Condition-dependent expression of trophic polyphenism: effects of individual size and competitive ability

Understanding the adaptive significance of alternative phenotypes may require knowing how the internal state of an organism affects the relationship between phenotypic variation and fitness across selective environments. Here, we explore how individual state interacts with environmental variation to affect expression of a trophic polyphenism in larval amphibians. Following the consumption of fairy shrimp, typical omnivorous plains spadefoot toad tadpoles (Spea bombifrons) may express an alternative 'carnivore' phenotype. The carnivore phenotype confers rapid growth and development, but these benefits come at the expense of condition at metamorphosis. Larval habitats vary in longevity, food availability and tadpole morph frequency, each of which potentially affects the relationship between tadpole state (e.g. size) and morph fitness. Hence, we predicted that phenotype expression should depend on both tadpole size and larval environment. We found that small tadpoles were more likely to develop into carnivores than large tadpoles when each was raised in isolation. When tadpoles were raised in pairs, however, relatively smaller tadpoles were less likely to express the carnivore phenotype than larger tadpoles. We present results to support the hypothesis that these contrasting effects of absolute and relative size on carnivore morph expression stem from the effects of tadpole size on the ability to consume fairy shrimp. We conclude that competition for shrimp imposed by larger tadpoles may often inhibit relatively smaller tadpoles from expressing the carnivore phenotype. Thus, we find support for our prediction that morph expression in Spea depends on both an individual's internal state and larval environment. Our understanding of the adaptive significance and, ultimately, the evolution of this and other state-dependent responses may be enhanced by considering how interactions among individuals affect the relationships among fitness, internal state and phenotype expression across different selective environments

The Effects of Age and Lifetime Flight Behavior on Flight Capacity in Drosophila Melanogaster

The Effects of Flight Behavior on Physiology and Senescence May Be Profound in Insects Because of the Extremely High Metabolic Costs of Flight. Flight Capacity in Insects Decreases with Age; in Contrast, Limiting Flight Behavior Extends Lifespan and Slows the Age-Related Loss of Antioxidant Capacity and Accumulation of Oxidative Damage in Flight Muscles. in This Study, We Tested the Effects of Age and Lifetime Flight Behavior on Flight Capacity by Measuring Wingbeat Frequency, the Ability to Fly in a Hypo-Dense Gas Mixture, and Metabolic Rate in Drosophila Melanogaster. Specifically, 5-Day-Old Adult Flies Were Separated into Three Life-Long Treatments: (1) Those Not Allowed to Fly (No Flight), (2) Those Allowed - But Not Forced - to Fly (Voluntary Flight) and (3) Those Mechanically Stimulated to Fly (Induced Flight). Flight Capacity Senesced Earliest in Flies from the No-Flight Treatment, Followed by the Induced-Flight Group and Then the Voluntary Flight Group. Wingbeat Frequency Senesced with Age in All Treatment Groups, But Was Most Apparent in the Voluntary- and Induced-Flight Groups. Metabolic Rate during Agitated Flight Senesced Earliest and Most Rapidly in the Induced Flight Group, and Was Low and Uniform throughout Age in the No-Flight Group. Early Senescence in the Induced-Flight Group Was Likely Due to the Acceleration of Deleterious Aging Phenomena Such as the Rapid Accumulation of Damage at the Cellular Level, While the Early Loss of Flight Capacity and Low Metabolic Rates in the No-Flight Group Demonstrate that Disuse Effects Can Also Significantly Alter Senescence Patterns of Whole-Insect Performance

Size and shape: the developmental regulation of static allometry in insects

Among all organisms, the size of each body part or organ scales with overall body size, a phenomenon called allometry. The study of shape and form has attracted enormous interest from biologists, but the genetic, developmental and physiological mechanisms that control allometry and the proportional growth of parts have remained elusive. Recent progress in our understanding of body‐size regulation provides a new synthetic framework for thinking about the mechanisms and the evolution of allometric scaling. In particular, insulin/IGF signaling, which plays major roles in longevity, diabetes and the regulation of cell, organ and body size, might also be centrally involved in regulating organismal shape. Here we review recent advances in the fields of growth regulation and endocrinology and use them to construct a developmental model of static allometry expression in insects. This model serves as the foundation for a research program that will result in a deeper understanding of the relationship between growth and form, a question that has fascinated biologists for centuries

Time in a Bottle: The Evolutionary Fate of Species Discrimination in Sibling Drosophila Species

Disadvantageous hybridization favors the evolution of prezygotic isolating behaviors, generating a geographic pattern of interspecific mate discrimination where members of different species drawn from sympatric populations exhibit stronger preference for members of their own species than do individuals drawn from allopatric populations. Geographic shifts in species' boundaries can relax local selection against hybridization; under such scenarios the fate of enhanced species preference is unknown. Lineages established from populations in the region of sympatry that have been maintained as single-species laboratory cultures represent cases where allopatry has been produced experimentally. Using such cultures dating from the 1950s, we assess how Drosophila pseudoobscura and D. persimilis mate preferences respond to relaxed natural selection against hybridization. We found that the propensity to hybridize generally declines with increasing time in experimental allopatry, suggesting that maintaining enhanced preference for conspecifics may be costly. However, our data also suggest a strong role for drift in determining mating preferences once secondary allopatry has been established. Finally, we discuss the interplay between populations in establishing the presence or absence of patterns consistent with reinforcement

Species ranges and localities.

<p>The distribution of <i>Drosophila pseudoobscura</i> and <i>D. persimilis </i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031759#pone.0031759-Machado1" target="_blank">[57]</a>. Localities for allopatric populations of <i>D. pseudoobscura</i> are shown in black circles and sympatric populations in black diamonds. Localities for <i>D. persimilis</i> are indicated by open stars.</p

Copulation success.

<p>Copulation success rates for conspecific and both directions of sympatric (s) and allopatric (a) heterospecific pairings (male×female) between <i>D. pseudoobscura</i> (pseudo) and <i>D. persimilis</i> (persim). Panel is divided by the time of lineage collection. Clopper-Pearson exact binomial confidence intervals are given for each cross type and statistically significant pattern consistent with reinforcement is indicated with a star.</p

Latency data.

<p>Sample size and average courtship latency in seconds for each type of conspecific and heterospecific pairing for each of the three collection time points. Standard deviations shown in parentheses.</p

Analysis of mating success across collection times.

<p>Analysis of variation in (A) mating success and (B) Noor Score between sympatric and allopatric populations of <i>D. pseudoobscura</i> females paired with <i>D. persimilis</i> males from each of the three collection times. P-values in bold indicate values significant after sequential bonferroni correction, asterisk indicates pattern in the opposite direction from that expected under reinforcement.</p

Diet effects on mating success.

<p>Copulation success rates for both directions of sympatric (s) and allopatric (a) heterospecific pairings (male×female) between <i>D. pseudoobscura</i> (pseudo) and <i>D. persimilis</i> (persim) from the 2000s time point reared on sucrose only diet (black bars) and sucrose+dextrose diet (gray bars).</p