Amino acid δ15N differences consistent with killer whale ecotypes in the Arctic and Northwest Atlantic

Ecotypes are groups within a species with different ecological adaptations than their conspecifics. Eastern North Pacific (ENP) killer whale (Orcinus orca) ecotypes differ in their diet, behavior, and morphology, but the same is not known for this species in the eastern Canadian Arctic (ECA) and Northwest Atlantic (NWA). Using compound-specific stable isotope analysis (CSIA) of amino acids (AAs), we compared δ15N patterns of the primary trophic and source AA pair, glutamic acid/glutamine (Glx) and phenylalanine (Phe), in dentine collagen of (1) sympatric ENP killer whale ecotypes with well-characterized diet differences and (2) ECA/NWA killer whales with unknown diets. δ15NGlx-Phe was significantly higher in the ENP fish-eating (FE) than mammal-eating (ME) ecotype (19.2 ± 0.4‰ vs. 13.5 ± 0.7‰, respectively). Similar bimodal variation in δ15NGlx-Phe indicated analogous dietary divisions among ECA/NWA killer whales, with two killer whales having higher δ15NGlx-Phe (16.5 ± 0.0‰) than the others (13.5 ± 0.6‰). Inferences of dietary divisions between these killer whales were supported by parallel differences in threonine δ15N (–33.5 ± 1.6‰ and –40.4 ± 1.1‰, respectively), given the negative correlation between δ15NThr and TP across a range of marine consumers. CSIA-AA results for ECA/NWA whales, coupled with differences in tooth wear (a correlate for diet), are consistent with ecotype characteristics reported in ENP and other killer whale populations, thus adding to documented ecological divergence in this species worldwide.

Parasite resource manipulation drives bimodal variation in infection duration

Over a billion people on earth are infected with helminth parasites and show remarkable variation in parasite burden and chronicity. These parasite distributions are captured well by classic statistics, such as the negative binomial distribution. But the within-host processes underlying this variation are not well understood. In this study, we explain variation in macroparasite infection outcomes on the basis of resource flows within hosts. Resource flows realize the interactions between parasites and host immunity and metabolism. When host metabolism is modulated by parasites, we find a positive feedback of parasites on their own resources. While this positive feedback results in parasites improving their resource availability at high burdens, giving rise to chronic infections, it also results in a threshold biomass required for parasites to establish in the host, giving rise to acute infections when biomass fails to clear the threshold. Our finding of chronic and acute outcomes in bistability contrasts with classic theory, yet is congruent with the variation in helminth burdens observed in human and wildlife populations.

On the compositional variability of dalyite, K2ZrSi6O15: a new occurrence from Terceira, Azores

The rare potassium zirconium silicate dalyite has been identified for the first time on Terceira, Azores, within syenitic ejecta of the Caldeira-Castelinho Ignimbrite Formation. New quantitative analyses of this dalyite were combined with the small number of published analyses from various locations worldwide to evaluate the mineral's compositional variability. Additionally, solid-state modelling has been applied to assess the site allocations of substituting elements. The new analyses yield the average formula (K1.84Na0.15)∑=1.99(Zr0.94Ti0.012Hf0.011Fe0.004)∑=0.967Si6.03O15. Model results predict the placement of substituting Hf and Ti in the octahedral site, and highlight the overall complexity in the incorporation of Fe, Mg and Ba. The combined dataset reveals that dalyite found within peralkaline granites and syenites is generally defined by higher Na↔K substitution and lower Ti↔Zr substitution relative to dalyite from highly potassic rocks. The Terceira dalyite exhibits a bimodal variation in the degree of Na↔K substitution which is attributed to a K-enrichment trend induced by late-stage pore wall crystallization and albitization, coupled with the control of pore size upon the degree of supersaturation required to initiate nucleation of dalyite in pores of varying size.

Repeatability of Foraging Tactics in Young Brook Trout, Salvelinus fontinalis

In this study, we repeatedly observed individually marked Brook Trout in a field setting to determine if the bimodal variation in foraging tactics previously observed in young salmonid populations (without distinct morphological differences) is generated by individuals specializing at different foraging tactics. We found significant but low repeatability in several foraging movement parameters. This indicated that while individuals did have tendencies to be sedentary versus highly active, there was considerable variation in foraging activity within individuals. These results suggest that relatively consistent differences among individuals may facilitate selection for specialized morphology and that there may be a heritable component to activity. Erratum included.

Genetic control of immune responses to parasites: selection for responsiveness and non-responsiveness to Trichuris muris in random-bred mice

Populations of Schofield strain, random-bred mice were shown to have a bimodal variation in ability to bring about immune expulsion of the nematode Trichuris muris. This variation was genetically determined and independent of the size of infection experienced. The proportion of mice unable to achieve worm expulsion (non-responders) was relatively constant in various populations of the strain but was increased by selective breeding from mice of known status. Crosses made between non-responder and responder mice produced progeny that were almost all (92%) of responder phenotype, showing that the ability to achieve worm expulsion was inherited as a dominant characteristic. It is suggested that the genetic control involves a small number of genes; the possible immunological mechanisms by which control is mediated are briefly discussed.