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D Berrigan

Publications and source records attributed to D Berrigan.

8 recordsLinked to original sources
PubMed2001

Strength and tempo of directional selection in the wild.

Directional selection is a major force driving adaptation and evolutionary change. However, the distribution, strength, and tempo of phenotypic selection acting on quantitative traits in natural populations remain unclear across different study systems. We reviewed the literature (1984-1997) that reported the strength of directional selection as indexed by standardized linear selection gradients (beta). We asked how strong are viability and sexual selection, and whether strength of selection is correlated with the time scale over which it was measured. Estimates of the magnitude of directional selection (absolute value of beta) were exponentially distributed, with few estimates greater than 0.50 and most estimates less than 0.15. Sexual selection (measured by mating success) appeared stronger than viability selection (measured by survival). Viability selection that was measured over short periods (days) was typically stronger than selection measured over longer periods (months and years), but the strength of sexual selection did not vary with duration of selection episodes; as a result, sexual selection was stronger than viability selection over longer time scales (months and years), but not over short time scales (days).

Animals↗
PubMed2000

Rapid evolution of a geographic cline in size in an introduced fly.

The introduction and rapid spread of Drosophila subobscura in the New World two decades ago provide an opportunity to determine the predictability and rate of evolution of a geographic cline. In ancestral Old World populations, wing length increases clinally with latitude. In North American populations, no wing length cline was detected one decade after the introduction. After two decades, however, a cline has evolved and largely converged on the ancestral cline. The rate of morphological evolution on a continental scale is very fast, relative even to rates measured within local populations. Nevertheless, different wing sections dominate the New versus Old World clines. Thus, the evolution of geographic variation in wing length has been predictable, but the means by which the cline is achieved is contingent.

Animals↗
PubMed2000

Life-history correlates of evolution under high and low adult mortality.

Life-history theory predicts evolutionary changes in reproductive traits and intrinsic mortality rates in response to differences in extrinsic mortality rates. Trade-offs between life- history traits play a pivotal role in these predictions, and such trade-offs are mediated, at least in part, by physiological allocations. To gain insight into these trade-offs, we have been performing a long-term experiment in which we allow fruitflies, Drosophila melanogaster, to evolve in response to high (HAM) and low (LAM) adult mortality rates. Here we analyze the physiological correlates of the life-history trade-offs. In addition to changing development time and early fecundity in the direction predicted, high adult mortality affected three traits expressed early in life-body size, growth rate, and ovariole number-but had little or no effect on body composition (relative fat content), viability, metabolic rate, activity, starvation resistance, or desiccation resistance. Correlations among lines revealed trade-offs between early fecundity, late fecundity, and starvation resistance, which appear to be mediated by differential allocation of lipids.

Animals↗
PubMed1997

Influence of temperature and activity on the metabolic rate of adult Drosophila melanogaster.

We measured metabolic rates of adult male Drosophila melanogaster allowed to evolve in the laboratory at 18 and 25 degrees C and compared these with measurements of metabolic rates of flies collected along a latitudinal gradient in Australia. Metabolic rates of flies that had evolved in the laboratory at low temperature were 5-7% higher than those of flies allowed to evolve at high temperature. Metabolic rates of field collected increased with latitude when measured at 18 degrees C but not at higher temperature (25 degrees C) and were about 9% greater in high latitude (approximately 41'00) flies than low latitude (16'53) flies. Metabolic rate was strongly influenced by measurement temperature; estimated Q10s ranged from 1.79 to 2.5 for measurements made at 18 and 25 degrees C. Metabolic rate scaled isometrically with body mass; the estimated slope of a ln-ln regression of metabolic rate and body mass was 1.03 +/- 0.1. We used our measures of metabolic rate and activity to estimate the minimum cost of transport (MCOT) while walking. The estimates of MCOT have high standard errors (lab, 34.30 +/- 14.2 ml O2/g/km; and field, 38.0 +/- 17.0 ml O2/g/km); however, they differ by only 3-9% from predicted values based on allometric relationships reported in the literature.

Animals↗
PubMed1995

Questioning paradigms: caste-specific ventilation in harvester ants, Messor pergandei and M. julianus (Hymenoptera: Formicidae)

Do developmental constraints in ant colonies limit gas exchange strategies to those displayed by female alates (presumptive queens)? In the xeric harvester ant genus Messor, we found that M. pergandei and M. julianus female alates ventilated highly discontinuously, as predicted, but M. julianus workers ventilated less discontinuously and M. pergandei workers (which occur in more xeric habitats) ventilated continuously. We present the salient characteristics of the discontinuous ventilation cycles of the species and the manner in which they are modulated by CO2 emission rates at a single temperature (24 °C). We demonstrate that, in M. julianus workers, open-spiracle phase CO2 emission rate only slightly exceeds overall CO2 emission rate, making discontinuous ventilation marginal, a state extrapolated in M. pergandei to continuous ventilation. However, workers are plainly capable of far greater rates of CO2 emission than when inactive at 24 °C, so the lack of discontinuous ventilation in M. pergandei under normoxic conditions is not likely to be imposed by physiological constraints and may, in fact, be a response to its xeric environment. We hypothesize ­ aside from phylogenetic effects ­ that discontinuous ventilation occurs primarily in insects that may experience hypoxic and hypercapnic conditions, such as ant queens during claustral colony foundation and perhaps workers within the nest environment; that discontinuous ventilation is not necessarily essential to reduce respiratory water loss; and that it will not necessarily occur in castes or species routinely exposed to xeric but normoxic conditions.

Journal Article↗
PubMed1993

Bioenergetic and kinematic consequences of limblessness in larval Diptera.

We report the cost of transport and kinematics of terrestrial locomotion by larval blowflies (Protophormia terraenovae, Diptera: Calliphoridae). We contrast inter- and intra-individual methods for estimating minimum cost of transport (MCOT) and the relationship between speed, contraction frequency and distance traveled per contraction. The minimum cost of transport calculated from intra-individual data is 2297 +/- 317 J kg-1 m-1 (S.E.M.) and the MCOT calculated from inter-individual comparisons is statistically indistinguishable at 1910 +/- 327 J kg-1 m-1. These values are almost ten times higher than the predicted value for a similar-sized limbed arthropod. Fly larvae travel by repeated peristaltic contractions and individual contractions cost about the same amount as individual strides in limbed insects. Both contraction frequency and distance traveled per contraction increase linearly with speed. Doubling the contraction frequency or the distance traveled per contraction approximately doubles speed. The cost of transport in fly larvae is among the highest recorded for terrestrial locomotion, confirming the suggestion that biomechanical and kinematic properties of limbless organisms with hydraulic skeletons lead to very high costs of transport.

Animals↗