Individual Variation in Male Size and Behavioral Repertoire in the Sailfin Molly Poecilia latipinna

Variation among individuals in the expression of behaviors and associations of behaviors in different contexts can lead to the maintenance of behavioral polymorphisms. Individual variation in morphology is often associated with behavioral polymorphism, yet the degree to which morphology predicts behavioral phenotype is not well understood. We measured individual variation in size and behaviors in the sailfin molly, Poecilia latipinna, by comparing the behavior of individual males of different sizes across four different contexts (mating, exploratory tendency, sociability, and predator inspection). We also investigated the degree to which male size, a fixed genetic trait, influenced the expression of each behavior and associations between behaviors. We found that male mollies show strong associations between certain behaviors and only some of these are predicted by male size. For example, size has a strong influence on the courtship‐boldness axis with larger males showing higher rates of courtship displays and being bolder in predator inspection. A positive association was found between exploratory tendency, sociability, and gonopodial thrusting rates, yet the expression of these behaviors was independent of male size. Thus, sailfin mollies, like many fish species, show associations of behaviors that contribute to differences among males in personality type. The fixed genetic effect of male size at maturity influences courtship and boldness, but individual variation in exploratory tendency, sociability, and sneak copulation attempts through gonopodial thrusts is independent of male size. Such variation among males in behavioral associations within and between different contexts may slow the rate at which populations of P. latipinna can diverge in individual behaviors.     

Size Matters: Ryanodine Receptor Cluster Size Heterogeneity Potentiates Calcium Waves

Ryanodine receptors (RyRs) mediate calcium (Ca)-induced Ca release and intracellular Ca homeostasis. In a cardiac myocyte, RyRs group into clusters of variable size from a few to several hundred RyRs, creating a spatially nonuniform intracellular distribution. It is unclear how heterogeneity of RyR cluster size alters spontaneous sarcoplasmic reticulum (SR) Ca releases (Ca sparks) and arrhythmogenic Ca waves. Here, we tested the impact of heterogeneous RyR cluster size on the initiation of Ca waves. Experimentally, we measured RyR cluster sizes at Ca spark sites in rat ventricular myocytes and further tested functional impacts using a physiologically detailed computational model with spatial and stochastic intracellular Ca dynamics. We found that the spark frequency and amplitude increase nonlinearly with the size of RyR clusters. Larger RyR clusters have lower SR Ca release threshold for local Ca spark initiation and exhibit steeper SR Ca release versus SR Ca load relationship. However, larger RyR clusters tend to lower SR Ca load because of the higher Ca leak rate. Conversely, smaller clusters have a higher threshold and a lower leak, which tends to increase SR Ca load. At the myocyte level, homogeneously large or small RyR clusters limit Ca waves (because of low load for large clusters but low excitability for small clusters). Mixtures of large and small RyR clusters potentiates Ca waves because the enhanced SR Ca load driven by smaller clusters enables Ca wave initiation and propagation from larger RyR clusters. Our study suggests that a spatially heterogeneous distribution of RyR cluster size under pathological conditions may potentiate Ca waves and thus afterdepolarizations and triggered arrhythmias.     

Adaptive Dynamics of Regulatory Networks: Size Matters

To accomplish adaptability, all living organisms are constructed of regulatory networks on different levels which are capable to differentially respond to a variety of environmental inputs. Structure of regulatory networks determines their phenotypical plasticity, that is, the degree of detail and appropriateness of regulatory replies to environmental or developmental challenges. This regulatory network structure is encoded within the genotype. Our conceptual simulation study investigates how network structure constrains the evolution of networks and their adaptive abilities. The focus is on the structural parameter network size. We show that small regulatory networks adapt fast, but not as good as larger networks in the longer perspective. Selection leads to an optimal network size dependent on heterogeneity of the environment and time pressure of adaptation. Optimal mutation rates are higher for smaller networks. We put special emphasis on discussing our simulation results on the background of functional observations from experimental and evolutionary biology.     

A Quantitative Analysis of Growth and Size Regulation in Manduca sexta: The Physiological Basis of Variation in Size and Age at Metamorphosis

Body size and development time are important life history traits because they are often highly correlated with fitness. Although the developmental mechanisms that control growth have been well studied, the mechanisms that control how a species-characteristic body size is achieved remain poorly understood. In insects adult body size is determined by the number of larval molts, the size increment at each molt, and the mechanism that determines during which instar larval growth will stop. Adult insects do not grow, so the size at which a larva stops growing determines adult body size. Here we develop a quantitative understanding of the kinetics of growth throughout larval life of Manduca sexta, under different conditions of nutrition and temperature, and for genetic strains with different adult body sizes. We show that the generally accepted view that the size increment at each molt is constant (Dyar’s Rule) is systematically violated: there is actually a progressive increase in the size increment from instar to instar that is independent of temperature. In addition, the mass-specific growth rate declines throughout the growth phase in a temperature-dependent manner. We show that growth within an instar follows a truncated Gompertz trajectory. The critical weight, which determines when in an instar a molt will occur, and the threshold size, which determines which instar is the last, are different in genetic strains with different adult body sizes. Under nutrient and temperature stress Manduca has a variable number of larval instars and we show that this is due to the fact that more molts at smaller increments are taken before threshold size is reached. We test whether the new insight into the kinetics of growth and size determination are sufficient to explain body size and development time through a mathematical model that incorporates our quantitative findings.     

Size Matters: Use of YACs,BACs and PACs in Transgenic Animals

In 1993, several groups, working independently, reported the successful generation of transgenic mice with yeast artificial chromosomes (YACs) using standard techniques. The transfer of these large fragments of cloned genomic DNA correlated with optimal expression levels of the transgenes, irrespective of their location in the host genome. Thereafter, other groups confirmed the advantages of YAC transgenesis and position-independent and copy number-dependent transgene expression were demonstrated in most cases. The transfer of YACs to the germ line of mice has become popular in many transgenic facilities to guarantee faithful expression of transgenes. This technique was rapidly exported to livestock and soon transgenic rabbits, pigs and other mammals were produced with YACs. Transgenic animals were also produced with bacterial or P1-derived artificial chromosomes (BACs/PACs) with similar success. The use of YACs, BACs and PACs in transgenesis has allowed the discovery of new genes by complementation of mutations, the identification of key regulatory sequences within genomic loci that are crucial for the proper expression of genes and the design of improved animal models of human genetic diseases. Transgenesis with artificial chromosomes has proven useful in a variety of biological, medical and biotechnological applications and is considered a major breakthrough in the generation of transgenic animals. In this report, we will review the recent history of YAC/BAC/PAC-transgenic animals indicating their benefits and the potential problems associated with them. In this new era of genomics, the generation and analysis of transgenic animals carrying artificial chromosome-type transgenes will be fundamental to functionally identify and understand the role of new genes, included within large pieces of genomes, by direct complementation of mutations or by observation of their phenotypic consequences.     

Size Matters: Concurrency and the Epidemic Potential of HIV in Small Networks

Background

Generalized heterosexual epidemics are responsible for the largest share of the global burden of HIV. These occur in populations that do not have high rates of partner acquisition, and research suggests that a pattern of fewer, but concurrent, partnerships may be the mechanism that provides the connectivity necessary for sustained transmission. We examine how network size affects the impact of concurrency on network connectivity.

Methodology/Principal Findings

We use a stochastic network model to generate a sample of networks, varying the size of the network and the level of concurrency, and compare the largest components for each scenario to the asymptotic expected values. While the threshold for the growth of a giant component does not change, the transition is more gradual in the smaller networks. As a result, low levels of concurrency generate more connectivity in small networks.

Conclusions/Significance

Generalized HIV epidemics are by definition those that spread to a larger fraction of the population, but the mechanism may rely in part on the dynamics of transmission in a set of linked small networks. Examples include rural populations in sub-Saharan Africa and segregated minority populations in the US, where the effective size of the sexual network may well be in the hundreds, rather than thousands. Connectivity emerges at lower levels of concurrency in smaller networks, but these networks can still be disconnected with small changes in behavior. Concurrency remains a strategic target for HIV combination prevention programs in this context.     

Size Matters: Metastatic Cluster Size and Stromal Recruitment in the Establishment of Successful Prostate Cancer to Bone Metastases

Prostate cancer (PCa) impacts over 180,000 men every year in the USA alone, with 26,000 patients expected to succumb to the disease (cancer.gov). The primary cause of death is metastasis, with secondary lesions most commonly occurring in the skeleton. Prostate cancer to bone metastasis is an important, yet poorly understood, process that is difficult to explore with experimental techniques alone. To this end we have utilized a hybrid (discrete–continuum) cellular automaton model of normal bone matrix homeostasis that allowed us to investigate how metastatic PCa can disrupt the bone microenvironment. Our previously published results showed that PCa cells can recruit mesenchymal stem cells (MSCs) that give rise to bone-building osteoblasts. MSCs are also thought to be complicit in the establishment of successful bone metastases (Lu, in Mol Cancer Res 4(4):221–233, 2006). Here we have explored the aspects of early metastatic colonization and shown that the size of PCa clusters needs to be within a specific range to become successfully established: sufficiently large to maximize success, but not too large to risk failure through competition among cancer and stromal cells for scarce resources. Furthermore, we show that MSC recruitment can promote the establishment of a metastasis and compensate for relatively low numbers of PCa cells seeding the bone microenvironment. Combined, our results highlight the utility of biologically driven computational models that capture the complex and dynamic dialogue between cells during the initiation of active metastases.     

Tooth Size Variation in Prehistoric India

Permanent dental crown dimensions are largely unknown for living and prehistoric populations of South Asia. This paper describes permanent tooth crown measurements and indices for the Late Chalcolithic skeletal series from Inamgaon (1700-700 B.C.) in western India. These data are compared with tooth size data for prehistoric populations in India and both living and prehistoric populations outside the South Asian subcontinent. In summed cross-sectional area, the Inamgaon (1,218 mm²) permanent teeth are most similar to prehistoric skeletal series from Mahurjhari, India, Non Nok Tha, Thailand, and Bellan Bandi Palassa, Sri Lanka. The Inamgaon total crown area is only 3.1% smaller than the figure reported for early Neolithic skeletons from Mehr-garh, Pakistan, indicating the relatively large size of the Inamgaon dentition. Large tooth size at Inamgaon is interpreted as a biological adaptation to coarse dietary items, basic food preparation methods, and a mixed economy that included hunting wild game and collecting wild fruit. Dental indices of "ethnic" significance are perhaps better interpreted as indicators of masticatory stress and differential dental reduction. Maxillary and mandibular third molars show minimal reduction in crown size, but mandibular second molar teeth are distinctly reduced in size. The Incisor Breadth Index may indicate mixed genetic ancestry of the Inamgaon people or similar dietary stresses in genetically different populations.     

Social Spacing in Small Mammals: Patterns of Individual Variation

The pattern of social spacing in small mammals differs fromthat observed in many other vertebrates. Small mammals frequentlyhave non-exclusive territories and tolerate a large amount ofoverlap with other conspecifics. The determinant factors ofhome range or territory size in small mammals are not knownfor most species. We carried out a study of the determinantfactors of home range size in a model small mammal, the easternchipmunk, Tamias striatus. The population was studied for fiveyears. The effect of experimental perturbations on food supplyand population density offered strong evidence that the meanhome range size in the population was determined by resourceabundance. Changes in population density had little or no measurableeffect. We noted that even when mean home range size decreasedsignificantly in response to an increase in available food,a great deal of variability in individual home range sizes remained.We hypothesized that this pattern of variation among individualswas also resource related; large home ranges would be locatedin areas of low resource density and small home ranges wouldbe located in areas of high resource density. Our data to datedo not offer support for this hypothesis; however our researchhas shown that the data needed to convincingly reject the nullhypothesis are very complex. We discuss the evidence requiredto study patterns of individual variation, and how models ofoptimal territory size may be useful. Research that examinespatterns of individual variation are few in number, yet studiesof individual variation will ultimately provide the best insightson the dynamics of evolutionary ecology.     

An Individual Stand Growth Model for Mean Plant Size Based on the Rule of Self-thinning

A growth model for pure, even-aged stands of plants is asymptoticallybounded above by the self-thinning rule that relates maximumplant size to stand density. The model characterizes accretionin mean size as a deviation from the limiting size. It consistsof a function relating mean size to time and density and a companionsurvival model. The growth model is obtained by substitutingthe survival model for density in the mean size relationship.Model flexibility is demonstrated by fitting it to annual remeasurementsof mean size and number of plants per unit area in a stand ofPinus taeda L. 3/2-power rule, mortality, survival, stand dynamics, plant growth model, loblolly pine     

Genome Size Variation in Some Tropical Hardwoods

4-C DNA values of 36 tropical hardwood species belonging to 13 families show a range from 2.08 to 20.07 pg, a 9.64-fold difference. DNA per chromosome values show a 10-fold difference. The minimum range of variation (1.2-fold) is shown by Annonaceae and Sapindaceae while the maximum range (6.23-fold) is shown by Euphorbiaceae, and Fabaceae and Rutaceae show 1.7 and 1.9-fold differences, respectively. On an average, Euphorbiaceae and Rutaceae have been found to possess the largest and the smallest genome sizes respectively.     

Limited Genome Size Variation in Sesleria albicans

The extent and significance of intraspecific genome size variationin plants continues to be a matter of discussion: in some speciesconsiderable variation has been described, while no variationhas been detected in other taxa. In the present study, intraspecificgenome size variation was analysed in a perennial grass Sesleriaalbicans Kit. ex Schult. (Poaceae). Flow cytometry was usedfor the analysis of nuclear DNA content in ten geographicallyisolated populations ofS. albicans . Despite long-term isolationand lack of gene-flow between the populations, only negligibleinter-population differences were found. Although the differencesbetween the populations were statistically significant, themaximum inter-population difference reached only 1.6% of themean 2C value (9.78 ± 0.04 pg). The variation was notcorrelated with geographical location or with altitude of thepopulations analysed. The present study clearly demonstratesthat S. albicans belongs to the plant taxa with a highly stablegenome size. Copyright 2000 Annals of Botany Company Sesleria albicans, genome size, nuclear DNA content, intraspecific variation, flow cytometry, Europe     

Egg Size Versus Number of Offspring Trade-Off: Female Age Rather Than Size Matters in a Domesticated Arctic Charr Population

Understanding how organisms adjust reproductive allocation trade-offs between offspring size versus number (OSN trade-off) is a central question in evolutionary biology. In organisms with indeterminate growth, changes in OSN according to maternal size or age have been reported in numerous taxa. The relative contribution of age and size remains largely unclear, as they are often highly correlated. In this study, we investigated how females adjust the offspring size versus number trade-off and analyzed the relative contribution of female age and size in a domesticated population of Arctic charr Salvelinus alpinus (Linnaeus, 1758) that exhibit large variation in size within five age classes. Our results show that the reproductive output (i.e. as measured by the clutch mass), was strongly correlated to female mass and age suggesting that the proportion of resources allocated to reproduction do not vary along lifetime. Egg mass and fecundity (egg number) increased with female mass overall. However, within an age class, larger females had higher fecundity but egg mass was poorly related to female mass. At the population level, a positive relationship was observed between fecundity and egg mass but within each class age the relation was negative revealing a OSN trade-off. Overall, our results show that, in our model Arctic charr population, allocation trade-off to reproduction and the way females allocate to egg mass and fecundity is largely determined by their age rather than mass.