Factors affecting soldier allocation in clonal aphids: a life-history model and test

Aphid species using a defensive soldier caste offer us the opportunity to study allocation decisions by eusocial groups, without the hindrance of genetic dissimilarity between colony members, which often impair studies involving Hymenopteran or Isopteran systems. When the entire aphid clone is considered the adaptive unit of organization, understanding soldier allocation strategies is tantamount to understanding the outcome of the tradeoff between clonal growth (i.e., asexual reproduction) and clonal defense. Under this framework, we present the results of a dynamic programming effort aimed at determining the optimal ontogeny of defensive allocation strategies by eusocial clonal organisms. We consider the allocation decision for clones with both obligately and facultatively sterile soldiers, under various levels of predation, and favorable and unfavorable ecological conditions. We test predictions of the model with the eusocial aphid, Pemphigus spyrothecae. Our model predicts that defensive investment should be dependent on the time of the season, with clones discounting defense nearer the end of season. Defensive investment should also vary inversely with clonal productivity and be sensitive to the current state (e.g., level of defense) of the clone. Census data collected in Burnaby, British Columbia, Canada, conform to patterns of clonal composition derived from allocation decisions generated in the model. Finally, qualitative predictions about patterns of clonal organization under "good" and "poor" ecological conditions were upheld by comparing clones in preferred and less-preferred galling sites. Copyright 2004.colony defense; dynamic programming model; eusocial aphids; Pemphigus spyrothecae; soldier allocation strategies; tradeoffs

Pouncing spider, flying mosquito: blood acquisition increases predation risk in mosquitoes

Female mosquitoes dramatically increase their mass when blood feeding on their hosts. Such an increase could impact mosquito mortality risk by reducing escape speed and/or agility. We used two laboratory-based experiments to test this notion. In the first, we allowed mature female Anopheles gambiae mosquitoes to feed from 0 to 4 min and then attacked those females with an artificial predator. We videotaped subsequent escape response of each mosquito. Analysis of those responses clearly demonstrated an inverse relationship between increased mass and escape speed. In the second experiment, we exposed both blood-engorged and unfed A.gambiae females to single zebra spiders (Salticus scenicus) in small plexiglass cages. Here, we focused on mosquito escapes from searching and pouncing spiders. We found that engorged mosquitoes were three times less likely to escape searching spiders compared to unfed conspecifics. Thus we conclude that blood feeding has substantial state-dependent risk both at the host (experiment 1) and after feeding (experiment 2). Such risk can be extended to a broad range of taxa. Copyright 2003.

Experimental demonstration of ecological character displacement

Background: The evolutionary consequences of competition are of great interest to researchers studying sympatric speciation, adaptive radiation, species coexistence and ecological assembly. Competition's role in driving evolutionary change in phenotypic distributions, and thus causing ecological character displacement, has been inferred from biogeographical data and measurements of divergent selection on a focal species in the presence of competitors. However, direct experimental demonstrations of character displacement due to competition are rare. Results We demonstrate a causal role for competition in ecological character displacement. Using populations of the bacterium Escherichia coli that have adaptively diversified into ecotypes exploiting different carbon resources, we show that when interspecific competition is relaxed, phenotypic distributions converge. When we reinstate competition, phenotypic distributions diverge. Conclusion This accordion-like dynamic provides direct experimental evidence that competition for resources can cause evolutionary shifts in resource-related characters.Mathematics, Department ofZoology, Department ofNon UBCScience, Faculty ofReviewedFacult

Metabolic Changes Associated With Adaptive Diversification in Escherichia coli

During a 1000-generation evolution experiment, two types of morphologically and kinetically distinct bacteria repeatedly diverged from a common ancestor in a fully sympatric seasonal environment containing glucose and acetate. To investigate the metabolic modifications associated with this adaptive diversification, we compared transcription profiles of the two derived types and the common ancestor. Both derived types share a suite of common metabolic changes that may represent adaptation to the environment preceding the diversification event. These include improved translation efficiency, glucose uptake capacity via the mal/lamB genes, upregulation of various transporters during stationary phase, and likely the disruption of the rbs operon. The diversification event is associated with the overexpression of genes involved in the TCA cycle, glyoxylate shunt, acetate consumption, and anaerobic respiration in one type and in acetate excretion in the other. These results reveal that competition for both carbon and oxygen have likely played an important role in the adaptation of Escherichia coli during this adaptive diversification event, where one derived type mainly consumes glucose at a fast rate when oxygen is not limiting, and the other derived type consumes glucose and acetate at a slower rate, even when oxygen is limiting