Metabolic cost of calcification in bivalve larvae under experimental ocean acidification

Physiological increases in energy expenditure frequently occur in response to environmental stress. Although energy limitation is often invoked as a basis for decreased calcification under ocean acidification, energy-relevant measurements related to this process are scant. In this study we focus on first-shell (prodissoconch I) formation in larvae of the Pacific oyster, Crassostrea gigas. The energy cost of calcification was empirically derived to be ≤ 1.1 µJ (ng CaCO3)−1. Regardless of the saturation state of aragonite (2.77 vs. 0.77), larvae utilize the same amount of total energy to complete first-shell formation. Even though there was a 56% reduction of shell mass and an increase in dissolution at aragonite undersaturation, first-shell formation is not energy limited because sufficient endogenous reserves are available to meet metabolic demand. Further studies were undertaken on larvae from genetic crosses of pedigreed lines to test for variance in response to aragonite undersaturation. Larval families show variation in response to ocean acidification, with loss of shell size ranging from no effect to 28%. These differences show that resilience to ocean acidification may exist among genotypes. Combined studies of bioenergetics and genetics are promising approaches for understanding climate change impacts on marine organisms that undergo calcification.

Spatiotemporal distributions of intestinal helminths in female lesser scaupAythya affinisduring spring migration from the upper Midwest, USA

We examined the associations between intestinal helminth infracommunity structure and infection parameters and the age, size, and year and region of collection of 130 female lesser scaup (Aythya affinis) during their 2014–2015 spring migrations through the upper Midwest, USA. We identified a total of 647,174 individual helminths from 40 taxa, including 20 trematodes, 14 cestodes, 4 nematodes and 2 acanthocephalans parasitizing lesser scaup within the study area. Lesser scaup were each infected with 2–23 helminth taxa. One digenean,Plenosoma minimum, is reported for the first time in lesser scaup and in the Midwest. Mean trematode abundance and total helminth abundance was significantly less in 2015 than 2014, and we suspect that colder weather late in 2015 impacted the intermediate host fauna and caused the observed differences. Brillouin's species diversity of helminths was greatest in the northernmost region of the study area, which coincides with the range of a non-indigenous snail that indirectly causes annual mortality events of lesser scaup. While host age and size were not determined to be influential factors of helminth infracommunity structure, non-parametric ordination and permutational analysis of co-variance revealed that year and region of collection explained differences in helminth infracommunities. Our results suggest that spatiotemporal variations play an important role in the structure of intestinal helminth infracommunities found in migrating lesser scaup hosts, and may therefore impact host ability to build endogenous reserves at certain stopover locations in the Midwest.

Reproductive traits of horned octopus Eledone cirrhosa in Atlantic Iberian waters

Length–weight relationships, sex-ratio, maturity patterns, size at first maturity, reproductive outputs, fecundity and spawning period of horned octopus Eledone cirrhosa in north-west Iberian coast are presented for the first time. Samples were collected between February 2009 and July 2011 in four fishing ports along the north-west Iberian coast: Burela in north Galician waters (NGW), Ribeira or Bueu in western Galician waters (WGW), and Aveiro in western Portuguese waters (WPW). A total of 4127 individuals (1042 males, 3079 females and six undetermined) were sampled. Individuals ranged from 45 to 191 mm dorsal mantle length (ML) and 15–1159 g body weight (BW). The overall sex-ratio was biased towards females, accounting for 74.71% of whole sample. Main spawning season of this species in north-western Iberian waters extends from May to June. Size at first maturity (ML50%) of males was 108.9 mm in NGW, 99.25 mm in WGW, and 91.4 mm in WPW, whereas ML50% for females were 134.5 mm, 121.4 mm and 100.8 mm, respectively. Potential fecundity was 2452.88 ± 36.4 oocytes per ovary (N = 697). Mean oocyte length was 3.89 ± 0.025 mm (N = 697). The average number of fully developed spermatophores in mature males was 86.55 ± 1.9 (N = 223) with a mean length of 44.97 ± 0.29 mm (N = 224). Potential fecundity in females was significantly (P < 0.05) correlated with ML and BW. Results obtained suggest that energy for gonad growth comes from the diet rather than endogenous reserves.

Effects of ingesting [13C]glucose early or late into cold exposure on substrate utilization

One of the factors limiting the oxidation of exogenous glucose during cold exposure may be the delay in establishing a shivering steady state (∼60 min), reducing glucose uptake into skeletal muscle. Therefore, using indirect calorimetry and isotopic methodologies in non-cold-acclimatized men, the main purpose of this study was to determine whether ingesting glucose at a moment coinciding with the maximal shivering intensity could increase the utilization rate of the ingested glucose. 13C-enriched glucose was ingested (800 mg/min) from the onset (G0) or after 60 min (G60) of cold exposure when the thermogenic rate was stabilized to low-intensity shivering (∼2.5 times resting metabolic rate). For the same quantity of glucose ingested, the oxidation rate of exogenous glucose was 35% higher in G60 (159 ± 17 vs. 118 ± 17 mg/min in G0) between minutes 60 and 90. By the end of cold exposure, exogenous glucose oxidation was significantly greater in G0, reaching 231 ± 14 mg/min, ∼15% higher than the only rates previously reported. This considerably reduced the utilization of endogenous reserves over time and compared with the G60 condition. This study also demonstrates a fall in muscle glycogen utilization, when glucose was ingested from the onset of cold exposure (from ∼150 to ∼75 mg/min). Together, these findings indicate the importance of ingesting glucose immediately on exposure to a cold condition, relying on shivering thermogenesis and sustaining that consumption for as long as possible. This substrate not only provides an auxiliary fuel source for shivering thermogenesis, but, more importantly, preserves the limited endogenous glucose reserves.

Isotopic Evidence for Sources of Nutrients Allocated to Clutch Formation by Harlequin Ducks

Abstract. Waterfowl employ a broad array of strategies for acquiring the energy and nutrients needed for egg formation, ranging from storage of endogenous reserves prior to arrival on breeding areas to complete reliance on exogenous food sources available at breeding sites. We used stable isotope analyses (δ13C and δ15N) to quantify the relative nutrient inputs to Harlequin Duck (Histrionicus histrionicus) eggs and, therefore, to identify the strategy of nutrient acquisition and allocation used by females to meet the demands of egg production. Marine-derived endogenous nutrients are isotopically more enriched than freshwater dietary nutrients for Harlequin Ducks that migrate between marine wintering grounds and terrestrial breeding grounds. There was little evidence that endogenous reserves stored on marine wintering areas were allocated to clutch formation. Therefore, Harlequin Ducks relied on food available in streams on breeding grounds for egg formation, and reserves stored on marine areas were likely used during other energetically and nutritionally demanding periods.

Capital versus income breeding in a migratory passerine bird: evidence from stable-carbon isotopes

Birds meet the energetic demands of egg formation by using either endogenous reserves (capital breeding) or recently ingested nutrients (income breeding). Examining these strategies in migratory birds has been difficult because of the inability to assign the origin of egg nutrients. We used stable-carbon isotopes (δ13C values) to determine whether American Redstarts (Setophaga ruticilla (L., 1758)) form eggs using endogenous reserves acquired on tropical wintering areas or local dietary sources. Redstart diet tends to be enriched in 13C on tropical wintering areas; therefore, we predicted that if endogenous reserves are used to form eggs, then 13C would be enriched in first clutches relative to replacement clutches. We analyzed yolk (δ13CYK) samples from successive first, second, and third clutches and blood plasma (δ13CPL) sampled from females over the same time period. Values of δ13CYK in first-clutch and second-clutch eggs were significantly more positive than those in third-clutch eggs. Although the isotopic shift in yolk was in the direction predicted for a mixed capital–income strategy, δ13CPL, which represents the locally derived diet, varied seasonally in accordance with the shift in δ13CYK. Our findings indicate female Redstarts are primarily income breeders, forming eggs from an isotopically variable diet during the breeding season.

Body Mass of Long-Tailed Ducks (Clangula Hyemalis) During Incubation

We investigated body-mass dynamics during incubation of Long-tailed Ducks (Clangula hyemalis) nesting in Canada’s central Arctic, 1998–2003. Long-tailed Duck females (n = 37) lost 7% of pre-incubation body mass during incubation; on average, females weighed 618 ± 15 g (mean ± SE) at clutch completion and 575 ± 11 g at hatch. Given the differences in body size, Long-tailed Ducks relied less on endogenous reserves than sympatric King Eiders (Somateria spectabilis), but lost less mass than similar-sized waterfowl species nesting in temperate climates. Preliminary data suggest that Long-tailed Ducks maintain similar or higher nest-attendance rates than temperate-nesting waterfowl of similar size, and we suggest that access to locally abundant, high-quality foods enable Long-tailed Duck females to maintain high incubation constancy without sacrificing female body condition. Nevertheless, Long-tailed Ducks appear to differ widely from most Arctic-nesting waterfowl in nutritional strategy for nesting. Masse corporelle chez l’Harelde kakawi (Clangula hyemalis) au cours de l’incubation