Efficacy of solar disinfection of Escherichia coli, Shigella flexneri, Salmonella Typhimurium and Vibrio cholerae

AIMS: To determine the efficacy of solar disinfection (SODIS) for enteric pathogens and to test applicability of the reciprocity law. METHODS AND RESULTS: Resistance to sunlight at 37 degrees C based on F99 values was in the following order: Salmonella Typhimurium>Escherichia coli>Shigella flexneri>Vibrio cholerae. While F90 values of Salm. Typhimurium and E. coli were similar, F99 values differed by 60% due to different inactivation curve shapes. Efficacy seemed not to be dependent on fluence rate for E. coli stationary cells. Sensitivity to mild heat was observed above a temperature of 45 degrees C for E. coli, Salm. Typhimurium and Sh. flexneri, while V. cholerae was already susceptible above 40 degrees C. CONCLUSIONS: Salmonella Typhimurium was the most resistant and V. cholerae the least resistant enteric strain. The reciprocity law is applicable for stationary E. coli cells irradiated with sunlight or artificial sunlight. SIGNIFICANCE AND IMPACT OF THE STUDY: Escherichia coli might not be the appropriate indicator bacterium to test the efficacy of SODIS on enteric bacteria and the physiological response to SODIS might be different among enteric bacteria. The applicability of the reciprocity law indicates that fluence rate plays a secondary role in SODIS efficacy. Stating inactivation efficacy with T90 or F90 values without showing original data is inadequate for SODIS studies.     

Effects of geographic distance,sea barriers and habitat on the genetic structure and diversity of all-hybrid water frog populations

The history of population size and migration patterns leaves its mark in the genetics of populations. We investigate the genetic structure of the edible frog, Pelophylax esculentus in the Danish archipelago and adjacent countries. This frog is of particular interest because it is a hybrid that, in this area, forms all-hybrid populations of diploid (LR) and triploid (LLR and LRR) genomotypes with no (or very few) adults of the parental species (LL and RR). This study is the first to cover the entire geographic range of Danish, Swedish and German all-hybrid populations, documenting their extent and providing a broad picture of their diversity of neutral genetic markers and genomotype proportions. With 18 microsatellite markers, we found that genetic diversity declines northwards in agreement with the glacial refuge and central-marginal hypotheses; however, populations on small and medium-sized islands are no less diverse than those on large islands and continental peninsulas. Isolation by distance exists across the archipelago with limited influence of fragmentation by brackish seawater. The extremely low genetic diversity in all-hybrid populations, compared with adjacent populations, may be responsible for the maintenance of their special breeding system. We also show large variation among ponds in proportions of LLR, LR and LRR genomotypes, but little geographic pattern in their distribution. Instead, we found relationships between the genomotype proportions and some of 15 habitat parameters monitored. Body size differences among LLR, LR and LRR further suggest ecological differences.     

Molecular definitions of cell death subroutines: recommendations of the Nomenclature Committee on Cell Death 2012

In 2009, the Nomenclature Committee on Cell Death (NCCD) proposed a set of recommendations for the definition of distinct cell death morphologies and for the appropriate use of cell death-related terminology, including 'apoptosis', 'necrosis' and 'mitotic catastrophe'. In view of the substantial progress in the biochemical and genetic exploration of cell death, time has come to switch from morphological to molecular definitions of cell death modalities. Here we propose a functional classification of cell death subroutines that applies to both in vitro and in vivo settings and includes extrinsic apoptosis, caspase-dependent or -independent intrinsic apoptosis, regulated necrosis, autophagic cell death and mitotic catastrophe. Moreover, we discuss the utility of expressions indicating additional cell death modalities. On the basis of the new, revised NCCD classification, cell death subroutines are defined by a series of precise, measurable biochemical features.     

The Effect of Assortative Mating on the Coexistence of a Hybridogenetic Waterfrog and Its Sexual Host

In central Europe, the hybridogenetic waterfrog Rana esculenta, a hybrid between Rana ridibunda and Rana lessonae, lives in sympatry with one of its parental species, the poolfrog Rana lessonae. As R. esculenta has to backcross constantly with R. lessonae in order to produce viable offspring, this coexistence is obligatory for R. esculenta. Since R. esculenta has a higher primary fitness than R. lessonae, a mechanism is required that prevents the hybrid from driving the parental species, and hence itself, to extinction. Here, we present an analytical model and a computer simulation that investigate whether assortative mating can operate as a such a control mechanism. Our results show that assortative mating is very effective in regulating coexistence in such a hybrid-host system. This is particularly true when choice is affected by the proportion of the two male types in the population. Furthermore, we could show that even if the species composition in a mixed hybrid-host population may be largely influenced by differences in life-history parameters, assortative mating still plays a very important role by stabilizing coexistence. Thus, mating behavior turns out to be more important for the populations dynamics of hybridogenetic waterfrog systems than previously assumed.     

Male vocalization and female choice in the hybridogenetic Rana lessonae/Rana esculenta complex

In many species, females can improve their fitness by preferring particular males over others. In Palaearctic water frogs of the Rana lessonae/R. esculenta complex the consequences of such mate choice are particularly pronounced. To produce viable offspring, the hybrid R. esculenta (genotype RL) must mate with the parental species R. lessonae (LL); but R. lessonae should avoid mating with R. esculenta, because the resulting hybrid offspring will eliminate the L genome from the germline (hybridogenesis). Hence, there exists a conflict between the sexual parasite (RL) and its sexual host (LL) over the best mating partner. Previous studies have shown a preference for LL males in LL and RL females; but they have also shown that females cannot usually realize their choice when in close proximity to males, because the males forcefully and indiscriminately amplex them. We tested whether females use male vocalizations as a long-distance signal to increase their chances of mating with the preferred LL males. We exposed female R. lessonae and R. esculenta to playbacks of single LL and RL mating calls (experiment 1) and to choruses with a 3:1 excess of LL and RL calls, respectively (experiment 2). In experiment 1, both female types were attracted more by the LL than by the RL calls. In experiment 2, no discrimination between LL- and RL-dominated choruses was observed. The results suggest that females do not use distant male vocalization to approach preferentially ponds or arenas within a pond that hold an excess of LL males. But once they have arrived in a chorus, mating calls from nearby males can direct them to the preferred LL mates. We discuss possible reasons for the failure to discriminate between choruses and the chances for successful choice between individuals within choruses. Copyright 2000 The Association for the Study of Animal Behaviour.     

The importance of food quantity and quality for reproductive performance in alpine water pipits (Anthus spinoletta)

Studies relating reproduction to food availability are usually restricted to food quantity, but ignore food quality and the effects of habitat structure on obtaining the food. This is particularly true for insectivorous birds. In this study we relate measures of reproductive success, time of reproduction and nestling size of water pipits (Anthus spinoletta) to biomass, taxonomic composition and nutritional content of available food, and to vegetation structure and distance to feeding sites. Clutch size was positively correlated with the proportion of grass at the feeding sites, which facilitates foraging. This suggests that water pipits adapt their clutch size to environmental conditions. Also, pipits started breeding earlier and produced more fledglings when abundant food and a large proportion of grass were available, probably because these conditions allow the birds to gain more energy in less time. The number of fledglings was positively correlated with the energy content of available food. No significant relationships were found between feeding conditions and nestling size or the time that nestlings took to fledge. This suggests that water pipits do not invest more in individual nestlings when food conditions are favourable but rather start breeding earlier and produce more young. Taxonomic composition and nutritional content of prey were not correlated with any of the reproductive parameters, indicating that profitability rather than quality of food affects reproductive success. Received: 31 May 1996/Accepted: 12 August 1996     

PERFORMANCE OF TADPOLES FROM THE HYBRIDOGENETIC RANA ESCULENTA COMPLEX: INTERACTIONS WITH POND DRYING AND INTERSPECIFIC COMPETITION

The performance of three genotypes (LL, LR, RR) of tadpoles resulting from the hybrid mating system of Rana lessonae (phenotype L, genotype LL) and Rana esculenta (phenotype E, genotype LR) was determined in artificial ponds. The effects of interspecific competition and pond drying on growth, development, and survival of tadpoles were used to measure the performance of genotypes and the relative fitness of offspring. Among the three genotypes, tadpoles from the homogametic mating RR had the lowest survival, growth, and development under all environmental conditions. Body size of the LL and LR genotype tadpoles at metamorphosis was reduced by competition and pond drying. Days to metamorphosis were also higher for the LL and LR genotype tadpoles in competition ponds. The proportion of individuals metamorphosing of each genotype was differentially lowered by competition and pond drying. The LL genotype produced more metamorphs than the LR genotype in the constant water level ponds, but the LR genotype produced more in drying ponds. In competition ponds, the LR genotype produced more metamorphs than the LL genotype, but the LL genotype produced more metamorphs in ponds without competition. The RR genotype produced no metamorphs in any of the experimental environments. Increased performance of LR offspring from the heterogametic mating, in harsh conditions, and reduced performance of RR offspring from the homogametic mating, even under favorable conditions, relative to the parental genotype (LL) suggests that the population dynamics of this hybridogenetic system is strongly dependent on mate choice in mixed populations and the subsequent pond environment females select for oviposition and larval development.     

Dissociation of somatic growth,time of sexual maturity,and life expectancy by overexpression of an RGD‐deficient IGFBP‐2 variant in female transgenic mice

Impaired growth is often associated with an extension of lifespan. However, the negative correlation between somatic growth and life expectancy is only true within, but not between, species. This can be observed because smaller species have, as a rule, a shorter lifespan than larger species. In insects and worms, reduced reproductive development and increased fat storage are associated with prolonged lifespan. However, in mammals the relationship between the dynamics of reproductive development, fat metabolism, growth rate, and lifespan are less clear. To address this point, female transgenic mice that were overexpressing similar levels of either intact (D‐mice) or mutant insulin‐like growth factor‐binding protein‐2 (IGFBP‐2) lacking the Arg‐Gly‐Asp (RGD) motif (E‐ mice) were investigated. Both lines of transgenic mice exhibited a similar degree of growth impairment (?9% and ?10%) in comparison with wild‐type controls (C‐mice). While in D‐mice, sexual maturation was found to be delayed and life expectancy was significantly increased in comparison with C‐mice, these parameters were unaltered in E‐mice in spite of their reduced growth rate. These observations indicate that the RGD‐domain has a major influence on the pleiotropic effects of IGFBP‐2 and suggest that somatic growth and time of sexual maturity or somatic growth and life expectancy are less closely related than thought previously.     

Avian Helpers at the Nest: Are they Psychologically Castrated?

In cooperatively breeding pied kingfishers (Ceryle rudis) blood plasma levels of LH and testosterone (T) were compared among three types of males: breeders, primary (= related) helpers and secondary (= unrelated) helpers. These categories did not differ in LH, but primary helpers had significantly lower T titers than breeders and secondary helpers. The low levels were paralleled by small gonad sizes and no sperm production, suggesting that primary helpers were not able to fertilize eggs. The differences in T levels could neither be attributed to stochastic variation nor to differences in age, stress, molt, or reproductive activities. The most likely explanation arises from the observation that primary helpers are behaviorally dominated by breeders, whereas secondary helpers are not. The adaptive significance of low T titers and reduced fertility as a result from being dominated is discussed on the basis of empirical data and theoretical models. We argue that primary helpers in the pied kingfisher, and subordinate helpers in many other cooperative breeders, apparently are not “unwillingly” suppressed in their sexual development; they rather “choose” delayed reproduction when the costs from sexual competition with breeders exceed the benefits from cooperative breeding. In contrast, helpers that benefit more from competition than from cooperation, as secondary helpers do, cannot be expected to show reduced fertility.