Early-life conditions impact juvenile telomere length, but do not predict later life-history strategies or fitness in a wild vertebrate

Environmental conditions experienced during early life may have long-lasting effects on later-life phenotypes and fitness. Individuals experiencing poor early-life conditions may suffer subsequent fitness constraints. Alternatively, individuals may use a strategic “Predictive Adaptive Response” (PAR), whereby they respond—in terms of physiology or life-history strategy—to the conditions experienced in early life to maximize later-life fitness. Particularly, the Future Lifespan Expectation (FLE) PAR hypothesis predicts that when poor early-life conditions negatively impact an individual's physiological state, it will accelerate its reproductive schedule to maximize fitness during its shorter predicted life span. We aimed to measure the impact of early-life conditions and resulting fitness across individual lifetimes to test predictions of the FLE hypothesis in a wild, long-lived model species. Using a long-term individual-based dataset, we investigated how early-life conditions are linked with subsequent fitness in an isolated population of the Seychelles warbler Acrocephalus sechellensis. How individuals experience early-life environmental conditions may vary greatly, so we also tested whether telomere length—shorter telomers are a biomarker of an individual's exposure to stress—can provide an effective measure of the individual-specific impact of early-life conditions. Specifically, under the FLE hypothesis, we would expect shorter telomeres to be associated with accelerated reproduction. Contrary to expectations, shorter juvenile telomere length was not associated with poor early-life conditions, but instead with better conditions, probably as a result of faster juvenile growth. Furthermore, neither juvenile telomere length, nor other measures of early-life conditions, were associated with age of first reproduction or the number of offspring produced during early life in either sex. We found no support for the FLE hypothesis. However, for males, poor early-life body condition was associated with lower first-year survival and reduced longevity, indicating that poor early-life conditions pose subsequent fitness constraints. Our results also showed that using juvenile telomere length as a measure of early-life conditions requires caution, as it is likely to not only reflect environmental stress but also other processes such as growth

Island invasives: scaling up to meet the challenge

Management and eradication techniques for invasive alien birds remain in their infancy compared to invasive mammal control methods, and there are still relatively few examples of successful avian eradications. Since 2011, five separate eradication programmes for invasive birds have been conducted on three islands by the Seychelles Islands Foundation (SIF). Target species were prioritised according to their threat level to the native biodiversity of the UNESCO World Heritage Sites of the Seychelles, Aldabra Atoll and Vallée de Mai, which SIF is responsible for managing and protecting. Red-whiskered bulbuls (Pycnonotus jocosus) and Madagascar fodies (Foudia madagascariensis) occurred on Assumption, the closest island to Aldabra, which, at the time, had no known introduced bird species. The growing population of ring-necked parakeets (Psittacula krameri) on Mahé posed a threat to endemic Seychelles black parrots (Coracopsis barklyi) on Praslin where the Vallée de Mai forms their core breeding habitat. In 2012, red-whiskered bulbuls and Madagascar fodies were detected on Aldabra, so an additional eradication was started. All eradications used a combination of mist-netting and shooting. The intensive part of each eradication lasted three years or less. On Assumption, 5,279 red-whiskered bulbuls and 3,291 Madagascar fodies were culled; on Mahé, 545 parakeets were culled; and on Aldabra 262 Madagascar fodies and one red-whiskered bulbul were culled. Each programme underwent 1–2 years of follow-up monitoring before eradication was confirmed, and four of the five eradications have been successful so far. None of these species had previously been eradicated in large numbers from other islands so the successes substantially advance this field of invasive species management. The challenges and insights of these eradications also provide unique learning opportunities for other invasive avian eradications

Rapid loss of flight in the Aldabra white-throated rail

Flight loss has evolved independently in numerous island bird lineages worldwide, and particularly in rails (Rallidae). The Aldabra white-throated rail (Dryolimnas [cuvieri] aldabranus) is the last surviving flightless bird in the western Indian Ocean, and the only living flightless subspecies within Dryolimnas cuvieri, which is otherwise volant across its extant range. Such a difference in flight capacity among populations of a single species is unusual, and could be due to rapid evolution of flight loss, or greater evolutionary divergence than can readily be detected by traditional taxonomic approaches. Here we used genetic and morphological analyses to investigate evolutionary trajectories of living and extinct Dryolimnas cuvieri subspecies. Our data places D. [c.] aldabranus among the most rapid documented avian flight loss cases (within an estimated maximum of 80,000–130,000 years). However, the unusual intraspecific variability in flight capacity within D. cuvieri is best explained by levels of genetic divergence, which exceed those documented between other volant taxa versus flightless close relatives, all of which have full species status. Our results also support consideration of Dryolimnas [cuvieri] aldabranus as sufficiently evolutionary distinct from D. c. cuvieri to warrant management as an evolutionary significant unit. Trait variability among closely related lineages should be considered when assessing conservation status, particularly for traits known to influence vulnerability to extinction (e.g. flightlessness)

Hard times in paradise? : oxidative status, physiology and fitness in the tropical Seychelles warbler

Al leven de Seychellenzangers dan min of meer in het paradijs, ook zij hebben te kampen met de schadelijke invloed van oxidanten in hun lichaam. Janske van de Crommenacker toonde met haar onderzoek interessante verbanden aan tussen oxidatieve stress bij de Seychellenzanger en de levensomstandigheden van de vogel. Het bleek dat de oxidatieve stress hoog was in vogels die in slechte voedselomstandigheden verkeerden of die last hadden van een parasitaire infectie (malaria). Het gebruik van zuurstof voor energieproductie - bij de verbranding van voedsel - heeft als gevolg dat er voortdurend oxidanten (agressieve zuurstofradicalen) geproduceerd worden die schade kunnen toebrengen aan belangrijke moleculen in het lichaam. Organismen proberen deze schade te beperken met een beschermende antioxidant-barrière. Maar, wanneer meer oxidanten worden geproduceerd dan de antioxidant-barrière kan neutraliseren, kan toch oxidatieve stress optreden. Uiteindelijk zal langdurige oxidatieve stress, en de opeenstapeling van de hierdoor ontstane schade aan cellen en weefsels, leiden tot ouderdomsziekten en versnelling van verouderingsprocessen. Omdat de productie van oxidanten voornamelijk wordt gestimuleerd door verhoging van de stofwisseling – omdat het lichaam hard moet werken vanwege fysieke werkbelasting of extra activiteit van het immuunsysteem - en de antioxidant-barrière essentiële bestanddelen vereist, wordt aangenomen dat oxidatieve stress een belangrijke rol speelt in processen die van invloed zijn op fitness (overleving en voortplantingssucces). Van de Crommenacker vond inderdaad hoge oxidatieve stress bij Seychellenzangers in slechte voedselomstandigheden of met een parasitaire (malaria)infectie. Dit laatste was vooral het geval bij geïnfecteerde vogels die ook nog belast waren met de zorg voor hun jongen. Daarnaast vond zij ook een verband tussen het geslacht, de sociale status en de broedactiviteit enerzijds en de oxidatieve status anderzijds: in de weken voor dat zij hun eieren legden bleken de vrouwtjes hogere antioxidantniveaus te hebben, mogelijk om deze extra antioxidanten door te kunnen geven aan hun kuikens. Hoewel Van de Crommenacker geen verbanden tussen oxidatieve status en fitness heeft kunnen vaststellen, laat haar onderzoek zien dat tal van omgevingsgerelateerde, gedragsmatige of individugebonden variabelen hun uitwerking kunnen hebben op de oxidatieve status van een individu. Het is daarom belangrijk om deze variabelen eerst te identificeren, voordat men uitspraken doet over de invloed van oxidatieve stress op bepaalde fitnessaspecten. In her study on the wild-living Seychelles warbler Janske van de Crommenacker found a number of interesting relationships between oxidative imbalance (oxidative stress) on one hand and poor environmental conditions or suffering from parasitic infection (malaria) on the other hand. The use of oxygen for energy generation results in the continuous production of reactive oxygen species (oxidants) that can damage body molecules. Organisms attempt to reduce this harm by use of their antioxidant defence barrier. Yet, when more oxidants are produced than can be neutralized by this protective barrier, a state of oxidative stress may occur. Chronic oxidative stress and accumulation of oxidative damage to cells and tissues can stimulate the ageing process and the onset of degenerative diseases. As elevations in metabolism (e.g. through workload or immune activation) can stimulate oxidant generation, and as antioxidant defences require valuable resources, oxidative stress is proposed to be an important mediator of life-history trade-offs. In her study on the wild-living Seychelles warbler Van de Crommenacker found a number of interesting relationships: oxidative imbalance (oxidative stress) was high when birds experienced poor environmental conditions or suffered from parasitic infection (malaria). The latter was particularly true for infected birds that were enduring the workload of provisioning their young. Sex, social status and reproductive stage appeared also to be linked with oxidative status: reproducing females had higher antioxidant capacity in the weeks before egg-laying, possibly to enhance the quality of their offspring. Although Van de Crommenacker found no clear evidence for relationships between oxidative status and fitness (reproductive success and survival), her study shows that various environmental-, behavioural- and individual-related variables were associated with oxidative status. The results emphasize the importance to first identify these ecological covariates before drawing general conclusions about oxidative stress as a life-history determinant.

Assessing the Cost of Helping: The Roles of Body Condition and Oxidative Balance in the Seychelles Warbler (Acrocephalus sechellensis)

In cooperatively breeding species, helping close relatives may provide important fitness benefits. However, helping can be energetically expensive and may result in increased generation of reactive oxygen species. Consequently, an oxidant/antioxidant imbalance can lead to higher oxidative stress susceptibility. Given the potential costs of helping, it may be that only individuals with a sufficiently good body condition and/or stable oxidative balance can afford to help. Knowledge about relationships between social status and oxidative balance in cooperatively breeding systems is still limited. Studying these relationships is important for understanding the costs of helping and physiological pressures of reproduction. Here we evaluate the relationship between helping behaviour, body condition and oxidative balance in a wild population of the cooperatively breeding Seychelles warbler (Acrocephalus sechellensis). In this species, some subordinate individuals help dominant birds with the rearing of young, while others refrain from any assistance. We assessed body condition and oxidative parameters of birds of different social status caught during different breeding stages. We found that, prior to breeding, female subordinates that did not subsequently help (non-helpers) had significantly lower body condition and higher ROMs (reactive oxygen metabolites) than helpers and dominants. During the later stages of breeding, body condition was low in dominants and helpers, but high in non-helpers. Differences in oxidative balance between individuals of different social status were found only during nest care: Dominant males occupied with guarding behaviours tended to have relatively high oxidative stress susceptibility. Furthermore, dominant and helper females showed elevated antioxidant capacity (measured as OXY) in the weeks just prior to egg-laying, possibly representing a change in their reproductive physiology. The results imply that an individuals' oxidative balance may be influenced by factors related to reproduction, which can differ with sex and—within cooperative breeding systems—social status

Parasitic infection and oxidative status are associated and vary with breeding activity in the Seychelles warbler

Parasites can have detrimental effects on host fitness, and infection typically results in the stimulation of the immune system. While defending against infection, the immune system generates toxic oxidants; if these are not sufficiently counteracted by the antioxidant system, a state of oxidative stress can occur. Here, we investigated the relationship between parasitic infection—using malarial infection as a model—and oxidative status in a natural population of the Seychelles warbler, while taking into account potentially interacting environmental covariates. We found that malaria is associated with increased susceptibility to oxidative stress, but this depends on the breeding stage: only during the energetically demanding provisioning stage did infected birds have higher oxidative stress susceptibility than non-infected birds. The imbalance in oxidative status was caused by a marked increase in oxidant levels observed only in infected birds during provisioning and by an overall reduction in antioxidant capacity observed in all birds across the breeding cycle. This finding implies that higher workload while dealing with an infection could aggravate oxidative repercussions. Malarial infection was not associated with body condition loss, suggesting that even when conditional effects are not directly visible, detrimental effects may still manifest themselves over the longer term through the oxidative consequences