A skeletochronological study on a subtropical, riparian ranid (Rana swinhoana) from different elevations in Taiwan

We estimated the age, longevity, and growth patterns of a subtropical ranid, Rana swinhoana from high (Lishing) and low (Wulai) elevations using skeletochronology. In addition, we also measured body mass and length of frogs from five other localities. Results showed that both snout-vent length and body mass of frogs were significantly correlated with altitudes for both sexes. Frogs of Lishing were significantly larger and older than that of Wulai. We used LAGs to estimate the age and growth of frogs and found that the growth of Wulai frog of both sexes slowed down at an earlier age than that of Lishing frogs. Male and female frogs from Wulai did not exceed 6 and 7 years, respectively, while the maximum age of males and females of Lishing was 7 and 11 years, respectively. Results suggest that the LAGs observed in R. swinhoana correspond to low temperature and/or decreased food availability instead of desiccation during the harsh annual period (November to February). Skeletochronological data suggest that the variations of body size of R. swinhoana among elevations are likely associated with the growth, age at sexual maturity, and longevity.     

Validation and Application of Skeletochronology for Age Determination of the Ryukyu Ground Gecko,Goniurosaurus kuroiwae （Squamata： Eublepharidae）

Skeletochronology is a method commonly used for estimating the age of amphibians and reptiles in the wild. However, the number of lines of arrested growth （LAGs） does not necessarily reflect age in some species. We validated the applicability of this method to an endangered eublepharid gecko, Goniurosaurus kuroiwae, then inferred its longevity and age structures in wild populations. We classified young geckos into three groups using previously published data for early growth： Group 1 contained hatchlings before the first winter, Group 2 contained hatchlings after the first win- ter, and Group 3 included yearlings after the second winter. LAG numbers in these groups were then compared. All individuals in Group 1 possessed a single LAG, which was considered as a hatching line. Most individuals in Groups 2 and 3 possessed one and two additional LAGs, respectively （LAG1 and LAG2）, corroborating the notion that LAGs are formed annually. A few geckos exhibited fewer LAGs than expected. Analysis of variations in LAG and marrow cavity diameter demonstrated that in animals with fewer LAGs, endosteal resorption or fusion of hatching line and LAG1 had occurred. LAG2 was never lost by endosteal resorption and was identifiable by its diameter. Thus, the age of adult geckos could be determined by counting LAGs outward from LAG2. Application of this method to wild populations re- vealed that the longevity of this species is not less than 83 months, but that almost all individuals in fragmented habitats die before 50 months, suggesting lower population sustainability in such habitats.     

Determination of age, longevity and age at reproduction of the frogMicrohyla ornata by skeletochronology

Skeletochronological estimation of age, longevity, age at sexual maturity and breeding of Microhyla ornata was done. Frogs (n=62) were collected locally in August (rainy season) 1997 and brought to the laboratory. Body mass and snout-vent-length (SVL) of each frog was recorded; the 4th toe of both the hind limbs was clipped under anaesthesia, fixed in 10% formalin, demineralized in 5% nitric acid and processed for histology. Limb bones (femur, humerus, tibiofibula and radioulna) of 6 large sized frogs were also processed for skeletochronology in order to study the rate of resorption. Gonads of 25 frogs (belonging to different body size ranges) were processed for histology in order to ascertain the gametogenic status of individual frogs. One to four growth rings consisting of growth zones and lines of arrested growth (LAGs) were noticed in frogs of different body sizes; the number of LAGs remained identical in all the limb bones and phalanges in 5 out of 6 frogs. Back calculation indicated that the resorption rate is very low in this frog. Male frogs possessed sperm bundles in seminiferous tubules in the 1st year, while females showed yolky follicles in the ovary in the 2nd year. Frogs found in amplexus were 3 5 years old. The results suggest that this frog may live for a maximum of 5 years in the natural population.     

Wide‐scale comparative analysis of longevity genes and interventions

Hundreds of genes, when manipulated, affect the lifespan of model organisms (yeast, worm, fruit fly, and mouse) and thus can be defined as longevity‐associated genes (LAGs). A major challenge is to determine whether these LAGs are model‐specific or may play a universal role as longevity regulators across diverse taxa. A wide‐scale comparative analysis of the 1805 known LAGs across 205 species revealed that (i) LAG orthologs are substantially overrepresented, from bacteria to mammals, compared to the entire genomes or interactomes, and this was especially noted for essential LAGs; (ii) the effects on lifespan, when manipulating orthologous LAGs in different model organisms, were mostly concordant, despite a high evolutionary distance between them; (iii) LAGs that have orthologs across a high number of phyla were enriched in translational processes, energy metabolism, and DNA repair genes; (iv) LAGs that have no orthologs out of the taxa in which they were discovered were enriched in autophagy (Ascomycota/Fungi), G proteins (Nematodes), and neuroactive ligand–receptor interactions (Chordata). The results also suggest that antagonistic pleiotropy might be a conserved principle of aging and highlight the importance of overexpression studies in the search for longevity regulators.     

RGS9-2 is a negative modulator of mu-opioid receptor function

Regulators of G-protein signaling (RGS) 9-2 is a striatal enriched protein that controls G protein coupled receptor signaling duration by accelerating Galpha subunit guanosine triphosphate hydrolysis. We have previously demonstrated that mice lacking the RGS9 gene show enhanced morphine analgesia and delayed development of tolerance. Here we extend these studies to understand the mechanism via which RGS9-2 modulates opiate actions. Our data suggest that RGS9-2 prevents several events triggered by mu-opioid receptor (MOR) activation. In transiently transfected PC12 cells, RGS9-2 delays agonist induced internalization of epitope HA-tagged mu-opioid receptor. This action of RGS9-2 requires localization of the protein near the cell membrane. Co-immunoprecipitation studies reveal that RGS9-2 interacts with HA-tagged mu-opioid receptor, and that this interaction is enhanced by morphine treatment. In addition, morphine promotes the association of RGS9-2 with another essential component of MOR desensitization, beta-arrestin-2. We also show that over-expression of RGS9-2 prevents opiate-induced extracellular signal-regulated kinase phosphorylation. Our data indicate that RGS9-2 plays an essential role in opiate actions, by negatively modulating MOR downstream signaling as well as the rate of MOR endocytosis.     

Biology of the amphioxus,Branchiostoma belcheri in the Ariake Sea,Japan I. Population structure and growth

We investigated the population structure and growth of the amphioxus Branchiostoma belcheri for four years in the southern Ariake Sea, Japan. We counted 62-66 myotomes and 251-310 dorsal fin-ray chambers, and these results support that this species is an intermediate form of B. belcheri and its subspecies B. belcheri tsingtauense. The ratio of females to males was 1:1.12. Males were more numerous than females among small individuals (< 40 mm body length), but we found no significant differences among large animals (50 mm body length). Spawning occurred from mid June to early July. Groups of newly settled young appeared from January to June of their second year. We observed a large fluctuation between years in the numbers of newly settled young. The estimated size of one-year-old individuals was 19.4 mm in body length; within the next 12 months, they reached 32.1 mm. Three- and four-year-old individuals measured 38.6 mm and 45.8 mm, respectively. Few grew beyond 60 mm; the largest specimen collected was a 64 mm male.     

Growth and Abundance of Pacific Sand Lance, Ammodytes hexapterus, under differing Oceanographic Regimes

Dramatic changes in seabird and marine mammal stocks in the Gulf of Alaska have been linked to shifts in abundance and composition of forage fish stocks over the past 20 years. The relative value (e.g., size and condition of individual fish, abundance) of specific forage fish stocks to predators under temporally changing oceanographic regimes is also expected to vary. We inferred potential temporal responses in abundance, growth, and age structure of a key forage fish, sand lance, by studying across spatially different oceanographic regimes. Marked meso-scale differences in abundance, growth, and mortality existed in conjunction with these differing regimes. Growth rate within stocks (between years) was positively correlated with temperature. However, this relationship did not exist among stocks (locations) and differing growth rates were better correlated to marine productivity. Sand lance were least abundant and grew slowest at the warmest site (Chisik Island), an area of limited habitat and low food abundance. Abundance and growth of juvenile sand lance was highest at the coolest site (Barren Islands), an area of highly productive upwelled waters. Sand lance at two sites located oceanographically between the Barren Islands and Chisik Island (inner- and outer-Kachemak Bay) displayed correspondingly intermediate abundance and growth. Resident predators at these sites are presented with markedly different numbers and quality of this key prey species. Our results suggest that at the decadal scale, Gulf of Alaska forage fish such as sand lance are probably more profoundly affected by changes in abundance and quality of their planktonic food, than by temperature alone.     

The evolutionary dynamics of the lion Panthera leo revealed by host and viral population genomics

The lion Panthera leo is one of the world's most charismatic carnivores and is one of Africa's key predators. Here, we used a large dataset from 357 lions comprehending 1.13 megabases of sequence data and genotypes from 22 microsatellite loci to characterize its recent evolutionary history. Patterns of molecular genetic variation in multiple maternal (mtDNA), paternal (Y-chromosome), and biparental nuclear (nDNA) genetic markers were compared with patterns of sequence and subtype variation of the lion feline immunodeficiency virus (FIV(Ple)), a lentivirus analogous to human immunodeficiency virus (HIV). In spite of the ability of lions to disperse long distances, patterns of lion genetic diversity suggest substantial population subdivision (mtDNA Phi(ST) = 0.92; nDNA F(ST) = 0.18), and reduced gene flow, which, along with large differences in sero-prevalence of six distinct FIV(Ple) subtypes among lion populations, refute the hypothesis that African lions consist of a single panmictic population. Our results suggest that extant lion populations derive from several Pleistocene refugia in East and Southern Africa ( approximately 324,000-169,000 years ago), which expanded during the Late Pleistocene ( approximately 100,000 years ago) into Central and North Africa and into Asia. During the Pleistocene/Holocene transition ( approximately 14,000-7,000 years), another expansion occurred from southern refugia northwards towards East Africa, causing population interbreeding. In particular, lion and FIV(Ple) variation affirms that the large, well-studied lion population occupying the greater Serengeti Ecosystem is derived from three distinct populations that admixed recently.     

Interactions Between Competition and Predation Shape Early Growth and Survival of Two Neotropical Hylid Tadpoles

Experimental studies in temperate regions have revealed that competition and predation interact to shape aquatic communities. Predators typically reduce the effect of competition on growth and competitors provide alternative prey subjects, which may also alter predation. Here, we examine the independent and combined effects of competition and predation on the survival and growth of hatchling tadpoles of two widespread co‐occurring Neotropical hylid frogs (Agalychnis callidryas and Dendropsophus ebraccatus). Using 400 L mesocosms, we used a 2 × 3 factorial substitutive design, which crossed tadpole species composition with the presence or absence of a free‐roaming predator (Anax amazili dragonfly larva). Dragonflies were effective predators of both species, but had larger effects on A. callidryas survival. Both species had similar growth rates when alone, whereas A. callidryas grew 30 percent faster than D. ebraccatus when they co‐occurred, suggesting interspecific rather than intraspecific competition had relatively stronger effects on D. ebraccatus growth, while the opposite was true for A. callidryas. Predator presence dramatically reduced growth rates of both species and erased this asymmetry. Results suggest that the effects of predator induction (i.e., nonconsumptive effects) on growth were larger than both consumptive and competitive effects. Our study demonstrates that predators have strong effects on both survival and growth of prey, highlighting the potential importance of predators in shaping prey populations and tropical aquatic food web interactions. Abstract in Spanish is available at http://www.blackwell‐synergy.com/loi/btp .     

A skeletochronological study of age, growth and longevity in a population of the frog Rana ridibunda from southern Europe

Age at sexual maturity and longevity in a population of Rana ridibunda from north-eastern Greece were studied by skeletochronology performed on the phalanges. Analysis of the age structure was based on counting the lines of arrested growth (LAGs). Sexual maturity for both sexes arises during the first year or after the first hibernation. Ages ranged from 1 to 5 years (mean=2.96) among 52 males and from 1 to 5 years (mean=3.73) among 56 females. The mean snout-vent length was 69.03+/-12.6mm in males and 82.38+/-13.27 mm in females. The difference between the sexes in age and size was significant. Growth of individuals was fitted on? The von Bertalanffy model. The growth coefficient (K) was 0.57 in males and 0.54 in females, mainly due to faster male growth between metamorphosis and maturation.     

Patterns of natural selection on size at metamorphosis in water frogs

Strategies for optimal metamorphosis are key adaptations in organisms with complex life cycles, and the components of the larval growth environment causing variation in this trait are well studied empirically and theoretically. However, when relating these findings to a broader evolutionary or ecological context, usually the following assumptions are made: (1) size at metamorphosis positively relates to future fitness, and (2) the larval growth environment affects fitness mainly through its effect on timing of and size at metamorphosis. These assumptions remain poorly tested, because data on postmetamorphic fitness components are still rare. We created variation in timing of and size at metamorphosis by manipulating larval competition, nonlethal presence of predators, pond drying, and onset of larval development, and measured the consequences for subsequent terrestrial survival and growth in 1564 individually marked water frogs (Rana lessonae and R. esculenta), raised in enclosures in their natural environment. Individuals metamorphosing at a large size had an increased chance of survival during the following terrestrial stage (mean linear selection gradient: 0.09), grew faster and were larger at maturity than individuals metamorphosing at smaller sizes. Late metamorphosing individuals had a lower survival rate (mean linear selection gradient: -0.03) and grew more slowly than early metamorphosing ones. We found these patterns to be consistent over the three years of the study and the two species, and the results did not depend on the nature of the larval growth manipulation. Furthermore, individuals did not compensate for a small size at metamorphosis by enhancing their postmetamorphic growth. Thus, we found simple relationships between larval growth and postmetamorphic fitness components, and support for this frequently made assumption. Our results suggest postmetamorphic selection for fast larval growth and provide a quantitative estimate for the water frog example.     

Socioeconomic variation in estimated growth velocity of schoolchildren from a rural, subsistence agricultural community in southern Mexico

Socioeconomic variation in estimated growth velocities (annual growth increments) of several anthropometric dimensions was considered in schoolchildren from a rural, subsistence agricultural community in the Valley of Oaxaca in southern Mexico. The children (114 males, 99 females), 6-13 years of age, were measured twice, approximately one year apart. Annual growth increments were computed by subtracting measurements taken in the fall of 1978 from those taken in the fall of 1979. Information on household land holdings and appliances and parental occupation was used to compute an index of socioeconomic status (SES). Analysis of annual increments among upper SES (65 males, 45 females) and lower (49 males, 54 females) children indicated negligible differences. The results suggest that growth deficits evident in the children at school age occurred in infancy and early childhood so that there was little, if any, SES variation in growth rate at the school ages.     

Allometric growth in juvenile marine turtles: possible role as an antipredator adaptation

Female marine turtles produce hundreds of offspring during their lifetime but few survive because small turtles have limited defenses and are vulnerable to many predators. Little is known about how small turtles improve their survival probabilities with growth though it is assumed that they do. We reared green turtles (Chelonia mydas) and loggerheads (Caretta caretta) from hatchlings to 13 weeks of age and documented that they grew wider faster than they grew longer. This pattern of allometric growth might enable small turtles to more quickly achieve protection from gape-limited predators, such as the dolphinfish (Coryphaena hippurus). As a test of that hypothesis, we measured how dolphinfish gape increased with length, reviewed the literature to determine how dolphinfish populations were size/age structured in nearby waters, and then determined the probability that a small turtle would encounter a fish large enough to consume it if it grew by allometry vs. by isometry (in which case it retained its hatchling proportions). Allometric growth more quickly reduced the probability of a lethal encounter than did isometric growth. On that basis, we suggest that allometry during early ontogeny may have evolved because it provides a survival benefit for small turtles.     

Branching in Amyloid Fibril Growth

Using the peptide hormone glucagon and Aβ(1-40) as model systems, we have sought to elucidate the mechanisms by which fibrils grow and multiply. We here present real-time observations of growing fibrils at a single-fibril level. Growing from preformed seeds, glucagon fibrils were able to generate new fibril ends by continuously branching into new fibrils. To our knowledge, this is the first time amyloid fibril branching has been observed in real-time. Glucagon fibrils formed by branching always grew in the forward direction of the parent fibril with a preferred angle of 35-40°. Furthermore, branching never occurred at the tip of the parent fibril. In contrast, in a previous study by some of us, Aβ(1-40) fibrils grew exclusively by elongation of preformed seeds. Fibrillation kinetics in bulk solution were characterized by light scattering. A growth process with branching, or other processes that generate new ends from existing fibrils, should theoretically give rise to different fibrillation kinetics than growth without such a process. We show that the effect of adding seeds should be particularly different in the two cases. Our light-scattering data on glucagon and Aβ(1-40) confirm this theoretical prediction, demonstrating the central role of fibril-dependent nucleation in amyloid fibril growth     

BUOYANCY CONTROL IN AMMONOIDS

A specimen of Buchiceras bilobatum is shown to have been able to maintain neutral buoyancy in water despite the ever increasing weight of epifaunal oysters which it carried on its shell. It is deduced that before settlement of the oyster spat, the camerae of the ammonite contained several grammes of water and that this was slowly pumped out as the oysters grew. Revised calculations on the densities of other ammonoids suggest that the presence of large quantities of liquid in cephalopod camerae was a common occurrence. The significance of this liquid in the growth, mode of life, and evolution of ammonoids is discussed.     

Validation of back‐calculated body lengths and timing of growth mark deposition in Hawaiian green sea turtles

Somatic growth rate data for wild sea turtles can provide insight into life‐stage durations, time to maturation, and total lifespan. When appropriately validated, the technique of skeletochronology allows prior growth rates of sea turtles to be calculated with considerably less time and labor than required by mark‐–recapture studies. We applied skeletochronology to 10 dead, stranded green turtles Chelonia mydas that had previously been measured, tagged, and injected with OTC (oxytetracycline) during mark–recapture studies in Hawaii for validating skeletochronological analysis. We tested the validity of back‐calculating carapace lengths (CLs) from diameters of LAGs (lines of arrested growth), which mark the outer boundaries of individual skeletal growth increments. This validation was achieved by comparing CLs estimated from measurements of the LAG proposed to have been deposited closest to the time of tagging to actual CLs measured at the time of tagging. Measureable OTC‐mark diameters in five turtles also allowed us to investigate the time of year when LAGs are deposited. We found no significant difference between CLs measured at tagging and those estimated through skeletochronology, which supports calculation of somatic growth rates by taking the difference between CLs estimated from successive LAG diameters in humerus bones for this species. Back‐calculated CLs associated with the OTC mark and growth mark deposited closest to tagging indicated that annual LAGs are deposited in the spring. The results of this validation study increase confidence in utilization of skeletochronology to rapidly obtain accurate age and growth data for green turtles.     

Expression of acidic fibroblast growth factor cDNA confers growth advantage and tumorigenesis to Swiss 3T3 cells.

Acidic fibroblast growth factor (aFGF), a polypeptide with a mol. wt of approximately 16,000, is a potent mitogen for a variety of cells and shares 55% amino acid sequence identity with basic FGF. The recent isolation of three new oncogenes which share 35-45% amino acid sequence similarity with the FGFs suggests that the coding sequences for the FGFs themselves may be oncogenic under certain circumstances. To test this hypothesis, we cotransfected 3T3 NR6 cells with factors expressing the aFGF coding sequence and the bacterial neomycin gene. The aFGF produced by cotransfected cells was found only in the cellular homogenate and not in medium conditioned by the cells. Cells expressing aFGF grew to 10 times the density of control cells at saturation and were multilayered and disorganized, similar to transformed cells. The cotransfected cells do not grow in soft agar, but show enhanced soft agar growth relative to controls in the presence of added aFGF and heparin. The aFGF-producing cells formed small, non-progressive tumors when injected subcutaneously into nude mice. Our data suggest that expression of aFGF in NR6 cells results in enhanced growth, and that several traits characteristic of the transformed phenotype are partially expressed.     

Selection on increased intrinsic growth rates in coho salmon, Oncorhynchus kisutch

Substantial evidence from the animal kingdom shows that there is a trade-off between benefits and costs associated with rapid somatic growth. One would therefore expect growth rates under natural conditions to be close to an evolutionary optimum. Nevertheless, natural selection in many salmonid species appears to be toward larger size and earlier emergence from spawning redds, indicating a potential for increased growth rate to evolve. We tested how selection for genetic variants (growth hormone transgenic coho salmon, Oncorhynchus kisutch, with more than doubled daily growth rate potential relative to wild genotypes) depended on predator timing and food abundance during the early period of life (fry stage). In artificial redds, fry of the fast-growing genotypes showed a highly significant developmental shift, emerging from gravel nests approximately two weeks sooner, but with an 18.6% reduced survival, relative to wild-genotype fry. In seminatural streams, fry of the fast-growing genotypes suffered higher predation than those of wild genotypes when predators were present at the time of fry emergence, but this difference was less pronounced when food was scarce. In streams where predators were introduced after emergence, fry survived equally well regardless of food availability. Surviving fry grew faster in habitats provided with more food, and fast-growing genotypes also grew faster than wild genotypes when predators arrived late and food was abundant. Fewer fish migrated downstream past a waterfall when food availability was high and in the presence of predators, and wild-genotype fry were more likely to migrate than fry of the fast-growing genotypes. After being returned to the experimental streams after migration, fast-growing genotypes survived equally well as those of the same genotypes that did not migrate, whereas migrating wild genotypes experienced higher mortality relative to those of the same genotypes that did not migrate. Comparisons of growth rates between siblings retained under hatchery conditions and those from habitats with the fastest growth in the experimental stream revealed that growth rates were similar for wild genotypes in both environments, whereas the fast-growing genotypes in the streams only realized 90% of their growth potential. The present study has shown that a major shift in developmental timing can alter critical early stages affecting survival and can have a significant effect on fitness. Furthermore, ecological conditions such as food abundance and predation pressure can strongly influence the potential for fast-growing variants to survive under natural conditions. The large-scale removal of many predatory species around the world may augment the evolution of increased intrinsic growth rates in some taxa.