Greet De Coster

Variation in innate immunity in relation to ectoparasite load, age and season: a field experiment in great tits (Parus major)

SUMMARY It remains largely unknown which factors affect the innate immune responses of free-living birds. Nevertheless, the degree of innate immunity may play a crucial role in an individuals survival as it procures the first defence against pathogens. We manipulated the ectoparasite load of great tit (Parus major) nests by infesting them with hen fleas (Ceratophyllus gallinae) before egg laying. We subsequently quantified natural antibody (NAb) concentration and complement activation in nestlings and adult females during breeding and post-breeding periods. NAb concentrations increased in nestlings and adult females breeding in flea-infested nest boxes during the nestling provisioning period, but not in breeding females during incubation. In contrast, parasite abundance did not affect levels of complement activity in females. NAb levels of nestlings were already fully developed at the end of the nestling stage, but complement activation was only observed post-fledging. Concentrations of NAbs and complement activation of adult females were significantly lower during the breeding season compared with post-breeding levels, but did not differ between incubation and chick rearing. Further experimental studies in species that vary in life-history strategies will allow us to unravel the mechanisms underlying the observed variation in innate immune defences.

Fluctuating asymmetry and environmental stress: understanding the role of trait history

While fluctuating asymmetry (FA; small, random deviations from perfect symmetry in bilaterally symmetrical traits) is widely regarded as a proxy for environmental and genetic stress effects, empirical associations between FA and stress are often weak or heterogeneous among traits. A conceptually important source of heterogeneity in relationships with FA is variation in the selection history of the trait(s) under study, i.e. traits that experienced a (recent) history of directional change are predicted to be developmentally less stable, potentially through the loss of canalizing modifiers. Here we applied X-ray photography on museum specimens and live captures to test to what extent the magnitude of FA and FA-stress relationships covary with directional shifts in traits related to the flight apparatus of four East-African rainforest birds that underwent recent shifts in habitat quality and landscape connectivity. Both the magnitude and direction of phenotypic change varied among species, with some traits increasing in size while others decreased or maintained their original size. In three of the four species, traits that underwent larger directional changes were less strongly buffered against random perturbations during their development, and traits that increased in size over time developed more asymmetrically than those that decreased. As we believe that spurious relationships due to biased comparisons of historic (museum specimens) and current (field captures) samples can be ruled out, these results support the largely untested hypothesis that directional shifts may increase the sensitivity of developing traits to random perturbations of environmental or genetic origin.

Effects of early developmental conditions on innate immunity are only evident under favourable adult conditions in zebra finches

Long-term effects of unfavourable conditions during development can be expected to depend on the quality of the environment experienced by the same individuals during adulthood. Yet, in the majority of studies, long-term effects of early developmental conditions have been assessed under favourable adult conditions only. The immune system might be particularly vulnerable to early environmental conditions as its development, maintenance and use are thought to be energetically costly. Here, we studied the interactive effects of favourable and unfavourable conditions during nestling and adult stages on innate immunity (lysis and agglutination scores) of captive male and female zebra finches (Taeniopygia guttata). Nestling environmental conditions were manipulated by a brood size experiment, while a foraging cost treatment was imposed on the same individuals during adulthood. This combined treatment showed that innate immunity of adult zebra finches is affected by their early developmental conditions and varies between both sexes. Lysis scores, but not agglutination scores, were higher in individuals raised in small broods and in males. However, these effects were only present in birds that experienced low foraging costs. This study shows that the quality of the adult environment may shape the long-term consequences of early developmental conditions on innate immunity, as long-term effects of nestling environment were only evident under favourable adult conditions.

Intraclutch variation in avian eggshell pigmentation: the anaemia hypothesis

Many passerine species lay eggs that are speckled with dark protoporphyrin pigmentation. Because protoporphyrin is mainly derived from the blood, we here formulate and test a new hypothesis that links an increase in anaemia along the laying sequence to within-clutch variation in egg pigmentation. More intense pigmentation is expected if pigments accumulate during enhanced red blood cell production in response to anaemia. Reduced pigmentation is expected if pigments are derived from the degradation of red blood cells that circulate in smaller numbers due to blood loss. To test this hypothesis, we manipulated anaemia in great tit (Parus major) females by infesting the nests with hen fleas (Ceratophyllus gallinae) prior to egg laying. Polychromatophil (i.e., immature red blood cells) percentage, as a measure of blood cell production, was positively correlated with parasite load confirming that female great tits experienced stronger anaemia when infested with haematophagous parasites during egg laying. We found a positive relationship between spot darkness and laying order that weakened under high parasite load. This result suggests that anaemia in females due to blood-sucking parasites led to diminished protoporphyrin from disintegrated red blood cells and hence a decreased deposition of protoporphyrin. However, the overall increase in pigment darkness along the laying sequence suggests that pigments also accumulate by enhanced red blood cell production caused by anaemia due to egg production itself.

Intra-clutch variation in avian eggshell pigmentation covaries with female quality

AbstractAmong the most eye-catching traits of avian eggs are their background coloration and pigmentation, consisting in many passerine birds of dark protoporphyrin spots. Although variation in protoporphyrin pigmentation among clutches has been shown to reflect female quality, within-clutch variation in egg pigmentation remains less well understood. Here, we hypothesize that female quality may also be reflected in within-clutch variation in egg pigmentation as a result of energetic constraints and/or increased susceptibility to oxidative stress, and test this hypothesis in a free-living population of Great Tits (Parus major). Within clutches, both pigment ‘darkness’ and ‘spread’ (reflecting intensity, distribution and size of pigment) increased with laying order. For pigment ‘darkness’, this was most strongly so in larger females and in females showing lysis (as a measure of constitutive innate immunity), suggesting that intra-clutch variation in pigment ‘darkness’ positively relates to both structural as well as condition-dependent female traits. In contrast, for pigment ‘spread’, no relationships were detected with body size, body condition, age, and two components of constitutive innate immunity. Among clutches, ‘darkness’ and ‘spread’ of pigments also varied. However, this variation was not related to any of the female characteristics we measured. To the best of our knowledge, this study is the first one to relate intra-clutch variation in protoporphyrin egg pigmentation to structural and condition-dependent traits of laying females. Further experimental study is, however, required to better understand the underlying causal mechanisms.ZusammenfassungUnterschiede in der Pigmentierung der Eierschalen innerhalb eines Geleges sind ein Hinweis auf die Qualität des Weibchens Auffälligste Merkmale von Vogeleiern sind deren Hintergrundfarbe und die Pigmentierung, die bei vielen Singvögeln aus dunklen Punkten aus Protoporphyrin bestehen. Obwohl bei Unterschieden in der Protoporphyrin-Pigmentierung zwischen Gelegen gezeigt werden konnten, dass sie die Qualität des Weibchens widerspiegeln, ist über die Unterschiede in der Pigmentierung von Eiern innerhalb eines Geleges noch wenig bekannt. Hier stellen wir die Hypothese auf, dass sich die Qualität eines Weibchens auch in den Unterschieden der Pigmentierung innerhalb eines Geleges widerspiegelt, und zwar aufgrund von energetischen Einschränkungen und/oder einer erhöhten Empfänglichkeit für oxidativen Stress. Wir prüften diese Hypothese an einer frei lebenden Population von Kohlmeisen (Parus major). Innerhalb von Gelegen stiegen sowohl „Dunkelheit“als auch „Ausbreitung“der Pigmente (Maße für Intensität, Verteilung und Größe der Pigmente) mit der Legereihenfolge. Bei Pigment-Dunkelheit zeigte sich dies am stärksten bei größeren Weibchen und bei Weibchen, die Lyse zeigten (als Maß einer angeborenen Immunität), was darauf hindeutet, dass Unterschiede in der Dunkelheit der Pigmente innerhalb von Gelegen positiv korreliert sowohl mit strukturellen als auch gesundheits-abhängigen Merkmalen der Weibchen. Dagegen konnte für die Pigment-„Ausbreitung“kein Zusammenhang gefunden werden mit Körpergröße, Alter, Gesundheitszustand oder zwei Komponenten einer angeborenen Immunität. „Dunkelheit“und „Ausbreitung“der Pigmente unterschieden sich auch zwischen den Gelegen. Allerdings zeigten diese Unterschiede keinen Zusammenhang mit einer der gemessenen Größen der Weibchen. Soweit wir wissen ist dies die erste Untersuchung, in der Unterschiede in der Protoporphyrin-Pigmentierung der Eier in Zusammenhang gebracht werden mit strukturellen und gesundheits-abhängigen Merkmalen legender Weibchen. Allerdings sind weitere experimentelle Untersuchungen notwendig, um die zugrunde liegenden kausalen Mechanismen besser zu verstehen.

Human health risks of forest conservation

In PNAS, Myers et al. (1) present a paper in which they discuss adverse effects of ecosystem degradation on human health. We sincerely think that this is one of the more comprehensive papers in this field, but would like to draw attention to a number of findings from studies on Brazilian forest ecosystems that the authors seem to have overlooked. Conservationists customarily highlight benefits—in terms of goods and services— that result from the protection of natural ecosystems, but they often fail to mention that the latter may also adversely affect human welfare. In their report, Myers et al. indeed convincingly demonstrate that anthropogenic land-use changes can increase the prevalence of several diseases (1), but they overlook the fact that natural forest may also act as wild reservoirs that propitiate disease outbreaks. For example, infections with Rickettsia rickettsii, a major tick-borne zoonotic disease in Brazil that causes spotted fever, mainly occur where humans and dogs live in close contact to forests (2). Additionaly, various vectors of cutaneous and visceral leishmaniasis (sand flies Lutzomyia spp.) are present in an Atlantic Forest region in the state of Rio de Janeiro that is popular with ecotourists (3). Finally, it has been recently shown that malaria incidence tends to increase with forest cover in the Brazilian Amazon (4). Concealing such patterns may hamper a better understanding of relationships between natural ecosystems and human health risks. Indeed, there are many open questions on relationships between landscape structure and disease dynamics (5). For example, what is the functional role of forest fragments in the maintenance of zoonoses? How does the connectivity of forest fragments influence the dispersal of disease vectors? Neglecting these questions may hamper scenarios to minimize human health risks during, for example, forest conservation and restoration (4). In summary, the purpose of this letter is to urge conservationists to cover the full range of consequences of ecosystem alteration and protection, which may or may not be as anticipated and may or may not contribute to human welfare. In addition to being more ethically correct, we sincerely believe that this impartiality will eventually benefit both man and nature.

Home range characteristics of the Near Threatened Giant Conebill Oreomanes fraseri in fragmented Polylepis forest

Summary The Giant Conebill Oreomanes fraseri is a specialist of high Andean Polylepis forest remnants.With the aid of radio-tracking and visual observations, the average 100% minimum convex poly-gon home range size of seven adult individuals was 7.15 ha. Range size decreased with increasingtree density, and for equal tree densities, it was larger in the study site with larger Polylepis frag-ments. Home ranges often comprised areas that were largely or entirely devoid of trees. Withinhome ranges, space use significantly varied with time of day, and this pattern tended to be largelyconsistent among days. Given the large extent of variation in size and structure already observedin this small sample of home ranges, we suggest that apart from the size, shape, structure and degreeof isolation of the remaining forest patches, also t heir topographic location, and hence sun exposure,may be an important consideration when designing conservation strategies for Giant Conebill. Introduction Forest fragmentation ranks among the most important drivers of the decline of bird populationsworldwide (Renjifo 1999), and its impact depends both on the degree of loss, deterioration andisolation of the remaining habitat and on the level of habitat specialization and mobility of thebird species involved (Andre´n1994, Brown and Sullivan 2005). A decline in population size andreduced exchange of individuals in small, isolated fragments may result in increased levels ofdemographic and genetic stochasticity (Lande 1988, Turner 1996). This, in turn, may reduce thelong-term viability of populations (Lande 1988). In addition, habitat fragmentation may alsoaffect home range properties and habitat use by individual birds (Andreassen et al. 1998, Rolando2002). Whether or not habitat fragmentation affects habitat use depends on its spatial scale, inparticular the relationship between fragment size and home range size (Andreassen et al. 1998).Organisms can thereby show three possible responses to habitat fragmentation, based on theirintrinsic space requirements and social behaviour. A fusion response is expected from socialindividuals when fragment size is reduced, with smaller home ranges and increased home rangeoverlap. Home ranges of territorial organisms show less overlap, but are also reduced if the sizeof the habitat patch is close to their minimum space requirement (fission response). If habitatpatches become too small to contain individual home ranges, home ranges will expand to includemore than one habitat patch (expansion response; Ims et al. 1993). Next to fragment size, habitatquality within a fragment may affect home range size in the way that smaller home ranges canbe found in better habitat (Doster and James 1998). Furthermore, habitat quality, and foodavailability in particular, may strongly affect habitat selection and movement patterns (Rolando2002, Santos et al. 2008).