Seasonality influences cuticle melanization and immune defense in a cricket: support for a temperature-dependent immune investment hypothesis in insects

To improve thermoregulation in colder environments, insects are expected to darken their cuticles with melanin via the phenoloxidase cascade, a phenomenon predicted by the thermal melanin hypothesis. However, the phenoloxidase cascade also plays a significant role in insect immunity, leading to the additional hypothesis that the thermal environment indirectly shapes immune function via direct selection on cuticle color. Support for the latter hypothesis comes from the cricket Allonemobius socius, where cuticle darkness and immune-related phenoloxidase activity increase with latitude. However, thermal environments vary seasonally as well as geographically, suggesting that seasonal plasticity in immunity may also exist. Although seasonal fluctuations in vertebrate immune function are common (because of flux in breeding or resource abundance), seasonality in invertebrate immunity has not been widely explored. We addressed this possibility by rearing crickets in simulated summer and fall environments and assayed their cuticle color and immune function. Prior to estimating immunity, crickets were placed in a common environment to minimize metabolic rate differences. Individuals reared under fall-like conditions exhibited darker cuticles, greater phenoloxidase activity and greater resistance to the bacteria Serratia marcescens. These data support the hypothesis that changes in the thermal environment modify cuticle color, which indirectly shapes immune investment through pleiotropy. This hypothesis may represent a widespread mechanism governing immunity in numerous systems, considering that most insects operate in seasonally and geographically variable thermal environments

Investigations into Salmonella Serovar and Antimicrobial Resistance Patterns in Commercial Swine Herds.

The goal of this study was to monitor 36 US commercial swine herds at slaughter to determine farm specific Salmonella serovar patterns and farm specific antimicrobial resistance patterns. During this study the following isolates (228) were identified: S. agona(IO); S. anatum(l7), S. derby(64), S. enteriditis(1), S. harthford(2), S. heidelberg (5), S. infantis(2),S. mbandaka(3), S. monophasic(2), S. muenchen(3), S. muenster(2), S. ohio(4), S. oranienburg (1), S. schwarzengrund(l), S. typhimurium(36), and S. typhimurium copenhagen(75). Isolates were tested for resistance against 17 different antimicrobials. Of the 36 herds, no detectable resistance was observed in 5 herds. Resistance to 1 antimicrobial was found in 1 herd, to 3 antimicrobials in 2 herds, to 4 antimicrobials in 4 herds, to 5 antimicrobials in 11 herds, to 6 antimicrobials in 9 herds, to 7 antimicrobials in 2 herds, and to 8 antimicrobials in 2 herds. S. typhimurium, S. typhimurium copenhagen and S. derby had the widest range of antimicrobial resistance

Antimicrobial susceptibility of salmonella isolates from swine

The emergence of antimicrobial resistance among bacteria is of growing concern to practitioners and producers. Problems associated with the emergence of resistance include treatment failure, prolonged shedding, and the development oflong term carriage of the resistant bacteria in the host. The emergence of resistance among Salmonella species is particularly worrisome as it is a zoonotic agent and is ubiquitous in nature

National antimicrobial resistance monitoring system: Results for swine

Use of antimicrobics has increased in both human and veterinary medicine. This is due in part to the availability of the antimicrobics and the efficacy they impart in control of certain infectious diseases. However, use of antimicrobics can lead to the development of resistance to the antirnicrobics. Antimicrobial resistance can diminish effectiveness and may even render an antimicrobic ineffective as a therapeutic. Although use may result in a portion of bacteria that are resistant, the exact fate of this population in terms of persistence and transmission has been difficult to determine. Use panerns in veterinary medicine (therapeutic versus preventive versus growth promotion use) also complicates the picture. Additionally, while transmission of resistant bacteria from animals to humans occurs, it has been difficult to assess the extent to which this occurs and the impact transmission has on actual dissemination of resistant populations

Prevalence of Salmonella Typhimurium DT104 and Related Phage Types from NARMS-EB, 1997-2000

While antimicrobial resistance is recognized as a global problem, multiple resistances are occurring more frequently. In the mid-1990s a pentaresistant S. typhimurium Definitive Type 104 (DT104) reached epidemic proportions in the United Kingdom in both humans and animals

Intralocus Sexual Conflict Diminishes the Benefits of Sexual Selection

Evolution based on the benefits of acquiring “good genes” in sexual selection is only plausible with the reliable transmission of genetic quality from one generation to the next. Accumulating evidence suggests that sexually antagonistic (SA) genes with opposite effects on Darwinian fitness when expressed in the two different sexes may be common in animals and plants. These SA genes should weaken the potential indirect genetic benefits of sexual selection by reducing the fitness of opposite-sex progeny from high-fitness parents. Here we use hemiclonal analysis in the fruit fly, Drosophila melanogaster, to directly measure the inheritance of fitness across generations, over the entire genome. We show that any potential genetic benefits of sexual selection in this system are not merely weakened, but completely reversed over one generation because high-fitness males produce low-fitness daughters and high-fitness mothers produce low-fitness sons. Moreover, male fitness was not inherited by sons, consistent with both theory and recent evidence connecting this form of SA variation with the X chromosome. This inheritance pattern may help to explain how genetic variation for fitness is sustained despite strong sexual selection, and why the ZW sex chromosome system found in birds and butterflies appears to foster the evolution of extreme secondary sexual characters in males

Direct and indirect transmission of four Salmonella enterica serotypes in pigs

<p>Abstract</p> <p>Background</p> <p>Feed-borne spread of <it>Salmonella </it>spp. to pigs has been documented several times in recent years in Sweden. Experiences from the field suggest that feed-associated serotypes might be less transmittable and subsequently easier to eradicate from pig herds than other serotypes more commonly associated to pigs. Four <it>Salmonella </it>serotypes were selected for experimental studies in pigs in order to study transmissibility and compare possible differences between feed-assoociated (<it>S </it>Cubana and <it>S </it>Yoruba) and pig-associated serotypes (<it>S </it>Derby and <it>S </it>Typhimurium).</p> <p>Methods</p> <p>Direct contact transmission was studied in four groups of pigs formed by six 10-week-old salmonella negative pigs commingled with two fatteners excreting one of the four salmonella serotypes. Indirect transmission was studied by putting six 10-week-old salmonella negative pigs in each of four salmonella contaminated rooms. Each room had previously housed a group of pigs, excreting one of the four selected serotypes.</p> <p>All pigs were monitored for two weeks with respect to the faecal excretion of salmonella and the presence of serum antibodies. At the end of the trial, eight samples from inner tissues and organs were collected from each pig at necropsy.</p> <p>Results</p> <p>In the four direct transmission groups, one pig shed <it>Salmonella </it>(Cubana) at one occasion. At necropsy, <it>S </it>Typhimurium was isolated from one pig.</p> <p>In the indirect transmission groups, two pigs in the Yoruba room and one pig in each of the other rooms were excreting detectable levels of <it>Salmonella </it>once during the study period of two weeks. At necropsy, <it>S </it>Derby was isolated from one of six pigs in the Derby room and <it>S </it>Typhimurium was isolated from four of the six pigs in the Typhimurium room.</p> <p>No significant serological response could be detected in any of the 48 pigs.</p> <p>Conclusions</p> <p>These results show that all four selected serotypes were able to be transmitted in at least one of these field-like trials, but the transmission rate was low in all groups and no obvious differences between feed-associated and pig-associated serotypes in the transmission to naïve pigs and their subsequent faecal shedding were revealed. However, the post mortem results indicated a higher detection of <it>S </it>Typhimurium in the ileocecal lymph nodes of pigs introduced into a contaminated environment in comparison with the other three serotypes.</p

Effects of some methodologic factors on detection of Salmonella in swine feces

Bacteriologic culture of feces for Salmonella continues to be a central component of epidemiologic studies. We conducted a series of experiments on fecal samples collected from commercial swine farms to evaluate the effects of several methodologic factors on detection of Salmonella. Factors examined included fecal sample storage (no storage, 4C, -15C) and fecal sample weight. In addition we compared the standard method (Method I) used in our laboratory [JOg feces/buffered peptone water pre-enrichment/selective enrichment in Rappaport Vassiliadis (RV) broth] with another method (Method 2) used by ourselves and others in the USA (=I g sample/primary enrichments in tetrathionate and Hajna GN broths/secondary enrichment in RV broth). Inunediate processing of samples yielded the best recovery of Salmonella, although storage at 4C for 6 days did not significantly reduce detection. Freezing of fecal samples resulted in significant reduction of detection. The weight of feces sampled had a marked linear effect on the detection of Salmonella using method I. Direct comparison of Method I and Method 2 indicated comparable results, with Method I tending to yield higher detection of Salmonella. However, when conducted on samples of equal weight, Method 2 had significantly better detection than Method I. The choice of methods can markedly affect the results of fecal sample culture. The preferred methodology for epidemiologic studies will be determined by many factors including logistics and cost. Our data highlight the imperfect sensitivity of culture methods, and the need for researchers to consider the sensitivity of their bacteriologic methods in the design and interpretation of field studies based on fecal culture

Large Numbers of Matings Give Female Field Crickets a Direct Benefit but not a Genetic Benefit

Female crickets can potentially gain both direct and indirect benefits from mating multiple times with different males. Most studies have only examined the effects of small numbers of matings, although female crickets are capable of mating many times. The goal of this paper is to examine the direct and indirect benefits of mating large numbers of times for female reproductive success. In a previous experiment, female Gryllus vocalis were found to gain diminishing direct benefits from mating large numbers of times. In this study I attempt to determine whether mating large numbers of times yields similar diminishing returns on female indirect benefits. Virgin female Gryllus vocalis crickets were assigned to mate five, ten or 15 times with either the same or different males. Females that mated more times gained direct benefits in terms of laying more eggs and more fertilized eggs. Females that mated with different males rather than mating repeatedly with the same male did not have higher offspring hatching success, a result that is contrary to other published results comparing female reproductive success with repeated versus different partners. These results suggest that females that mate large numbers of times fail to gain additional genetic benefits from doing so

Male Mating Rate Is Constrained by Seminal Fluid Availability in Bedbugs, Cimex lectularius

Sexual selection, differences in reproductive success between individuals, continues beyond acquiring a mating partner and affects ejaculate size and composition (sperm competition). Sperm and seminal fluid have very different roles in sperm competition but both components encompass production costs for the male. Theoretical models predict that males should spend ejaculate components prudently and differently for sperm and seminal fluid but empirical evidence for independent variation of sperm number and seminal fluid volume is scarce. It is also largely unknown how sperm and seminal fluid variation affect future mating rate. In bedbugs we developed a protocol to examine the role of seminal fluids in ejaculate allocation and its effect on future male mating rate. Using age-related changes in sperm and seminal fluid volume we estimated the lowest capacity at which mating activity started. We then showed that sexually active males allocate 12% of their sperm and 19% of their seminal fluid volume per mating and predicted that males would be depleted of seminal fluid but not of sperm. We tested (and confirmed) this prediction empirically. Finally, the slightly faster replenishment of seminal fluid compared to sperm did not outweigh the faster decrease during mating. Our results suggest that male mating rate can be constrained by the availability of seminal fluids. Our protocol might be applicable to a range of other organisms. We discuss the idea that economic considerations in sexual conflict research might benefit from distinguishing between costs and benefits that are ejaculate dose-dependent and those that are frequency-dependent on the mating rate per se