ORCID Profile
0000-0002-9454-7562
Current Organisation
University of Veterinary Medicine Vienna
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Publisher: Wiley
Date: 07-12-2021
DOI: 10.1111/MEC.16296
Abstract: Telomeres are protective, nucleoprotein structures at the end of chromosomes that have been associated with lifespan across taxa. However, the extent to which these associations can be attributed to absolute length vs. the rate of telomere shortening prior to s ling remains unresolved. In a longitudinal study, we examined the relationship between lifespan, telomere length and the rate of telomere shortening in wild, purple‐crowned fairy‐wrens ( Malurus coronatus coronatus ). To this end, we measured telomere length using quantitative polymerase chain reaction in the blood of 59 in iduals s led as nestlings and 4–14 months thereafter, and in 141 known‐age in iduals s led on average three times across adulthood. We applied within‐subject centring analyses to simultaneously test for associations between lifespan and average telomere length and telomere shortening. We reveal that the rate of telomere shortening and to a lesser extent telomere length in the first year of life independently predicted lifespan, with in iduals with faster shortening rates and/or shorter telomeres living less long. In contrast, in adulthood neither telomere shortening nor telomere length predicted lifespan, despite a considerably larger data set. Our results suggest that telomere length measured very early in life (during development) and longitudinal assessments of telomere shortening during the first year of life constitute more useful biomarkers of total life expectancy than either telomere length measured after development, or telomere shortening later in adulthood.
Publisher: The Royal Society
Date: 04-11-2020
Abstract: Although crucial for host survival when facing persistent parasite pressure, costly immune functions will inevitably compete for resources with other energetically expensive traits such as reproduction. Optimizing, but not necessarily maximizing, immune function might therefore provide net benefit to overall host fitness. Evidence for associations between fitness and immune function is relatively rare, limiting our potential to understand ultimate fitness costs of immune investment. Here, we assess how measures of constitutive immune function (haptoglobin, natural antibodies, complement activity) relate to subsequent fitness outcomes (survival, reproductive success, dominance acquisition) in a wild passerine ( Malurus coronatus ). Surprisingly, survival probability was not positively linearly predicted by any immune index. Instead, both low and high values of complement activity (quadratic effect) were associated with higher survival, suggesting that different immune investment strategies might reflect a dynamic disease environment. Positive linear relationships between immune indices and reproductive success suggest that in idual heterogeneity overrides potential resource reallocation trade-offs within in iduals. Controlling for body condition (size-adjusted body mass) and chronic stress (heterophil-lymphocyte ratio) did not alter our findings in a s le subset with available data. Overall, our results suggest that constitutive immune components have limited net costs for fitness and that variation in immune maintenance relates to in idual differences more closely.
Publisher: The Royal Society
Date: 04-2022
DOI: 10.1098/RSOS.212012
Abstract: Telomere length (TL) shortens with age but telomere dynamics can relate to fitness components independent of age. Immune function often relates to such fitness components and can also interact with telomeres. Studying the link between TL and immune function may therefore help us understand telomere–fitness associations. We assessed the relationships between erythrocyte TL and four immune indices (haptoglobin, natural antibodies (NAbs), complement activity (CA) and heterophil-lymphocyte (HL) ratio n = 477–589), from known-aged in iduals of a wild passerine ( Malurus coronatus ). As expected, we find that TL significantly declined with age. To verify whether associations between TL and immune function were independent of parallel age-related changes (e.g. immunosenescence), we statistically controlled for s ling age and used within-subject centring of TL to separate relationships within or between in iduals. We found that TL positively predicted CA at the between-in idual level (in iduals with longer average TL had higher CA), but no other immune indices. By contrast, age predicted the levels of NAbs and HL ratio, allowing inference that respective associations between TL and age with immune indices are independent. Any links existing between TL and fitness are therefore unlikely to be strongly mediated by innate immune function, while TL and immune indices appear independent expressions of in idual heterogeneity.
Publisher: Elsevier BV
Date: 04-2019
Publisher: Wiley
Date: 28-07-2023
DOI: 10.1111/COBI.14110
Abstract: Fisheries bycatch is a critical threat to sea turtle populations worldwide, particularly because turtles are vulnerable to multiple gear types. The Canary Current is an intensely fished region, yet there has been no demographic assessment integrating bycatch and population management information of the globally significant Cabo Verde loggerhead turtle ( Caretta caretta ) population. Using Boa Vista island (Eastern Cabo Verde) subpopulation data from capture–recapture and nest monitoring (2013–2019), we evaluated population viability and estimated regional bycatch rates (2016–2020) in longline, trawl, purse‐seine, and artisanal fisheries. We further evaluated current nesting trends in the context of bycatch estimates, existing hatchery conservation measures, and environmental (net primary productivity) variability in turtle foraging grounds. We projected that current bycatch mortality rates would lead to the near extinction of the Boa Vista subpopulation. Bycatch reduction in longline fisheries and all fisheries combined would increase finite population growth rate by 1.76% and 1.95%, respectively. Hatchery conservation increased hatchling production and reduced extinction risk, but alone it could not achieve population growth. Short‐term increases in nest counts (2013–2021), putatively driven by temporary increases in net primary productivity, may be masking ongoing long‐term population declines. When fecundity was linked to net primary productivity, our hindcast models simultaneously predicted these opposing long‐term and short‐term trends. Consequently, our results showed conservation management must ersify from land‐based management. The masking effect we found has broad‐reaching implications for monitoring sea turtle populations worldwide, demonstrating the importance of directly estimating adult survival and that nest counts might inadequately reflect underlying population trends.
Publisher: Springer Science and Business Media LLC
Date: 29-06-2021
Publisher: Oxford University Press (OUP)
Date: 21-11-2022
Abstract: Recent evidence suggests that female ornaments can commonly act as signals. However, how signaling functions might be affected by the tendency for reduced ornament elaboration in relation to males is less well-understood. We address this in mutually ornamented purple-crowned fairy-wrens. We investigated putatively ornamental (tail, ear coverts, crown) and non-ornamental (throat, back) plumage patches in females and compared our findings to previous studies in males. Both sexes have brown backs, buff-white throats, and turquoise-blue tails (bluer in males), while ear coverts are rufous in females and black in males. Both sexes also have a seasonal crown (slate-gray in females, black-and-purple in males). Dominant (breeder) females expressed more complete and grayer (more ornamented) crowns, although variation in coloration should not be discriminable by in iduals. Unexpectedly, subordinates showed more colorful (saturated) rufous ear coverts, which should be discriminable. Condition-dependence was only evident for crown completeness (% slate-gray cover). Females with more reddish-brown backs were more reproductively successful. Variation in plumage characteristics did not explain differential allocation by mates or chances of gaining dominance. Our outcomes were not entirely consistent with findings in males. The most notable disparity was for the crown, a signal used in male-male competition that in females seems to be expressed as an incomplete version of the male crown that is not associated with fitness benefits. Our study shows that in a species, multiple traits can vary in their information content and that female ornaments can sometimes be less informative than in males, even those that are produced seasonally.
Publisher: Elsevier BV
Date: 09-2021
DOI: 10.1016/J.CUB.2021.06.070
Abstract: Understanding the major evolutionary transition from solitary in iduals to complex societies is h ered by incomplete insight into the drivers of living in cooperative groups.
Publisher: Elsevier BV
Date: 04-2019
Publisher: Wiley
Date: 03-2019
DOI: 10.1111/MEC.15002
Abstract: Poor conditions during early development can initiate trade-offs that favour current survival at the expense of somatic maintenance and subsequently, future reproduction. However, the mechanisms that link early and late life-history are largely unknown. Recently it has been suggested that telomeres, the nucleoprotein structures at the terminal end of chromosomes, could link early-life conditions to lifespan and fitness. In wild purple-crowned fairy-wrens, we combined measurements of nestling telomere length (TL) with detailed life-history data to investigate whether early-life TL predicts fitness prospects. Our study differs from previous studies in the completeness of our fitness estimates in a highly philopatric population. The association between TL and survival was age-dependent with early-life TL having a positive effect on lifespan only among in iduals that survived their first year. Early-life TL was not associated with the probability or age of gaining a breeding position. Interestingly, early-life TL was positively related to breeding duration, contribution to population growth and lifetime reproductive success because of their association with lifespan. Thus, early-life TL, which reflects growth, accumulated early-life stress and inherited TL, predicted fitness in birds that reached adulthood but not noticeably among fledglings. These findings suggest that a lack of investment in somatic maintenance during development particularly affects late life performance. This study demonstrates that factors in early-life are related to fitness prospects through lifespan, and suggests that the study of telomeres may provide insight into the underlying physiological mechanisms linking early- and late-life performance and trade-offs across a lifetime.
Publisher: University of Chicago Press
Date: 03-2019
DOI: 10.1086/702310
Abstract: Investment in immune function can be costly, and life-history theory predicts trade-offs between immune function and other physiological demands. Environmental heterogeneity may constrain or change the optimal strategy and thereby alter baseline immune function (possibly mediated by stress responses). We tested several hypotheses relating variation in climatic, ecological, and social environments to chronic stress and levels of baseline innate immunity in a wild, cooperatively breeding bird, the purple-crowned fairy-wren (Malurus coronatus coronatus). From s les collected biannually over 5 yr, we quantified three indexes of constitutive innate immune function (haptoglobin/PIT54, natural antibodies, complement activity) and one index of chronic stress (heterophil-lymphocyte ratio n = 513 - 647 ). Using an information-theoretic and multimodel inference statistical approach, we found that habitat quality and social group size did not affect any immune index, despite hypothesized links to resource abundance and parasite pressure. Rather, short-term variation in temperature and rainfall was related to immune function, while overall differences between seasons were small or absent, despite substantial seasonal variation in climate. Contrary to our expectation, we found no evidence that physiological stress mediated any effects of short-term climatic variables on immune indexes, and alternative mechanisms may be involved. Our results may be interpreted from the perspective of reactive scope models, whereby predictive homeostasis maintains standing immune function relative to long-term demands, while short-term environmental change, being less predictable, has a greater influence on baseline immune function.
Publisher: Inter-Research Science Center
Date: 28-07-2022
DOI: 10.3354/ESR01198
Abstract: We assessed the relationship between body size and several important life history parameters to understand the demographic significance of interpopulation variability in the body size of loggerhead turtles Caretta caretta nesting on Boa Vista Island (Cabo Verde). The adult growth rate (0.34 ± 0.60 cm yr -1 ), annual mortality rate (0.13, 95% CI: 0.12-0.15) and remigration interval (3.1 ± 1.2 yr) were independent of curved carapace length (minimum curved carapace length [CCLmin]). Conversely, the body condition index decreased significantly with female CCLmin. The clutch size, mean egg mass, mean hatchling straight carapace length and mean hatchling mass increased significantly with female CCLmin. However, there was no relationship between female size and hatching success. Randomization and bootstrapping were used to incorporate variability when calculating the average in idual fecundity over 20 yr, a period that accumulated, on average, 94% of the adult mortality. The overall fecundity during this period increased with carapace length at first maturity (71 cm CCLmin: 815 eggs, 95% CI: 653-863 80 cm CCLmin: 906 eggs, 95% CI: 822-959 90 cm CCLmin: 1089 eggs, 95% CI: 926-1415). However, only 8% of the adult females nesting on Boa Vista Island are larger than 90 cm CCLmin, and they produce less than 12% of the total annual egg production. The scarcity of large females might result from a shortage of high-quality foraging grounds where females may reach first sexual maturity at a large carapace length and from the combined effect of a small carapace length at first sexual maturity, low adult somatic growth and high adult mortality.
Publisher: Oxford University Press (OUP)
Date: 08-02-2021
Abstract: Sexual ornaments are often considered honest signals of quality because potential costs or constraints prevent their display by low-quality in iduals. Testing for potential physiological costs of ornaments is difficult, as this requires experimentally forcing in iduals to produce and display elaborate ornaments. We use this approach to test whether a sexually selected trait is physiologically costly to male superb fairy-wrens (Malurus cyaneus). Male fairy-wrens molt from brown to blue breeding plumage at different times of the year, and females strongly prefer the few males that are blue early, during winter. We used short-acting testosterone implants to stimulate males to produce “early-blue” plumage and assessed costs during and after molt using a panel of physiological indices. Testosterone-implanted, T-males molted in winter and produced blue plumage 6 weeks before control-implanted, C-males. T-males molted while in lower body condition, tended to have lower fat reserves, and were more likely to be parasitized by lice. However, we detected no negative effects on immune function, blood parasites, exposure to stressors, or survival. Juvenile males never naturally display early-blue plumage, but we found no evidence for increased costs paid by juvenile T-males. Instead, juvenile T-males molted later than adult T-males, suggesting that age presents an absolute constraint on ornament exaggeration that cannot be fully overcome by testosterone treatment. Together, these small costs and large, age-related constraints may enforce signal honesty, and explain female preference for early-blue males.
Publisher: University of Chicago Press
Date: 2022
DOI: 10.1086/717937
Abstract: AbstractAging is associated with declines in physiological performance declining immune defenses particularly could have consequences for age-related fitness and survival. In aging vertebrates, adaptive (memory-based) immune responses typically become impaired, innate (nonspecific) responses undergo lesser declines, and inflammation increases. Longitudinal studies of immune functions in wild animals are rare, yet they are needed to understand immunosenescence under evolutionarily relevant conditions. Using longitudinal data from a tropical passerine (
Publisher: Wiley
Date: 25-06-2018
Abstract: The evolution of conspicuous male traits is thought to be driven by female mate choice or male-male competition. These two mechanisms are often viewed as distinct processes, with most studies focusing on female choice. However, both mechanisms of sexual selection can act simultaneously on the same trait (i.e., dual function) and/or interact in a synergistic or conflicting way. Dual-function traits are commonly assumed to originate through male-male competition before being used in female choice yet, most studies focusing on such traits could not determine the direction of change, lacking phylogenetic information. We investigated the role of conspicuous male seasonal plumage in male-male competitive interactions in the purple-crowned fairy-wren Malurus coronatus, a cooperatively breeding bird. Male breeding plumage in most Malurus species is selected by female choice through extra-pair mate choice, but unlike its congeners, M. coronatus is genetically monogamous, and females do not seem to choose males based on breeding plumage acquisition. Our study shows that, within groups, subordinate males that were older, and therefore higher-ranked in the queue for breeder position inheritance, produced a more complete breeding plumage. In line with this, subordinate males that were older and/or displayed a more complete breeding plumage were more successful in competitively acquiring a breeder position. A role as a signal of competitive ability was experimentally confirmed by presenting models of males: in breeding colours, these received more aggression from resident breeder males than in nonbreeding colours, but elicited limited response from females, consistent with competitors in breeding plumage being perceived as a bigger threat to the breeder male. The role of the conspicuous breeding plumage in mediating male-male interactions might account for its presence in this genetically monogamous species. As phylogenetic reconstructions suggest a past female choice function in M. coronatus, this could represent a sexual trait that shifted functions, or a dual-function trait that lost one function. These evolutionary scenarios imply that intra- and intersexual functions of ornaments may be gained or lost independently and offer new perspectives in understanding the complex dynamics of sexual selection.
No related grants have been discovered for Michael James Roast.