Biomedical subjects

Jennifer H Fewell

Publications and source records attributed to Jennifer H Fewell.

10 recordsLinked to original sources

PubMed2006

Population-wide lineage frequencies predict genetic load in the seed-harvester ant Pogonomyrmex.

Many populations of the seed-harvester ant Pogonomyrmex barbatus exhibit genetic caste determination (GCD) generated by the interbreeding of two distinct yet interdependent lineages. Same-lineage matings are genetically predestined to become female reproductives (gynes) whereas alternate-lineage matings become workers. The perpetuation of this system requires that reproductives of both lineages are available for mating and are thus part of the effective population. We label these dependent lineage populations, because each lineage depends on the alternate lineage for worker production. Here we investigate the potential costs associated with GCD in a population with highly skewed lineage frequencies. We reared colonies using newly mated queens from a GCD population and an ecologically equivalent Pogonomyrmex rugosus population with environmental caste determination. GCD founding queens suffer a genetic load from mating randomly and produce fewer brood with advanced development compared with environmental caste determination queens. Our results indicate that GCD queens acquiring a high proportion of same-lineage sperm are unlikely to found a colony successfully. Given model parameters of random mating and founding queens mating with three males on average, there was a close fit between theoretical expectations of variation in colony worker production based on mating and lineage frequencies and empirical deficits in worker production. As expected, severely decreased worker production was specific to the common lineage, suggesting that negative frequency-dependent selection acts to stabilize a dependent lineage system.

Animals↗

PubMed2006

Distribution and evolution of genetic caste determination in Pogonomyrmex seed-harvester ants.

We examined the distribution and ancestral relationships of genetic caste determination (GCD) in 46 populations of the seed-harvester ants Pogonomyrmex barbatus and P. rugosus across the east-to-west range of their distributions. Using a mtDNA sequence and two nuclear markers diagnostic for GCD, we distinguished three classes of population phenotypes: those with GCD, no evidence of GCD, and mixed (both GCD and non-GCD colonies present). The GCD phenotype was geographically widespread across the range of both morphospecies, occurring in 20 of 46 sampled populations. Molecular data suggest three reproductively isolated and cryptic lineages within each morphospecies, and no present hybridization. Mapping the GCD phenotype onto a mtDNA phylogeny indicates that GCD in P. rugosus was acquired from P. barbatus, suggesting that interspecific hybridization may not be the causal agent of GCD, but may simply provide an avenue for GCD to spread from one species (or subspecies) to another. We hypothesize that the origin of GCD involved a genetic mutation with a major effect on caste determination. This mutation generates genetic conflict and results in the partitioning and maintenance of distinct allele (or gene set) combinations that confer differences in developmental caste fate. The outcome is two dependent lineages within each population; inter-lineage matings produce workers, while intra-lineage matings produce reproductives. Both lineages are needed to produce a caste-functional colony, resulting in two reproductively isolated yet interdependent lineages. Pogonomyrmex populations composed of dependent lineages provide a unique opportunity to investigate genetic variation underlying phenotypic plasticity and its impact on the evolution of social structure.

Animals↗

PubMed2006

Behavioral regulation of genetic caste determination in a Pogonomyrmex population with dependent lineages.

The fate of a social insect colony is partially determined by its ability to allocate individuals to the caste most appropriate for the requirements for growth, maintenance, and reproduction. In pairs of dependent lineages of Pogonomyrmex barbatus, the allocation of individuals to the queen or worker caste is constrained by genotype, a system known as genetic caste determination (GCD). In mature GCD colonies, interlineage female eggs develop into sterile workers, while intralineage eggs become reproductively capable queens. Although the population-level consequences of this system have been intensively studied, the proximate mechanisms for GCD remain unknown. To elucidate these mechanisms, we brought newly mated queens into the laboratory and allowed them to establish colonies, nearly half of which unexpectedly produced virgin queens only seven months after colony founding. We genotyped eggs, workers, and the virgin queens from these colonies. Our results showed that queens in young colonies produce both interlineage and intralineage eggs, demonstrating that queens of GCD colonies indiscriminately use sperm of at least two lineages to fertilize their eggs. Intralineage eggs were more frequent in colonies producing virgin queens. These findings suggest that intralineage eggs are predetermined to become queens and that workers may cull these eggs when colonies are not producing queens. Virgin queens produced by young GCD colonies were smaller than field-caught virgin queens, and often had developmental problems. Hence, they are probably nonfunctional and represent an intense resource drain for developing colonies, not a contribution to colony fitness.

Animals↗

PubMed2004

Normalized mutual entropy in biology: quantifying division of labor.

Division of labor is one of the primary adaptations of sociality and the focus of much theoretical work on self-organization. This work has been hampered by the lack of a quantitative measure of division of labor that can be applied across systems. We divide Shannon's mutual entropy by marginal entropy to quantify division of labor, rendering it robust over changes in number of individuals or tasks. Reinterpreting individuals and tasks makes this methodology applicable to a wide range of other contexts, such as breeding systems and predator-prey interactions.

Animals↗

PubMed2003

Social insect networks.

Social insect colonies have many of the properties of adaptive networks. The simple rules governing how local interactions among individuals translate into group behaviors are found across social groups, giving social insects the potential to have a profound impact on our understanding of the interplay between network dynamics and social evolution.

Animals↗

PubMed2003

Colony response to graded resource changes: an analytical model of the influence of genotype, environment, and dominance.

Successful social groups must respond dynamically to environmental changes. However, a flexible group response requires the coordination of many individuals. Here we offer a static analytical model that integrates variation in environment-based cues for performance of a task with genetically and environmentally based variation in individual responses, and predicts the resultant colony behavior for that task. We also provide formulae for computing effective number of alleles in a haplo-diploid colony founded by any number of parents. Variable colony resources combined with variation among worker phenotypes generate known patterns of colony flexibility, allowing us to explicitly test how the number of loci, dominance/codominance, and the phenotype's environment influences group response. Our model indicates that the number of loci strongly influences colony behavior. For one or two loci, the proportion of workers foraging for pollen remain constant over vast increases in colony pollen stores, but then drops dramatically when the pollen stores increase past a specific threshold. As the number of loci controlling pollen foraging increases, graded increases in pollen stores result in a graded drop in the proportion of the worker population foraging for pollen. The effect of number of alleles is less strong, a result we discuss in light of the fact that a low number of effective alleles are expected in a colony. Comparisons of our model with empirical honey bee (Apis mellifera) data indicate that worker foraging response to pollen stores is driven by one or two loci, each with dominant allelic effects. The growing body of evidence that genotype has strong effects on task performance in social insect colonies, and the variation in within-colony genetic diversity across social insect taxa, make our model broadly applicable in explaining social group coordination.

Alleles↗

PubMed2003

Effects of load type (pollen or nectar) and load mass on hovering metabolic rate and mechanical power output in the honey bee Apis mellifera.

In this study we tested the effect of pollen and nectar loading on metabolic rate (in mW) and wingbeat frequency during hovering, and also examined the effect of pollen loading on wing kinematics and mechanical power output. Pollen foragers had hovering metabolic rates approximately 10% higher than nectar foragers, regardless of the amount of load carried. Pollen foragers also had a more horizontal body position and higher inclination of stroke plane than measured previously for honey bees (probably nectar foragers). Thorax temperatures ranked pollen > nectar > water foragers, and higher flight metabolic rate could explain the higher thorax temperature of pollen foragers. Load mass did not affect hovering metabolic rate or wingbeat frequency in a regression-model experiment. However, using an analysis of variance (ANOVA) design, loaded pollen and nectar foragers (mean loads 27% and 40% of body mass, respectively) significantly increased metabolic rate by 6%. Mean pollen loads of 18% of body mass had no effect on wingbeat frequency, stroke amplitude, body angle or inclination of stroke plane, but increased the calculated mechanical power output by 16-18% (depending on the method of estimating drag). A rise in lift coefficient as bees carry loads without increasing wingbeat frequency or stroke amplitude (and only minimal increases in metabolic rate) suggests an increased use of unsteady power-generating mechanisms.

Animals↗

PubMed2003

Juvenile hormone and division of labor in honey bee colonies: effects of allatectomy on flight behavior and metabolism.

Three experiments were performed to determine why removal of the corpora allata (the glands that produce juvenile hormone) causes honey bees to fail to return to their hive upon initiating flight. In Experiment 1, the naturally occurring flights of allatectomized bees were tracked with radar to determine whether the deficit is physical or cognitive. The results indicated a physical impairment: allatectomized bees had a significantly slower ground speed than sham and untreated bees during orientation flights, but otherwise attributes such as flight range and area were normal. Flight impairment was confirmed in Experiment 2, based on observations of takeoff made in the field at the hive entrance. The allatectomized group had a significantly smaller percentage of flightworthy bees than did the sham and untreated groups. Experiment 3 confirmed the flight impairment in laboratory tests and showed that allatectomy causes a decrease in metabolic rate. Allatectomized bees had significantly lower metabolic rates than untreated and sham bees, while allatectomized bees receiving hormone replacement had intermediate values. These results indicate that allatectomy causes flight impairment, probably partly due to effects on metabolic rate. They also suggest that juvenile hormone plays an additional, previously unknown, role in coordinating the physiological underpinning of division of labor in honey bee colonies.

Animals↗

PubMed2002

Genetic determination of the queen caste in an ant hybrid zone.

The question of how reproductives and sterile workers differentiate within eusocial groups has long been a core issue in sociobiology because it requires the loss of individual direct fitness in favor of indirect or group-level fitness gains. The evolution of social behavior requires that differentiation between workers and female reproductives be environmentally determined, because genetically determined sterility would be quickly eliminated. Nevertheless, we report clear evidence of genetic caste determination in populations of two seed harvester ant species common to the southwestern USA, Pogonomyrmex rugosus and Pogonomyrmex barbatus. The genetic differentiation between workers and queens is found only in areas of sympatry of the two species, and thus appears to arisen from hybridization. Our data suggest that this hybridization has had a profound historical effect on the caste determination systems and mating patterns of each of these species.

Animals↗

PubMed2002

Environmental and genetic influences on flight metabolic rate in the honey bee, Apis mellifera.

Flying honey bees demonstrate highly variable metabolic rates. The lowest reported values (approximately 0.3 Wg(-1)) occur in tethered bees generating the minimum lift to support their body weight, free-flying 2-day old bees, winter bees, or bees flying at high air temperatures (45 degrees C). The highest values (approximately 0.8 Wg(-1)) occur in foragers that are heavily loaded or flying in low-density air. In different studies, flight metabolic rate has increased, decreased, or remained constant with air temperature. Current research collectively suggests that this variation occurs because flight metabolic rates decrease at thorax temperatures above or below 38 degrees C. At 30 degrees C, approximately 30% of colonial energy is spent during typical foraging, so variation in flight metabolic rate can strongly affect colony-level energy balance. Higher air temperatures tend to increase colonial net gain rates, efficiencies and honey storage rates due to lower metabolic rates during flight and in the hive. Variation in flight metabolism has a clear genetic basis. Different genetic strains of honey bees often differ in flight metabolic rate, and these differences in flight physiology can be correlated with foraging effort, suggesting a possible pathway for selection effects on flight metabolism.

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