Causes and consequences of individual variation in migratory behaviour of Cory’s Shearwaters

A migração diferencial pode dar origem a diferente fitness experienciado para os indivíduos de uma população devido a efeitos de carry-over, i.e. o efeito das condições experienciadas durante uma época nas fases seguintes do ciclo de vida. A maioria das populações de animais migradores correspondem a migradores parciais, nas quais uma parte da população migra e a outra permanece residente durante todo o ano. Apesar de ser uma estratégia muito observada e importante na compreensão da evolução e das consequências ecológicas das decisões migratórias, a migração parcial tem sido pouco estudada. As espécies de aves pertencentes à ordem Procellariiformes são um modelo interessante para o estudo da migração. Estas aves marinhas distinguem-se de outros taxa de aves classicamente estudados, uma vez que o seu voo planado dinâmico reduz o custo do voo e têm a capacidade de se alimentar em viagem ativa (sem necessidade de efectuar paragens). O objetivo desta tese de doutoramento é investigar as causas e consequências da migração diferencial, particularmente a migração parcial, em cagarras Calonectris diomedea. As cagarras passam o período não reprodutor em várias zonas oceânicas distintas no Oceano Atlântico e no Oceano Índico, sendo que uma proporção de machos permanece na Corrente das Canárias durante todo o ano. Esta tese combina o seguimento remoto em grande escala, durante dois anos, com uma abordagem multidisciplinar, respondendo às seguintes questões: i i. A estratégia migratória correlaciona-se com a personalidade nas cagarras? ii ii. A estratégia migratória e o sucesso reprodutor têm consequências na época reprodutora seguinte em termos de condição física? iii iii. As cagarras migradoras e residentes estão diferencialmente expostas a poluentes durante o período não reprodutor? Foram realizados testes comportamentais para avaliar o comportamento exploratório e a reação à extração do ninho em machos de cagarras, e testámos correlações com a estratégia migratória. Embora o comportamento exploratório não tenha estado relacionado com a estratégia migratória, os machos residentes mostraram maior probabilidade de não reagir à extração do ninho. A estratégia migratória e o insucesso reprodutor precoce tiveram implicações na imunidade inata, stress e massa corporal residual de machos no regresso à colónia no ano seguinte. As aves residentes mostraram uma menor intensidade das malformações nas penas caudais (fault bars - um indicador de stress durante o período não reprodutor), em comparação com as migradoras. A estratégia migratória e o esforço reprodutivo não tiveram outros impactos na condição fisiológica. Neste estudo, foi quantificada a extensão da exposição ao mercúrio durante o período não reprodutor em indivíduos que passaram esse período em diferentes áreas, e relacionado com a posição trófica. As cagarras que permaneceram residentes na Corrente das Canárias tiveram concentrações de mercúrio nas penas mais baixas do que as migradoras, como resultado da posição trófica significativamente mais baixa ocupada pelos residentes durante o período não reprodutor. As diferenças na reação comportamental e fisiológica ao stress entre machos migradores e residentes sugerem que os primeiros podem-se distinguir pelo limiar de stress. Demonstrado que a manutenção somática após eventos de ciclos anuais com elevado custo seja priorizada e que a migração tenha um custo baixo nas cagarras. Mesmo assim, é claro que os subgrupos da população experienciam diferentes condições ao longo da época não reprodutora, evidenciada na posição trófica e exposição ao mercúrio. Estas diferenças no ambiente experienciado, em conjunto com as diferenças endógenas da personalidade (coping style), sugerem que a migração diferencial tem o potencial de gerar mudanças demográficas nesta população. Este estudo sublinha a importância das variações interindividuais na ecologia e evolução populacional.Differential migration can result in subgroups of a population experiencing differential fitness as a result of carry-over effects, where conditions experienced over one season influence future life-history stages. Most migratory populations across the animal kingdom display partial migration, whereby a portion of the population migrates while the other remains resident year-round. Despite its ubiquity and its utility in understanding the evolution and ecological consequences of migratory decisions, partial migration has been under-studied. Tubenoses (Order Procellariiformes) are interesting model species for migration research; they differ from other avian taxa classically studied since dynamic soaring reduces the cost of flight, and they are able to feed while on the move. The aim of this doctoral thesis is to investigate aspects surrounding the causes and consequences of differential migration, particularly partial migration, in Cory’s Shearwater Calonectris diomedea. Cory’s Shearwaters spend the non-breeding season in several distinct oceanic zones across the Atlantic and into the Indian Ocean, while a proportion of males remain resident in the Canary Current year-round. Specifically, this thesis merges large-scale year-round remote tracking over two years with a multidisciplinary approach to ask: i i. Does migratory strategy correlate with personality traits in the Cory’s Shearwater? ii ii. Do migration and reproductive success carry-over to the following breeding season in terms of physical condition? iii iii. Are migrant and resident Cory’s Shearwaters differentially exposed to pollutants over the non-breeding period? We carried out behavioural tests evaluating exploratory behaviour and reaction to extraction from the nest in male Cory’s Shearwaters, and tested for correlations with migratory strategy. While exploratory behaviour was unrelated to migratory strategy, males that were resident were more likely to be unreactive towards extraction from the nest. We investigated whether migratory strategy and early reproductive failure had implications on innate immunity, stress, and residual body mass of males on return to the colony the following year. Residents had a lower tail feather fault bar intensity, an indicator of stress during the non-breeding period, compared to migrants. Migratory strategy and reproductive effort had no impact on physiological condition otherwise. We quantified the extent of over-winter mercury exposure in individuals spending the non-breeding period in different areas, and related it to trophic position. Cory’s Shearwaters that remained resident in the Canary Current had lower feather mercury concentrations than migrants, as a result of the significantly lower trophic position residents occupied during the non-breeding season studied. The differences in behavioural and physiological stress response between migratory and resident males suggest that they may be distinguishable by their stress threshold. While we show that somatic maintenance after costly annual cycle events is prioritised and that migration is cheap in the Cory’s Shearwater, it is clear that sub-groups of the population experience different conditions over the non-breeding season, evidenced in trophic position and mercury exposure. Both this and endogenous differences in coping style suggest that differential migration has the potential to drive demographic changes in this population. This collection of studies continues to bring to the forefront the importance of inter-individual variations in population ecology and evolution

Migrants and residents of a long‐lived seabird differ in their behavioural response to a stressor

Inter-individual variation in behaviour has been recognised as a major driver of population ecology, but its relationship to migratory strategy has been ill-explored. Here, we investigated whether male migrant and resident Cory’s shearwaters Calonectris borealis, a long-lived partially migratory seabird, are distinguishable by their temperament at the colony. We tracked a large number of individuals over two winters using GLS devices and assessed whether exploratory behaviour and reaction to extraction from the nest corresponded to migratory strategy over this period. While exploratory behaviour was unrelated to migratory strategy, birds that were resident were more likely to be unreactive towards extraction from the nest. This difference in behavioural stress response, together with previous findings that migrants display higher physiological stress over winter, suggests that migrants and residents may be distinguishable by their stress threshold.Fundação para a Ciência e a Tecnologia - FCTinfo:eu-repo/semantics/publishedVersio

Higher mercury contamination is associated with shorter telomeres in a long-lived seabird – A direct effect or a consequence of among-individual variation in phenotypic quality?

Mercury is a heavy metal, which is pervasive and persistent in the marine environment. It bioaccumulates within organisms and biomagnifies in the marine food chain. Due to its high toxicity, mercury contamination is a major concern for wildlife and human health. Telomere length is a biomarker of aging and health, because it predicts survival, making it a potential tool to investigate sublethal effects of mercury contamination. However, the relationship between telomeres and mercury contamination is unclear. We measured feather mercury concentration in Cory's Shearwaters Calonectris borealis, long-lived seabirds and top predators, between 9 and 35 years of age and related it to telomere length in erythrocytes. Cory's Shearwaters with higher mercury concentrations had shorter telomeres and the effect was sex-dependent, reaching significance in males only. This may be explained by the fact that males have longer telomeres and higher and more variable mercury concentrations than females in this population. The mercury effect on telomere length was stronger on longer telomeres in the genome within individuals. We discuss the hypotheses that the negative correlation could either be a direct effect of mercury on telomere shortening and/or a consequence of variation in phenotypic quality among individuals that results in a covariation between mercury contamination and telomere length.Fundação para a Ciência e Tecnologia - FCTinfo:eu-repo/semantics/publishedVersio

Fracture properties characterization of nuclear fuel using micro-cantilever bending

International audienc

Untangling causes of variation in mercury concentration between flight feathers

Bird feathers are one of the most widely used animal tissue in mercury biomonitoring, owing to the ease of collection and storage. They are also the principal excretory pathway of mercury in birds. However, limitations in our understanding of the physiology of mercury deposition in feathers has placed doubt on the interpretation of feather mercury concentratoins. Throughout the literature, moult sequence and the depletion of the body mercury pool have been taken to explain patterns such as the decrease in feather mercury from the innermost (P1) to the outermost primary feather (P10) of the wing. However, it has been suggested that this pattern is rather a measurement artefact as a result of the increased feather mass to length ratio along the primaries, resulting in a dilution effect in heavier feathers. Here, we attempt to untangle the causes of variation in feather mercury concentrations by quantifying the mercury concentration as μg of mercury (i) per gram of feather, (ii) per millimetre of feather, and (iii) per day of feather growth in the primary feathers of Bulwer's Petrel Bulweria bulwerii chicks, effectively controlling for some of the axes of variation that may be acting in adults, and monitoring the growth rate of primary feathers in chicks. The mercury concentration in Bulwer's Petrel chicks' primaries increased from the innermost to the outermost primary for all three concentration measures, following the order of feather emergence. These observations confirm that the pattern of mercury concentration across primary feathers is not an artefact of the measure of concentration, but is likely an effect of the order of feather growth, whereby the earlier grown feathers are exposed to higher blood mercury concentrations than are later moulted feathers as a result of blood mercury depletion.Fundação para a Ciência e Tecnologia - FCTinfo:eu-repo/semantics/publishedVersio