Addressing assumptions: variation in stable isotopes and fatty acids of marine macrophytes can confound conclusions of food web studies

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MN Dethier, *EA Sosik, *AWE Galloway, DO Duggins, *CA Simenstad. 2013. Feature Article, open access. Marine Ecology Progress Series 478:1-14.

http://www.int-res.com/abstracts/meps/v478/

*Authors from SAFS

Research on food webs increasingly relies on sampling biomarkers (stable isotopes and fatty acids) in consumers and their potential prey. In studies of macroalgal and seagrass biomarkers in the northeast Pacific, Dethier and coworkers found substantial variation in biomarkers across dates and sites. This natural variation means that incorrect conclusions may be drawn from assumptions that a particular biomarker value corresponds to a given food item in a consumer’s diet. Biomarkers are relatively consistent at the phylum level, but spatial and temporal variation at the species level is fairly high. The importance of this ‘noise’ in biomarker values was tested by running Bayesian mixing models with a theoretical consumer given diets whose biomarker values varied at scales seen in nature.

Ocean food provision index is seriously biased

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Branch TA, Hively DJ, Hilborn R (2013) Is the ocean food provision index biased? Nature 495:E5-E6

How close to maximum sustainable food provision is current seafood harvest from the world’s oceans? Halpern et al. [1] suggest that the answer is 25% from a global index of food provision, part of their multifaceted index of ocean health. Rigorous methods used for management, however, demonstrate that their food provision index is uncorrelated with actual food provision, and that global ocean food provision is in the range of 71–95%. Their results stem from an uncertain method of estimating maximum sustainable yield (MSY), and we believe that this approach should be avoided as a measure of food provision.

[1] Halpern BS et al. (2012) An index to assess the health and benefits of the global ocean. Nature 488:615-620

Temporal variation in selection on body length and date of return in a wild population of coho salmon, Oncorhynchus kisutch.

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Temporal variation in selection on body length and date of return in a wild population of coho salmon, Oncorhynchus kisutch.

BMC Evol Biol. 2012;12:116

Authors: Kodama M, Hard JJ, Naish KA

Abstract
BACKGROUND: A number of studies have measured selection in nature to understand how populations adapt to their environment; however, the temporal dynamics of selection are rarely investigated. The aim of this study was to assess the temporal variation in selection by comparing the mode, direction and strength of selection on fitness-related traits between two cohorts of coho salmon (Oncorhynchus kisutch). Specifically, we quantified individual reproductive success and examined selection on date of return and body length in a wild population at Big Beef Creek, Washington (USA).
RESULTS: Reproductive success and the mode, direction and strength of selection on date of return and body length differed between two cohorts sampled in 2006 and 2007. Adults of the first brood year had greater success over those of the second. In 2006, disruptive selection favored early and late returning individuals in 2-year-old males, and earlier returning 3-year-old males had higher fitness. No evidence of selection on date of return was detected in females. In 2007, selection on date of return was not observed in males of either age class, but stabilizing selection on date of return was observed in females. No selection on body length was detected in males of both age classes in 2006, and large size was associated with higher fitness in females. In 2007, selection favored larger size in 3-year-old males and intermediate size in females. Correlational selection between date of return and body length was observed only in 2-year-old males in 2006.
CONCLUSIONS: We found evidence of selection on body length and date of return to the spawning ground, both of which are important fitness-related traits in salmonid species, but this selection varied over time. Fluctuation in the mode, direction and strength of selection between two cohorts was likely to be due to factors such as changes in precipitation, occurrence of catastrophic events (flooding), the proportion of younger- versus older-maturing males, sex ratio and densities of spawners.

PMID: 22805481 [PubMed – indexed for MEDLINE]

via pubmed: school of aquatic an… http://www.ncbi.nlm.nih.gov/PubMed/22805481?dopt=Abstract

Phenotype flexibility in wild fish: Dolly Varden regulate assimilative capacity to capitalize on annual pulsed subsidies.

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Phenotype flexibility in wild fish: Dolly Varden regulate assimilative capacity to capitalize on annual pulsed subsidies.

J Anim Ecol. 2013 Mar 19;

Authors: Armstrong JB, Bond MH

Abstract
Large digestive organs increase rates of energy gain when food is plentiful but are costly to maintain and increase rates of energy loss when food is scarce. The physiological adaptations to this trade-off differ depending on the scale and predictability of variation in food abundance. Currently, there is little understanding of how animals balance trade-offs between the cost and capacity of the digestive system in response to resource pulses: rare, ephemeral periods of resource superabundance. We investigated the physiological and behavioural tactics of the fish Dolly Varden (Salvelinus malma) that rear in watersheds with low in situ productivity, but experience annual resource pulses from the spawning migrations of Pacific salmon. The eggs of Pacific salmon provide high-energy food for Dolly Varden. Dolly Varden sampled 6 weeks prior to the resource pulse exhibited atrophy of the stomach, pyloric caeca, intestine and liver. Throughout the portion of the growing season prior to the resource pulse, fish exhibited empty stomachs, low indices of energy condition and muscle isotope signatures reflecting the previous resource pulse. During the resource pulse, Dolly Varden exhibited large digestive machinery, gorged on salmon eggs and rapidly stored energy in fat reserves, somatic growth and gonad development. Dolly Varden appeared to achieve nearly their entire annual energy surplus during the ∼5-week period when sockeye salmon spawn. Digestive flexibility provides Dolly Varden the energy efficiency required to survive and reproduce when resource abundance is concentrated into an annual pulse that is predictable, yet highly ephemeral. Although fish are known to incur extremely variable energy budgets, our study is one of the first to document digestive flexibility in wild fish. Our study emphasizes that fish can rely heavily on rare, high-magnitude foraging opportunities. Human actions that attenuate spikes in food abundance may have stronger than anticipated effects on consumer energy budgets.

PMID: 23510107 [PubMed – as supplied by publisher]

via pubmed: school of aquatic an… http://www.ncbi.nlm.nih.gov/PubMed/23510107?dopt=Abstract

How Stock of Origin Affects Performance of Individuals across a Meta-Ecosystem: An Example from Sockeye Salmon.

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How Stock of Origin Affects Performance of Individuals across a Meta-Ecosystem: An Example from Sockeye Salmon.

PLoS One. 2013;8(3):e58584

Authors: Griffiths JR, Schindler DE, Seeb LW

Abstract
Connectivity among diverse habitats can buffer populations from adverse environmental conditions, influence the functioning of meta-ecosystems, and ultimately affect the reliability of ecosystem services. This stabilizing effect on populations is proposed to derive from complementarity in growth and survival conditions experienced by individuals in the different habitats that comprise meta-ecosystems. Here we use the fine scale differentiation of salmon populations between diverse lake habitats to assess how rearing habitat and stock of origin affect the body condition of juvenile sockeye salmon. We use genetic markers (single nucleotide polymorphisms) to assign individuals of unknown origin to stock group and in turn characterize ecologically relevant attributes across habitats and stocks. Our analyses show that the body condition of juvenile salmon is related to the productivity of alternative habitats across the watershed, irrespective of their stock of origin. Emigrants and residents with genetic origins in the high productivity lake were also differentiated by their body condition, poor and high respectively. These emigrants represented a substantial proportion of juvenile sockeye salmon rearing in the lower productivity lake habitat. Despite emigrants originating from the more productive lake, they did not differ in body condition from the individuals spawned in the lower productivity, recipient habitat. Genetic tools allowed us to assess the performance of different stocks groups across the diverse habitats comprising their meta-ecosystem. The ability to characterize the ecological consequences of meta-ecosystem connectivity can help develop strategies to protect and restore ecosystems and the services they provide to humans.

PMID: 23505539 [PubMed – in process]

via pubmed: school of aquatic an… http://www.ncbi.nlm.nih.gov/PubMed/23505539?dopt=Abstract

Size-selective fishing affects sex ratios and the opportunity for sexual selection in Alaskan sockeye salmon Oncorhynchus nerka

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Authors
N. W. Kendall and T. P. Quinn,
Oikos 122: 411–420, 2013

Abstract
Selective exploitation can cause adverse ecological and evolutionary changes in wild populations and also affect sex ratios but few studies have empirically documented skewed sex ratios in exploited fishes (other than species with extreme sexual size dimorphism, SSD). To investigate the possibility of sex-selective fishing on Alaskan sockeye salmon Oncorhynchus nerka, we assessed sex ratios in fish at two spatial scales: within each of five fishing districts and among 13 breeding populations in one of these districts. We predicted that populations’ sex ratios would vary based on the average size of fish and SSD because size affects vulnerability to fishing. At the larger scale, we found a small but significant bias in fish returning to four of the five fishing districts (average  52% females), and in four of the five districts males were caught at significantly higher rates than females. At the finer scale there was marked variation in sex ratio on the breeding grounds, ranging from 36% to 47% males. Populations with fish of intermediate sizes experienced the greatest sex ratio biases; the greater vulnerability of males than females to fishing resulted from a combination of larger SSD and different harvest rates between the sexes associated with the fishery size-selectivity curve shape. Skewed sex ratios may change competition and behavior on the breeding grounds, relaxing selection on male traits associated with mate choice by females or intrasexual competition and altering demographic and evolutionary pressures on the fish. Assessment of the size selectivity of fishing gear and the population’s SSD can help to illuminate if and how exploitation can affect sex ratios. Future studies examining  size-selective fishing should also evaluate the consequences for sex ratios, as this might help explain changes in harvested population structure and sustainability.

Reproductive success of captively bred and naturally spawned Chinook salmon colonizing newly accessible habitat.

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Reproductive success of captively bred and naturally spawned Chinook salmon colonizing newly accessible habitat.

Evol Appl. 2013 Feb;6(2):165-79

Authors: Anderson JH, Faulds PL, Atlas WI, Quinn TP

Abstract
Captively reared animals can provide an immediate demographic boost in reintroduction programs, but may also reduce the fitness of colonizing populations. Construction of a fish passage facility at Landsburg Diversion Dam on the Cedar River, WA, USA, provided a unique opportunity to explore this trade-off. We thoroughly sampled adult Chinook salmon () at the onset of colonization (2003-2009), constructed a pedigree from genotypes at 10 microsatellite loci, and calculated reproductive success (RS) as the total number of returning adult offspring. Hatchery males were consistently but not significantly less productive than naturally spawned males (range in relative RS: 0.70-0.90), but the pattern for females varied between years. The sex ratio was heavily biased toward males; therefore, inclusion of the hatchery males increased the risk of a genetic fitness cost with little demographic benefit. Measurements of natural selection indicated that larger salmon had higher RS than smaller fish. Fish that arrived early to the spawning grounds tended to be more productive than later fish, although in some years, RS was maximized at intermediate dates. Our results underscore the importance of natural and sexual selection in promoting adaptation during reintroductions.

PMID: 23467446 [PubMed – in process]

via pubmed: school of aquatic an… http://www.ncbi.nlm.nih.gov/PubMed/23467446?dopt=Abstract

Seminar: “Ecologically-driven evolution: insights from the salmonid immune and oxygen delivery systems”

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Visiting post-doctoral researcher, Melissa Evans (Memorial University of Newfoundland, Canada) will be giving an informal brown bag seminar titled:

“Ecologically-driven evolution: insights from the salmonid immune and oxygen delivery systems”

Location: Fish 203
Date: Monday March 11th
Time: 12:30 pm

All are welcome to attend.

Contact Peter Westley at (resolute@uw.edu) if you would like to arrange a time to meet with Melissa.

Melissa’s Research background
Broadly speaking, Melissa is an evolutionary ecologist interested in the mechanisms animals use to respond to environmental variation. Her research is currently exploring physiological, behavioural, and genomic variation in salmon populations, and links between these traits and the evolutionary trajectories of populations and species. In April 2012 Melissa began a post-doc in Ian Fleming’s lab at Memorial University of Newfoundland where she is exploring the behavioural and evolutionary ecology of Atlantic salmon at sea. Prior to this Melissa was an NSERC postdoctoral fellowship in Dr. Louis Bernatchez’s lab (Univ. Laval), where she examined the role of physiological trait divergence in the ongoing speciation of European and lake whitefish. She completed my PhD degree in 2010 under the supervision of Dr. Bryan Neff (Univ. Western Ontario) and Dr. Daniel Heath (Univ. Windsor). Her PhD research focused on parasite-driven natural selection and the intersection between natural and sexual selection pressures in populations of Chinook salmon in British Columbia.

Representative propaganda
M.L. Evans, M. Dionne, K.M. Miller, and L. Bernatchez (2012) Mate choice for MHC genetic divergence as a bet-hedging strategy in Atlantic salmon (Salmo salar). Proceedings of the Royal Society of London Series B 279:379-386.

M.L. Evans, and L. Bernatchez (2012) Oxidative phosphorylation gene transcription in whitefish species pairs reveals patterns of parallel and non-parallel physiological divergence. Journal of Evolutionary Biology 25:1823-1834

M.L. Evans, B.D. Neff, and D.D. Heath (2010) Quantitative genetic and translocation experiments reveal genotype-by-environment effects on juvenile life-history traits in two populations of Chinook salmon (Oncorhynchus tshawytscha). Journal of Evolutionary Biology 23:687-698.

M.L. Evans, and B.D. Neff (2009) MHC heterozygote advantage and widespread bacterial infections in populations of Chinook salmon (Oncorhynchus tshawytscha). Molecular Ecology 18:4716-4729

Stage-specific effects of androgens and estradiol-17beta on the development of late primary and early secondary ovarian follicles of coho salmon (Oncorhynchus kisutch) in vitro.

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Stage-specific effects of androgens and estradiol-17beta on the development of late primary and early secondary ovarian follicles of coho salmon (Oncorhynchus kisutch) in vitro.

Biol Reprod. 2012 Sep;87(3):64

Authors: Forsgren KL, Young G

Abstract
An in vitro system was used to analyze the effects of sex steroids on the development of primary (late perinucleolar stage) and early secondary, previtellogenic (early cortical alveolus stage) ovarian follicles of coho salmon cultured for up to 21 days. Late perinucleolar-stage follicles increased significantly in size after 7 days of treatment with low concentrations of 11-ketotestosterone (11-KT), a nonaromatizable androgen. An androgen receptor antagonist (flutamide) inhibited this growth-promoting effect, and the highest concentration resulted in atresia of follicles, implicating androgens as survival factors at this stage. Testosterone (T) was less effective than 11-KT in promoting growth, but blocking aromatization with exemestane resulted in a growth response similar to that of 11-KT. Estradiol-17beta (E2) had no effect on growth at this stage. After 21 days of culture, E2 was the most potent steroid in increasing the number of follicles containing cortical alveoli and the number of cortical alveoli within those follicles. At the early cortical alveolus stage, low doses of E2 promoted growth and strongly stimulated synthesis of cortical alveoli, actions that were inhibited by an estrogen receptor antagonist (tamoxifen). 11-KT displayed moderate growth-promoting effects, and 11-KT and T stimulated moderate to substantial increases in abundance of cortical alveoli. This study shows that the predominant role of androgens is the promotion of growth of late perinucleolar-stage follicles, while E2 stimulates both the growth and accumulation of cortical alveoli in early cortical alveolus-stage follicles.

PMID: 22674392 [PubMed – indexed for MEDLINE]

Read the publication online on PubMed.