimo equation to those determined with a general model which accounts for age structure instability and egg mortality in two Daphnic~ pulr~x populations.
Abstract: An equation independently derived by Edmondson and Paloheimo for estimating instantaneous birth rates without a knowledge of mortality rates has been extensively employed by zooplankton ecologists. This expression is exactly true only under the unlikely conditions that the age distribution is stable and that egg mortality is equal to that averaged across the entire population. Here I compare estimates of instantaneous birth rates ( h )using the Edmondson-Paloheimo equation to those determined with a general model which accounts for age structure instability and egg mortality in two Daphnic~ pulr~x populations. Despite the fact that the assumptions of the Edmondson-Paloheimo model are rarely met, it mimics the seasonal pattern of b quite well, with few exceptions. An analysis of variance suggests that the model will provide an adequate approximation of the true population birth rate when a variance in b of 0.003 can be tolerated. A much more critical factor in the analysis of instantaneous rates in plankton populations is the development of accurate sampling techniques. Key n,ord.s: birth rutes; Clrrdoc~eru; Daphnia pulex; dr,nzogrcrphy; egg rc~tio; rotifcrs; ;ooplanXton. A great deal can often be inferred about the factors h,,, = INN, + C,) In(N,) regulating population densities from measures of two n population parameters, the instantaneous birth and mortality rates, h and m. The estimation of h has been --In(l + E ) (2) D thought to be particularly simple for planktonic cladocerans and rotifers whose adulta bear live young (Edmondson 1968). The attractiveness of both of these which are easily enumerated in preserved samples and expressions lies in their independence from m which whose egg development rates are simple functions of is often the final product of interest. Given an additemperature. Edmondson (1960) first introduced the tional estimate of the actual rate of population growth, egg ratio technique as a means of estimating instanr , the population mortality rate can then be detertaneous birth rates with preserved samples of plankmined by difference using the relation tonic rotifers. In theory the method can be extended m = h r . (3) to any population characterized by continuous growth. Under the special conditions of zero population Since few populations are either free from egg morgrowth, zero egg mortality and a stable age distributality o r stable in size or age distribution, Eqs. 1 and tion, the age distribution of eggs will be even, and the 2 would seem to be inappropriate. However, the use finite birth rate of the population is of Eq. 2 has been further encouraged by a derivation p = EID by Paloheimo (1974) which, despite its incorporation of egg mortality, turns out to be independent of morwhere E = C,IN, is the average number of eggs per tality and identical to Eq. 2. This convenient absence individual in the population (the egg ratio), C, and N, of egg mortality from Eq. 2 occurs only when the morbeing the total number of eggs and individuals in the tality rate of eggs is exactly equal to that averaged population at time t , and D is the duration of egg across the entire population ( m ) . Furthermore, the indevelopment (days). Under these constraints, p is redependence of Eq. 2 from r is still a consequence of lated to the instantaneous birth rate by assuming a stable population age distribution. Threlkeld (1979) has suggested that the accuracy of birth rate estimates could be improved by examining the age distribution of eggs. Although this approach would seem to be an advance over the Edmondson-Palohei(1) mo model, it is not yet clear whether the additional An alternate expression for h which makes no aswork is warranted. sumptions about the age distribution of eggs, but A large part of the problem is that, with few excepwhich still assumes zero population growth and zero tions (DeMott 1980. Keen and Nassar 1981), previous egg mortality, is investigations involving the egg ratio method have not attempted to estimate the variance of the rates in Eq. Manuscript received 25 September 1980; revised 5 ~~~~h 3. In the absence of such information it is not only 1981; accepted 27 April 1981. impossible to compare the adequacy of different tech1 Febr~~u l -y 1982 ZOOPLANKTON BIRTH RATES 13 niques, but a comparison of instantaneous rates between dates o r sites is risky at best. An analysis of variance for b and r becomes particularly critical when /?I is estimated by difference. Many studies show dramatic fluctuations in in over very short time intervals (Clark and Carter 1974, Kwik and Carter 1975, Goldman et al. 1979). and without variance estimates these cannot be identified a s real o r artifactual. Negative estimates of in, which often arise from Eq. 3, are usually attributed to the hatching of uncensused resting eggs, although they are just as likely to be a consequence of poor estimates of r resulting from inadequate sampling or biased determinations of h resulting from faulty assumptions of the EdmondsonPaloheimo model. Despite these problems, zooplankton ecologists continue to rely heavily on Eq. 2 (see Bottrell et al. 1976, Goldman et al. 1979. Kerfoot and Peterson 1979, Lynch 1979 for several recent applications), and it seems likely that many will continue to d o so in the interest of time. Thus. it is of interest to know the extent to which deviations from the assumptions inherent in the Edmondson-Paloheimo equation are reflected in Door estimates of birth rates in field studies. Such an analysis has not been possible in the past because the magnitude by which the assumptions have been violated has been difficult to quantify. Computer simulations are of only limited value in examining this problem (Seitz 1979) because the choice of input parameters is necessarily subjective. The application of a sequential sampling technique for estimating sizespecific mortality rates in cladoceran populations (M. Lynch, pc~r~oncll oh,cert~atiotl) now allows the collection of the necessary information. This paper provides an empirical test of the efficacy of the Edmondson-Paloheimo model by comparing estimates of b by Eq. 2 with those obtained for two Daphnicl p~rlex populations for which instabilities in age structure and differential egg mortality are accounted for. Since a generalized model for estimating instantaneous birth rates from egg ratio data has not been previously published I will start by deriving such an expression. Throughout this paper I will assume a homogeneous population, i.e., one in which all individuals are exposed to the same physical and biological factors. I also assume that egg development times and size-specific rates of growth, egg laying, and mortality are constant over the interval ( t L), t). (Since the structure of the population may change over [t D, t] , this does not imply constancy of these rates as population parameters.) For populations for which L) is on the order of a few days, as it is in most of the planktonic organisms to which the egg ratio model has been applied, such approximations do not seem unreasonable. However, where these assumptions are significantly violated, no simple expression for estimating b by an egg ratio method can be derived, and alternate empirical approaches must be sought. The ideal egg ratio model makes no assumptions about the internal structure of the population, but considers the individual contribution of each class of individuals to the total population birth rate. Although the classification scheme is arbitrary, I will derive the model in the context of a population of an arbitrary number of size classes ( i t , ) since most organisms may be more easily classifed by size than by age. The total number of eggs derived from size class x which hatch during time ( t , t + dt) is equal to the total number of eggs laid during time ( t L), t L) + dt ) by individuals of that size class which survive to hatching (most planktonic organisms, especially cladocerans, do not change size classes while carrying a clutch), b,. N,., ,tit = tit, I,.N,, , , e r = l J e i \" ~ (4) where h,. = the instantaneous birth rate of size class x (day-'), N,,,, = the number of individuals in size class s at time t (number per square metre), r,. = (In &,,, In N,,,-7)/~ is the growth rate of size class x (day-') I , = the instantaneous rate of egg laying by size class x (day-'), and tn, = the instantaneous mortality rate of size class x (day-'). The size-specific rate of egg laying, I,. , can be re-expressed in terms of the mean size-specific clutch size E,{ . as follows. The total number of eggs carried by size class x at time r is