Geographic variation of freeze-tolerance in the earthworm Dendrobaena octaedra

Freeze-tolerance and some of the underlying biochemical defence mechanisms in the earthworm Dendrobaena octaedra was investigated. Survival after slow cooling to -2 degrees C, -4 degrees C, or -6 degrees C was analysed in D. octaedra from three geographic regions representing large differences in winter temperature (Denmark, Finland and Greenland). A large variation in freeze-tolerance between the three populations of D. octaedra was found. Earthworms from the northern populations (Finland and Greenland) tolerated lower temperatures (-6 degrees C) than earthworms from the Danish population (poor survival at -4 degrees C and -2 degrees C). In the Finnish population, freezing led to the production of high concentrations of glucose, which reached values much higher than controls (94 mg g(-1) vs. 2 mg g(-1) dry weight). Other potential cryoprotectants were not elevated after freezing. The Danish and Greenlandic populations had substantially lower mean glucose levels after freezing than the Finnish population (about 15 mg g(-1)). Danish earthworms rapidly frozen did not accumulate glucose, and did not survive freezing at -2 degrees C. Danish earthworms exposed to osmotic stress in Ringer's solutions, containing different concentrations of glycerol, showed significantly elevated glucose levels, but did not survive rapid freezing. It was determined if freezing had an influence on the reproduction of the earthworms. After warming to summer temperatures (15 degrees C), survivors of freezing produced viable cocoons. In a field experiment it was tested if natural acclimatization during autumn and winter months had an effect on freeze-tolerance in the Danish population. There was a significant increase of post-freeze survival during this period. The results of the freezing experiments are discussed in relation to the general ecology of D. octaedra.     

Sublethal parameters in morphologically deformed Chironomus larvae: clues to understanding their bioindicator value

1. Parameters of condition between normal and deformed fourth instar larvae of Chironomus gr. thummi (Kieffer 1911) were compared in four populations: one reference (PE) and two metal-polluted sites (NP and SCH) in the River Dommel, and one site polluted by domestic sewage and copper in the River Ijse (NEI).
2. The site PE ranked lowest for metal body burdens, deformities, mortalities and emergence duration, while SCH and NEI ranked highest.
3. Deformed and non-deformed larvae most often did not differ in length and weight ( in situ end-points for growth); when differences occurred, deformed larvae tended to be smaller.
4. The energy content and dry weights in one population (NEI) were lower in normal larvae than in the weakly deformed ones. The percentage of ash-free dry weight was lower in deformed larvae of the polluted Dommel sites, compared to the normal ones.
5. The in vitro emergence rate (end-point for development of fourth instars) for the reference population PE, both in its own sediment and in artificial cellulose substrate, was better than for the other sites. In two populations (NEI, SCH) the development of deformed larvae in their own sediment was slower, with higher mortality, than for the normal larvae. In one population (NP), normal and deformed larvae survived and developed equally well. The emergence rates of the respective populations were similarly ranked when the larvae were raised in an artificial cellulose substrate.
6. Elution peaks of alleged metal-binding proteins were lower in deformed larvae from SCH and NEI, but higher in deformed larvae from NP, than in normal larvae.
7. A different development rate and mortality of deformed larvae in non-adapted populations and the possibility of metal adaptation, as in site NP, may modulate the final outcome of deformity frequencies, thus having an impact on the biomarker value of deformities in benthic midge larvae.     

Chromosomal aberrancy and the level of fluctuating asymmetry in black-striped mouse (Apodemus agrarius): effects of disturbed environment

Analysis of chromosomal aberrations in bone marrow cells and determination of the level of fluctuating asymmetry (FA) for eight bilateral cranial traits were used to estimate effects of disturbed environment on natural populations of small mammals. During the spring and fall of 1994-2000 (except in 1999) black-striped mice (Apodemus agrarius) were collected from a polluted industrial area (Pancevo) and from an unpolluted reference site (Cer) in Serbia and Montenegro. Mice from the polluted area had significantly higher mean number of aberrant cells per individual than those in the reference site (p<0.01). Both sexes had the greater number of lesions in the polluted site than in the reference one. Also, there were no significant differences between sexes, neither within the same site/season nor between sites/seasons. Chi-square analysis of the difference between lesions per individual and aberrant cells per individual among sites showed that no site deviated from the expected difference (p=1.000). Developmental stability, assessed as FA, was reduced in the polluted area for two traits (width of lower jaw and length of the diastema lower jaw). Juvenile animals from the polluted area had significantly higher levels of FA compared to those from the reference site for three traits (length of the foramina incisiva, distance between incisor and the third upper molar, and length of the upper molars row). Juvenile animals from the polluted area had significantly higher levels of FA for three traits (length of the foramina incisiva, length of the lower molars row and width of lower jaw) compared to adult ones. In the polluted area seasonal differences were detected for two traits (length of the foramina incisiva and length of the upper molars row). Finally, Apodemus agrarius may be an important species for environmental quality evaluation studies based on an assay using a combination of end-points.     

Pollution-related changes in diets of two insectivorous passerines

Insectivorous birds living in polluted areas are not only exposed to pollutants but they may also be affected by changes in their invertebrate food. The populations of many invertebrate species are affected by environmental pollution and such changes may lead to differences in the diet of insectivorous birds. We examined nestling food quality (invertebrate composition and heavy metal levels) and breeding performance of two cavity-nesting passerines, the Great tit, Parus major, and the pied flycatcher, Ficedula hypoleuca, in an area with long-term heavy metal pollution by a copper smelter. There were no differences in feeding frequencies or the amount of food that parents provided to their nestlings between polluted and unpolluted sites, but food quality in a polluted area differed from that of the control area in both bird species. P. major took more beetles and variable “flying insects” and less caterpillars (of smaller size) and moths in the polluted area as compared to the unpolluted one. F. hypoleuca ate more beetles and larvae and less moths and spiders in the polluted area. Breeding success of P. major was better when the nestling diet contained a large proportion of caterpillars and the relationship was especially strong in the polluted area. On the contrary, F. hypoleuca broods succeeded equally well with variable diets. Our data suggest that a more opportunistic forager, F. hypoleuca, is less vulnerable to a changing invertebrate composition caused by human environmental impacts than a caterpillar specialist, P. major. In a heavy metal polluted area, F. hypoleuca seems to be more sensitive to a decreased amount of Ca rich food items (e.g. snails) while P. major suffers especially from the lack of carotenoid rich caterpillars. Our results emphasize the importance of secondary environmental changes, like food quality, in addition to direct impacts of pollutants.     

Heavy-metal adaptation in terrestrial invertebrates: A review of occurrence,genetics, physiology and ecological consequences

1. The occurrence of genetic adaptation to heavy metals in natural populations of terrestrial invertebrates is evaluated from literature data. Five criteria for adaptation evidence are applied, with concepts from ecotoxicology, ecology, life-history theory and quantitative genetics.2. There is strong evidence for the occurrence of adaptation in natural populations of the isopod Porcellio scaber (Isopoda), the springtails Isotoma notabilis, Onychiurus armatus and Orchesella cincta (Collembola), the blowfly Lucilia cuprina and the fruit fly Drosophila melanogaster (Diptera). Adaptation to metal-containing pesticides has been demonstrated in ticks (Acarina). Population divergence indicates acclimation or adaptation in many other species.3. Metal adaptation has been achieved within a few generations under laboratory conditions in some species; adapted populations occur at field sites that have been polluted for decades, or longer.4. Genetic variation for tolerance and life-history characteristics, allowing for adaptation, was quantified in a reference population of Orchesella cincta. Tolerance and life-history patterns in exposed field populations matched predictions from genetic variation.5. Adaptation involves modification and intensification of existing physiological mechanisms for metal assimilation, excretion, immobilization or compartmentalized storage. There are indications ofinter-population divergence in metal-binding proteins in a snail. In the fruit fly Drosophila melanogaster metal adaptation is achieved by duplication of the metallothionein gene.6. An altered life-history is often part of the complex adaptation syndrome. Metal-adapted invertebrates have a shorter life-cycle and a higher reproductive effort.7. Possible consequences of adaptation, consisting of costs of tolerance determined by genetic correlations, and probably of reduced genetic variation for tolerance and other features, are discussed. Reduced genetic variation is suggested by results for the springtail Orchesella cincta.8. The distinction between “costs of tolerance” on the one hand and linkage disequilibrium or direct selection for altered life-history patterns on the other hand is discussed.9. Species with high sensitivity (i.e. a low NOEC), that do not have populations maintaining sufficient genetic variation to evolve tolerance or modified life-history characteristics, or that have costly tolerance mechanisms, or both, are most at risk for extinction at sites with increasing metal pollution.10. Metal adaptation in terrestrial invertebrates appears to be of degree rather than of kind: indications for a specific metal-fauna, equivalent to metal-vegetation, are lacking.     

Freeze tolerance in Aporrectodea caliginosa and other earthworms from Finland

Earthworms that live in subarctic and cold temperate areas must deal with frost even though winter temperatures in the soil are often more moderate than air temperatures. Most lumbricid earthworms can survive temperatures down to the melting point of their body fluids but only few species are freeze tolerant, i.e. tolerate internal ice formation. In the present study, earthworms from Finland were tested for freeze tolerance, and the glycogen reserves and glucose mobilization (as a cryoprotectant) was investigated. Freeze tolerance was observed in Aporrectodea caliginosa, Dendrobaena octaedra, and Dendrodrilus rubidus, but not in Lumbricus rubellus. A. caliginosa tolerated freezing at -5 degrees C with about 40% survival. Some individuals of D. octaedra tolerated freezing even at -20 degrees C. Glycogen storage was largest in D. octaedra where up to 13% of dry weight consisted of this carbohydrate, whereas the other species had only 3-4% glycogen of tissue dry weight. Also glucose accumulation was largest in D. octaedra which was the most freeze-tolerant species, but occurred in all four species upon freezing. It is discussed that freeze tolerance may be a more common phenomenon in earthworms than previously thought.     

Cold acclimation and lipid composition in the earthworm Dendrobaena octaedra

We have investigated the lipid chemistry during cold acclimation in the freeze tolerant earthworm Dendrobaena octaedra. The dominant phospholipid fatty acids (PLFA) of D. octaedra were 20:4, 20:5 and 20:1 (50% of total PLFA) followed by 18:0, 18:1 and 18:2omega6,9 (25% of total PLFA). The ability to tolerate freezing in this species was acquired after acclimation at low temperature for 2-4 weeks. During this period one particular membrane PLFA, 18:2omega6,9, increased significantly and there was a good correlation between the proportion of this PLFA and the survival of freezing. The composition of neutral lipid fatty acids (NLFA), most likely representing storage lipids (triacylglycerides), also changed during cold acclimation so that the overall degree of unsaturation increased. Using a common-garden experiment approach, we compared lipid composition of three genetically different populations (Denmark, Finland and Greenland) that differed in their freeze tolerance. Inter-populational differences and differences due to cold acclimation in overall fatty acid composition were evident in both PLFAs and NLFAs. Specifically, the PLFAs, 20:4 and 20:5, were considerably more represented in worms from Greenland, and this contributed to a higher UI of PLFAs in this population.     

Mountain birch under multiple stressors – heavy metal‐resistant populations co‐resistant to biotic stress but maladapted to abiotic stress

Stress adaptations often include a trade‐off of weakened performance in nonlocal conditions, resulting in divergent selection, and potentially, genetic differentiation and evolutionary adaptation. Results of a two‐phase (greenhouse and field) common garden experiment demonstrated adaptation of mountain birch (Betula pubescens subsp. czerepanovii) populations from industrially polluted areas of the Kola Peninsula, north‐western Russia, to heavy metals (HM), whereas no adaptations to wind or drought stress were detected in populations from wind‐exposed sites. HM‐adapted seedlings were maladapted to drought but less palatable (co‐resistant) to insect herbivores, even under background HM concentrations. The absence of adaptations to harsh microclimate and the generally high adaptive potential of mountain birch, a critical forest forming tree in subarctic Europe, need to be accounted for in models predicting consequences of human‐driven environmental changes, including the projected climate change.     

Determining factors for cryoprotectant accumulation in the freeze-tolerant earthworm, Dendrobaena octaedra

The freeze-tolerant earthworm Dendrobaena octaedra is found in most of the European forest and tundra, Siberia, North America and Greenland where it over-winters in the top soil and encounters winter frost. In response to freezing this earthworm rapidly synthesises glucose which acts as a cryoprotectant. Frost tolerance varies extensively between geographical populations, and of the populations studied so far, the Finnish worms are most and the Danish worms least frost tolerant. Little is known about the determining factors for glucose synthesis and this study therefore investigated possible roles of acclimation and the cues for synthesis of glucose, in Finnish and Danish worms. The Finnish population had significantly larger glycogen reserves than the Danish during acclimation and in all worms, glucose synthesis was the result of an almost stoichemical reduction in glycogen stores. Maximum glucose levels were reached after the onset of freezing and were significantly higher in Finnish worms where the sugar accounted for as much as 5% of the fresh weight. On average, both the total glycogen phosphorylase activity and the active enzyme pool increased during acclimation in the Finnish but not the Danish populations. However, the increase in this enzyme was only significant during the freezing process. In this study, we show contrary to previous theory that glucose synthesis is initiated before the onset of freezing and that in this species, cryoprotectant synthesis is sensitive to very small temperature changes below 0 degrees C without the presence of ice.     

Postponed reproduction as an adaptation to winter conditions in Drosophila melanogaster: evidence for clinal variation under semi-natural conditions

Patterns of climatic adaptation in drosophila and other insects have largely been inferred from laboratory comparisons of traits that vary clinally. Here, we extend this research to comparisons under semi-natural conditions. To test for clinal variation in reproductive patterns and survival over winter, Drosophila melanogaster populations were initiated from seven collection sites along the eastern coast of Australia, ranging from tropical to temperate regions. The fecundity and survival of these populations were monitored in field cages at a temperate location until all adults had died more than 5 months later. Total fecundity showed a curvilinear relationship with latitude, due to higher egg production by high- and low-latitude populations. Adults from temperate locations survived winter conditions better than those from subtropical populations but not tropical ones. There was a linear cline in the timing of egg production: temperate populations produced eggs later than populations from lower latitudes. This cline is likely to be adaptive because egg-to-adult viability experiments indicated that only eggs laid in spring developed successfully to the adult stage. There was no evidence for climatic adaptation in the immature stages. The adult mortality rate increased gradually over winter, and in some populations was also correlated with the minimum ambient temperature. These results indicate that adaptation to winter conditions in D. melanogaster has involved shifts in reproductive patterns.     

Physiology of cold hardiness in cocoons of five earthworm taxa (Lumbricidae: Oligochaeta)

Earthworm cocoons are mostly found in the uppermost soil layers and are therefore often exposed to low temperatures during winter. In the present study, cocoons of five taxa of earthworms were investigated for their tolerance to freezing, melting points of cocoon fluids and dehydration of cocoons when exposed to a frozen environment. Embryos of the taxa investigated were freeze intolerant. The melting points of fully hydrated cocoon fluids were high (above –0.3°C) and thermal hysteresis factors were absent. Exposure to a frozen environment caused the cocoons to dehydrate drastically and dehydrated cocoons showed significantly lower super-cooling points than fully hydrated cocoons, reducing the risk of freezing for dehydrated cocoons. It is proposed therefore that the cold-hardiness strategy of the earthworm cocoons is based on dehydration upon exposure to subzero temperatures in the frozen environment. Cocoons of three surface-dwelling taxa, Dendrobaena octaedra, Dendrodrilus rubidus tenuis and Dendrodrilus rubidus norvegicus had lower supercooling points and survived frost exposure better than cocoons of two deeper-dwelling taxa, Aporrectodea caliginosa and Allolobophora chlorotica. One of the investigated taxa, D. r. norvegicus, was collected from a cold alpine habitat. However, it was not more cold hardy than the closely related D. r. tenuis collected from a lowland temperate habitat. D. octaedra was the most cold hardy taxon, its cocoons being able to withstand –8°C for 3 months and –13.5°C for 2 weeks in frozen soil.Abbreviations dw dry weight - fw fresh weight - SCP supercooling point     

Elevated standard metabolic rate in a freshwater shrimp (Palaemonetes paludosus) exposed to trace element-rich coal combustion waste

I conducted a transplant experiment to determine whether standard metabolic rate (SMR) of a freshwater shrimp (Palaemonetes paludosus) would be affected by exposure to trace element-enriched coal combustion waste (‘coal ash'). Shrimp were transplanted into replicate cages in a coal ash-polluted site and a reference site for 8 months. The coal ash-polluted site was characterized by elevated sediment concentrations of As, Cd, Cr, Cu, Ni, Pb, and Se compared to sediments in the reference site. After 8 months in the study sites, shrimp in the polluted site appeared to have accumulated As, Cd, and Se from the habitat, but there were no differences in survival between the study sites. However, mean SMR of shrimp (measured as O₂ consumption at rest) held in the polluted site was 51% higher than mean SMR of shrimp held in the reference site. The elevation in SMR indicates that the energetic costs of maintenance are greater for shrimp chronically exposed to the coal-ash polluted environment than shrimp in the reference site. It is likely, therefore, that other physiological or behavioral processes may be modified in the pollution-exposed individuals to compensate for the increased energy demands for maintenance. Recent studies have reported similar elevations in SMR in an amphibian and a reptile chronically exposed to coal ash. Analogous physiological responses in such taxonomically diverse animals (a crustacean, an amphibian, and a reptile) indicate that elevated SMR may be a general response by many types of organisms exposed to the mixture of trace elements characteristic of coal ash. The relationships among pollution-induced elevations in maintenance expenditures, long-term health of individuals, and population-level parameters require further attention.     

Effects of waterborne copper or zinc on the osmoregulatory response of bluegill to a hypertonic NaCl challenge

1. Bluegill (Lepomis macrochirus) were exposed to copper (0.77 mg/1) or zinc (2.35 mg/1) for 7 days after which they were challenged by being placed in a 250 mM NaCl solution.2. Non-metal exposed controls started to die in the NaCl after 8 hr but those that had been exposed to copper survived at least 22 hr and some survived for at least 3 days. Zinc exposure also caused better survival in the hypertonic NaCl but not to the same extent.3. Blood plasma osmolality, chloride, and protein, as well as the hematocrit, muscle and liver water, and gill Na-K-activated ATPase were determined in fish before and after 8 hr in the NaCl.4. Metal exposure alone produced no significant effects on the variables measured except for a decline in plasma chloride in zinc-exposed fish.5. Both copper- and zinc-exposed fish exhibited less of an increase in chloride upon being challenged with the NaCl than did controls. Osmolality showed a similar effect from copper but not from zinc exposure. Metal exposure produced no other differences.6. All fish exhibited an elevated hematocrit but no change in plasma protein or tissue water when challenged. The elevated hematocrit is probably a non-specific stress response. The other data are consistent with the hypothesis that there was an influx of salt but little if any efflux of water while in the hypertonic NaCl.7. The data suggest indirectly that copper, and to a much lesser extent zinc, seemed to reduce the permeability of the gills to an influx of chloride in this stenohaline species.     

The effect of temperature on larval pre-settlement duration and metamorphosis for the sponge, <Emphasis Type="Italic">Rhopaloeides odorabile</Emphasis>

Rising sea temperatures may potentially affect the dispersive larval phase of sessile marine invertebrates with consequences for the viability of adult populations. This study demonstrated that the planktonic larvae of Rhopaloeides odorabile, a common Great Barrier Reef sponge, survived and metamorphosed when exposed to temperatures up to 9°C above the annual maximum (~29°C). Planktonic larval duration of 54 h, at ambient temperatures (~28°C), were reduced to 18 h for larvae exposed to elevated temperatures (32–36°C). Moreover, at ambient temperatures larvae began metamorphosing after 12 h, but at 32–36°C this reduced to only 2 h. Larvae survived and could still metamorphose at temperatures as high as 38°C, but were no longer functional at 40°C. These results imply that predicted increases in sea surface temperature may reduce planktonic larval duration and dispersal capabilities, thereby contributing to population subdivision of the species.     

Echinostoma revolutum: resistance to secondary and superimposed infections in mice

A complete or almost complete resistance (94-100%) to a superimposed Echinostoma revolutum infection existed in mice harboring 20-, 30-, and 40-day-old infections in the range of 2-4 to 30-35 worms, but no resistance was found at challenge Day 10. A similar high level of resistance (85-100%) also existed in mice for at least 6 weeks after natural expulsion of a primary 6 metacercarial infection and for at least 5 weeks after anthelmintic termination of a 30-day-old 20 metacercarial infection. Thymus-deficient nude mice failed to develop resistance to a superimposed infection, and the resistance in normal mice was inhibited by corticosteroid treatment. These findings are all in favor of a host immune response being responsible for the resistance against both a secondary and a superimposed infection. Nearly all the worms of a superimposed infection were, in resistant mice, expelled prior to 24 hr following infection (rapid expulsion), and the few worms circumventing this early expulsion persisted for at least 8 days. Newly excysted juvenile worms implanted intraduodenally into resistant mice were rejected to the same degree as juvenile worms from an oral metacercarial infection indicating that the newly excysted juvenile worms are the target of the host immune response. However, 7-day-old worms implanted intraduodenally into resistant mice survived indicating that adaptation to the host immune response had occurred. In conclusion, this host-parasite model is an example of concomitant immunity because the immunological mechanism responsible for the expulsion of the superimposed infection had no effect on the number of primary worms present.     

Linking temperature dependence of fitness effects of mutations to thermal niche adaptation

Fitness effects of mutations may generally depend on temperature that influences all rate-limiting biophysical and biochemical processes. Earlier studies suggested that high temperatures may increase the availability of beneficial mutations (‘more beneficial mutations’), or allow beneficial mutations to show stronger fitness effects (‘stronger beneficial mutation effects’). The ‘more beneficial mutations’ scenario would inevitably be associated with increased proportion of conditionally beneficial mutations at higher temperatures. This in turn predicts that populations in warm environments show faster evolutionary adaptation but suffer fitness loss when faced with cold conditions, and those evolving in cold environments become thermal-niche generalists (‘hotter is narrower’). Under the ‘stronger beneficial mutation effects’ scenario, populations evolving in warm environments would show faster adaptation without fitness costs in cold environments, leading to a ‘hotter is (universally) better’ pattern in thermal niche adaptation. We tested predictions of the two competing hypotheses using an experimental evolution study in which populations of two model bacterial species, Escherichia coli and Pseudomonas fluorescens, evolved for 2400 generations at three experimental temperatures. Results of reciprocal transplant experiments with our P. fluorescens populations were largely consistent with the ‘hotter is narrower’ prediction. Results from the E. coli populations clearly suggested stronger beneficial mutation effects at higher assay temperatures, but failed to detect faster adaptation in populations evolving in warmer experimental environments (presumably because of limitation in the supply of genetic variation). Our results suggest that the influence of temperature on mutational effects may provide insight into the patterns of thermal niche adaptation and population diversification across thermal conditions.     

Evolution of increased cold tolerance during range expansion of the elongate hemlock scale Fiorinia externa Ferris (Hemiptera: Diaspididae)

Abstract 1. Alien species often face novel challenges to their spread and population growth. One critical hurdle often involves an organism’s ability to tolerate environmental extremes characteristic of their invaded range. Although abiotic factors often determine range limits, there is less evidence for local adaptation in invasive organisms whose initial arrival and rapid population growth is separated by a lengthy lag period. 2. The invasive elongate hemlock scale Fiorinia externa feeds on Eastern hemlock, Tsuga canadensis, on the east coast of North America. Following its 1908 arrival, it remained localised until entering a period of rapid northward range expansion in the 1970s. 3. The present study tested the survival of overwintering F. externa populations from four sites in the north and south of the invaded range (n = 8 sites total) when exposed to ?15 °C for 0–36 h. 4. This experiment was repeated on F. externa offspring that had been reared in a common‐garden environment in order to control for parental effects. 5. Northern populations were more tolerant of exposure to cold temperatures than were southern populations. This held true in both the source‐population experiment and common‐garden experiment. The common‐garden experiment demonstrates that this difference has a genetic basis and may be the consequence of local adaptation to lower winter temperatures. 6. The results provide evidence for local adaptation to extreme temperatures in F. externa. This provides one possible explanation for the lag period between the arrival of this species and its eventual northward range expansion.     

Developmental time,body size and wing loading in Drosophila buzzatii from lowland and highland populations in Argentina

Genotype-by-temperature interaction is a necessary condition for adaptive evolution of fitness traits as a response to temperature. Several fitness-related traits (developmental time, pre-adult survival, thorax and wing lengths, and wing loading) were measured in laboratory-reared D. buzzatii from four populations sampled at different altitudes in north-western Argentina: a lowland population (407 m a.s.l.), two populations from intermediate altitude (780 to 950 m a.s.l.), and a highland population (2380 m a.s.l.). Temperature is the main climatic difference between the collection sites: lowland but not highland populations are exposed to physiologically high temperatures during both spring and summer in nature. Three growth temperatures (20, 25 and 30 degrees C) were used to test for population-by-temperature interactions. Both developmental time and pre-adult survival exhibit highly significant population-by-temperature interaction. Pre-adult survival at 30 degrees C is significantly higher in lowland than in highland populations, but not so at lower growth temperatures (20 and 25 degrees C). Both wing length and wing loading show no population-by-temperature interaction, indicating that these traits are not the direct targets of thermal adaptation in nature. Wing loading is higher in highland than in lowland populations, suggesting that flight performance is subject to stronger selection in the highland population. This hypothesis is consistent with ecological observations in both types of populations. There is no obvious among-population relationship between developmental time and body size, even though both traits are related within populations in a well-known trade-off. Overall, thermal adaptation is evident for developmental time and pre-adult survival but not for size-related traits.     

Experimentally induced plague infection in the northern grasshopper mouse (Onychomys leucogaster) acquired by consumption of infected prey

In this study, 20 laboratory reared Onychomys leucogaster from a parental population that is naturally exposed to plague were each fed a white mouse that had been inoculated with Yersinia pestis. Three of the 20 O. leucogaster died, four survived with antibody titers against Y. pestis and 13 survived with no titer against Y. pestis. In contrast, when 20 O. leucogaster from a plague naive parental population were fed infected prey, seven died and 13 survived with no antibody titer against Y. pestis. Our results suggest another means by which O. leucogaster from populations that are naturally exposed to plague may acquire the disease.     

Thermal adaptation in the fungal pathogen Mycosphaerella graminicola

Genetic differentiation in thermal adaptation can result from a trade-off between the performance of organisms across different temperatures or from the accumulation of deleterious mutations. In this experiment, we assayed thermal sensitivity of 138 genetically distinct Mycosphaerella graminicola isolates sampled from five host populations in four locations under two temperature regimes (22 and 15 °C) and found significant differences in growth rate and response to temperature among populations. On average, genetic differentiation accounted for more than 50% of phenotypic variation in thermal adaptation while plasticity contributed less than a quarter of phenotypic variation. Populations originating from warm places performed better under the high-temperature regime and had a larger positive response to increasing temperature. Pairwise population differentiation (Q(ST) ) in temperature sensitivity, measured by taking the ratio of growth rates at 22 to 15 °C, was positively and significantly correlated to the pairwise difference in annual mean temperature at the collection sites. Because overall Q(ST) in temperature sensitivity was significantly higher than overall G(ST) in neutral restriction fragment length polymorphism loci, we believe that the primary mechanism underlying this thermal adaptation is antagonistic pleiotropy. Our results indicate that temperature sensitivity is a better indicator of thermal adaptation than growth rate at individual temperatures.