Jorge S. Gutiérrez

Understanding the energetic costs of living in saline environments: effects of salinity on basal metabolic rate, body mass and daily energy consumption of a long-distance migratory shorebird

SUMMARY Many migratory vertebrates typically move between habitats with varying salinities during the annual cycle. These organisms clearly exhibit a remarkable phenotypic flexibility in their ‘osmoregulatory machinery’, but the metabolic consequences of salinity acclimatization are still not well understood. We investigated the effects of salinity on basal metabolic rate (BMR), body mass and daily energy consumption of a long-distance migratory shorebird, the dunlin (Calidris alpina), outside the breeding season. Mass-corrected BMR and daily energy consumption increased significantly by 17 and 20% between freshwater (0.3‰ NaCl) and saltwater (33.0–35.0‰ NaCl), respectively. Body mass in both captive and wild dunlins was lower (9–16%) in saline than in freshwater environments. These changes on BMR and body mass were quickly reversed by returning the birds to freshwater, suggesting that metabolic adjustment to saltwater and metabolic readjustment to freshwater are both processes that occur in a few days. Our findings support empirically that the processes of developing and maintaining an active osmoregulatory machinery are energetically expensive, and they could help to explain diet and/or habitat selection patterns along the flyway. Finally, we discuss whether body mass loss in saltwater may be a strategy to reduce maintenance cost in osmotically stressful conditions such as overwintering in marine habitats, and raise some methodological implications for studies of BMR-related outcomes using captive birds captured in saline environments.

When Siberia came to the Netherlands : The response of continental black-tailed godwits to a rare spring weather event

1. Extreme weather events have the potential to alter both short- and long-term population dynamics as well as community- and ecosystem-level function. Such events are rare and stochastic, making it difficult to fully document how organisms respond to them and predict the repercussions of similar events in the future. 2. To improve our understanding of the mechanisms by which short-term events can incur long-term consequences, we documented the behavioural responses and fitness consequences for a long-distance migratory bird, the continental black-tailed godwit Limosa limosa limosa, resulting from a spring snowstorm and three-week period of record low temperatures. 3. The event caused measurable responses at three spatial scales - continental, regional and local - including migratory delays (+19 days), reverse migrations (>90 km), elevated metabolic costs (+8·8% maintenance metabolic rate) and increased foraging rates (+37%). 4. There were few long-term fitness consequences, however, and subsequent breeding seasons instead witnessed high levels of reproductive success and little evidence of carry-over effects. 5. This suggests that populations with continued access to food, behavioural flexibility and time to dissipate the costs of the event can likely withstand the consequences of an extreme weather event. For populations constrained in one of these respects, though, extreme events may entail extreme ecological consequences.

Living in Environments with Contrasting Salinities: A Review of Physiological and Behavioural Responses in Waterbirds

Summary. During the course of their lives many vertebrates live and forage in environments characterized by different salinities and must therefore respond to changes in salt intake. This is particularly true for numerous species of migratory waterbirds, especially those that routinely commute between saltwater and freshwater wetlands throughout their annual cycle and/or within a season. These birds have evolved a suite of morphological, physiological and behavioural mechanisms to successfully maintain osmoregulatory balance. However, relatively little is known about the impacts of salinity on the distribution, physiological performance and reproductive success of waterbirds. Here I review the current knowledge of the physiological and behavioural mechanisms through which waterbirds cope with contrasting salinities and how some of the adjustments undertaken might interfere with relevant aspects of their performance. I argue that, because of their strong reliance on wetland ecosystems for foraging and breeding, waterbirds may be particularly vulnerable to climate-induced changes in salinity, especially in arid or semiarid tropical areas where increases in both temperature and salinity may affect their body condition and, ultimately, survival prospects. I conclude by offering some suggestions for future research that could take us beyond our current level of understanding of avian osmoregulation.

Avian BMR in marine and non-marine habitats: a test using shorebirds.

Basal metabolic rate (BMR) is closely linked to different habitats and way of life. In birds, some studies have noted that BMR is higher in marine species compared to those inhabiting terrestrial habitats. However, the extent of such metabolic dichotomy and its underlying mechanisms are largely unknown. Migratory shorebirds (Charadriiformes) offer a particularly interesting opportunity for testing this marine–non-marine difference as they are typically divided into two broad categories in terms of their habitat occupancy outside the breeding season: ‘coastal’ and ‘inland’ shorebirds. Here, we measured BMR for 12 species of migratory shorebirds wintering in temperate inland habitats and collected additional BMR values from the literature for coastal and inland shorebirds along their migratory route to make inter- and intraspecific comparisons. We also measured the BMR of inland and coastal dunlins Calidris alpina wintering at a similar latitude to facilitate a more direct intraspecific comparison. Our interspecific analyses showed that BMR was significantly lower in inland shorebirds than in coastal shorebirds after the effects of potentially confounding climatic (latitude, temperature, solar radiation, wind conditions) and organismal (body mass, migratory status, phylogeny) factors were accounted for. This indicates that part of the variation in basal metabolism might be attributed to genotypic divergence. Intraspecific comparisons showed that the mass-specific BMR of dunlins wintering in inland freshwater habitats was 15% lower than in coastal saline habitats, suggesting that phenotypic plasticity also plays an important role in generating these metabolic differences. We propose that the absence of tidally-induced food restrictions, low salinity, and less windy microclimates associated with inland freshwater habitats may reduce the levels of energy expenditure, and hence BMR. Further research including common-garden experiments that eliminate phenotypic plasticity as a source of phenotypic variation is needed to determine to what extent these general patterns are attributable to genotypic adaptation.

International importance of Extremadura, Spain, for overwintering migratory dabbling ducks: a role for reservoirs.

Many migratory waterbird populations are in decline and loss of natural wetlands is one of the main causes.However, some speciesmay respondpositively to artificial wetland recreation. In Extremadura (south-west Europe), several large reservoirs were created for irrigation since the 1960s and some comparatively small reservoirs were built from the late 1990s onwards close to rice fields. Here we analyse the abundance of wintering dabbling ducks (Anas spp.) in Extremadura before (1991–1994) and after (2007–2010) the creation of these new reservoirs in order to address the current importance of the area for this guild within the East Atlantic Flyway (EAF). A mean of 25,277 dabbling ducks wintered in the study area during 1991–1994, increasing to 46,163 individuals during 2007–2010. After controlling for environmental variables, Northern Pintail Anas acuta, Common Teal A. crecca and Northern Shoveler A. clypeata experienced significant increases in the area between both periods, and only Eurasian Wigeon A. penelope suffered a significant decrease. Mallard A. platyrhynchos and Gadwall A. strepera populations did not show any significant trend. The large older reservoirs experienced overall population decreases between the two periods, with four new reservoirs holding more than 35,000 wintering dabbling ducks. Our results reflect an overall improvement in habitat conditions, driven by the creation of reservoirs near to rice fields that could have resulted in a partial redistribution of wintering dabbling ducks in the EAF. The area emerges as one of the most important wintering sites for dabbling ducks in southern Europe, regularly exceeding two of the Ramsar Convention criteria for the conservation of several populations. The protection of these new reservoirs by legal mechanisms would guarantee the existence of a large functional wetland area, which could also mitigate the loss of natural wetlands for populations using the EAF.

Time Course and Metabolic Costs of a Humoral Immune Response in the Little Ringed Plover Charadrius dubius

Despite host defense against parasites and pathogens being considered a costly life-history trait, relatively few studies have assessed the energetic cost of immune responsiveness. Knowledge of such energetic costs may help to understand the mechanisms by which trade-offs with other demanding activities occur. The time course and associated metabolic costs of mounting a primary and secondary humoral immune response was examined in little ringed plovers Charadrius dubius challenged with sheep red blood cells. As was expected, the injection with this antigen increased the production of specific antibodies significantly, with peaks 6 d postinjection in both primary and secondary responses. At the peak of secondary antibody response, the antibody production was 29% higher than that observed during the primary response, but the difference was nonsignificant. Mounting the primary response did not significantly increase the resting metabolic rate (RMR) of birds, whereas the secondary response did by 21%, suggesting that the latter was more costly in terms of RMR. In spite of the fact that the primary response did not involve an increase in RMR, birds significantly decreased their body mass. This could imply an internal energy reallocation strategy to cope with the induced immune challenge. Last, we found that RMR and antibody production peaks were not coupled, which could help to conciliate the variable results of previous studies. Collectively, the results of this study support the hypothesis that humoral immunity, especially the secondary response, entails energetic costs that may trade-off with other physiological activities.

Sex-specific vulnerability to breeding conditions in chicks of the sexually monomorphic Gull-billed Tern

AbstractEnvironmental conditions during early development may differentially affect male and female offspring, and the effects of this sex–environment interaction in chick performance may be exaggerated under harsh conditions. In birds, most of the currently available evidence on sex-biased environmental sensitivity in nestlings is derived from species that display sexual size dimorphism, while studies on monomorphic or slightly dimorphic species are less abundant and have produced inconsistent results. We have evaluated sex-specific vulnerability to breeding conditions in chicks of the Gull-billed Tern (Gelochelidon nilotica), a semiprecocial species with only low sexual size dimorphism. We compared male and female mass growth and fledgling physiological condition (measured through plasma metabolite levels) in several colonies that differed in reproductive parameters. Chicks of both sexes grew more slowly and fledged with lower mass and poorer nutritional state in the colony with the worst breeding conditions, i.e., with later phenology and lower clutch size and reproductive success. Contrary to our expectations, chick vulnerability to rearing conditions was more pronounced for female than male fledglings. While males grew faster than females during the middle phase of growth regardless of colony, this difference disappeared later in the fledging period in all but the worst colony, where females maintained a lower mass and worse nutritional condition than males. These results add to the evidence that, even in monomorphic species, the environmental sensitivity of nestlings during development may vary in a sex-specific way that may select for sex-biased allocation of parental resources and sex ratio adjustments under specific breeding conditions.ZusammenfassungGeschlechtsspezifische Anfälligkeit gegen Aufzuchtsbedingungen bei Küken eines sexuell monomorphen Vogels, der Lachseeschwalbe Die Umweltbedingungen während der frühen Entwicklung können männliche und weibliche Nachkommen unterschiedlich beeinflussen, und diese Geschlechts-Umwelt-Interaktion in der Kükenperformanz kann unter harschen Bedingungen verstärkt sein. Bei Vögeln stammen die meisten Belege für geschlechtsspezifische Umweltempfindlichkeit aus Arten mit sexuellem Größendimorphismus, während Untersuchungen an monomorphen oder nur leicht dimorphen Arten seltener sind und widersprüchliche Ergebnisse erbracht haben. Hier schätzen wir die geschlechtsspezifische Anfälligkeit gegen die Aufzuchtsbedingungen bei Küken der Lachseeschwalbe (Gelochelidon nilotica) ab, einer halb-nestflüchtenden Art mit nur geringem sexuellen Größendimorphismus. Wir haben den Körpermassezuwachs von Männchen und Weibchen und ihre physiologische Kondition als Flügglinge (gemessen über den Plasmametabolitspiegel) in mehreren Kolonien, die sich in Fortpflanzungsparametern unterschieden, verglichen. Küken beiden Geschlechts wuchsen langsamer und wiesen beim Ausfliegen eine geringere Körpermasse und einen schlechteren Ernährungszustand auf in der Kolonie mit den schlechtesten Brutbedingungen, d.h. mit späterer Phänologie, kleinerer Gelegegröße und niedrigerem Fortpflanzungserfolg. Entgegen unserer Erwartungen waren weibliche Küken empfindlicher gegen die Aufzuchtsbedingungen als männliche. Während Männchen in der mittleren Wachstumsphase schneller wuchsen als Weibchen, unabhängig von der Kolonie, verschwand dieser Unterschied später in der Ausflugsperiode in allen Kolonien außer der schlechtesten, wo Weibchen weiterhin eine geringere Körpermasse und einen schlechteren Ernährungszustand als Männchen aufwiesen. Diese Ergebnisse liefern weitere Belege, dass selbst bei monomorphen Arten die Umweltempfindlichkeit der Nestlinge während der Entwicklung geschlechtsspezifisch variieren kann, was unter bestimmten Brutbedingungen eine verstärkte Zuteilung elterlicher Ressourcen zu einem Geschlecht sowie eine Anpassung des Geschlechterverhältnisses der Nachkommen begünstigen kann.

HCV seroconversion in a cohort of people who use drugs followed in a mobile harm reduction unit in Madrid: Breaking barriers for HCV elimination

Background and aims Harm reduction strategies have been shown to decrease the incidence of human immunodeficiency virus (HIV) infection in people who inject drugs (PWID), but the results have been inconsistent when it comes to prevention of hepatitis C virus (HCV) infection. We aimed to examine the rate of HCV seroconversion among people who use drugs (PWUD) followed at a mobile harm reduction unit (MHRU) to evaluate if a low-threshold methadone substitution program (LTMSP) is associated with a low HCV seroconversion rate and subsequently identify barriers for elimination. Materials and methods A cohort of PWUD have been followed at a MRHU in Madrid between 2013 and 2016. Individuals who were negative for HCV antibodies at baseline and who had at least one retest for HCV antibodies were eligible. Kaplan-Meier methods were employed to estimate the global incidence density. Results During the study period, 946 PWUD were screened for HCV at least once. At baseline 127 PWUD were negative for HCV antibodies and had at least one follow-up HCV antibodies test. The baseline HCV prevalence was 33%. After a median 0.89 (IQR 0.3–1.5) years of follow-up and 135 person-years of risk for HCV infection, 28 subjects seroconverted. The incidence density for HCV seroconversion for this sample was 20.7 cases (95% CI: 14.3–29.7) per 100 person-years. Injecting drugs in the last year was strongly associated to HCV seroconversion (AHR 15.5, 95%CI 4.3–55.8, p < 0.001). Methadone status was not associated to HCV seroconversion. Conclusions A high incidence of HCV infection was found among PWUD at a MHRU in Madrid. In this setting opiate substitutive treatment (OST) as a LTMSP does not appear to protect against HCV seroconversion.

Chilean Atacama site imperilled by lithium mining

Coral reefs are again in the spotlight, having suffered mass mortality over the past two years from global bleaching events. Before reef resilience runs out, researchers must move beyond lamenting corals’ lost pristine state and develop pragmatic solutions. In our view, these are likely to stem from a more diverse set of stakeholders than have participated so far. We must ensure that reefs can continue to provide wellbeing for millions of people in the future, despite widespread alterations in their biological state. Degraded reefs still have the potential to provide fisheries benefits, cultural value and other sources of revenue (such as tourism), although all of these are likely to be reduced. With 2018 designated the International Year of the Reef, fresh perspectives and approaches are needed (S. A. Hewlett et al. Harvard Bus. Rev. 91, 30; 2013). New recruits should come from a greater variety of sectors (such as development, health and governance) and from a wider set of disciplines (such as the social sciences — including psychology, economics, political science and geography) than today’s conservationists. Young scientists and researchers from the global south will be particularly important contributors. Gabby Ahmadia* World Wildlife Fund, Washington DC, USA. gabby.ahmadia@wwfus.org *On behalf of 14 co-signatories (see go.nature.com/2kwzqk7 for full list).