892 resultados para POSTNATAL MYOGENESIS
Resumo:
Phocoenids are generally considered to be nonwhistling species that produce only high-frequency pulsed sounds. Here our results show that neonatal finless porpoises (Neophocaena phocaenoides) frequently produce clear low-frequency (2-3 kHz) pulsed signals, without distinct high-frequency energy, just after birth and can produce both low- (2-3 kHz) and high-frequency (>100 kHz) pulsed signals simultaneously until about 20 days postnatal. The results indicate that low-frequency signals of neonatal finless porpoises are not an early form of high-frequency signals and suggest that low- and high-frequency signals may be produced by different sound production mechanisms. (C) 2008 Acoustical Society of America.
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Acoustic and concurrent behavioral data from one neonatal male Yangtze finless porpoise (Neophocaena phocaenoides asiaeorientalis) in captivity were presented. The calf click train was first recorded at 22 days postnatal, and the frequency of hydrophone-exploration behavior with head scanning motions in conjunction with emissions of click trains by the calf increased gradually with age. The echolocation clicks in the first recorded click train were indistinguishable from those of adults. Calf echolocation trains were found to decrease in maximum click-repetition rate, duration, and number of clicks per train with age while the. minimum click-repetition rate remained more consistent. (c) 2007 Acoustical Society of America.
Resumo:
本研究探讨了新生期的触觉刺激(tactile stimulation,TS)和母婴分离(maternal separation,MS)经历对大鼠成年后空间工作记忆和空间参考记忆的影响,以及对海马-前额叶神经通路的突触可塑性产生的效应。Wistar品系的母鼠分娩后,以split-litter方法对仔鼠进行分组:NTS组的仔鼠不接受触觉刺激和母婴分离;TS组的仔鼠在出生后第2-9天(postnatal day 2-9,PND2-9),或者PND10-17内,每天接受短暂(约30s)的人为抓握,并进行体表标记;TS/MS组的仔鼠在PND2-9,或者PND10-17内,接受TS组相同方式的抓握并在不同体表部位进行标记后,被单独地放入一个杯子中,杯中有取自鼠巢的垫料,每天与母鼠分离1h后返回鼠巢。按照常规方法饲养这些在新生期有不同经历的大鼠,待其成年后(3月龄),采用交互延缓作业(纠正错误法和不纠正错误法)、空间分辨作业及反转学习作业测试雄性大鼠的学习记忆功能,并观察多巴胺D1受体激动剂A77636对不同组成年雄鼠的工作记忆是否产生影响。采用活体电生理方法,高频刺激海马腹侧部在前额叶记录突触效能长时程增强(long-term potentiation,LTP),对PND2-9有不同经历的成年大鼠(雌雄兼用)的海马-前额叶LTP进行比较。 结果:(1)各组仔鼠间在PND30、PND60和PND90的体重都没有显著性差异,表明本研究中的新生期TS处理和MS处理不影响仔鼠的体重发育。 (2)在交互延缓作业-纠正错误法中,各组成年雄鼠在0s延缓期的达标天数没有显著性差异;0s延缓期达标后,再经过30天的训练,PND2-9TS组和PND10-17TS组的成年雄鼠达到的最长延缓期明显高于NTS组,而且在30s—50s延缓期内达标(正确率≥86.7%)的大鼠数量明显较多(与NTS组相比)。采用交互延缓作业-不纠正错误法,各组成年雄鼠在0s延缓期的训练成绩没有显著性差异,但是,PND2-9TS组和PND10-17TS组的成年雄鼠在40s延缓期的训练正确率明显高于NTS组,表明新生期的TS处理明显改善成年雄性大鼠成年后的空间工作记忆。 (3)各组成年雄鼠在空间分辨作业及反转学习作业中的成绩没有明显差异,表明新生期TS经历对雄鼠成年后空间学习记忆的影响是任务依赖性的:与前额叶有关的空间工作记忆功能比较容易受到新生期TS经历的影响,而空间参考记忆相对不容易受到新生期TS经历的影响。 (4)多巴胺D1受体激动剂A77636只有1个剂量(0.1mg/kg)对NTS组成年雄鼠的交互延缓作业成绩具有明显的改善效应。对PND2-9TS组成年雄鼠的交互延缓作业成绩,A77636的0.1mg/kg和1mg/kg剂量都具有明显改善效应。对PND10-17TS组成年雄鼠的交互延缓作业成绩,A77636的0.01mg/kg、0.1mg/kg和1mg/kg剂量都具有明显改善效应。与NTS组相比,A77636对这2个TS组成年雄性大鼠的有效改善剂量范围较宽,提示新生期TS处理经历对雄性大鼠成年后空间工作记忆的改善效应与其前额叶的多巴胺D1受体功能上调有关。 (5)与NTS组相比,PND2-9TS组雄性和雌性成年大鼠的海马-前额叶神经通路的LTP幅度都明显增加。由于海马-前额叶神经通路在空间工作记忆功能中起重要作用,新生期TS经历增强大鼠成年后的海马-前额叶神经通路的突触可塑性,为新生期TS经历增强大鼠成年后的空间工作记忆提供了电生理学的证据。TS成年大鼠海马-前额叶LTP增强可能与其前额叶的D1受体功能上调有关。 (6)本研究中,TS/MS组的新生期仔鼠在PND2-9或者PND10-17内,除了接受与TS组相同方式的抓握并在不同部位标记外,每天与母鼠分离1h,因此通过不同日龄段的TS/MS组与TS组的比较,拟对新生期MS处理的效应进行评估。结果发现,无论是对成年雄性大鼠的各项行为测试(空间分辨作业、交互延缓作业、A77636影响交互延缓作业的量效曲线),还是对成年雌性大鼠的行为测试(明/暗箱作业、一次性被动回避反应,论文Ⅱ),或者对海马-前额叶神经通路的LTP,新生期的MS处理对本研究中的所有测试指标在统计上都没有显著性的差异,说明新生期每天1h的母婴分离经历对大鼠成年后的学习记忆等行为及前额叶突触可塑性没有产生明显的影响,对前额叶D1受体功能也没有明显影响。 (7)对所有测试指标,本研究采用的2个仔鼠日龄段PND2-9和PND10-17之间的统计比较没有明显差异,提示PND2-9和PND10-17甚至整个泌乳期都是仔鼠神经系统对外界环境刺激比较敏感的发育关键期。 结论:新生期的触觉刺激经历改善雄性大鼠成年后的空间工作记忆,增强海马-前额叶神经通路的突触可塑性和前额叶D1受体功能;新生期短时间的母婴分离经历对大鼠成年后的空间工作记忆和前额叶突触可塑性等没有产生明显的影响,可能具有一定的生物学适应意义。
Resumo:
The notochord is one of the diagnostic features of the phylum Chordata. Despite the similarities in the early morphogenetic patterns of the notochords of various chordates, they are strikingly distinct from one another at the histological level. The amphioxus notochord is one example of an evolutionary novelty because it is made up of muscle cells. Our previous expressed sequence tag analysis, targeting messenger RNAs expressed in the adult amphioxus notochord, demonstrated that many muscle-related genes are expressed there. To characterize amphioxus notochord cells and to gain insights into the myogenic program in the notochord, we determined the spatial and temporal expression patterns of these muscle-related genes during amphioxus development. We found that BbNA1 (notochord actin), Amphi-Trop I (troponin I), Amphi-TPmyosin (tropomyosin), Amphi-MHC2 (myosin heavy chain), Amphi-nMRLC (notochord-specific myosin regulatory light chain), AmphinTitin/MLCK (notochord-specific titin/myosin light chain kinase), Amphi-MLP/CRP3 (muscle LIM protein), and Amphi-nCalponin (notochord-specific calponin) are expressed with characteristic patterns in notochord cells, including the central cells, dorsally located cells, and ventrally located cells, suggesting that each notochord cell has a unique molecular architecture that may reflect its function. In addition, we characterized two MyoD genes (Amphi-MyoD1 and Amphi-MyoD2) to gain insight into the genetic circuitry governing the formation of the notochord muscle. One of the MyoD genes (Amphi-MyoD2) is expressed in the central notochord cells, and the coexistence of Amphi-MyoD2 transcripts along with the Amphi-MLP/CRP3 transcripts implies the participation of Amphi-MyoD2 in the myogenic program in the notochord muscle.
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Myogenin is a bHLH transcription factor of the MyoD family. It plays a crucial role in myoblast differentiation and maturation. We report here the isolation of flounder myogenin gene and the characterization of its expression patterns. Sequence analysis indicated that flounder myogenin shared a similar structure and the conserved bHLH domain with other vertebrate myogenin genes. Flounder myogenin gene contains 3 exons and 2 introns. Sequence alignment and phylogenetic showed that flounder myogenin was more homologous with halibut (Hippoglossus hippoglossus) myogenin and striped bass (Morone saxatilis) myogenin. Whole-mount embryo in situ hybridization revealed that flounder myogenin was first detected in the medial region of somites that give rise to slow muscles, and expanded later to the lateral region of the somite that become fast muscles. The levels of myogenin transcripts dropped significantly in matured somites at the trunk region. Its expression could only be detected in the caudal somites, which was consistent with the timing of somite maturation. Transient expression analysis showed that the 546 bp flounder myogenin promoter was sufficient to direct muscle-specific GFP expression in zebrafish embryos. (c) 2007 Elsevier Inc. All rights reserved.
Resumo:
Myf-5, a member of the myogenic regulatory factors (MRF), has been shown to be expressed in muscle precursors in early stage zebrafish embryos. The MRFs, including MyoD, Myf-5, Myogenin and MR-F4, belong to the basic Helix-Loop-Helix transcription factors that contain a conserved basic Helix-Loop-Helix (bHLH) domain. To better understand the role of Myf-5 in the development of fish muscles, we have isolated the Myf-5 genomic sequence and cDNA from Flounder (Paralichthys olivaceus), and analyzed its structures and patterns of expression. Promoter analysis identified several putative transcription factor binding sites such as an E-box, NF-Y sites that might confer muscle-specific expression. Myf-5 transcripts were first detected in the paraxial mesoderm that gives rise to slow muscles. During somitogenesis, Myf-5 expression was found in developing somites. Myf-5 expression decreased gradually in somites in the anterior region, but remained strong in the newly formed somites. In the hatching stage, the expression was also detected in other muscle cells such as head muscle and fin muscle. In the growing fish, RT-PCR results showed that Myf-5 was expressed in the skeletal muscle and intestine. (c) 2006 Elsevier Inc. All rights reserved.
Resumo:
Specification and differentiation of skeletal muscle cells are driven by the activity of genes encoding members of the myogenic regulatory factors (MRFs). In vertebrates, the MRF family includes MyoD, Myf5, myogenin, and MRF4. The MRFs are capable of converting a variety of nonmuscle cells into myoblasts and myotubes. To better understand their roles in fish muscle development, we isolated the MyoD gene from flounder (Paralichthys olivaceus) and analyzed its structure and patterns of expression. Sequence analysis showed that flounder MyoD shared a structure similar to that of vertebrate MRFs with three exons and two introns, and its protein contained a highly conserved basic helix-loop-helix domain (bHLH). Comparison of sequences revealed that flounder MyoD was highly conserved with other fish MyoD genes. Sequence alignment and phylogenetic analysis indicated that flounder MyoD, seabream (Sparus aurata) MyoD1, takifugu (Takifugu rubripes) MyoD, and tilapia (Oreochromis aureus) MyoD were more likely to be homologous genes. Flounder MyoD expression was first detected as two rows of presomitic cells in the segmental plate. From somitogenesis, MyoD transcripts were present in the adaxial cells that give rise to slow muscles and the lateral somitic cells that give rise to fast muscles. After 30 somites formed, MyoD expression decreased in the somites except the caudal somites, coincident with somite maturation. In the hatching stage, MyoD was expressed in other muscle cells and caudal somites. It was detected only in muscle in the growing fish.
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本文研究了栖息在高寒地区的高原鼠兔(Ochotona curzoniae)的体温、热代谢和肩胛部BAT随个体发育的变化,讨论了高原鼠兔热代谢发育特征及发育策略。结果表明新生个体具有初步的热调节能力,但环境温度变化时,还不能维持稳定的体温。体重为12.5克的幼体(约1-3日龄),其最低代谢离为3.028(mlO_2/g·h),相对于Kleiber期望值的百分率为167%,热传导率为0.518(mlO_2/g·h· ℃),相对于Bradley-Deavers期望值的百分率为200%,热中性区下临界温度为32.7 ℃。随着个体的发育,最低代谢率趋于下降,但其相对于Kleiber期望值的百分率在体重增长到大约90克前,趋于增加,其后才略有下降,热传导率及其相对于Bradley-Deavers期望值的百分率和热中性区的下临界温度随个体的发育趋于降低。所以在各环境温度下,高原鼠兔的体温随着个体发育表现出上升的变化。高原鼠兔BAT在整个发育时期都存在。刚出生时BAT发达,相对重量高,结构成熟,BAT细胞充满小而多的脂肪滴,线粒分布致密。随着个体发育,BAT相对重量和水分含量均迅速降低,结构呈退化趋势。高原鼠兔幼体主要利用小气候环境和BAT产热抵抗低温压力,高原鼠兔热调节发育的特征和对小气候环境的利用有利于减少体温调节耗能,促进生长发育。而发育到成体时,最低代谢率和热传导率对其期望值的偏离反映出高原鼠兔对西息环境的适应。另外,高原鼠兔通过行为热调节对生理调节加以补充。
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Background: ‘Birth Satisfaction’ is a term that encompasses a woman’s evaluation of her birth experience. The term includes factors such as her appraisal of the quality of care she received, a personal assessment of how she coped, and her reconstructions of what happened on that particular day. Her accounts may be accurate or skewed, yet correspond with her reality of how events unfolded. Objective: To evaluate properties of an instrument designed to measure birth satisfaction in a Greek population of postnatal women. Study design: We assessed factor structure, internal consistency, divergent validity and known-groups discriminant validity of the 30-item Greek Birth Satisfaction Scale – Long Form (30-item G-BSS-LF) and its revised version the 10-item Greek-BSS-Revised (10-item-G-BSS-R), using survey data collected in Athens. Participants: A convenience sample of healthy Greek postnatal women (n = 162) aged 22–46 years who had delivered between 34 and 42 weeks’ gestation. Results: The 30-item-G-BSS-LF performed poorly in terms of factor structure. The short-form 10-item-G-BSS-R performed well in terms of measurement replication of the English equivalent version as a multidimensional instrument. The short-form 10-item-G-BSS-R comprises three subscales which measure distinct but correlated domains of: (1) quality of care provision (4 items), (2) women’s personal attributes (2 items), and (3) stress experienced during labour (4 items). Key conclusions: The 10-item-G-BSS-R is a valid and reliable multidimensional psychometric instrument for measuring birth satisfaction in Greek postnatal women.
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Growth/differentiation factor 5 (GDF5) and glial cell line-derived neurotrophic factor (GDNF) are neurotrophic factors that promote the survival of midbrain dopaminergic neurons in vitro and in vivo. Both factors have potent neurotrophic and neuroprotective effects in rat models of Parkinson's disease (PD), and may represent promising new therapies for PD. The aim of the present study was to investigate the endogenous expression and function of GDF5 and GDNF in the nigrostriatal dopaminergic system during development and in rat models of PD. Examination of the temporal expression patterns of endogenous GDF5, GDNF, and their respective receptors, in the developing and adult nigrostriatal dopaminergic system suggest that these factors play important roles in promoting the survival and maturation of midbrain dopaminergic neurons during the period of postnatal programmed cell death. The relative levels of GDF5 and GDNF mRNAs in the midbrain and striatum, and their individual temporal expression patterns during development, suggest that their modes of actions are quite distinct in vivo. Furthermore, the sustained expression of GDF5, GDNF, and their receptors into adulthood suggest roles for these factors in the continued support and maintenance of mature nigrostriatal dopaminergic neurons. The present study found that endogenous GDF5, GDNF, and their receptors are differentially expressed in two 6-hydroxydopamine-induced lesion adult rat models of PD. In both terminal and axonal lesion models of PD, GDF5 mRNA levels in the striatum increased at 10 days post-lesion, while GDNF mRNA levels in the nigrostriatal system decreased at 10 and 28 days post-lesion. Thus, despite the fact that exogenous GDF5 and GDNF have similar effects on midbrain dopaminergic neurons in vitro and in vivo, their endogenous responses to a neurotoxic injury are quite distinct. These results highlight the importance of studying the temporal dynamic changes in neurotrophic factor expression during development and in animal models of PD.
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Eczema prevalence rates among Irish infants are unreported, despite eczema being the most common inflammatory condition of infancy. Maternal and infant nutritional status including vitamin D and other fat-soluble vitamins as well as early infant feeding have been linked with eczema initiation and development. Therefore, early nutrition could be a potential modifiable risk factor. The objective of this thesis was to prospectively describe early infant feeding and complementary feeding practices, to evaluate infant vitamin D supplementation practice, to quantify cord serum 25-hydroxyvitamin D [25(OH)D] and propose reference intervals for vitamin D metabolites, to report eczema prevalence and explore the potential role of infant nutrition and eczema. These research needs were investigated through the Cork BASELINE (Babies After SCOPE: Evaluating the Longitudinal Impact with Neurological and Nutritional Endpoints) Birth Cohort Study (n 2137). This thesis was the first comprehensive report from the birth cohort, therefore it was important to describe the cohort sociodemographic profile. Although socio-demographic characteristics compared well with national data, there was an over-representation of educated mothers which may limit the generalizability of the results. From August 2008 through November 2011, comprehensive postnatal assessments were completed at day 2 and at 2, 6, 12 and 24 months. Breastfeeding rates were low, while complementary feeding practices were broadly compliant with national guidelines. The implementation of a national infant vitamin D supplementation policy had a major impact on supplementation practice. Low levels of serum 25(OH)D were universal among Irish neonates. Eczema is a complex and multifaceted disease, which is increasing globally. This was the first report of eczema prevalence data among Irish infants which compared with international reports. Given the high prevalence and considerable burden eczema has on the lives of sufferers, intensive research efforts to identify a cause and therapeutic strategies to prevent/reduce eczema was re-emphasized in this thesis.
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The goal of neonatal nutrition in the preterm infant is to achieve postnatal growth and body composition approximating that of a normal fetus of the same postmenstrual age and to obtain a functional outcome comparable to infants born at term. However, in clinical practice such a pattern is seldom achieved, with growth failure and altered body composition being extensively reported. The BabyGrow preterm nutrition study was a longitudinal, prospective, observational study designed to investigate nutrition and growth in 59 preterm infants following the implementation of evidence-based nutrition guidelines in the neonatal unit at Cork University Maternity Hospital. Nutrient delivery was precisely measured during the entire hospital stay and intakes were compared with current international recommendations. Barriers to nutrient delivery were identified across the phases of nutritional support i.e. exclusive parenteral nutrition and transition (establishment of enteral feeds) phases of nutrition and nutritional strategies to optimise nutrient delivery were proposed according to these phases. Growth was measured from birth up to 2 months corrected age and body composition was assessed in terms of fat mass and lean body mass by air displacement plethysmography (PEA POD) at 34 weeks gestation, term corrected age and 2 months corrected age. Anthropometric and body composition data in the preterm cohort were compared with a term reference group from the Cork BASELINE Birth Cohort Study (n=1070) at similar time intervals. The clinical and nutritional determinants of growth and body composition during the neonatal period were reported for the first time. These data have international relevance, informing authoritative agencies developing evidence-based practice guidelines for neonatal nutritional support. In the future, the nutritional management of preterm infants may need to be individualised to consider gestational age, birth weight as well as preterm morbidity.
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The amygdala is a limbic structure that is involved in many of our emotions and processing of these emotions such as fear, anger and pleasure. Conditions such as anxiety, autism, and also epilepsy, have been linked to abnormal functioning of the amygdala, owing to improper neurodevelopment or damage. This thesis investigated the cellular and molecular changes in the amygdala in models of temporal lobe epilepsy (TLE) and maternal immune activation (MIA). The kainic acid (KA) model of temporal lobe epilepsy (TLE) was used to induce Ammon’s-horn sclerosis (AHS) and to investigate behavioural and cytoarchitectural changes that occur in the amygdala related to Neuropeptide Y1 receptor expression. Results showed that KA-injected animals showed increased anxiety-like behaviours and displayed histopathological hallmarks of AHS including CA1 ablation, granule cell dispersion, volume reduction and astrogliosis. Amygdalar volume and neuronal loss was observed in the ipsilateral nuclei which was accompanied by astrogliosis. In addition, a decrease in Y1 receptor expressing cells in the ipsilateral CA1 and CA3 sectors of the hippocampus, ipsi- and contralateral granule cell layer of the dentate gyrus and ipsilateral central nucleus of the amygdala was found, consistent with a reduction in Y1 receptor protein levels. The results suggest that plastic changes in hippocampal and/or amygdalar Y1 receptor expression may negatively impact anxiety levels. Gamma-aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the brain and tight regulation and appropriate control of GABA is vital for neurochemical homeostasis. GABA transporter-1 (GAT-1) is abundantly expressed by neurones and astrocytes and plays a key role in GABA reuptake and regulation. Imbalance in GABA homeostasis has been implicated in epilepsy with GAT-1 being an attractive pharmacological target. Electron microscopy was used to examine the distribution, expression and morphology of GAT-1 expressing structures in the amygdala of the TLE model. Results suggest that GAT-1 was preferentially expressed on putative axon terminals over astrocytic processes in this TLE model. Myelin integrity was examined and results suggested that in the TLE model myelinated fibres were damaged in comparison to controls. Synaptic morphology was studied and results suggested that asymmetric (excitatory) synapses occurred more frequently than symmetric (inhibitory) synapses in the TLE model in comparison to controls. This study illustrated that the amygdala undergoes ultrastructural alterations in this TLE model. Maternal immune activation (MIA) is a risk factor for neurodevelopmental disorders such as autism, schizophrenia and also epilepsy. MIA was induced at a critical window of amygdalar development at E12 using bacterial mimetic lipopolysaccharide (LPS). Results showed that MIA activates cytokine, toll-like receptor and chemokine expression in the fetal brain that is prolonged in the postnatal amygdala. Inflammation elicited by MIA may prime the fetal brain for alterations seen in the glial environment and this in turn have deleterious effects on neuronal populations as seen in the amygdala at P14. These findings may suggest that MIA induced during amygdalar development may predispose offspring to amygdalar related disorders such as heightened anxiety, fear impairment and also neurodevelopmental disorders.
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Background: The first childbirth has the greatest impact on a woman’s pelvic floor when major changes occur. The aim of this study was to comprehensively describe pelvic floor dysfunction (PFD) in young nulliparous women, and its correlation with postnatal pathology. Methods: A prospective study was performed at Cork University Maternity Hospital, Ireland. Initially 1484 nulliparous women completed the validated Australian Pelvic Floor Questionnaire at 15 weeks’ gestation and repeatedly at one year postnatally (N=872). In the second phase, at least one year postnatally, 202 participants without subsequent pregnancies attended the clinical follow up which included: pelvic organ prolapse quantification, a 3D-Transperineal ultrasound scan and collagen level assessment. Results: A high pre-pregnancy prevalence of various types of PFD was detected, which in the majority of cases persisted postnatally and included multiple types of PFD. The first birth had a negative impact on severity of pre-pregnancy symptoms in <15% of cases. Apart from prolapse, vaginal delivery, including instrumental delivery did not increase the risk of PFD symptoms, where as Caesarean section was protective for all types of PFD. The first birth had a bigger impact on pre-existing symptoms of overactive bladder compared to stress urinary incontinence. Pelvic organ prolapse is extremely prevalent in young primiparous women, however usually it is low grade and asymptomatic. Congenital factors and high collagen type III levels play an important role in the aetiology of pelvic organs prolapse. Levator ani trauma is present in one in three women after the first pregnancy and delivery. Conclusion: The main damage to the pelvic floor most likely occurs due to an undiagnosed congenital intrinsic weakness of the pelvic floor structures. PFD is highly associated with first childbirth, however it seems that pregnancy and delivery are contributing factors only which unmask the congenital intrinsic weakness of the pelvic floor support.
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Limb, trunk, and body weight measurements were obtained for growth series of Milne-Edwards's diademed sifaka, Propithecus diadema edwardsi, and the golden-crowned sifaka, Propithecus tattersalli. Similar measures were obtained also for primarily adults of two subspecies of the western sifaka: Propithecus verreauxi coquereli, Coquerel's sifaka, and Propithecus verreauxi verreauxi, Verreaux's sifaka. Ontogenetic series for the larger-bodied P. d. edwardsi and the smaller-bodied P. tattersalli were compared to evaluate whether species-level differences in body proportions result from the differential extension of common patterns of relative growth. In bivariate plots, both subspecies of P. verreauxi were included to examine whether these taxa also lie along a growth trajectory common to all sifakas. Analyses of the data indicate that postcranial proportions for sifakas are ontogenetically scaled, much as demonstrated previously with cranial dimensions for all three species (Ravosa, 1992). As such, P. d. edwardsi apparently develops larger overall size primarily by growing at a faster rate, but not for a longer duration of time, than P. tattersalli and P. verreauxi; this is similar to results based on cranial data. A consideration of Malagasy lemur ecology suggests that regional differences in forage quality and resource availability have strongly influenced the evolutionary development of body-size variation in sifakas. On one hand, the rainforest environment of P. d. edwardsi imposes greater selective pressures for larger body size than the dry-forest environment of P. tattersalli and P. v. coquereli, or the semi-arid climate of P. v. verreauxi. On the other hand, as progressively smaller-bodied adult sifakas are located in the east, west, and northwest, this apparently supports suggestions that adult body size is set by dry-season constraints on food quality and distribution (i.e., smaller taxa are located in more seasonal habitats such as the west and northeast). Moreover, the fact that body-size differentiation occurs primarily via differences in growth rate is also due apparently to differences in resource seasonality (and juvenile mortality risk in turn) between the eastern rainforest and the more temperate northeast and west. Most scaling coefficients for both arm and leg growth range from slight negative allometry to slight positive allometry. Given the low intermembral index for sifakas, which is also an adaptation for propulsive hindlimb-dominated jumping, this suggests that differences in adult limb proportions are largely set prenatally rather than being achieved via higher rates of postnatal hindlimb growth.(ABSTRACT TRUNCATED AT 400 WORDS)