Niche segregation and genetic structure of Campylobacter jejuni populations from wild and agricultural host species

Bacterial populations can display high levels of genetic structuring but the forces that influence this are incompletely understood. Here, by combining modelling approaches with multilocus sequence data for the zoonotic pathogen Campylobacter, we investigated how ecological factors such as niche (host) separation relate to population structure. We analysed seven housekeeping genes from published C. jejuni and C. coli isolate collections from a range of food and wild animal sources as well as abiotic environments. By reconstructing genetic structure and the patterns of ancestry, we quantified C. jejuni host association, inferred ancestral populations, investigated genetic admixture in different hosts and determined the host origin of recombinant C. jejuni alleles found in hybrid C. coli lineages. Phylogenetically distinct C. jejuni lineages were associated with phylogenetically distinct wild birds. However, in the farm environment, phylogenetically distant host animals shared several C. jejuni lineages that could not be segregated according to host origin using these analyses. Furthermore, of the introgressed C. jejuni alleles found in C. coli lineages, 73% were attributed to genotypes associated with food animals. Our results are consistent with an evolutionary scenario where distinct Campylobacter lineages are associated with different host species but the ecological factors that maintain this are different in domestic animals such that phylogenetically distant animals can harbour closely related strains.     

Long‐term impacts of invasive species on a native top predator in a large lake system

1. Declining abundances of forage fish and the introduction and establishment of non‐indigenous species have the potential to substantially alter resource and habitat exploitation by top predators in large lakes. 2. We measured stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N) in field‐collected and archived samples of Lake Ontario lake trout (Salvelinus namaycush) and five species of prey fish and compared current trophic relationships of this top predator with historical samples. 3. Relationships between δ¹⁵N and lake trout age were temporally consistent throughout Lake Ontario and confirmed the role of lake trout as a top predator in this food web. However, δ¹³C values for age classes of lake trout collected in 2008 ranged from 1.0 to 3.9‰ higher than those reported for the population sampled in 1992. 4. Isotope mixing models predicted that these changes in resource assimilation were owing to the replacement of rainbow smelt (Osmerus mordax) by round goby (Neogobius melanostomus) in lake trout diet and increased reliance on carbon resources derived from nearshore production. This contrasts with the historical situation in Lake Ontario where δ¹³C values of the lake trout population were dominated by a reliance on offshore carbon production. 5. These results indicate a reduced capacity of the Lake Ontario offshore food web to support the energetic requirements of lake trout and that this top predator has become increasingly reliant on prey resources that are derived from nearshore carbon pathways.     

A comparison between two models for plant competition

The differential equation of de Wit (1970) which predicts the growth of plant species in mixtures from their yield–density response in monocultures is compared with a simpler equation. This model is also based on the yield–density response of species grown in monocultures, but is static and predicts only the net result of plant competition during discrete time periods. Data from successive harvests in yield–density experiments in monocultures of one grass and two legume species were fitted to both models and the relative reproductive rate and the relative replacement rate were calculated from model predictions. Predictions from our model agreed more closely with observations than predictions from the de Wit model. It is concluded that our model deserves further attention in the studies of population dynamics in mixtures when the final outcome of competition is the main interest.     

Microreticulation in Cambrian Ostracoda and its relation to similar patterns in tertiary and Recent Ostracoda

The Cambrian bradoriid ? Parahoulongdongella sp. is shown to have a microreticulate (2nd order) surface sculpture. A possible organic sheet‐like origin is proposed for this reticulation. The relation between this second order pattern and those found in tertiary to Recent Ostracoda is discussed.     

Interrelationship between Meristematic Regions of Developing Inflorescences of Four Cereal Species

A cultivar from each of four cereal species (Avena sativa L.,cv. Swan, Hordeum vulgare, L., cv. Clipper, Triticum aestivumL., cv. Gabo, and Secale cereale L., cv. South Australian Rye)was grown in controlled environment chambers in a 10-h photoperiod(short days) or 10-h photoperiod supplemented with a 6-h extensionby incandescent light. The developmental morphology of the inflorescenceswas followed to ascertain whether there were any common developmentalinterrelationships between the species. Inflorescence internodeelongation was initiated when the floret initial first appeared,irrespective of whether it occurred on the most advanced lateralspikelet or on the terminal spikelet of the rachis. The glumes(infertile bracts) of the terminal spikelet of the rachis wereinitiated when the first second-order inflorescence branch appeared,irrespective of whether the second-order inflorescence branchwas a floret initial or a lateral spikelet, as in Triticum sp.,or an inflorescence (panicle) branch, as in Avena sp. Cessationof the activity of the apical meristem, as measured by primordiumformation, was not correlated with any particular stage of floraldevelopment but appeared to be due to a lack of nutrients causedby an increasing competitiveness for the available nutrientsfrom the developing spikelets which are situated closer to thevascular system than the apical meristem.     

Variation in social rank acquisition influences lifetime reproductive success in black-capped chickadees

Dominance relationships structure many animal societies, yet the process of rank attainment is poorly understood. We investigated acquisition of social dominance in winter flocks and its fitness consequences in male black-capped chickadees (Poecile atricapillus) over a 10-year period. Age was the best predictor of rank, and paired comparisons showed high-ranked males to be older than their low-ranked flock-mates. When controlling for age, morphological variables did not predict male social rank, but high-ranked males were heavier, had lower fat scores and were in leaner condition than low-ranked males. Males that survived between years tended to increase in rank over time; however, the rate of rank advancement varied individually. Rank reversals between familiar contestants were rare, and changes in male social rank were associated with changes in flock membership. Average lifetime reproductive success (LRS) of males and females was variable and best predicted by lifespan. Male rank history also influenced realized reproductive success. Birds with higher average rank over their lifespan were more likely to reproduce successfully. However, among successful birds, average rank did not significantly predict LRS. Thus, birds that lived longer and attained high social rank earlier had higher fitness, but this effect was not manifested as fine-scale differences among successful individuals. Taken together, these findings demonstrate the importance of social factors influencing individual fitness.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 85–95.     

The influence of habitat management on the breeding success of the Great Bittern Botaurus stellaris in Britain

Great Bitterns Botaurus stellaris have experienced a population decline in the UK, such that in 1997 the total number of breeding males was just 11. This study aimed to identify factors affecting productivity, and how management could be used to manipulate this. An intensive study of Great Bittern breeding success was conducted between 1997 and 2001. The date that males established their booming territories was closely correlated with when females started nesting. Wetter sites with greater fish densities had males that established their booming territories earlier in the season. However, only the date that males started booming determined when females started nesting. The mean clutch size of Great Bitterns was four and the only cause of nest failure was predation. Of eight nests suspected to be second attempts the mean interval between these first and second attempts was 12.25 ± 0.88 (sd) days (range 8–15). The fate of radiotagged chicks followed to fledging revealed that the overall probability of a chick surviving to fledge was 39.1%. Daily losses of Great Bittern chicks due to starvation/exposure accounted for 76.25% and predation 21.25%. The youngest chicks in poor condition were most likely to die, particularly in periods of high rainfall. A simulated renesting model allowed estimation of Great Bittern productivity as 1.24 chicks per female and 1.52 nesting attempts per female. Habitat management, or lack of water control that resulted in sites being drier in spring, delayed nesting, although statistically there was no difference in productivity compared with wetter sites.