Ecological Generalists Research Articles

Are endemic snakes with a narrow distribution more specialist than their wide-ranging counterparts? Evidence from the prey composition and morphometric correlates of the diet in Zamenis lineatus, a rat snake endemic to southern Italy

Abstract The snakes of the Mediterranean regions are in general characterised as wide ranging with relatively unspecialised ecological traits (e.g., feeding ecology and diet composition). The few endemic snake species with a narrow range can be of great interest to control whether the relative ecological non-specialization is truly general for Mediterranean snakes or if, on the contrary, those species with a small range are so because of their more specialised ecology. Here, we study the case of the Italian Aesulapian snake, Zamenis lineatus, which is endemic to southern Italy and the island of Sicily, and that has been for long time considered merely as a subspecies of the widespread Zamenis longissimus. We studied the diet of this species in the wild, and also examined snout-vent length and head length in several museum vouchers in order to highlight the eventual morphometric correlates of diet composition. Our results showed (i) a diet based on small mammals and birds, (ii) an evident ontogenetic shift in diet composition (from ectotherms to endotherms), and (iii) a lack of significant intersexual difference in diet composition. In addition, morphometric data revealed no intersexual differences in average snout-vent-length or head length. The general implications of these results are discussed. We conclude that, based on this study case, Zamenis lineatus feeding ecology was very similar to that of the widespread and ecological generalist Zamenis longissimus, and this is contrary to the hypothesis that endemic, narrowly distributed Mediterranean snakes may be more specialist than their widespread counterparts.

Evolution of Species: Explosive speciation in a cricket

Evolution of Species: Explosive speciation in a cricket

Neogastroplites meets Metengonoceras: morphological response of an endemic hoplitid ammonite to a new invader in the mid-Cretaceous Mowry Sea of North America

High levels of morphological variability have been attributed to various ecological and developmental mechanisms, including selection for ecological generalists in an unstable environment, inherent developmental plasticity, and the absence of competitors in an empty ecosystem. The late Albian–early Cenomanian hoplitid ammonite Neogastroplites of the Mowry Sea of North America, notorious for its extreme levels of intraspecific variability, is used as a test case of the idea that a lack of competitors promotes variability. The group responded to the invasion of a second ammonite, the engonoceratid Metengonoceras, into the Mowry Sea by spreading into a previously unoccupied region of morphospace, suggesting possible ecological character displacement and a release from constructional constraints. However, morphological variability did not decrease, as would be predicted by the competition model. The variability of Neogastroplites might instead result from environmental instability or developmental flexibility.

Biotic effects of late Maastrichtian mantle plume volcanism: implications for impacts and mass extinctions

During the late Maastrichtian, DSDP Site 216 on Ninetyeast Ridge, Indian Ocean, passed over a mantle plume leading to volcanic eruptions, islands built to sea level, and catastrophic environmental conditions for planktic and benthic foraminifera. The biotic effects were severe, including dwarfing of all benthic and planktic species, a 90% reduction in species diversity, exclusion of all ecological specialists, near-absence of ecological generalists, and dominance of the disaster opportunist Guembelitria alternating with low O 2-tolerant species. These faunal characteristics are identical to those of the K–T boundary mass extinction, except that the fauna recovered after Site 216 passed beyond the influence of mantle plume volcanism about 500 kyr before the K–T boundary. Similar biotic effects have been observed in Madagascar, Israel, and Egypt. The direct correlation between mantle plume volcanism and biotic effects on Ninetyeast Ridge and the similarity to the K–T mass extinction, which is generally attributed to a large impact, reveal that impacts and volcanism can cause similar environmental catastrophes. This raises the inevitable question: Are mass extinctions caused by impacts or mantle plume volcanism? The unequivocal correlation between intense volcanism and high-stress assemblages necessitates a review of current impact and mass extinction theories.

Disaster opportunists Guembelitrinidae: index for environmental catastrophes

Blooms of the disaster opportunist Guembelitria species are proxies for environmental catastrophes, whether impact or volcanism, leading to severe biotic stress crises that may range from temporary exclusion of ecological specialists and generalists to mass extinctions. During the late Maastrichtian and early Danian (zones P0 and Pla), Guembelitria blooms show global distributions, but with the largest blooms (40–80% Guembelitria) in low and middle latitudes and only minor blooms (10–20%) in high latitudes. Late Maastrichtian Guembelitria blooms are, so far, known from the Indian Ocean and eastern Tethys. The most intense Guembelitria blooms (>60% Guembelitria) occurred in shallow continental shelf areas, slope/shelf margins and volcanic provinces of the Indian Ocean. What these environments have in common is high nutrient influx (eutrophication) either from continental runoff, upwelling along continental margins or volcanic input. At times of biotic crises, Guembelitria blooms may have spread rapidly to the exclusion of most or all other species, much like today's red tides, but with near global distributions. A simple model can explain the ecological succession and recovery phases that follow major biotic perturbations caused by impacts or volcanism that lead to exclusion of specialist and most generalist species. Within such highly stressed environments, Guembelitria is the only genus to thrive, and without competition, rapidly reproduce and exponentially increase their populations. When nutrients are depleted, populations rapidly decrease, leading to ecologic niches for other generalists and ecosystem recovery. Small low-O 2-tolerant heterohelicid populations mark this second stage, followed by small trochospiral and planispiral species. With further environmental recovery, increasing competition, niche development and restoration of a well-stratified water mass, oligotrophic conditions are restored, opening habitats for the highly specialized and diverse species and a return to normal diverse assemblages. This ecological succession is observed in association with mantle plume volcanism in the Indian Ocean and eastern Tethys during the late Maastrichtian, and in association with the K–T impact and volcanism during the early Tertiary.

Ecological correlates of fish movement in a network of Virginia streams

Identifying factors that influence fish movement is a key step in predicting how populations respond to environmental change. Using mark–recapture (four species) and trap capture (eight species) data, we examined relationships between three attributes of movement and 15 ecological variables. The probability of emigrating from a reach was positively related to intermittency (one species) and body size (one species) and negatively related to distance from the mainstem creek (two species) and habitat complexity (one species). The number of fish moving upstream through traps was positively related to increases in flow (five species), day length (three species), and water temperature (two species); the number moving through downstream traps was positively associated with increases in flow (three species). Distance moved was greater for fish moving through unsuitable reaches (one species). Floods have a pervasive effect on fish movement, and human activities that affect flows will have widespread implications. The importance of other factors varies interspecifically, which may translate into variation in persistence and colonization rates. For example, species that exhibit reach fidelity in complex habitats may increase movement if habitats are homogenized. These species may suffer population declines because of the cost of increased movement and may ultimately be replaced by ecological generalists.

Patterns of resource use in early Homo and Paranthropus

Conventional wisdom concerning the extinction of Paranthropus suggests that these species developed highly derived morphologies as a consequence of specializing on a diet consisting of hard and/or low-quality food items. It goes on to suggest that these species were so specialized or stenotopic that they were unable to adapt to changing environments in the period following 1.5 Ma. The same conventional wisdom proposes that early Homo species responded very differently to the same environmental challenges. Instead of narrowing their niche it was the dietary and behavioral flexibility (eurytopy) exhibited by early Homo that enabled that lineage to persist. We investigate whether evidence taken across eleven criteria supports a null hypothesis in which Paranthropus is more stenotopic than early Homo. In six instances (most categories of direct evidence of dietary breadth, species diversity, species duration, susceptibility to dispersal, dispersal direction, and non-dietary adaptations) the evidence is inconsistent with the hypothesis. Only one line of indirect evidence for dietary breadth—occlusal morphology—is unambiguously consistent with the null hypothesis that Paranthropus' ability to process tough, fibrous food items (e.g., leaves) was reduced relative to early Homo. Other criteria (habitat preference, population density, direct and indirect evidence of dietary breadth related to incisor use) are only consistent with the hypothesis under certain conditions. If those conditions are not met, then the evidence is either inconsistent with the hypothesis, or ambiguous. On balance, Paranthropus and early Homo were both likely to have been ecological generalists. These data are inconsistent with the conventional wisdom that stenotopy was a major contributing factor in the extinction of the Paranthropus clade. Researchers will need to explore other avenues of research in order to generate testable hypotheses about the demise of Paranthropus. Ecological models that may explain the evolution of eurytopy in early hominins are discussed.

Ecological strategies in the ancient asexual animal group Darwinulidae (Crustacea, Ostracoda)

Summary We investigated the relationship between geographical distribution and ecological tolerance within the ancient asexual family Darwinulidae. Distribution maps were compiled based on data from the literature, the Non‐marine Ostracod Distribution in Europe database and personal collections. Ecological tolerance was assessed experimentally by exposing individual ostracods to a combination of eight different salinities (range from 0 to 30 g L−1) and three different temperatures (10, 20 and 30 °C). The type species of the family, Darwinula stevensoni, is ubiquitous and cosmopolitan; the two species Penthesilenula brasiliensis and Microdarwinula zimmeri also have an intercontinental distribution. Two other darwinulid species tested here (Vestalenula molopoensis and P. aotearoa) are known only from their type localities. The latter is also true for most extant darwinulids. Darwinula stevensoni and P. brasiliensis had a broad salinity tolerance, tolerating distilled water and also salinity up to 25–30 g L−1, whereas the maximum salinity tolerance of V. molopoensis was 12 g L−1 and of P. aotearoa, 20 g L−1. The results indicate that both ecological specialists and generalists, as well as intermediate forms, exist in the Darwinulidae and that taxa with the broadest ecological tolerance also have the widest distribution.

Planktonic foraminiferal response to the latest Maastrichtian abrupt warm event: a case study from South Atlantic DSDP Site 525A

An abrupt global warming of 3–4°C occurred near the end of the Maastrichtian at 65.45–65.10 Ma. The environmental effects of this warm event are here documented based on stable isotopes and quantitative analysis of planktonic foraminifera at the South Atlantic DSDP Site 525A. Stable isotopes of individual species mark a rapid increase in temperature and a reduction in the vertical water mass stratification that is accompanied by a decrease in niche habitats, reduced species diversity and/or abundance, smaller species morphologies or dwarfing, and reduced photosymbiotic activity. During the warm event, the relative abundance of a large number of species decreased, including tropical–subtropical affiliated species, whereas typical mid-latitude species retained high abundances. This indicates that climate warming did not create favorable conditions for all tropical–subtropical species at mid-latitudes and did not cause a massive retreat in the local mid-latitude population. A noticeable exception is the ecological generalist Heterohelix dentata Stenestad that dominated during the cool intervals, but significantly decreased during the warm event. However, dwarfing is the most striking response to the abrupt warming and occurred in various species of different morphologies and lineages (e.g. biserial, trochospiral, keeled globotruncanids). Dwarfing is a typical reaction to environmental stress conditions and was likely the result of increased reproduction rates. Similarly, photosymbiotic activity appears to have been reduced significantly during the maximum warming, as indicated by decreased δ 13C values. The foraminiferal response to climate change is thus multifaceted resulting in decreased species diversity, decreased species populations, increased competition due to reduced niche habitats, dwarfing and reduced photosymbiotic activity.

Space Use and Multi-Scale Habitat Selection of Adult Raccoons in Central Mississippi

Raccoons (Procyon lotor) are important furbearers and ecological generalists that exist in a variety of landscapes. Numerous studies have examined raccoon space and macrohabitat use, but information detailing these parameters within pine-dominated landscapes is lacking. Furthermore, no studies using radiotracking have examined raccoon habitat use at multiple spatial scales. We radiomonitored 131 adult raccoons (99 M, 32 F) during 1991-1997 in central Mississippi, USA. We subsequently assessed space use and habitat selection at 3 spatial scales. Males maintained larger home ranges and core areas than females. Size of home ranges differed by season, but raccoons maintained similar-size core areas across seasons. Habitat use differed by gender only at the coarsest spatial scale. Raccoons consistently used mature (>30 years old) pine and hardwood habitats over other available habitats at all spatial scales. Although hardwood-dominated habitats were important to raccoons, our findings suggest that in pine-dominated landscapes, raccoons select multiple seral stages of pine. Raccoons also readily used ≤8-year-old pine habitats, likely because of increased foraging opportunities within these habitats, particularly, during spring and summer. Our findings illustrate the importance of juxtaposition of habitat types for raccoons in pine-dominated landscapes, specifically the availability of mature pine and hardwood habitats, as well as early-successional habitats capable of providing beneficial foraging resources. Additionally, our findings offer evidence that prescribed burning may alter landscape use by raccoons, providing the potential that manipulating burning frequencies may allow managers to manage raccoon habitat-use patterns.

HABITAT CHARACTERISTICS OF ASHMUNELLA (GASTROPODA: PULMONATA: POLYGYRIDAE) AT WHITE SANDS MISSILE RANGE AND FORT BLISS, NEW MEXICO

We studied the habitat characteristics of 7 species of montane land snails in the genus Ashmunella in southern New Mexico from July 1999 to September 2000. We compared 9 numeric variables and 4 categorical variables by species. Geographic differences in microhabitat variables exist among these species; however, these differences tend to be obscured when comparing species, because some species are ecological generalists that occupy a wide range of habitat types. Although this study determined that different populations occupy ecologically distinct habitats in a broad range of environmental conditions, it remains unclear whether these factors influence the morphological characters on which past workers assigned species status. Management plans for the conservation of these species should take careful note of demonstrated habitat differences among and within the species.

Species richness and habitat diversification of bryophytes in submontane rain forest and fallows of Bolivia

An analysis of corticolous bryophyte diversity on whole trees in primary rain forest and 4-15-y-old fallows at 500-650 m in the Alto Beni, Bolivia, showed a significantly decreased diversity of bryophyte families and moss species in the fallows. However, liverwort diversity was scarcely lower in the fallows, except in the very young (4 y old) ones. Fallows had a significantly higher percentage of smooth mat species (72%), which may reflect the warmer, drier microclimate in the fallows. About half of the bryophyte species of the rain forest had re-established in the 10-15-y-old fallows. The majority of these are ecological generalists and sun epiphytes; a small minority are shade epiphytes. Re-establishment of ecological specialists is slower than that of generalists. Species richness in the primary forest is highest in the canopy; in the fallows it is highest in the understorey due to striking shifts of species and specialized growth types (rough mats, fans, tails) towards lower heights on the trees in the fallows. These shifts correspond well with measured changes in air temperature and air humidity in the fallows as compared with the forest.

The frasnian-famennian conodont mass extinction and recovery in South China

Conodonts are most important for the study of the Frasnian/Famennian Late Devonian mass extinction and recovery. Conodont mass extinction occurred stepwise (poly-episodes) in the latest Frasnian (latelinguiformis Zone) and was of very short timespan and global scale. Five steps of the conodont mass extinction can be recognized, with the same as in other sections in the world. Conodont recovery occurred in the earliest Famennian marked by the first appearance ofPalmatolepis triangularis. The timespan of the conodont recovery interval can be estimated as much less than 0.5 m.y. An independent survival interval cannot be determined. All of the Early- and Middletriangularis Zone should be assigned to the recovery interval, in which conodonts recovered also in a stepwise pattern and on a global scale.Pal. praetriangularis, Pal. triangularis andIcriodus alternatus, I. praealternatus, I. deformatus asymmetricus are crisis progenitor taxa, which are important for conodont recovery in the pelagic and neritic facies respectively. Some species ofPolygnathus andIcriodus are ecological generalists.

Paleoecology of the Cretaceous–Tertiary mass extinction in planktonic foraminifera

Paleobiogeographic patterns of the Cretaceous–Tertiary (K–T) mass extinction in planktonic foraminifera in Tunisia, spanning environments from open marine upper bathyal, to shelf and shallow marginal settings, indicate a surprisingly selective and environmentally mediated mass extinction. This selectivity is apparent in all of the environmental proxies used to evaluate the mass extinction, including species richness, ecological generalists, ecological specialists, surface and subsurface dwellers, whether based on the number of species or the relative percent abundances of species. The following conclusions can be reached for shallow to deep environments: about three quarters of the species disappeared at or near the K–T boundary and only ecological generalists able to tolerate wide variations in temperature, nutrients, salinity and oxygen survived. Among the ecological generalists (heterohelicids, guembelitrids, hedbergellids and globigerinellids), only surface dwellers survived. Ecological generalists which largely consisted of two morphogroups of opportunistic biserial and triserial species also suffered selectively. Biserials thrived during the latest Maastrichtian in well stratified open marine settings and dramatically declined in relative abundances in the early Danian. Triserials thrived only in shallow marginal marine environments, or similarly stressed ecosystems, during the latest Maastrichtian, but dominated both open marine and restricted marginal settings in the early Danian. This highly selective mass extinction pattern reflects dramatic changes in temperature, salinity, oxygen and nutrients across the K–T boundary in the low latitude Tethys ocean which appear to be the result of both long-term environmental changes (e.g., climate, sea level, volcanism) and short-term effects (bolide impact).

Competitive ability, body size and geographical range size in small mammals

AimWhy are some species widespread and abundant while others are restricted and rare?Darwin (1859) and others have claimed that some species have become widespread because they are competitively dominant over related, geographically restricted species. An alternative hypothesis is that wide‐ranging species are ecological generalists that have been able to opportunistically colonize many kinds of new, disturbed and/or marginal habitats, whereas related narrow‐ranging species are ecological specialists that competitively dominate specific kinds of relatively stable habitats/resources. We tested these opposing hypotheses using small mammals, for which considerable data on competitive interactions and geographical range sizes are available.LocationNorth America, Europe, Asia, Africa and Australia.MethodsWe analysed data for forty‐three competitive interactions between congeneric species in twenty genera, seven families, and four orders of small mammals. Competitive dominance was identified from both field and laboratory experiments, which were lumped because they showed similar results.ResultsWe found that (1) when all studies were analysed as individual data points, species with smaller geographical ranges tended to be dominant over congeneric species with larger geographical ranges, (2) lumping of interaction pairs sharing one or more of the same species yielded a similar result, (3) lumping all interactions involving the same genus also showed the same result, although it was not statistically significant, probably because of the small sample size resulting from this attempt to remove phylogenetic effects. Examination of the taxonomic relationships of the studied genera revealed no obvious phylogenetic effects on the relationship of competitive dominance with geographical range size. Furthermore, although body‐size differences appeared to have played a role in the results observed, they cannot completely explain them.Main conclusionsWe tentatively conclude that Darwin's hypothesis is falsified for small mammals, while the alternative hypothesis that geographically restricted species are competitively dominant over related widespread species receives some support.

Seasonal Habitat Selection by Raccoons (Procyon lotor) in Intensively Managed Pine Forests of Central Mississippi

Raccoons (Procyon lotor) are ecological generalists, existing in diverse landscapes. Although general habitat use patterns of raccoons have been extensively described, little research has examined raccoon habitat selection within landscapes managed intensively for wood fiber production. Furthermore, no published studies using radio-telemetry have detailed raccoon habitat selection at multiple spatial scales. We monitored 31 raccoons on a 2000 ha area characterized by short-rotation (<35 y) pine forests in central Mississippi during 1996–1997 and examined seasonal habitat selection at three spatial scales. Habitat selection at the home range scale differed (P = 0.004) between genders. Gender and season interacted to affect habitat selection at the core area scale of selection. Both male and female core areas contained greater proportions of mature hardwood habitats during breeding and young-rearing. Habitat use within home ranges, as determined by point locations, did not differ (P > 0.440) with gender or season. However, raccoons used habitats disproportionately (P = 0.016) relative to habitat composition of the home range. Our findings illustrate the importance of examining individual habitat selection at multiple scales, as raccoon habitat selection in our study varied by scale. Furthermore, our results indicate the importance of hardwood dominated habitats for raccoons existing in pine-dominated landscapes.

Aggressive interactions between freshwater turtle, Chelodina oblonga, hatchlings and freshwater crayfish, Cherax spp.: implications for the conservation of the critically endangered western swamp turtle, Pseudemydura umbrina

Interactions between turtle hatchlings of Chelodina oblonga and the marron, Cherax tenuimanus, the gilgie, C. quinquecarinatus, the koonac, C. preissii (freshwater crayfish native to Western Australia) and the introduced yabby, Cherax. sp., were observed in laboratory-based trials in uncluttered aquaria. Marron, koonacs and yabbies, but not gilgies, showed aggressive and predatory behaviour towards the hatchlings. In total, 59 attacks were observed in 26 of the 80 trials. On 12 occasions, crayfish captured hatchlings in their chelae. On two occasions, the attack of the crayfish was so quick that the hatchling was killed instantly. Compared with movement when alone, movement of hatchlings was significantly greater in the presence of koonacs and yabbies, but significantly less in the presence of marron and gilgies. The range of non-native yabbies currently is expanding into Ellen Brook Nature Reserve which harbours the last naturally persisting population of the critically endangered western swamp turtle, Pseudemydura umbrina. No native crayfish occur in the habitat of P. umbrina in this reserve. The possible invasion by the ecological generalist yabby poses a new threat to the survival of P. umbrina.

The end-cretaceous mass extinction in the marine realm: year 2000 assessment

The current database indicates that the terminal decline and extinction, or near extinction, of many groups commonly attributed to an asteroid or comet impact at the Cretaceous–Tertiary (K–T) boundary (e.g., ammonites, bivalves, planktic foraminifera) began during the last 500 k.y. of the Maastrichtian. By the time of the K–T boundary, extinction-prone tropical and subtropical marine faunas and floras were almost gone, or had severely reduced species populations struggling to survive. The K–T boundary kill-effect was largely restricted to these struggling tropical and subtropical populations that accounted for 2/3 of the species among planktic foraminifera, but less than 10% of the total foraminiferal population. No significant extinctions occurred among ecological generalists that dominated across latitudes. No single kill mechanism can account for this mass extinction pattern. The last 500 k.y. of the Maastrichtian were characterized by a series of rapid and extreme climate changes characterized by 3–4°C warming between 65.4 and 65.2 Ma , major volcanic activity between 65.4 and 65.2 Ma , a spherule-producing event between 65.3 and 65.2 Ma , and an impact at the K–T boundary ( 65.0 Ma ). All of these events caused major environmental perturbations and biotic stresses that resulted in severe reductions in species populations and extinctions that culminated at the K–T boundary. The mass extinction pattern, and the parallel environmental changes during the last 500 k.y. of the Maastrichtian, suggest that both long-term (climate, sea-level) and short-term (impact, volcanism) events contributed to the K–T boundary mass extinction.

Localized acidification near sour gas processing plants: are forest floor macro-invertebrates affected?

The diversity and activity of forest floor invertebrates, particularly carabid beetles, were studied along a sharp acidification gradient in pine and aspen forests close to a sulfur block near a sour gas processing plant in SW central Alberta, Canada. Invertebrates were sampled by continuous unfenced pitfall traps at all sites, and fenced pitfall traps and core samples at selected sites. High sulfur contamination and subsequent acidification had a clear negative effect on earthworms, snails, and on several carabid species. Carabid beetles along the sharp acidification gradient in the pine forest were classified as vulnerable ( Scaphinotus marginatus, Platynus decentis, Calathus ingratus, Stereocerus haematopus and Pterostichus riparius), resistant ( Pterostichus adstrictus, Calathus advena and Agonum placidum) or favored ( Amara hyperborea). Ecological specialists were those most vulnerable to acidification, whereas ecological generalists were resistant. Few species dominated the assemblage at the acidified pine site. Fenced and unfenced pitfall samples produced similar results for carabid beetles and manual devegetation did not affect overall seasonal carabid catches. High levels of sulfur contamination at the aspen site substantially reduced ground plant cover but not pH and catches of most carabids were similar to the non-polluted aspen site. It is concluded that faunal structure at the acidified pine sites is severely affected negatively and further studies are warranted to study the consequences of reduced diversity for ecosystem processes such as organic matter decomposition.

Sex, Lineages, and Pathogenesis

F or microbiology, times have never been so good; we are luxuriating in a surfeit of data. The more genomes we see, the greater the opportunity for comparative analysis. There is no shortage of leads for new drugs and vaccines and no lack of putative virulence determinants to explore. But to reap the full benefits of this research, we need to consider the big picture. People are not infected with one organism alone—we are host to communities of many species, most of which do us little harm. We need to spot the shift in the dynamics between microbe and host that tells us when harm might follow. This issue of Science addresses some of the wider implications of the current renaissance in microbiology. Ochman and Moran (p. [1096][1]) argue that sequencing the genomes of pathogens gives us a distorted view of bacterial diversity, because pathogens are a small, modern, and unusual proportion of bacterial species. Although a quick-change act is an advantage to a pathogen, the development of clonal lineages is the hallmark of many microbial infections. Read and Taylor (p. [1099][2]) observe that within an afflicted individual, the competition between lineages will influence disease severity and transmission—factors that are often ignored in clinical decisions. Baranowski et al. (p. [1102][3]) point out that small changes in viral genomes can mean a significant change in the distribution of the virus in the host, which will have important repercussions for vaccine use and the risks from xenotransplantation. Although some retroviruses, such as HIV, are notorious for their high rates of sequence variation, Overbaugh and Bangham (p. [1106][4]) explain that viruses that do adapt rapidly tend to be ecological generalists. As Woolhouse et al. (p. [1109][5]) discuss, these include the many zoonotic human infections of increasing public health concern. Although the mammalian gut is packed with microorganisms, inflammatory responses are rare. Levin and Antia (p. [1112][6]) examine the immune responses to bacteria, comparing it to predator-prey dynamics and pointing out the risk of mounting a full inflammatory immune response to infection. Hooper and Gordon (p. [1115][7]) expand on the cross-talk between gut commensals and the host, and Russell and Rychlik (p. [1119][8]) describe the specialized symbioses of ruminants and how they are affected by animal husbandry. In News, Carl Zimmer describes how genetic analyses of living pathogens are enabling researchers to reconstruct the origins and evolution of disease (p. [1090][9]). Zimmer also details the extraordinary antics of Wolbachia—perhaps the most common infectious bacterium on Earth—and how it manipulates the sex lives of its hosts to ensure its own survival (p. [1093][10]). The plethora of new data should help answer long-standing questions about infection, revealing unique metabolisms vulnerable to drugs and vital surface molecules open to vaccine attack. More important, they will offer new insights into the ecology and evolution of infection. (For Web resources related to this issue, see [www.sciencemag.org/feature/data/diseases/index.shtml][11]) [1]: /lookup/doi/10.1126/science.1058543 [2]: /lookup/doi/10.1126/science.1059410 [3]: /lookup/doi/10.1126/science.1058613 [4]: /lookup/doi/10.1126/science.1059128 [5]: /lookup/doi/10.1126/science.1059026 [6]: /lookup/doi/10.1126/science.1058879 [7]: /lookup/doi/10.1126/science.1058709 [8]: /lookup/doi/10.1126/science.1058830 [9]: /lookup/doi/10.1126/science.292.5519.1090 [10]: /lookup/doi/10.1126/science.292.5519.1093 [11]: http://www.sciencemag.org/feature/data/diseases/index.shtml