Birds often face various stressors during feather renewing, for example, enduring infection with blood parasites. Because nutritional resources are typically limited, especially for wild animals, when an individual allocates energy to one physiological system, there is subsequently less for other processes, thereby requiring a trade‐off. Surprisingly, potential trade‐offs between malaria infection and feather growth rate have not been experimentally considered yet. Here, we conducted three studies to investigate whether a trade‐off occurs among feather growth rate, malaria infection and host health conditions. First, we explored whether naturally infected and uninfected house sparrows differed in feather growth rate in the wild. Second, we asked whether experimental inoculation of malaria parasites and/or forcing the renewal of a tail feather. Lastly, we evaluated whether individual condition was affected by experimentally‐induced feather regrowth and/or malaria experimental infection. Our findings showed that feather growth rate was negatively affected by natural malaria infection status in free‐living birds and by experimental infection in captive birds. Furthermore, birds that did not increase body mass or hematocrit during the experimental study had slower feather growth. Together our results suggest that infection with blood parasites has more negative health effects than the growth of tail feathers and that these two processes (response to blood parasite infection and renewal of feathers) are traded‐off against each other. As such, our results highlight the role of malaria parasites as a potential mechanism driving other trade‐offs in wild passerines.
Amphibian declines are a global phenomenon but responses of populations to specific threats are often context dependent and mediated by individual physiological condition. Habitat degradation due to reduced riparian forest cover and parasitism are two threats facing the hellbender salamander (Cryptobranchus alleganiensis), but their potential to interact in nature remains largely unexplored. We investigated associations between forest cover, parasitic infection and physiology of hellbenders to test the hypotheses that physiological condition responds to infection and/or habitat degradation. We sampled 17 stream reaches in southwest Virginia, USA, on a year-round basis from 2013 to 2016 and recorded 841 captures of 405 unique hellbenders. At each capture we documented prevalence of two blood-associated parasites (a leech and trypanosome) and quantified up to three physiological condition indices (body condition, hematocrit, white blood cell [WBC] differentials). We used generalized linear mixed models to describe spatiotemporal variation in parasitic infection and each condition index. In general, living in the most heavily forested stream reaches, where hellbender density was highest, was associated with the greatest risk of parasitism, elevated neutrophil-to-lymphocyte (N:L) ratios and eosinophils, slightly lower hematocrit and lower mean body condition in hellbenders. All condition indices fluctuated temporally in a manner consistent with seasonal variation in hellbender metabolic demands and breeding phenology and were associated with land use during at least part of the year. Paradoxically, relatively low levels of forest cover appeared to confer a potential advantage to individuals in the form of release from parasites and improved body condition. Despite improved body condition, individuals from less forested areas failed to exhibit fluctuating body condition in response to spawning, which was typical in hellbenders from more forested habitats. We postulate this lack of fluctuation could be due to reduced conspecific competition or reproductive investment and/or high rates of filial cannibalism in response to declining forest cover.
more » « less- NSF-PAR ID:
- 10488223
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Conservation Physiology
- Volume:
- 12
- Issue:
- 1
- ISSN:
- 2051-1434
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Secretive species are difficult to study and often of conservation concern, as exemplified by the Eastern Hellbender (Cryptobranchus alleganiensis). Traditional methods for sampling Hellbenders involves moving rocks, which damages essential habitat. Use and installation of artificial shelters has made studying Hellbenders less dangerous for the animal and less disruptive to stream habitat; however, researchers using shelters generally capture occupying animals to identify them. We tested the ability of a submersible portable Passive Integrated Transponder (PIT) antenna to accurately detect PIT-tagged Hellbenders in shelters. We tested the effects of the presence and depth of cover rocks on top of shelters, PIT tag location within the shelter, and tag orientation on detection efficiency of Hellbenders. For the 32 shelters occupied by a tagged individual with cover rocks in place, the scanner accurately detected 31% of the animals versus 88% when cover rocks were removed. The detection efficiency of the scanner dropped below 50% once cover rock depth exceeded 11 cm. Tags placed near the interface of the entrance tunnel and chamber, or along the chamber walls, had higher detection efficiencies than those in other locations within the shelter. Vertically oriented tags were 18% more likely to be detected than horizontally oriented tags. Our study demonstrates that while this technology has certain limitations, it shows potentmore » « less
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Here, we investigated how multiple colour signals relate to their information content, examined the role of T as a potential mediator of these relationships and how environmental factors explain colour signal variation.
We performed an integrative study to examine the covariation between three colour signals (melanin‐based black, carotenoid‐based yellow–orange and structural UV), physiological performance, parasitism, T levels and environmental factors (microclimate, forest cover) in male common lizards
Zootoca vivipara from 13 populations.We found that the three colour signals conveyed information on different aspects of male condition, supporting a multiple message hypothesis. T influenced only parasitism, suggesting that T does not directly mediate the relationships between colour signals and their information content. Moreover, colour signals became more saturated in forested habitats, suggesting an adaptation to degraded light conditions, and became generally brighter in mesic conditions, in contradiction with the thermal melanism hypothesis.
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Abstract Artificial shelters show considerable promise as tools for studying imperiled hellbender salamanders. Their full utility has not yet been fully reached in practice, however, because during initial trials shelters often became blocked by sediment or dislodged during high stream discharge events. To determine whether these challenges could be overcome, we deployed 438 artificial shelters of two different designs across 10 stream reaches and three rivers in the upper Tennessee River Drainage in 2013–2018. We recorded shelter entrance availability during surveys, and recorded which shelters became dislodged following high discharge events. We evaluated two hypotheses: (a) shelter availability was driven by shelter placement and maintenance frequency and (b) shelter stability was driven by shelter design and shelter placement. Shelters were available 78.6% of the time on average (range = 0–100%), and 88.6% (388 of 438) of shelters were stable across all high discharge events. Shelter availability was maximized by clearing sediment from shelter entrances at least once every 40 days (more often in impaired reaches with high siltation) and after large storm events, situating the shelter within 1 m of ≥5 boulders, and orienting shelters such that their entrances do not face directly downstream. Shelter stability with our initial shelter design was 77.5% (169 of 218), but approached 100% (219 of 220) for heavier (~40 kg vs. ~25 kg) shelters with recessed lids, and in reaches with abundant large boulders. Our findings demonstrate that with an improved design and careful placement, artificial shelters can serve as valuable tools for monitoring hellbenders in reaches with modest siltation.
