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Glucocorticoid Manipulations in Free-Living Animals: Considerations of Dose Delivery, Life-History Context, and Reproductive State

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2015-06-23
Abstract: 

1. Experimental glucocorticoid (GC) manipulations can be useful for identifying the mechanisms that drive life history and fitness variation in free-living animals, but predicting the effects of GC treatment can be complicated. Much of the uncertainty about the effects of GC manipulations stems from their multi-faceted role in organismal metabolism, and their variable influence with respect to life-history stage, ecological context, age, sex, and individual variation.

2. Glucocorticoid hormones have been implicated in the regulation of parental care in many vertebrate taxa but in two seemingly contradictory ways, which sets up a potential corticosterone-induced “reproductive conflict”. GCs mediate adaptive physiological and behavioural responses to stressful events, and elevated levels can lead to trade-offs between reproductive effort and survival (e.g. the current reproduction versus survival hypothesis). The majority of studies examining the fitness effects of GC manipulations extend from this hypothesis. However, when animals are not stressed (likely most of the time) baseline GCs act as key metabolic regulators of daily energy balance, homeostasis, osmoregulation, and food acquisition, with pleiotropic effects on locomotor activity or foraging behaviour. Slight increases in circulating baseline levels can then have positive effects on reproductive effort (e.g. the corticosterone fitness/adaptation hypotheses), but comparatively few GC manipulation studies have targeted these small, non-stress induced increases.

3. We review studies of GC manipulations and examine the specific hypotheses used to predict the effects of manipulations in breeding wildlife. We argue that given the dichotomous function of GCs the current ‘reproduction versus survival’ paradigm is unnecessarily restrictive and predicts only deleterious GC effects on fitness. Therefore, a broader set of hypotheses should be considered when testing the fitness effects of GC manipulations.

4. When framing experimental manipulation studies, we urge researchers to consider three key points: life-history context (e.g. long- vs. short-lived, semelparous vs. iteroparous, etc), ecological context, and dose delivery.

 

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Experimental Reduction of Hematocrit Affects Reproductive Performance in European Starlings, Sturnus Vulgaris

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2015-08-03
Abstract: 
  1. Given the function of hemoglobin and observed increases in hematocrit during periods of increased energetic demands, hematocrit and hemoglobin are assumed to be related to aerobic capacity. Reductions in hematocrit and hemoglobin during reproduction are similar in magnitude to increases associated with aerobically demanding activities and therefore we sought to investigate whether these reductions in hematology have consequences for reproductive performance.
  2. We analyzed associations between natural variation in hematology in free-living European starlings (Sturnus vulgaris) and reproductive performance. To test whether transient reductions in hematology during different stages of reproduction (egg production and late incubation/early chick rearing) affected measures of reproductive performance, we also manipulated hematology using phenylhydrazine (PHZ), which lyses red blood cells.
  3. To investigate effects of reductions of hematology during egg-laying, we treated females with PHZ or saline (control) upon completion of their unmanipulated first clutch and removed eggs to induce the production and rearing of a replacement clutch. To investigate effects of reductions of hematology during chick rearing, we treated females during incubation of the unmanipulated first clutch and then monitored the subsequent hatching and rearing of the clutch.
  4. Individuals with higher hematocrit and hemoglobin initiated nesting earlier.  Furthermore, higher hemoglobin levels during incubation were associated with a greater number of chicks fledged. 
  5. PHZ treatment prior to egg production resulted in a significant delay in the laying of replacement clutches, but had no effect on provisioning rate or the size or number of chicks fledged. PHZ treatment during incubation and early chick rearing resulted in decreased hatchling mass in all years and a decrease in the size and number of fledglings in one of two years. The year that the effect of PHZ was observed appeared to be a particularly difficult year, since hatchling mass, brood size at hatching and at fledging were low among control females compared to other years.
  6. Our results suggest that a reduction in hematology during reproduction can be functionally significant, but that these costs are context-dependent.

 

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Individual Quality and Double-brooding in a Highly Synchronous Songbird Population

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2016-03-09
Abstract: 

Multiple brooding, the production of more than one set of offspring per breeding season, is a life history trait potentially doubling or tripling fecundity, but the factors responsible for variation in occurrence of multiple brooding within species remain poorly understood. We investigated the potential causes and consequences of double-brooding in the highly-synchronously breeding European starlings (Sturnus vulgaris), where we predicted that ‘date’ (clutch initiation) would have little effect on double-brooding propensity compared to individual ‘quality’. Double-brooding effectively doubled annual fecundity in European starlings (based on annual number of chicks fledged), but on average only 38% of individual females was double-brooded. Furthermore, 39% of females that initiated a second clutch experienced total failure of their second brood, thus accrued no fecundity advantage from their decision to double-brood. As we predicted variation in propensity for, and success of double-brooding was independent of laying date, but also of other putative measures of individual ‘quality’ (clutch size, egg mass, relative age, and provisioning rate). However, we found no evidence of a cost of double-brooding; double-brooded females had significantly higher return rate, and similar breeding productivity in the year after double-brooding compared with single-brooding females. Thus, a small proportion (~20%) of “high quality” female European starlings effectively double their potential breeding productivity through double-brooding without apparently paying a cost or experiencing simple trade-offs.

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Article
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Individual Quality and Double-Brooding in a Highly Synchronous Songbird Population

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2016-12-31
Abstract: 

Multiple brooding, the production of more than one set of offspring per breeding season, is a life-history trait that potentially doubles or triples fecundity, but the factors responsible for variation in the occurrence of multiple brooding within species remain poorly understood. We investigated the potential causes and consequences of double-brooding in the highly synchronously breeding European Starling (Sturnus vulgaris), for which we predicted that clutch initiation date would have little effect on double-brooding propensity compared with individual quality. Double brooding effectively doubled annual fecundity in European Starlings (based on the annual number of chicks fledged), but on average only 38% of individual females had a second brood. Furthermore, 39% of females that initiated a second clutch experienced total failure of their second brood, and thus accrued no advantage in fecundity from their decision to double-brood. As we predicted, variation in the propensity for, and success of, double-brooding was independent of laying date, but also of other putative measures of individual quality (clutch size, egg mass, relative female age, and nestling provisioning rate). However, we found no evidence of a cost of double-brooding; females that doublebrooded had significantly higher return rates and similar breeding productivity in the year after double-brooding compared with single brooding females. Thus, a small proportion (~20%) of ‘high-quality’ female European Starlings effectively double their potential breeding productivity through double-brooding without apparently paying a cost or experiencing any simple tradeoffs.

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Article
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Coherent Assessments of Europe’s Marine Fishes Show Regional Divergence and Megafauna Loss

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2017-08
Abstract: 

Europe has a long tradition of exploiting marine fishes and is promoting marine economic activity through its Blue Growth strategy. This increase in anthropogenic pressure, along with climate change, threatens the biodiversity of fishes and food security. Here, we examine the conservation status of 1,020 species of European marine fishes and identify factors that contribute to their extinction risk. Large fish species (greater than 1.5 m total length) are most at risk; half of these are threatened with extinction, predominantly sharks, rays and sturgeons. This analysis was based on the latest International Union for Conservation of Nature (IUCN) European regional Red List of marine fishes, which was coherent with assessments of the status of fish stocks carried out independently by fisheries management agencies: no species classified by IUCN as threatened were considered sustainable by these agencies. A remarkable geographic divergence in stock status was also evident: in northern Europe, most stocks were not overfished, whereas in the Mediterranean Sea, almost all stocks were overfished. As Europe proceeds with its sustainable Blue Growth agenda, two main issues stand out as needing priority actions in relation to its marine fishes: the conservation of marine fish megafauna and the sustainability of Mediterranean fish stocks.

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Article
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Unpredictable Perturbation Reduces Breeding Propensity Regardless of Pre-Laying Reproductive Readiness in a Partial Capital Breeder

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2016-12-31
Abstract: 

Theoretically, individuals of migratory species should optimize reproductive investment based on a combination of timing of and body condition at arrival on the breeding grounds. A minimum threshold body mass is required to initiate reproduction, and the timing of reaching this threshold is critical because of the trade-off between delaying breeding to gain in condition against the declining value of offspring with later reproductive timing. Long-lived species have the flexibility within their life history to skip reproduction in a given year if they are unable to achieve this theoretical mass threshold. Although the decision to breed or not is an important parameter influencing population dynamics, the mechanisms underlying this decision are poorly understood. Here, we mimicked an unpredictable environmental perturbation that induced a reduction in body mass of Arctic pre-breeding (before the laying period) female common eiders Somateria mollissima; a long-lived migratory seaduck, while controlling for individual variation in the pre-laying physiological reproductive readiness via vitellogenin (VTG) – a yolk-targeted lipoprotein. Our aim was to causally determine the interaction between body condition and pre-laying reproductive readiness (VTG) on breeding propensity by experimentally reducing body mass in treatment females. We first demonstrated that arrival body condition was a key driver of breeding propensity. Secondly, we found that treatment and VTG levels interacted to influence breeding propensity, indicating that our experimental manipulation, mimicking an unpredictable food shortage, reduced breeding propensity, regardless of the degree of pre-laying physiological reproductive readiness (i.e. timing of ovarian follicles recruitment). Our experiment demonstrates that momentary environmental perturbations during the pre-breeding period can strongly affect the decision to breed, a key parameter driving population dynamics.

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Article
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Global Priorities for Conserving the Evolutionary History of Sharks, Rays, and Chimaeras

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2018-01-18
Abstract: 

In an era of accelerated biodiversity loss and limited conservation resources, systematic prioritization of species and places is essential. In terrestrial vertebrates, evolutionary distinctness has been used to identify species and locations that embody the greatest share of evolutionary history. We estimate evolutionary distinctness for a large marine vertebrate radiation on a dated taxon-complete tree for all 1,192 chondrichthyan fishes (sharks, rays and chimaeras) by augmenting a new 610-species molecular phylogeny using taxonomic constraints. Chondrichthyans are by far the most evolutionarily distinct of all major radiations of jawed vertebrates—the average species embodies 26 million years of unique evolutionary history. With this metric, we identify 21 countries with the highest richness, endemism and evolutionary distinctness of threatened species as targets for conservation prioritization. On average, threatened chondrichthyans are more evolutionarily distinct—further motivating improved conservation, fisheries management and trade regulation to avoid significant pruning of the chondrichthyan tree of life.

Document type: 
Article

Associations Between Imprinted Gene Expression in the Placenta, Human Fetal Growth and Preeclampsia

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2017-11-29
Abstract: 

Genomic imprinting is essential for normal placental and fetal growth. One theory to explain the evolution of imprinting is the kinship theory (KT), which predicts that genes that are paternally expressed will promote fetal growth, whereas maternally expressed genes will suppress growth. We investigated the expression of imprinted genes using microarray measurements of expression in term placentae. Correlations between birthweight and the expression levels of imprinted genes were more significant than for non-imprinted genes, but did not tend to be positive for paternally expressed genes and negative for maternally expressed genes.  Imprinted genes were more dysregulated in preeclampsia (a disorder associated with placental insufficiency) than randomly selected genes, and we observed an excess of patterns of dysregulation in preeclampsia that would be expected to reduce nutrient allocation to the fetus, given the predictions of the KT. However, we found no evidence of coordinated regulation among these imprinted genes. A few imprinted genes have previously been shown to be associated with fetal growth and preeclampsia, and our results indicate that this is true for a broader set of imprinted genes.

Document type: 
Article

Maximum Intrinsic Rate of Population Increase in Sharks, Rays, and Chimaeras: The Importance of Survival to Maturity

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2016-06-10
Abstract: 

The maximum intrinsic rate of population increase rmax  is a commonly estimated demographic parameter used in assessments of extinction risk. In teleosts, rmax can be calculated using an estimate of spawners per spawner, but for chondrichthyans, most studies have used annual reproductive output b instead. This is problematic as it effectively assumes all juveniles survive to maturity. Here, we propose an updated rmax equation that uses a simple mortality estimator which also accounts for survival to  maturity: the reciprocal of average lifespan. For 94 chondrichthyans, we now estimate that rmax values are on average 10% lower than previously published. Our updated rmax estimates are lower than previously published for species that mature later relative to maximum age and those with high annual fecundity. The most extreme discrepancies in rmax values occur in species with low age at maturity and low annual reproductive output. Our results indicate that chondrichthyans that mature relatively later in life, and to a lesser extent those that are highly fecund, are less resilient to fishing than previously thought.

Document type: 
Article

Canada's Wild Salmon Policy: an Assessment of Conservation Progress

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2017-08-21
Abstract: 

Canada’s Policy for Conservation of Wild Pacific Salmon has been heralded as a transformative approach to the management of wild salmon whereby conservation is the highest priority. Given that changes to the Policy are under consideration, it is timely that we understand whether our state of knowledge and the status of wild salmon in Canada have indeed improved after its adoption in 2005. To answer these questions, we used two indices of improvement: (i) monitoring effort and (ii) abundance of spawning adults. Our results, based on data for all species from British Columbia’s north and central coasts, show that monitoring effort has continued to erode, abundance of spawning adults has significantly declined for several species, the status of many salmon Conservation Units are in zones of concern, and 42% of the Conservation Units that we assessed as Red (threatened) would have improved in status had the Canadian fishery been reduced. We conclude with recommendations to help improve our knowledge of the status of salmon and enable a robust and successfully implemented Wild Salmon Policy for the future.

Document type: 
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