Declining body size: a third universal response to warming?

A recently documented correlate of anthropogenic climate change involves reductions in body size, the nature and scale of the pattern leading to suggestions of a third universal response to climate warming. Because body size affects thermoregulation and energetics, changing body size has implications for resilience in the face of climate change. A review of recent studies shows heterogeneity in the magnitude and direction of size responses, exposing a need for large-scale phylogenetically controlled comparative analyses of temporal size change. Integrative analyses of museum data combined with new theoretical models of size-dependent thermoregulatory and metabolic responses will increase both understanding of the underlying mechanisms and physiological consequences of size shifts and, therefore, the ability to predict the sensitivities of species to climate change.     

Mitral regurgitation: when to intervene?

Although mitral regurgitation (MR) is the most common valvular heart disease, it should be regarded as a complex multifactorial disease that involves     

Host-parasitoid association and diffuse coevolution: when to be a generalist?

In host-parasitoid communities, hosts are subjected to selective pressures from numerous parasitoid species, and parasitoids may attack several host species. The specificity of host resistance and parasitoid virulence is thus a key factor in host-parasitoid coevolution. A continuum of strategies exists, from strict specificity to a generalist strategy. The optimal level of specificity may differ in host and parasitoid. I investigated the optimal level of resistance specificity using a model in which the host could be attacked by two parasitoid species, with variable levels of defense specificity. The fitness of a parasitoid attacking two host species with different levels of virulence specificity was also modeled. Finally, a fluctuating environment was simulated by introducing variable probabilities of encounters between antagonistic species over several generations. If the frequency of encounters with the antagonistic species is fixed, then both host and parasitoid gain from a strategy of exclusive specialization toward the most frequent antagonist. If the frequency of encounters fluctuates between generations, generalist host resistance and partially specialist parasitoid virulence are favored. Generalist host resistance may be considered to be a bet-hedging response to an unpredictable environment. This asymmetry in host-parasitoid coevolution may account for some of the genetic structures observed in the field for host-parasitoid associations.     

Estimating mutation rate: how to count mutations?

Mutation rate is an essential parameter in genetic research. Counting the number of mutant individuals provides information for a direct estimate of mutation rate. However, mutant individuals in the same family can share the same mutations due to premeiotic mutation events, so that the number of mutant individuals can be significantly larger than the number of mutation events observed. Since mutation rate is more closely related to the number of mutation events, whether one should count only independent mutation events or the number of mutants remains controversial. We show in this article that counting mutant individuals is a correct approach for estimating mutation rate, while counting only mutation events will result in underestimation. We also derived the variance of the mutation-rate estimate, which allows us to examine a number of important issues about the design of such experiments. The general strategy of such an experiment should be to sample as many families as possible and not to sample much more offspring per family than the reciprocal of the pairwise correlation coefficient within each family. To obtain a reasonably accurate estimate of mutation rate, the number of sampled families needs to be in the same or higher order of magnitude as the reciprocal of the mutation rate.     

Sclerotinia sclerotiorum: when "to be or not to be" a pathogen?

Sclerotinia sclerotiorum is unusual among necrotrophic pathogens in its requirement for senescent tissues to establish an infection and to complete the life cycle. A model for the infection process has emerged whereby the pathogenic phase is bounded by saprophytic phases; the distinction being that the dead tissues in the latter are generated by the actions of the pathogen. Initial colonization of dead tissue provides nutrients for pathogen establishment and resources to infect healthy plant tissue. The early pathogenicity stage involves production of oxalic acid and the expression of cell wall degrading enzymes, such as specific isoforms of polygalacturonase (SSPG1) and protease (ASPS), at the expanding edge of the lesion. Such activities release small molecules (oligo-galacturonides and peptides) that serve to induce the expression of a second wave of degradative enzymes that collectively bring about the total dissolution of the plant tissue. Oxalic acid and other metabolites and enzymes suppress host defences during the pathogenic phase, while other components initiate host cell death responses leading to the formation of necrotic tissue. The pathogenic phase is followed by a second saprophytic phase, the transition to which is effected by declining cAMP levels as glucose becomes available and further hydrolytic enzyme synthesis is repressed. Low cAMP levels and an acidic environment generated by the secretion of oxalic acid promote sclerotial development and completion of the life cycle. This review brings together histological, biochemical and molecular information gathered over the past several decades to develop this tri-phasic model for infection. In several instances, studies with Botrytis species are drawn upon for supplemental and supportive evidence for this model. In this process, we attempt to outline how the interplay between glucose levels, cAMP and ambient pH serves to coordinate the transition between these phases and dictate the biochemical and developmental events that define them.     

Integrin adhesion: when is a kinase a kinase?

Recent genetic studies in the worm Caenorhabditis elegans and fruitfly Drosophila have revealed the essential role integrin-linked kinase plays in integrin adhesion - but it apparently acts in this role as an adaptor rather than a kinase.     

Use of leaves to inspect ectoparasites in wild chimpanzees: a third cultural variant?

We report 26 cases of using leaves as tools with which wild chimpanzees (Pan troglodytes schweinfurthii) in the Sonso community, Budongo Forest, Uganda, appeared to inspect objects removed during grooming. Careful removal of potential ectoparasites and delicate lip or manual placement on leaves followed by intense visual examination characterised this behaviour. It appears to be done to judge whether either ingestion or discarding is most appropriate, the former occurring in most cases. This behaviour may represent a third variant of ectoparasite handling, different from those described at Taï and Gombe, yet sharing features with the latter. These two East African techniques may thus have evolved from leaf grooming.     

Is there a risk to living large? Large size correlates with reduced growth when stressed for knapweed populations

A central hypothesis in ecology is that plant life history evolution is constrained by fundamental “compromises between the conflicting selection pressures resulting from particular combinations of competition, stress, and disturbance”, with stress being defined as abiotic conditions that restrict production. Biogeographic differences among native and non-native ranges of invasive plants may provide unique opportunities for tests of this theory. We conducted a greenhouse experiment with Centaurea stoebe plants from North American and European populations. We compared the total biomass and phenotypic plasticity indices for plants from the native and non-native ranges under stressed and non-stressed conditions. The average size of Centaurea stoebe plants from 13 North American populations was greater than that of plants from 18 European populations regardless of stress treatment. However, when plants from the same populations were exposed to lower resources the differences in biomass between plants from North American and European populations were significantly less, suggesting that large plants were poorer stress tolerators. For all 31 populations the regression slope for the relationship between mean mass for populations in non-stressful conditions and mean mass in stressful conditions was less than 1.0, indicating that populations that produced large plants in good conditions also produced plants that grew disproportionately less in stressful conditions. These findings suggest that Centaurea stoebe may be evolving towards being a good “competitor” (sensu Grime, 1977) in its invasive range, but at the cost of being a good “stress tolerator”.     

Attraction of a predator to chemical information related to nonprey: when can it be adaptive?

Information specificity can be important to animals in makingoptimal decisions. However, it is not always necessary to useevery level of specificity. We analyzed the response of thepredatory mite Phytoseiulus persimilis to plant-produced informationrelated to a nonprey herbivore. This predator is a specialistfeeding on spider mites in the genus Tetranychus. Caterpillarsof Spodoptera exigua cannot serve as prey. Plants respond toan infestation by herbivores with the emission of volatilesthat attract carnivorous enemies of the herbivores. Conspecific plants infested with different herbivore species can emit blendsthat are qualitatively identical, while differing in the ratiosof blend components. However, different plant species emitvolatile blends that differ qualitatively. We demonstratedthat the predator P. persimilis is attracted to volatiles frombean plants infested with S. exigua caterpillars, but thatthis attraction is affected by predator starvation and host-plantexperience. One-hour and 24-h starved predators were made to represent predators that just lost a prey patch versus predatorsthat have totally lost a prey patch. Predators reared on spidermites on bean were attracted to bean plants infested with caterpillarswhen starved for 1 h but not when starved for 24 h. Both predatorgroups were attracted to bean plants infested with prey (i.e.,spider mites). One-hour starved predators can use the odorto relocate the rewarding prey patch they just lost contactwith, and using a general olfactory representation of the blendis sufficient for relocation. In contrast, for 24-h starvedpredators, the perception of a plant's odor blend is unlikelyto represent the prey patch lost, and discriminating betweenan odor blend representing prey or nonprey will avoid investingtime in finding a nonprey herbivore. In contrast, predatorsthat had been reared on spider mites on cucumber and thus hadexperienced a qualitatively different odor blend were not attractedto volatiles from caterpillar-infested bean plants. They wereattracted to spider mite-infested bean plants, irrespectiveof starvation level. To cucumber-experienced predators, theperception of bean plant odor cannot represent the prey patch lost, but only a new prey patch. Being discriminative and onlyresponding to prey-infested plants is adaptive in this situation.Our results are discussed in the context of optimal informationprocessing.     

The biomechanics of skipping gaits: a third locomotion paradigm?

Skipping, a gait children display when they are about four- to five-years-old, is revealed to be more than a behavioural peculiarity. By means of metabolic and biomechanical measurements at several speeds, the relevance of skipping is shown to extend from links between bipedal and quadrupedal locomotion (namely galloping) to understanding why it could be a gait of choice in low-gravity conditions, and to some aspects of locomotion evolution (ground reaction forces of skipping seem to originate from pushing the walking gait to unnaturally high speeds). When the time-courses of mechanical energy and the horizontal ground reaction force are considered, a different locomotion paradigm emerges, enabling us to separate, among the bouncing gaits, the trot from the gallop (quadrupeds) and running from skipping (bipeds). The simultaneous use of pendulum-like and elastic mechanisms in skipping gaits, as shown by the energy curve analysis, helps us to understand the low cost of transport of galloping quadrupeds.     

Cell size: a matter of life or death?

Proper growth and development of multicellular organisms require the tight regulation of cell growth, cell division and cell death. A recent study has identified a novel regulatory link between two of these processes: cell growth and cell death.     

How to reach the right size?

Very little is known about how the size of an organism, or a specific tissue in an organism, is regulated. Coordinating and regulating the size of tissues is necessary for proper development, wound healing, and regeneration. Defects in a tissue-size regulation mechanism could lead to birth defects or cancer. In addition, there is a strong psychological aspect to some areas of tissue size regulation, as many cosmetic surgery procedures involve enlarging or reducing the size of some body parts. This review addresses the little bit that we know about size regulation. A key concept is that the size of a tissue is the size of the component cells multiplied by the number of those cells. This breaks the size regulation problem down to two parts. The size of cells can be regulated by nutrient sensing and secreted factors, and may have an upper limit due to an upper limit of a genome's ability to produce mRNA's and thus proteins. To regulate the number of cells in a tissue, there are several simple theoretical models involving secreted factors. In one case, the cells can secrete a characteristic factor and the concentration of the factor will increase with the number of cells secreting it, allowing the tissue to sense its own size. In another scenario, a specific cell secretes a limited amount of a factor necessary for the survival of a target population, and this then limits the size of the target population. There are currently several examples of secreted factors that regulate tissue size, including myostatin, which regulates the amount of muscles, leptin, which regulates adipose tissue, and growth hormone and insulin-like growth factors which regulate total mass. In addition, there are factors such as the found in Dictyostelium that regulate the breakup of a tissue into sub-groups. A better understanding of how these factors regulate size will hopefully allow us to develop new therapeutic procedures to treat birth defects or diseases that affect tissue size.     

Estimating ancestral geographical distributions: a Gondwanan origin for aphid parasitoids?

We tested the published hypothesis of a Gondwanan origin for the overwhelmingly northern hemisphere aphid parasitoids (Aphidiinae) as follows: (i) finding their sister group by a phylogenetic analysis of the entire Braconidae (Insecta: Hymenopterai using sequence data from approximately 500 bp fragments of both the nuclear 28S (D2 region) and mitochondrial 16S rDNA genes, (ii) using this sister-group relationship and the more informative 28S D2 gene to estimate the phylogeny of the Aphidiinae and (iii) estimating the ancestral distribution for the Aphidiinae using maximum-likelihood and maximum-parsimony methods. Both methods indicated a Gondwanan origin.     

Egg size in relation to body size in rotifers: an indication of reproductive strategy?

Egg sizes and body sizes of 43 egg-bearing rotifer species of numerous, mostly tropical, general have been recorded. Larger absolute egg volumes have been found for larger rotifer species, but the increase was lower than expected in proportion to body size, i.e. the relative egg volume decreased with increasing body size. Obviously the relative investment per offspring is smaller in larger rotifer species.     

ATP synthase: what dictates the size of a ring?

Recent data suggest the source of F(0)F(1) ATP synthase determines a significant and surprising difference in the size of a putative rotating ring of integral membrane subunits of F(0); this can be correlated with biochemical data suggesting there is variation in the number of protons translocated per ATP synthesised.     

Re-entry: a guide to success?

This article is based upon a former prisoner/parolee’s first hand account and analyzes some of the more obvious obstacles awaiting parolees when released from prison. Included is an examination of some basic resources the author considered necessary for successful re-entry. Potential conflicts between providing helpful resources and the status quo within the current Prison-Industrial Complex are also considered.