Isolation and characterization of microsatellite loci from the apple maggot fly Rhagoletis pomonella (Diptera: Tephritidae)

We report the isolation and development of 81 novel primers for amplifying microsatellite loci in the Rhagoletis pomonella sibling species complex, and the sequencing, characterization and analysis of basic population genetic parameters for nine of these genes. We also report the successful cross‐species amplification of several of these loci. The R. pomonella sibling species complex is a textbook example of genetic differentiation in sympatry via host‐plant shifting. Microsatellite markers can be useful for mapping host‐plant‐associated adaptations in Rhagoletis that generate reproductive isolation and facilitate speciation, as well as for resolving the genetic structure and evolutionary history of fly populations.     

Organismal, Ecological, and Evolutionary Aspects of Heat-Shock Proteins and the Stress Response: Established Conclusions and Unresolved Issues

How heat-shock proteins function in diverse organisms from diverseenvironments, and how this diversification has evolved, is anemerging focus of research on molecular chaperones. As molecularchaperones, heat-shock proteins play diverse cellular roles,typically in minimizing dysfunction that may occur when otherproteins are in non-native conformations. The standard aspectsof these roles in vitro, in isolated cells, and in typical modelorganisms in the laboratory are now well-established, as arethe ubiquity of heat-shock proteins in organisms, the rangeof stresses that induce heat-shock proteins, the major familiesof heatshock proteins, their expression in nature, and theirvariation along natural gradients of stress. These aspects mayno longer require extensive examination. By contrast, the frequencyof natural expression of heat-shock proteins, their exact physiologicalroles in stress tolerance at levels of biological organizationabove the cell, the exact molecular mechanisms by which heat-shockprotein expression and function has become tuned to the prevailinglevel of environmental stress, and the fitness consequencesof heat-shock protein expression in nature are among the numerousunresolved issues in this area.     

Natural and Genetic Engineering of the Heat-Shock Protein Hsp70 in Drosophila melanogaster: Consequences for Thermotolerance

SYNOPSIS. Larvae of the fruit fly, Drosophila melanogaster,live within necrotic fruit, a challenging environment in whichlarvae can experience severe thermal stress. One response tothermal stress, the expression of heat-shock proteins (Hsps),has evolved distinctively in this species; the gene encodingHsp70 has undergone extensive duplication and accounts for thebulk of Hsps that are expressed upon heat shock. Genetic engineeringof hsp70 copy number is sufficient to affect thermotoleranceat some (but not all) life stages. Increases in Hsp70, moreover,can protect intact larvae against thermal inactivation of theenzyme alcohol dehydrogenase and thermal inhibition of feeding.Deleterious consequences of high levels of Hsp70, however, maylimit further evolutionary proliferation of hsp70 genes. Thesefindings illustrate how the perspectives of integrative andcomparative biology, if applied to even well-studied model organisms,can lead to novel findings.     

CUTANEOUS GAS EXCHANGE IN VERTEBRATES: DESIGN, PATTERNS, CONTROL AND IMPLICATIONS

1. The exchange of oxygen and carbon dioxide between skin and environment is commonplace in the vertebrates. In many lower vertebrates, the skin is the major or even sole avenue for respiration.
2. As implied by the physical laws governing diffusion of gases, the skin diffusion coefficient, surface area, gas diffusion distance and transcutaneous gas partial pressures may independently or jointly affect cutaneous respiration. In vertebrates, each of these variables has undergone modification that may be related to dependence upon cutaneous gas exchange.
3. Both theoretical models and experimental data suggest that cutaneous gas exchange is limited by the rate of diffusion. However, changes in convection of the respiratory medium and of blood may partially compensate for diffusion limitation, and potentially function in the regulation of cutaneous gas exchange.
4. Typically, the skin is one of several gas exchangers, although many salamanders and some species in other vertebrate groups breathe solely through the skin. The cutaneous contribution to overall gas exchange is often most important in small animals, at cool temperatures, at low levels of activity and in normoxic and normocapnic conditions. Branchial and pulmonary respiration increasingly predominate in other circumstances.
5. Often, the skin figures more prominently in CO₂, excretion than in O₂, uptake.
6. Cutaneous gas exchange emerges in vertebrates as a process perhaps less effective and more constrained than branchial or pulmonary exchange but also less energetically costly. Its utility is indicated by its wide and successful exploitation in vertebrates occupying a diverse array of habitats.     

Ventilation and Its Effect on "Infinite Pool" Exchangers

SYNOPSIS. Unlike internal exchange surfaces, the skin contactsan "infinite pool" of air or water with which exchange of gases,water, ions, and other solutes may occur. Even though the "infinitepool" may be well mixed, an unstirred diffusion boundary layeris always present about the skin and may constitute a significantresistance to exchange. The thickness of the diffusion boundarylayer (as approximated by the fluid dynamic boundary layer)is related to the flow of the respiratory medium, viscosityand density of the medium, and the morphology of the exchangesurface. Oxygen microelectrode studies suggest that, in mostcircumstances, the diffusion boundary layer in water is at leastas thick as the blood-respiratory medium distance in amphibianskin. Accordingly, the movement of water about the skin {i.e.,skin ventilation) should have pronounced effects on cutaneousexchange, especially at low "free stream" velocities. Mountingphysiological evidence suggests that: (1) skin ventilation canaugment cutaneous gas exchange; and (2) some vertebrates activelyventilate their skins, especially in aquatic hypoxia. The ubiquityand significance of diffusion boundary layers are central toa general understanding of cutaneous exchange and all surface-mediatedexchange processes.     

Space,sympatry and speciation

Sympatric speciation remains controversial. ‘Sympatry’ originally meant “in the same geographical area”. Recently, evolutionists have redefined ‘sympatric speciation’ non‐spatially to require panmixia (m = 0.5) between a pair of demes before onset of reproductive isolation. Although panmixia is a suitable starting point in models of speciation, it is not a useful definition of sympatry in natural populations, because it becomes virtually impossible to find or demonstrate sympatry in nature. The newer, non‐spatial definition fails to address the classical debate about whether natural selection within a geographic overlap regularly causes speciation in nature, or whether complete geographic isolation is usually required. We therefore propose a more precise spatial definition by incorporating the population genetics of dispersal (or ‘cruising range’). Sympatric speciation is considerably more likely under this spatial definition than under the demic definition, because distance itself has a powerful structuring effect, even over small spatial scales comparable to dispersal. Ecological adaptation in two‐dimensional space often acts as a ‘magic trait’ that causes pleiotropic reductions of gene flow. We provide examples from our own research.     

Isolation and characterization of novel dinucleotide repeat microsatellites in the Jamaican click beetle Pyrophorus plagiophthalamus (Coleoptera: Elateridae)

We report 10 polymorphic microsatellite loci for the Jamaican click beetle, Pyrophorus plagiophthalamus. A survey of 36 individuals from three populations in Jamaica showed that these are highly variable, with three to 17 alleles per locus. Observed heterozygosity ranged from 0.250 to 0.917, and mean heterozygosity from 0.601 to 0.747. Most loci were in Hardy–Weinberg equilibrium, although excess of homozygotes was observed in four tests (out of 20), suggesting the possibility of null alleles. Significant linkage disequilibrium was observed for only one pair. These newly developed markers will be useful in understanding the population structure of click beetles in Jamaica, and in identifying possible selective factors responsible for bioluminescent colour variation.     

A genomic walking method for screening sequence length polymorphism

We adapted a recently developed nonrestrictional, nonligational genome walking method, Universal Fast Walking (UFW), for detection of length polymorphism in the proximal promoter region of genes. We demonstrate its efficacy at discovering naturally occurring transposition into heat‐shock genes of wild Drosophila and show that it surmounts limitations of simple polymerase chain reaction (PCR) approaches. We further present modifications to the standard UFW protocol and provide some guidelines to improve specificity. Although the resultant banding pattern of a standard UFW can be regarded as a DNA fingerprint, many amplicons result from false priming and not real polymorphisms. We describe ways to distinguish between UFW amplicons and false priming products in a high‐throughput assay.