Variance In Development Research Articles

Genotype–Trait (GT) Biplot Analysis for Yield and Quality Stability in Some Sweet Corn (Zea mays L. saccharata Sturt.) Genotypes

A strong statistical method for investigating the correlations between traits, assessing genotypes based on numerous traits, and finding individuals who excel in particular traits is genotype–trait (GT) biplot analysis. The current study was applied to evaluate 11 sweet corn (Zea mays L. saccharata) genotypes and correlate them based on genotype–trait (GT) biplot analysis for two cropping seasons in Erzurum, Türkiye using the RCBD experimental design with three reputations. The results showed that the genotypes were significantly different for the majority of the examined variables according to the combined analysis of variance findings at 0.01 probability level. An ecological analysis was performed to evaluate sweet corn varieties and environmental conditions and interactions between them (genotype × environmental conditions). Our results showed that the summation of the first two and second main components was responsible for 73.51% of the combined cropping years of the sweet corn growth and development variance, demonstrating the biplot graph’s optimum relative validity, which was obtained. In this study, the Khan F1 (G6) genotype was found to be the stablest genotype, and the Kompozit Seker (G7) genotype was the non-stable genotype, moreover based on the first cropping year, second cropping year, and the average mean of the two cropping years. As a conclusion, the Khan F1 (G6) genotype is the highest-yielding genotype, and the Kompozit Seker (G7) is the lowest. Based on the heat map dendrogram, the context of the differential extent of trait association of all genotypes into two clusters is indicated. The highest genetic distance was shown between the BATEM Tatlı (G3) and Febris (G5) genotypes. Our results provide helpful information about the sweet corn genotypes and environments for future breeding programs.

Maternal depression and infant social withdrawal as predictors of behaviour and development in vertically HIV-infected children at 3.5 years

ABSTRACT Background In low- and middle-income countries, there is a high prevalence of post-partum depression and it is often associated with HIV status. Maternal depression negatively affects mothering and can lead to social withdrawal in infants. Maternal depression and infant social withdrawal can have deleterious long-term effects on children’s behaviour and neurodevelopmental trajectories. Aim To investigate whether maternal depression and infant social withdrawal at 10–12 months post-partum were significant predictors of child behaviour and development at 42 months. Method Seventy-four mother–infant dyads living with HIV were followed in a prospective, longitudinal design. Mothers were assessed for depression using the Center for Epidemiologic Studies Depression scale (CES-D). Infant social withdrawal was assessed by the modified Alarm Distress Baby Scale (m-ADBB), and development and behaviour were evaluated by the Griffiths Mental Development Scales (GMDS) and the Child Behavior Checklist (CBCL), respectively. Results Maternal depression explained 4.8% of the variance in child behaviour (β = 0.98, t = 2.05, p < 0.05) and 10.3% of the variance in development (β = −0.30, t = −2.66, p < 0.05). Infant social withdrawal was not a significant predictor of behaviour (β = 3.27, t = 1.36, p = 0.18), but it did uniquely explain 7% of the variance in development (β = −1.32, t = −2.48, p < 0.05). Conclusion In the context of HIV, screening for maternal depression and the quality of mother–infant interactions are important (especially in the 1st year post-partum), given the significant long-term impact they have on behaviour and neurodevelopment. Abbreviations ANOVA: analysis of variance; ART: antiretroviral therapy; CBCL: Child Behavioral Checklist; CES-D: Center for Epidemiologic Studies Depression Scale; CHEI: children HIV-exposed and infected; CHER: Children with HIV Early Antiretroviral Treatment Trial; CHEU: children HIV-exposed and uninfected; CHUU: children HIV-unexposed and -uninfected; GMDS: Griffiths Mental Development Scales; HIV: human immunodeficiency virus; LMIC: low- and middle-income countries; m-ADBB: modified Alarm Distress Baby Scale; NRF: National Research Foundation; SAMRC: South African Medical Research Council; WHO: World Health Organization

Pregnancy in patients with systemic lupus erythematosus after cyclophosphamide therapy.

Systemic lupus erythematosus (SLE) often affects females of reproductive age and Cyclophosphamide, an alkylating agent leading to premature ovarian insufficiency (POF) and labelled category D for pregnancy is used as induction therapy for severe manifestations of lupus. There have been multiple case series reflecting variable outcomes of pregnancies after cyclophosphamide use for cancers and autoimmune diseases. With increasing maternal age, we have an increasing population of lupus patients who may wish to conceive after having received cyclophosphamide therapy. The objective of our study was to improve our understanding of the impact of cyclophosphamide exposure on fertility and pregnancy outcomes in patients with SLE.We retrospectively reviewed the charts of all patients who had received intravenous cyclophosphamide at our academic institute in the time period from 2000-2018 and identified 440 patients which included 157 female patients of reproductive age. There were 37 documented pregnancies after the cyclophosphamide infusion, of which 23 patients had successful outcomes; 4 elective abortion and 10 miscarriages. There were 17 patients who developed POF, of which 7 also had end stage renal disease. The average cumulative dose of cyclophosphamide in the patients who had successful pregnancy was 4080.37 mg compared to 2806.25 mg in those who had a miscarriage (p 0.164) and 5526.47 mg in those who developed POF (p 0.046). Using multiple regressions to evaluate risk factors impacting pregnancy outcomes, when taken as a set, the predictors including race, serological profile, exposure to steroids and Mycophenolate mofetil, age at cyclophosphamide infusion, age at pregnancy, and cumulative cyclophosphamide dose accounted for 46.29% of the variance in outcome of pregnancy (p 0.23) and 39.58% of the variance in development of premature ovarian failure (p 0.008). We noted statistical significance in the impact of maternal age at time of pregnancy (p 0.04) and duration of time between the last infusions to subsequent pregnancy (p 0.02) to pregnancy outcome.Our findings suggest that a longer time interval between the last cyclophosphamide infusion and subsequent pregnancy was favorable for a successful outcome and higher cumulative cyclophosphamide dose is more likely to be associated with premature ovarian failure.

Modeling the impact of temperature on the population abundance of the ambrosia beetle Xyleborus affinis (Curculionidae: Scolytinae) under laboratory-reared conditions.

Modeling the impact of temperature on each life stage of a beetle population represents a continuing challenge. This study evaluates the effects of five temperature treatments (20, 23, 26, 29 and 32°C) on population abundance and timing of a colony of ambrosia beetles Xyleborus affinis reared under laboratory conditions and use this data to develop demographic and phenological models. Abundances at each life stage (eggs, larvae, pupae and adult) were examined through periodic destructive sampling; given that it was not possible to track individuals. To assess the effects of temperature on oviposition, development and survival rates we developed a novel estimation strategy based on cohorts, which does not require individual developmental data. Since oviposition was entirely unwitnessed, we assessed competing empirical ovipositional models. Rates of development were computed using a modal rate curve for each life stage, and rates were projected to cohorts in life stages assuming log-normal developmental variance. Temperature-driven survival rates were assumed to be logistic with a quadratic exponent to capture modal temperature dependence. Parameters were estimated simultaneously using minimum negative log posterior likelihood, assuming Poisson distribution of observations and using priors to inform unobserved developmental rates and enforce mechanistic constraints on oviposition models. A parabolic function best described oviposition rate. Optimal developmental temperatures were 30.5°C, 29°C and 27.5°C, with maximum developmental rates of 0.26/day, 0.12/day and 0.23/day for eggs, larvae and pupae, respectively. The survival rates in the range 20-29 °C were equal to 1 in the eggs-to-larvae transition, from 0.72 to 0.35 in larvae-to-pupae transition, and from 0.2 to 0.89 in pupae-to-adults transition. This procedure effectively characterized the direct thermal effects on development and survival of each life stage in the X. affinis under laboratory conditions and would be suitable for estimating temperature dependence for other species in which individual observations are not possible.

Disentangled Intensive Triplet Autoencoder for Infant Functional Connectome Fingerprinting.

Functional connectome "fingerprint" is a highly characterized brain pattern that distinguishes one individual from others. Although its existence has been demonstrated in adults, an unanswered but fundamental question is whether such individualized pattern emerges since infancy. This problem is barely investigated despites its importance in identifying the origin of the intrinsic connectome patterns that mirror distinct behavioral phenotypes. However, addressing this knowledge gap is challenging because the conventional methods are only applicable to developed brains with subtle longitudinal changes and typically fail on the dramatically developing infant brains. To tackle this challenge, we invent a novel model, namely, disentangled intensive triplet autoencoder (DI-TAE). First, we introduce the triplet autoencoder to embed the original connectivity into a latent space with higher discriminative capability among infant individuals. Then, a disentanglement strategy is proposed to separate the latent variables into identity-code, age-code, and noise-code, which not only restrains the interference from age-related developmental variance, but also captures the identity-related invariance. Next, a cross-reconstruction loss and an intensive triplet loss are designed to guarantee the effectiveness of the disentanglement and enhance the inter-subject dissimilarity for better discrimination. Finally, a variance-guided bootstrap aggregating is developed for DI-TAE to further improve the performance of identification. DI-TAE is validated on three longitudinal resting-state fMRI datasets with 394 infant scans aged 16 to 874 days. Our proposed model outperforms other state-of-the-art methods by increasing the identification rate by more than 50%, and for the first time suggests the plausible existence of brain functional connectome "fingerprint" since early infancy.

Children’s development of semantic verbal fluency during summer vacation versus during formal schooling

Purpose: Children’s results on school-related achievements tests, such as aspects of math, reading and writing, have been shown to decline following a lengthy summer vacation. Few studies have investigated whether this also applies to vocabulary skills. The purpose of this study is to investigate how lexical organization and retrieval, assessed by a semantic verbal fluency (SVF) task, develops during a lengthy summer vacation versus formal schooling.Method: Sixty-eight children with mean age of 7.9 (ranging from 6.5 to 9.1), were assessed pre- and post-summer vacation and post-fall semester using two SVF categories (Animals and Clothes). The number of words produced in both categories gave the total score.Results: The result of the SVF tests decreased following summer vacation. The loss was recouped at the post-fall semester assessment, but no gains compared to initial testing were shown. Neither level of parental education, general language ability, non-verbal IQ, nor bilingualism explained the variance in development during the summer vacation or the fall semester.Conclusions: Our findings indicate that a lengthy summer vacation causes a recess in the expected development of SVF ability and that this recess is recouped after a semester of formal schooling. The findings are in line with previous research indicating that summer vacation may have negative impact on the development of important scholastic abilities in children.

Host and Viral Genetic Variation in HBV-Related Hepatocellular Carcinoma.

Hepatocellular carcinoma (HCC) is the fifth most common cancer in men and the second leading cause of cancer deaths globally. The high prevalence of HCC is due in part to the high prevalence of chronic HBV infection and the high mortality rate is due to the lack of biomarkers for early detection and limited treatment options for late stage HCC. The observed individual variance in development of HCC is attributable to differences in HBV genotype and mutations, host predisposing germline genetic variations, the acquisition of tumor-specific somatic mutations, as well as environmental factors. HBV genotype C and mutations in the preS, basic core promoter (BCP) or HBx regions are associated with an increased risk of HCC. Genome-wide association studies have identified common polymorphisms in KIF1B, HLA-DQ, STAT4, and GRIK1 with altered risk of HBV-related HCC. HBV integration into growth control genes (such as TERT), pro-oncogenic genes, or tumor suppressor genes and the oncogenic activity of truncated HBx promote hepatocarcinogenesis. Somatic mutations in the TERT promoter and classic cancer signaling pathways, including Wnt (CTNNB1), cell cycle regulation (TP53), and epigenetic modification (ARID2 and MLL4) are frequently detected in hepatic tumor tissues. The identification of HBV and host variation associated with tumor initiation and progression has clinical utility for improving early diagnosis and prognosis; whereas the identification of somatic mutations driving tumorigenesis hold promise to inform precision treatment for HCC patients.

Interest level in 2-year-olds with autism spectrum disorder predicts rate of verbal, nonverbal, and adaptive skill acquisition.

Recent studies have suggested that skill acquisition rates for children with autism spectrum disorders receiving early interventions can be predicted by child motivation. We examined whether level of interest during an Autism Diagnostic Observation Schedule assessment at 2 years predicts subsequent rates of verbal, nonverbal, and adaptive skill acquisition to the age of 3 years. A total of 70 toddlers with autism spectrum disorder, mean age of 21.9 months, were scored using Interest Level Scoring for Autism, quantifying toddlers' interest in toys, social routines, and activities that could serve as reinforcers in an intervention. Adaptive level and mental age were measured concurrently (Time 1) and again after a mean of 16.3 months of treatment (Time 2). Interest Level Scoring for Autism score, Autism Diagnostic Observation Schedule score, adaptive age equivalent, verbal and nonverbal mental age, and intensity of intervention were entered into regression models to predict rates of skill acquisition. Interest level at Time 1 predicted subsequent acquisition rate of adaptive skills (R(2) = 0.36) and verbal mental age (R(2) = 0.30), above and beyond the effects of Time 1 verbal and nonverbal mental ages and Autism Diagnostic Observation Schedule scores. Interest level at Time 1 also contributed (R(2) = 0.30), with treatment intensity, to variance in development of nonverbal mental age.

Normal Genetic Variation of the Human Foot: Part 2

Congenital deformities of the foot have been reported to correlate with regulatory epigenetic mechanisms that are also responsible for the timing and sequencing of developmental growth of the lower limb. Developmental variance of normal morphologic features has also been shown to vary between populations despite the retention of human foot characteristics. The molecular evidence for genetically controlled expressions of common evolved physical features is highly suggestive of regulatory control mechanisms that act together with developmental constraints to homogenize the retained functional characteristics of the foot. Genetic variance in morphologic features and functional plasticity when linked to morphometric change during gait may prove influential in clarifying kinematic and kinetic relationships.

MicroRNA profiling predicts a variance in the proliferative potential of cardiac progenitor cells derived from neonatal and adult murine hearts

Cardiac progenitor cells (CPCs) are multipotent cells that may offer tremendous potentials for the regeneration of injured myocardium. To expand the limited number of CPCs for effective clinical regeneration of myocardium, it is important to understand their proliferative potentials. Single-cell based assays were utilized to purify c-kitpos CPCs from human and mouse hearts. MicroRNA profiling identified eight differentially expressed microRNAs in CPCs from neonatal and adult hearts. Notably, the predicted protein targets were predominantly involved in cellular proliferation-related pathways. To directly test this phenotypic prediction, the developmental variance in the proliferation of CPCs was tested. Ki67 protein expression and DNA kinetics were tested in human and mouse in vivo CPCs, and doubling times were tested in primary culture of mouse CPCs. The human embryonic and mouse neonatal CPCs showed a six-fold increase in Ki67 expressing cells, a two-fold increase in the number of cells in S/G2-M phases of cell cycle, and a seven-fold increase in the doubling time in culture when compared to the corresponding adult CPCs. The over-expression of miR-17-92 increased the proliferation in adult CPCs in vivo by two-fold. In addition, the level of retinoblastoma-like 2 (Rbl2/p130) protein was two-fold higher in adult compared to neonatal-mouse CPCs. In conclusion, we demonstrate a differentially regulated cohort of microRNAs that predicts differences in cellular proliferation in CPCs during postnatal development and target microRNAs that are involved in this transition. Our study provides new insights that may enhance the utilization of adult CPCs for regenerative therapy of the injured myocardium.

How College Students' Engagement Affects Personal and Social Learning Outcomes

Recent calls for accountability in higher education underscore the need for evidence of the “value added” effect of college attendance. One of the espoused goals of higher education is to prepare individuals personally and socially for effective and civil participation in society. Increasingly, student affairs administrators are expected to demonstrate how campus programs and experiences serve these broader goals, but many college educators find assessment overwhelming and intimidating. Drawing on Astin’s I-E-O model and a new tool for administrators, I conduct several analyses to measure the influence of “good practice” experiences on 8,000 students’ personal/social learning. Results suggest that peer interactions, faculty-student interactions, and active learning experiences explain 24% of the variance in development. Findings hold promise in terms of future practice, policy, and research.

Gene polymorphisms and susceptibility to coronary artery disease

As pediatric cancer survivors age, long-term cardiovascular complications related to chemotherapeutic toxicities, as well as development of premature coronary artery disease (CAD) from radiation and increased prevalence of CAD risk factors such as obesity, are likely to become more prevalent. Despite advances in our understanding of CAD in the general population, a large amount of the variance in development of disease is unexplained. Given the strong heritability of CAD, some of this may be attributable to genetics. Premature CAD in particular segregates in families, and twin studies have shown that the genetic contribution is greater in premature CAD. In this article, we present a brief review of the literature on the genetics of CAD. Over 30 monogenic disorders feature CAD phenotypes. Recently, however, interest has shifted to understanding the genetic variation contributing to common, complex disease, where disease risk is polygenic and characterized by environmental factors, and gene-environment interactions. CAD epitomizes such a disease, and highlights the inherent difficulties in understanding the underlying genetic architecture of such diseases. Long-term cardiovascular complications in patients who survive pediatric cancers result in significant morbidity and mortality in this population. Clinicians need to be aware of screening and treatment strategies for primary and secondary prevention of cardiovascular complications in this group. Further research is necessary to define the epidemiology and risk factors of premature CAD in survivors of pediatric cancers, and to determine whether candidate genes for cardiovascular disease in the general population are also susceptibility genes in this vulnerable population.

Risk factors for psychopathology in children with intellectual disability: a prospective longitudinal population‐based study

This study examined risk factors for the development of psychopathology in children with intellectual disability (ID) in the developmental, biological, family and social-ecological domains. A population sample of 968 children, aged 6-18, enrolled in special schools in The Netherlands for educable and trainable ID were assessed at Time 1. A random 58% were re-contacted about 1 year later, resulting in a sample of 474 at Time 2. Psychopathology was highly consistent over 1 year. Risk factors jointly accounted for significant, but small, portions of the variance in development of psychopathology. Child physical symptoms, family dysfunction and previous parental mental health treatment reported at Time 1 were uniquely associated with new psychopathology at Time 2. Prevention and early intervention research to find ways to reduce the incidence of psychopathology, possibly targeting family functioning, appear important.

Moral Judgment Developmental Differences Between Gifted Youth and College Students

In order to better understand contributing factors of moral judgment development, gifted youth and college students were compared. Moral judgment development, ACT scores, attributional complexity, and descriptors of personality were assessed among 140 college students and 97 gifted youth. Important distinctions favoring the gifted sample were seen among aspects of all considered variables. Stepwise hierarchical regression models noted that there was variability in how these variables accounted for the moral judgment developmental variance of each group. Discussed are explanations for the differences seen in the gifted sample relative to the college sample. Efforts to understand populations prone to early advancement, such as the gifted, are recommended in the hopes of transferring gained knowledge to other populations.

A short‐lived herbivore on a long‐lived host: tree resistance to herbivory depends on leaf age

Short‐lived insect herbivores should be able to adapt to the resistance mechanisms of their long‐lived woody hosts because the life span of a single host will encompass numerous generations of herbivores. However, adaptation may be slowed down if host genotypes can create, in a single genotype, such large phenotypic variation in traits relevant for the herbivore that it matches variance among host genotypes. We tested this hypothesis by measuring leaf consumption by, and growth of, half‐sibs of the geometrid moth Epirrita autumnata on individual birch trees, during three instars. The instar×tree interaction, rather than tree identity alone, was a significant variance component for both consumption and growth, indicating that different larval instars ranked individual trees differently. Both consumption and growth varied most between the 3rd and the later (4th and 5th) instars, coinciding with rapid seasonal changes in numerous nutritive and phenolic traits of maturing leaves. Thus, developmental variance in the leaf quality of individual trees may reduce the likelihood of E. autumnata genotypes adapting to the defenses of their host trees. We did not find evidence of in the ability of different half‐sibs to utilize individual trees or leaf stages, indicating that E. autumnata larvae are generalists over a wide variety of host traits.

Metamorphosis in summer flounder: manipulation of rearing salinity to synchronize settling behavior, growth and development

In the aquaculture of summer flounder ( Paralichthys dentatus), the inherent variation in growth and settling behavior during metamorphosis may lead to cannibalism and necessitate increased labor due to size grading. Our goal was to use an environmental salinity change as a cue to synchronize settling behavior and produce a larger, more uniformly sized cohort of juvenile summer flounder. Early metamorphic flounder were exposed to either a 5-day fluctuating (30–20–30–20–30 ppt; “Flux”) or a single (30–20 ppt; “20 ppt”) drop in rearing salinity. A control (continuous 30 ppt) was used for comparison. Average values for a peak settlement interval (PSI; defined as the interval beginning on the day by which the first 20% had settled until the day 80% had settled) were not affected by salinity manipulation, though the 20-ppt treatment did significantly increase percent settled per day by 54 dah. Average fish size was increased by the 20-ppt treatment (19.3±0.5 mm), but not the flux treatment (17.2±0.4 mm), compared to the control (17.6±0.5 mm). Developmental stage was significantly increased in the 20-ppt treatment (3.2±0.1) in comparison to the Flux (2.9±0.1), but not the control (3.1±0.1). However, the 20-ppt treatment reduced variance in development. To confirm the positive effects of the 20-ppt treatment, a second experiment was performed. A single salinity drop (“20 ppt”), a previously successful ([Gavlik, S., Albino, M., Specker, J.L., 2002. Metamorphosis in summer flounder: Manipulation of thyoid status to synchronize settling behavior, growth, and development. Aquaculture 203 (3-4), 359-373]thyroid hormone manipulation treatment (“TH”) and a combination of the two (“TH+20 ppt”) were compared to a control (continuous 30 ppt, no thyroid manipulation). The mean PSI was significantly reduced by both TH (7±1 days) and TH+20 ppt (8±0 days) treatments, compared to the control (11±1 days). The PSI for the 20-ppt treatment (9±0 days) was not significantly different than the control. The percent flounder settled per day was significantly increased by 20 ppt salinity and significantly modified (decreased, then increased) by TH manipulation. Flounder exposed to 20-ppt salinity were both larger (20 ppt: 18.6±0.3 mm; TH+20 ppt: 18.3±0.3 mm) and more developmentally advanced (20 ppt: 3.1±0.04; TH+20 ppt: 3.2±0.03) than flounder in 30 ppt (TH: 17.8±0.3 mm/3.1±0.3; Control: 17.9±0.3 mm/3.0±0.05). Finally, 20-ppt treatment reduced variance in development, while TH treatment reduced variance in both growth and development. Percent survival was unaffected by treatment in both experiments. In summary, a decrease in rearing salinity, from 30 to 20 ppt, increased growth, settling behavior and development of metamorphosing summer flounder. A decrease in rearing salinity, in combination with a TH manipulation, should result in larger, more uniformly sized flounder cohorts. We expect this synchronization will reduce the cannibalism and labor costs associated with size grading of cultured, metamorphosing summer flounder.

Center-Based Evening Child Care: Implications for Young Children's Development

With increasing numbers of women joining the evening/nighttime workforce, there is a need for quality childcare during these hours. This project, conducted in Japan, sought to compare the effects of child day care, child evening care, and child night care on the development and adaptation of young children. Caregivers completed a survey on the childrearing environment at home, their feelings of self-efficacy, and the presence of support for childcare. Childcare professionals evaluated the development of children. The results of the discriminant analysis indicate that factors in the home environment, not type of center-based care, explained developmental variance.

A simple model of the relationship between asymmetry and developmental stability

Abstract The relationship between developmental stability and morphological asymmetry is derived under the standard view that structures on each side of an individual develop independently and are normally distributed. I use developmental variance of sizes of parts, VD, as the converse of developmental stability, and assume that VD follows a gamma distribution. Repeatability of asymmetry, a measure of how informative asymmetry is about VD, is quite insensitive to the variance in VD, for example only reaching 20% when the coefficient of variation of VD is 100%. The coefficient of variation of asymmetry, CVFA, also increases very slowly with increasing population variation in VD. CVFA values from empirical data are sometimes over 100%, implying that developmental stability is sometimes more variable than any previously studied type of trait. This result suggests that alternatives to this model may be needed.

Effects of temperature on morphological landmarks critical to growth and survival in larval Atlantic cod (Gadus morhua)

The morphology and function of structures important to energy acquisition were studied from spawning to the stage of transformation of larva to pelagic juvenile in Atlantic cod, Gadus morhua L., from December 1991 to July 1992. Fertilized eggs produced by adult fish from two genetically discrete populations (Newfoundland and Scotian Shelf) were raised under similar conditions in the laboratory at temperatures of 5 and 10°C. Subsamples of larvae were removed from cultures daily for 10 d, and then less frequently, and fixed for light microscopy and scanning electron microscopy. Nine functional morphological “landmarks” important to feeding, respiration and locomotion were chosen from observation of 280 ind. These landmarks defined 12 major developmental stages, from hatching to the pelagic juvenile stage. One of the feeding landmarks, intestinal stage, varied as a function of age and size and the variance in development was higher at 10°C than at 5°C; Newfoundland larvae developed more complex intestines than did Scotian Shelf larvae. In addition, Newfoundland larvae had significantly higher growth rates than those of Scotian Shelf larvae. Despite the higher growth rates and greater structural complexity of the intestine in Newfoundland larvae, the rate of yolk utilization was not significantly different between Newfoundland and Scotian Shelf larvae. Staging of respiratory landmarks showed that the gill arches were probably used preferentially in feeding while respiration was cutaneous. The gills, operculum and gill rakers developed late in larval life and accompanied the transition from cutaneous to branchial respiration. In the yolk-sac period, development of feeding and respiratory structures may be largely genetically controlled. During exogenous feeding, extrinsic factors also become important, as shown by the size and age-independent variation in intestinal development of larval cod raised at different temperatures.

Contractile properties of the developing diaphragm correlate with myosin heavy chain phenotype.

The objective of this study was to determine the relationship between developmental transitions in myosin heavy chain (MHC) composition and changes in maximum unloaded shortening velocity (Vo) and maximum specific force (Po) of the rat diaphragm muscle. The diaphragm was excised at postnatal days 0, 3, 7, 14, 21, and 28 and in adults. MHC isoform expression was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and laser densitometry. In muscle fiber bundles, Vo was determined at 15 degrees C by use of the "slack" test. Isometric Po was determined at 15 and 26 degrees C. Simple and stepwise regressions were used to evaluate the correlations between Vo, Po, and MHC phenotype transitions and the various developmental ages. The progressive increases in Vo and Po with age were found to be inversely correlated to MHC-neonatal isoform expression (r2 = -0.84 and -0.63, respectively) and positively correlated to MHC-2X (r2 = 0.78 and 0.57) and MHC-2B (r2 = 0.51 and 0.40) isoform expression (P < 0.001). Changes in MHC-neonatal isoform expression contributed to most of the developmental variance in Vo and Po, with changes in MHC-2X and MHC-2B expression also contributing significant increments to total variance. The postnatal increase in Vo most likely relates to differences in the actomyosin adenosinetriphosphatase activity between neonatal and adult fast MHC phenotypes. The increase in Po may reflect inherent differences in myofibrillar density, cross-bridge cycling kinetics, and/or the force produced per cross bridge among fibers composed of the different MHC isoforms.