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Proximate Causes (proximate + cause)
Selected AbstractsThe evolution of human fatness and susceptibility to obesity: an ethological approachBIOLOGICAL REVIEWS, Issue 2 2006Jonathan C. K. Wells ABSTRACT Human susceptibility to obesity is an unusual phenomenon amongst animals. An evolutionary analysis, identifying factors favouring the capacity for fat deposition, may aid in the development of preventive public health strategies. This article considers the proximate causes, ontogeny, fitness value and evolutionary history of human fat deposition. Proximate causes include diet composition, physical activity level, feeding behaviour, endocrine and genetic factors, psychological traits, and exposure to broader environmental factors. Fat deposition peaks during late gestation and early infancy, and again during adolescence in females. As in other species, human fat stores not only buffer malnutrition, but also regulate reproduction and immune function, and are subject to sexual selection. Nevertheless, our characteristic ontogenetic pattern of fat deposition, along with relatively high fatness in adulthood, contrasts with the phenotype of other mammals occupying the tropical savannah environment in which hominids evolved. The increased value of energy stores in our species can be attributed to factors increasing either uncertainty in energy availability, or vulnerability to that uncertainty. Early hominid evolution was characterised by adaptation to a more seasonal environment, when selection would have favoured general thriftiness. The evolution of the large expensive brain in the genus Homo then favoured increased energy stores in the reproducing female, and in the offspring in early life. More recently, the introduction of agriculture has had three significant effects: exposure to regular famine; adaptation to a variety of local niches favouring population-specific adaptations; and the development of social hierarchies which predispose to differential exposure to environmental pressures. Thus, humans have persistently encountered greater energy stress than that experienced by their closest living relatives during recent evolution. The capacity to accumulate fat has therefore been a major adaptive feature of our species, but is now increasingly maladaptive in the modern environment where fluctuations in energy supply have been minimised, and productivity is dependent on mechanisation rather than physical effort. Alterations to the obesogenic environment are predicted to play a key role in reducing the prevalence of obesity. [source] Not How, But Why ? Beyond proximate cause for environmental degradationCONSERVATION, Issue 1 2005David Rains Wallace [source] Temporal Variation in Cleanerfish and Client Behaviour: Does It Reflect Ectoparasite Availability?ETHOLOGY, Issue 6 2003Isabelle M. Côté We tested the importance of ectoparasites as the proximate cause of cleaning interactions by comparing the activity of Caribbean cleaning gobies (Elacatinus evelynae) and of their clients during three daily periods (early morning, midday, and late afternoon) in which ectoparasite availability varied naturally. Emergence from the benthos of gnathiid isopod larvae, the main target of cleaning goby predation, was higher at night, when cleaners were inactive, than during the day. As a result, overall ectoparasite loads on client fish tended to be higher in the morning. Inspection bouts by cleaning gobies were longest in the morning, but also at midday when ectoparasite availability on clients was lower. Client fish were observed at cleaning stations most often in the afternoon, when they harboured few ectoparasites, but they were more likely to adopt incitation poses, which increase the likelihood of being cleaned, in the morning than later in the day. Most cleaner and client behaviours therefore did not change predictably in response to natural diurnal variation in ectoparasite availability. Our study suggests that the ultimate and proximate causes of cleaning behaviour need not necessarily coincide. [source] Diagnosing the environmental causes of the decline in Grey Partridge Perdix perdix survival in FranceIBIS, Issue 1 2001ELISABETH BRO We studied Grey Partridge Perdix perdix mortality during breeding to identify the environmental causes of a long-term decline in adult survival. We radiotagged and monitored daily from mid-March to mid-September 1009 females on ten contrasting study sites in 1995-97. Simultaneously, we recorded habitat features and estimated the abundance of Hen and Marsh Harriers Circus cyaneus and C. aeruginosus Red Fox Vulpes vulpes and mustelids. We experimentally tested whether scavenging could have biased predation rates. We also examined, through the necropsy of 80 carcasses of Grey Partridge, whether disease, parasites or poisoning could have been ultimate causes of high predation rates. The survival rate of radiotagged females during spring and summer ranged from 0.25 to 0.65 across study areas. Mortality peaked in May, June and July when females were laying and incubating. The direct negative impact of farming practices was low (6%). Predation was the main proximate cause of female mortality during breeding (73%) and determined the survival rate, suggesting no compensation by other causes of mortality. Ground carnivores were responsible for 64% of predation cases, and raptors for 29%, but this proportion varied across study sites. Disease and poisoning did not appear to favour predation, and scavenging was not likely to have substantially overestimated predation rates. The predation rate on breeding females was positively correlated with the abundance of Hen and Marsh Harriers, suggesting an additional mortality in areas where harriers were abundant. The proportion of raptor predation was linearly related to harrier abundance. The predation rate was not correlated with the abundance of the Red Fox and mustelids. A potential density-dependent effect on the predation rate was confounded by the abundance of harriers. We found no convincing relationship between the predation rate and habitat features, but we observed a positive relationship between the abundance of Hen and Marsh Harriers and the mean field size. This suggested that habitat characteristics may contribute to high predation rates through predator abundance or habitat-dependent predation. [source] Optimizing Coding and Reimbursement to Improve Management of Alzheimer's Disease and Related DementiasJOURNAL OF AMERICAN GERIATRICS SOCIETY, Issue 11 2002Howard Fillit MD The objectives of this study were to review the diagnostic, International Classification of Disease, 9th Revision, Clinical Modification (ICD-9-CM), diagnosis related groups (DRGs), and common procedural terminology (CPT) coding and reimbursement issues (including Medicare Part B reimbursement for physicians) encountered in caring for patients with Alzheimer's disease and related dementias (ADRD); to review the implications of these policies for the long-term clinical management of the patient with ADRD; and to provide recommendations for promoting appropriate recognition and reimbursement for clinical services provided to ADRD patients. Relevant English-language articles identified from MEDLINE about ADRD prevalence estimates; disease morbidity and mortality; diagnostic coding practices for ADRD; and Medicare, Medicaid, and managed care organization data on diagnostic coding and reimbursement were reviewed. Alzheimer's disease (AD) is grossly undercoded. Few AD cases are recognized at an early stage. Only 13% of a group of patients receiving the AD therapy donepezil had AD as the primary diagnosis, and AD is rarely included as a primary or secondary DRG diagnosis when the condition precipitating admission to the hospital is caused by AD. In addition, AD is often not mentioned on death certificates, although it may be the proximate cause of death. There is only one ICD-9-CM code for AD,331.0,and no clinical modification codes, despite numerous complications that can be directly attributed to AD. Medicare carriers consider ICD-9 codes for senile dementia (290 series) to be mental health codes and pay them at a lower rate than medical codes. DRG coding is biased against recognition of ADRD as an acute, admitting diagnosis. The CPT code system is an impediment to quality of care for ADRD patients because the complex, time-intensive services ADRD patients require are not adequately, if at all, reimbursed. Also, physicians treating significant numbers of AD patients are at greater risk of audit if they submit a high frequency of complex codes. AD is grossly undercoded in acute hospital and outpatient care settings because of failure to diagnose, limitations of the coding system, and reimbursement issues. Such undercoding leads to a lack of recognition of the effect of AD and its complications on clinical care and impedes the development of better care management. We recommend continuing physician education on the importance of early diagnosis and care management of AD and its documentation through appropriate coding, expansion of the current ICD-9-CM codes for AD, more appropriate use of DRG coding for ADRD, recognition of the need for time-intensive services by ADRD patients that result in a higher frequency of use of complex CPT codes, and reimbursement for CPT codes that cover ADRD care management services. [source] Animals, Pain and MoralityJOURNAL OF APPLIED PHILOSOPHY, Issue 1 2005ALAN CARTER ABSTRACT While it is widely agreed that the infliction upon innocents of needless pain is immoral, many have argued that, even though nonhuman animals act as if they feel pain, there is no reason to think that they actually suffer painful experiences. And if our actions only appear to cause nonhuman animals pain, then such actions are not immoral. On the basis of the claim that certain behavioural responses to organismic harm are maladaptive, whereas the ability to feel pain is itself adaptive, this article argues that the experience of pain should be viewed as the proximate cause of such occasionally maladaptive behaviour. But as nonhuman animals also display such maladaptive traits, we have reason to conclude that they feel pain. Hence, we have reason to hold that it is indeed possible to inflict needless pain on nonhuman animals, which would be immoral. [source] Ectoparasites: are they the proximate cause of cleaning interactions?JOURNAL OF FISH BIOLOGY, Issue 2003I. M. Côté We tested the importance of ectoparasites in cleaning symbioses by comparing the activity of Caribbean cleaning gobies (Elacatinus evelynae) and of their clients during three daily periods (early morning, midday and late afternoon) in which ectoparasite availability varied naturally. Emergence from the benthos of gnathiid isopod larvae, the main target of cleaning goby predation, was higher at night, when cleaners are inactive, than during the day. Overall ectoparasite loads also tended to be higher on clients in the morning. This coincided with higher rates of visits to cleaning stations by client fish in the morning than at midday, but high rates of client visits were also recorded in the late afternoon. Clients were more likely to adopt stereotypical incitation poses, which increase the likelihood of being cleaned, in the morning than later in the day. Inspection bouts by cleaning gobies were longest in the morning. Cleaner and client behaviours therefore change predictably in response to natural diurnal variation in ectoparasite availability. These results add to a growing number of studies supporting the idea that cleaning symbioses are mutualisms dependent on ectoparasite removal. [source] Philosophical Issues in Tort LawPHILOSOPHY COMPASS (ELECTRONIC), Issue 4 2008John Oberdiek The union of contemporary philosophy and tort law has never been better. Perhaps the most dynamic current in contemporary tort theory concerns the increasingly sophisticated inquires into the doctrinal elements of the law of torts, with the tort of negligence in particular garnering the most attention from theorists. In this article, I examine philosophically rich issues revolving around each of the elements constituting the tort of negligence: compensable injury, duty, breach, actual cause, and proximate cause. [source] The causes of porotic hyperostosis and cribra orbitalia: A reappraisal of the iron-deficiency-anemia hypothesisAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 2 2009Phillip L. Walker Abstract Porosities in the outer table of the cranial vault (porotic hyperostosis) and orbital roof (cribra orbitalia) are among the most frequent pathological lesions seen in ancient human skeletal collections. Since the 1950s, chronic iron-deficiency anemia has been widely accepted as the probable cause of both conditions. Based on this proposed etiology, bioarchaeologists use the prevalence of these conditions to infer living conditions conducive to dietary iron deficiency, iron malabsorption, and iron loss from both diarrheal disease and intestinal parasites in earlier human populations. This iron-deficiency-anemia hypothesis is inconsistent with recent hematological research that shows iron deficiency per se cannot sustain the massive red blood cell production that causes the marrow expansion responsible for these lesions. Several lines of evidence suggest that the accelerated loss and compensatory over-production of red blood cells seen in hemolytic and megaloblastic anemias is the most likely proximate cause of porotic hyperostosis. Although cranial vault and orbital roof porosities are sometimes conflated under the term porotic hyperostosis, paleopathological and clinical evidence suggests they often have different etiologies. Reconsidering the etiology of these skeletal conditions has important implications for current interpretations of malnutrition and infectious disease in earlier human populations. Am J Phys Anthropol 2009. © 2009 Wiley-Liss, Inc. [source] Diagnosis and Management of Spontaneous Cerebrospinal Fluid-Middle Ear Effusion and Otorrhea,THE LARYNGOSCOPE, Issue 5 2004N. E. Brown MD Objectives/Hypothesis: Spontaneous leak of cerebrospinal fluid (CSF) into the middle ear can occur in adults without a history of temporal bone trauma or fracture, meningitis, or any obvious cause. Therefore, clues may be lacking that would alert the otolaryngologist that fluid medial to an intact eardrum, or fluid emanating from an eardrum perforation, is likely to be CSF fluid. A review of relevant medical literature reveals that herniation of the arachnoid membrane through a tegmen defect may be congenital, or CSF leak may occur when dynamic factors (i.e., brain pulsations or increases in intracranial pressure) produce a rent in the arachnoid membrane. Because tegmen defects may be multiple rather than single, identifying only one defect may not be sufficient for achieving definitive repair. Data on nine cases of spontaneous CSF leak to the ear in adult patients from four medical centers are presented and analyzed to provide collective information about a disorder that can be difficult to diagnose and manage. Study Design: Retrospective review of nine cases of spontaneous CSF middle ear effusion/otorrhea. Results: The majority of patients presented with symptoms of aural fullness and middle ear effusion. Many developed suspicious clear otorrhea only after insertion of a tympanostomy tube. Two patients had multiple defects in the tegmen and dura, and five patients had meningoencephaloceles confirmed intraoperatively. Five patients underwent combined middle cranial fossa/transmastoid repair. Materials used in repair included temporalis fascia, free muscle graft, Oxycel cotton, calvarial bone, pericranium, bone wax, and fibrin glue. Conclusions: CSF middle ear effusion/otorrhea can develop in adults without a prior history of meningitis or head trauma or any apparent proximate cause. Although presenting symptoms can be subtle, early suspicion and confirmatory imaging aid in establishing the diagnosis. Because surgical repair by way of a mastoid approach alone can be inadequate if there are multiple tegmen defects, a middle fossa approach alone, or in combination with a transmastoid approach, should be considered in most cases. [source] Spatial and temporal variability in predation on rainforest primates: do forest fragmentation and predation act synergistically?ANIMAL CONSERVATION, Issue 3 2009M. T. Irwin Abstract Predation is a constant risk for most primates, impacting demography, population dynamics, activity patterns and social behaviour. Data are limited on both the rates of predation and its spatial and temporal variability. We present long-term observations of Cryptoprocta ferox predation on rainforest sifakas in Madagascar, Propithecus diadema at Tsinjoarivo (22 group years) and Propithecus edwardsi at Ranomafana (73 group years), derived from intensive observations based on ongoing behavioural studies. Average per capita offtake rates are relatively low (0.06,0.07), but temporal variability is high (kills are clumped in time). This is consistent with Cryptoprocta ecology; individual home ranges are much larger than sifaka ranges, and individuals may hunt in a subsection of their range until prey density is decreased, then move on. These results have broad implications. First, in terms of the evolution of anti-predator strategies, it now becomes important to ask: (1) whether average or peak predation rates determine the strength of selection and (2) whether antipredator strategies (e.g. vigilance, sleeping site selection) fluctuate interannually, reflecting recent experience. Second, in terms of population ecology, Cryptoprocta may have disproportionately large impacts on the (small) sifaka groups, even driving groups to extinction (as observed at both sites). Third, the disappearance of groups has important implications for conservation. When this happens in continuous forest (as at Ranomafana), home ranges will likely be re-filled over time, whereas in isolated forest fragments (as at Tsinjoarivo), recolonization is less likely. Thus, conservation planners should consider predation as a potentially important proximate cause of extirpation in fragmented landscapes, even when resource density and quality could otherwise sustain populations. Considering the effects of predation can be useful in (1) decisions regarding the allocation of limited conservation resources, including which landscapes to invest resources in and (2) investigating ways to increase resilience of prey species. [source] Sex, Rank and Age Differences in the Japanese Macaque (Macaca fuscata yakui) Participation in Inter-Group EncountersETHOLOGY, Issue 5 2005Bonaventura Majolo In many species interactions among group are often characterized by agonistic behaviour. Although animals may participate in inter-group encounters in different ways, depending on their energetic requirements, reproductive tactics, and/or developmental stage, the proximate causes affecting an animal's participation in inter-group encounters are still poorly understood. Indeed, many studies have analysed the behaviour of males and females during inter-group encounters without considering the importance of additional factors (e.g. rank). This study focuses on wild non-provisioned Japanese macaques (Macaca fuscata yakui) living on Yakushima Island, Japan. It aims to determine how monkeys of different sex, age, and rank behave during inter-group encounters and it discusses the implications and consequences of their behaviour on group composition and male dispersal. Males participated significantly more than females in inter-group encounters, by displaying more aggressive or affiliative behaviour. High-ranking and/or adult males were more aggressive than low-ranking and/or subadult males during encounters occurring in the mating season and they also showed more herding behaviour. This trend was not found in inter-group encounters occurring during the non-mating season. Finally, males which then emigrated to new groups were low-ranking and/or subadult individuals. Those males displayed more affiliative behaviour towards foreign males than males which did emigrate. These data indicate that in non-territorial species with male dominance over female and high competition for mating partners males play an active, and often aggressive, role during inter-group encounter while female participation is scarce. Factors such as age, rank and period of the year (in seasonally breeding species) have to be taken into considerations when analysing interactions between groups and their effects on group composition and social behaviour. [source] Temporal Variation in Cleanerfish and Client Behaviour: Does It Reflect Ectoparasite Availability?ETHOLOGY, Issue 6 2003Isabelle M. Côté We tested the importance of ectoparasites as the proximate cause of cleaning interactions by comparing the activity of Caribbean cleaning gobies (Elacatinus evelynae) and of their clients during three daily periods (early morning, midday, and late afternoon) in which ectoparasite availability varied naturally. Emergence from the benthos of gnathiid isopod larvae, the main target of cleaning goby predation, was higher at night, when cleaners were inactive, than during the day. As a result, overall ectoparasite loads on client fish tended to be higher in the morning. Inspection bouts by cleaning gobies were longest in the morning, but also at midday when ectoparasite availability on clients was lower. Client fish were observed at cleaning stations most often in the afternoon, when they harboured few ectoparasites, but they were more likely to adopt incitation poses, which increase the likelihood of being cleaned, in the morning than later in the day. Most cleaner and client behaviours therefore did not change predictably in response to natural diurnal variation in ectoparasite availability. Our study suggests that the ultimate and proximate causes of cleaning behaviour need not necessarily coincide. [source] Plasticity in vertical behaviour of migrating juvenile southern bluefin tuna (Thunnus maccoyii) in relation to oceanography of the south Indian OceanFISHERIES OCEANOGRAPHY, Issue 4 2009SOPHIE BESTLEY Abstract Electronic tagging provides unprecedented information on the habitat use and behaviour of highly migratory marine predators, but few analyses have developed quantitative links between animal behaviour and their oceanographic context. In this paper we use archival tag data from juvenile southern bluefin tuna (Thunnus maccoyii, SBT) to (i) develop a novel approach characterising the oceanographic habitats used throughout an annual migration cycle on the basis of water column structure (i.e., temperature-at-depth data from tags), and (ii) model how the vertical behaviour of SBT altered in relation to habitat type and other factors. Using this approach, we identified eight habitat types occupied by juvenile SBT between the southern margin of the subtropical gyre and the northern edge of the Subantarctic Front in the south Indian Ocean. Although a high degree of variability was evident both within and between fish, mixed-effect models identified consistent behavioural responses to habitat, lunar phase, migration status and diel period. Our results indicate SBT do not act to maintain preferred depth or temperature ranges, but rather show highly plastic behaviours in response to changes in their environment. This plasticity is discussed in terms of the potential proximate causes (physiological, ecological) and with reference to the challenges posed for habitat-based standardisation of fishery data used in stock assessments. [source] Trypanosoma brucei brucei induces alteration in the head proteome of the tsetse fly vector Glossina palpalis gambiensisINSECT MOLECULAR BIOLOGY, Issue 6 2007T. Lefèvre Abstract Parasitic manipulations of host behaviour are known from a wide range of host,parasite associations. However, the understanding of these phenomena is far from complete and detailed investigation of their proximate causes is needed. Many studies report behavioural modifications, such as altered feeding rates in tsetse fly (Glossina) infected with the mature transmissible stage (i.e. metacyclic) of the trypanosomes. Here, bidimensional (2D) gel electrophoresis and mass spectrometry were employed to analyse and compare the head proteome between four Glossina palpalis gambiensis categories (uninfected, refractory, mature infection, immature infection). Twenty-four protein spots specifically present or absent in the head of metacyclic-infected flies were observed. These protein spots were subsequently identified and functionally classified as glycolitic, neurotransmiter synthesis, signalling, molecular chaperone and transcriptional regulation proteins. Our results indicate altered energy metabolism in the head of metacyclic-infected tsetse flies. Some of the proteins identified, such as casein kinase 2 and jun kinase have previously been shown to play critical roles in apoptosis in insect neurones. In addition, we found two pyridoxal-dependent decarboxylases (dopa decarboxylase and alpha methyldopa hypersensitive protein), suggesting a modification of serotonin and/or dopamine in the brain of metacyclic-infected tsetse flies. Our data pave the way for future investigation of the alteration of the glossina central nervous system during infection by trypanosomes. [source] The determinants of queen size in a socially polymorphic antJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 9 2009J. MEUNIER Abstract In social animals, body size can be shaped by multiple factors, such as direct genetic effects, maternal effects, or the social environment. In ants, the body size of queens correlates with the social structure of the colony: colonies headed by a single queen (monogyne) generally produce larger queens that are able to found colonies independently, whereas colonies headed by multiple queens (polygyne) tend to produce smaller queens that stay in their natal colony or disperse with workers. We performed a cross-fostering experiment to investigate the proximate causes of queen size variation in the socially polymorphic ant Formica selysi. As expected if genetic or maternal effects influence queen size, eggs originating from monogyne colonies developed into larger queens than eggs collected from polygyne colonies, be they raised by monogyne or polygyne workers. In contrast, eggs sampled in monogyne colonies were smaller than eggs sampled in polygyne colonies. Hence, eggs from monogyne colonies are smaller but develop into larger queens than eggs from polygyne colonies, independently of the social structure of the workers caring for the brood. These results demonstrate that a genetic polymorphism or maternal effect transmitted to the eggs influences queen size, which probably affects the social structure of new colonies. [source] Natal dispersal of European hare in FranceJOURNAL OF ZOOLOGY, Issue 4 2007Y. Bray Abstract Dispersal is a fundamental process with wide-ranging evolutionary and management consequences. To date, natal dispersal has never been described for the polygynous-promiscuous European hare Lepus europaeus. Using telemetry, we investigated the natal dispersal pattern in two zones that differed in hunting pressure and hare density. We quantified both the natal dispersal rates and distances using 84 juvenile hares. We tested for the influence of several factors (age, sex, density and period of the year) on these two variables. Overall, the mean dispersal rate was 43% and the median natal dispersal distances were 209 m for philopatric hares and 1615 m for dispersers. The maximum distance moved was 17.35 km. Natal dispersal rates were higher in the hunting zone with less density for both males and females, but males dispersed more frequently than females in the two zones although females moved over longer distances. Natal dispersal occurred preferentially between 4 and 6 months of age. This very fine description of the natal dispersal pattern allowed us to make inferences about both the evolutionary and proximate causes of natal dispersal. We also advocate that more attention should be paid to dispersal in studies on hare dynamics and on the conception of hare management, because dispersal seems to be more common than previously thought. [source] Calling in wild silvery gibbons (Hylobates moloch) in Java (Indonesia): behavior, phylogeny, and conservationAMERICAN JOURNAL OF PRIMATOLOGY, Issue 1 2006Thomas Geissmann Abstract Hardly any behavioral data are available for the silvery gibbon (Hylobates moloch), an endangered primate that is endemic to the island of Java, Indonesia. We studied the singing behavior of the easternmost population of this species in the Dieng mountains, central Java, in 1998,1999. We aimed to document the timing of singing, quantify the amount of singing by the respective sexes, and explore the role of bioacoustics in density estimation. A total of 122 song bouts in at least 12 groups were monitored. No duet songs were heard. Most of the song bouts (91.5%) were female solo song bouts or female scream bouts. In contrast to an earlier study on the westernmost population of silvery gibbons, during which few if any male songs were heard, at least 8.5% of the song bouts in our study were male solo song bouts. They were significantly longer in duration than the female songs. All male song bouts uttered before dawn (0520 hr) were produced in a chorus fashion, with at least three individuals participating. Choruses occurred about once every 8.5 days, and lasted longer and occurred earlier than female solo song bouts. Most male songs (60%) started between 0355,0440 hr, when it was still dark. All female songs, in contrast, started after 0500 hr, and female singing activity peaked around 0600. Regular male singing, male chorusing, and regular predawn singing have not previously been reported for silvery gibbons. Similarly separated periods of male and female solo songs and the absence of duetting have been observed in Kloss's gibbons (H. klossii) on the Mentawai Islands, and may represent synapomorphies shared by both species. The pronounced individual-specific song characteristics of silvery gibbons allow accurate mapping of groups. The density of gibbons at our study site was established to be 1.9,3.7 groups/km2, corresponding to 6.7,13.1 individuals/km2. We reassess the suitability of gibbon songs as a means of estimating the density and size of gibbon populations, and discuss the proximate causes for the absence of duetting in silvery gibbons. Am. J. Primatol. 68:1,19, 2006. © 2006 Wiley-Liss, Inc. [source] Geographic variation in offspring size of a widespread lizard (Takydromus septentrionalis): importance of maternal investmentBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2010WEI-GUO DU Geographic variation in offspring size is widespread, but the proximate causes of this variation have not yet been explicitly determined. We compared egg size and egg contents among five populations of a lizard (Takydromus septentrionalis, Günther, 1864) along a latitudinal gradient, and incubated eggs at two temperatures to determine the influence of maternal investment and incubation temperature on offspring size. The mean values for female size and egg size were both greater in the two northern populations (Chuzhou and Anji) than in the three southern populations (Lishui, Dongtou, and Ningde). The larger eggs were entirely attributable to the body size of females in the Anji population, but their increased size also stemmed from further enlargement of egg size relative to female body size in Chuzhou, the northernmost population sampled in this study. Eggs of the Chuzhou population contained more yolk and less water than those of southern populations. Despite the lower lipid content in the yolk, eggs from the Chuzhou population had higher energy contents than those from the two southern populations, owing to the larger egg size and increased volume of yolk. Hatchling size was not affected by incubation temperature, but differed significantly among populations, with hatchlings being larger in the Chuzhou population than in the other populations. Our data provide an inference that oviparous reptiles from cold climates may produce larger offspring, not only by increasing egg size but also by investing more energy into their eggs. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101, 59,67. [source] Thermal effects on reptile reproduction: adaptation and phenotypic plasticity in a montane lizardBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 3 2010RORY S. TELEMECO Interspecific comparisons suggest a strong association between cool climates and viviparity in reptiles. However, intraspecific comparisons, which provide an opportunity to identify causal pathways and to distinguish facultative (phenotypically plastic) effects from canalized (genetically fixed) responses, are lacking. We documented the reproductive traits in an alpine oviparous lizard, and manipulated thermal regimes of gravid females and their eggs to identify proximate causes of life-history variation. Embryonic development at oviposition was more advanced in eggs laid by females from high-elevation populations than in eggs produced by females from lower elevations. In the laboratory, experimentally imposed low maternal body temperatures delayed oviposition and resulted in more advanced embryonic development at oviposition. Warm conditions both in utero and in the nest increased hatching success and offspring body size. Our intraspecific comparisons support the hypothesis that viviparity has evolved in cold-climate squamates because of the direct fitness advantages that warm temperatures provide developing offspring. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 642,655. [source] A test of Rensch's rule in varanid lizardsBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 2 2010PETRA FRÝDLOVÁ In a model group of giant reptiles, we explored the allometric relationships between male and female body size and compared the effects of sexual and fecundity selection, as well as some proximate causes, on macroevolutionary patterns of sexual size dimorphism (SSD). Monitor lizards are a morphologically homogeneous group that has been affected by extreme changes in body size during their evolutionary history, resulting in 14-fold differences among the body sizes of recent species. Here, we analysed data concerning the maximum and/or mean male and female snout,vent lengths in 42 species of monitor lizard from literary sources and supplemented these data with measurements made in zoos. There was a wide scale of SSD from nearly monomorphic species belonging mostly to the subgenus Odatria and Prasinus group of the Euprepriosaurus to apparently male-larger taxa. The variable best explaining SSD was the body size itself; the larger the species, the higher the SSD. This pattern agrees with the currently discussed Rensch's rule, claiming that the relationship between male and female body size is hyperallometric, i.e. the allometric exponent of this relationship exceeds unity and thus SSD increases with body size in the case of male-larger taxa. All our estimates of the reduced major axis regression slopes of this relationship ranged from 1.132 to 1.155. These estimates are significantly higher than unity, and thus unequivocally corroborate the validity of Rensch's rule in this reptilian group. In spite of our expectation that the variation in SSD can be alternatively explained by variables reflecting the strength of sexual selection (presence of male combat), fecundity selection (e.g. clutch size and mass) and/or proximate ecological factors (habitat type), none of these variables had consistent effects on SSD, especially when the data were adjusted to phylogenetic dependence and/or body size. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 293,306. [source] The evolution of human fatness and susceptibility to obesity: an ethological approachBIOLOGICAL REVIEWS, Issue 2 2006Jonathan C. K. Wells ABSTRACT Human susceptibility to obesity is an unusual phenomenon amongst animals. An evolutionary analysis, identifying factors favouring the capacity for fat deposition, may aid in the development of preventive public health strategies. This article considers the proximate causes, ontogeny, fitness value and evolutionary history of human fat deposition. Proximate causes include diet composition, physical activity level, feeding behaviour, endocrine and genetic factors, psychological traits, and exposure to broader environmental factors. Fat deposition peaks during late gestation and early infancy, and again during adolescence in females. As in other species, human fat stores not only buffer malnutrition, but also regulate reproduction and immune function, and are subject to sexual selection. Nevertheless, our characteristic ontogenetic pattern of fat deposition, along with relatively high fatness in adulthood, contrasts with the phenotype of other mammals occupying the tropical savannah environment in which hominids evolved. The increased value of energy stores in our species can be attributed to factors increasing either uncertainty in energy availability, or vulnerability to that uncertainty. Early hominid evolution was characterised by adaptation to a more seasonal environment, when selection would have favoured general thriftiness. The evolution of the large expensive brain in the genus Homo then favoured increased energy stores in the reproducing female, and in the offspring in early life. More recently, the introduction of agriculture has had three significant effects: exposure to regular famine; adaptation to a variety of local niches favouring population-specific adaptations; and the development of social hierarchies which predispose to differential exposure to environmental pressures. Thus, humans have persistently encountered greater energy stress than that experienced by their closest living relatives during recent evolution. The capacity to accumulate fat has therefore been a major adaptive feature of our species, but is now increasingly maladaptive in the modern environment where fluctuations in energy supply have been minimised, and productivity is dependent on mechanisation rather than physical effort. Alterations to the obesogenic environment are predicted to play a key role in reducing the prevalence of obesity. [source] | |||||||||||||||||||||||||||||||