Early nighttime testosterone peaks are correlated with GnRH-induced testosterone in a diurnal songbird

Greives, Timothy J.; Eshleman, Michelle A.; Galante, Holland; Elderbrock, Emily K.; Deimel, Caroline; Hau, Michaela

doi:10.1016/j.ygcen.2021.113861

Cited by 6 publications

(5 citation statements)

References 72 publications

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“…Alternatively, this unexpected result might be attributable to our methods, as we quantified maximum levels of testosterone following a GnRH challenge, while the previously mentioned studies quantified natural, circulating levels of testosterone. When examining the relationship between testosterone and reproductive traits, max T is often more likely to be associated with the trait of interest than are circulating levels, which vary throughout the day (see discussion in 89 ). However, because circulating testosterone levels tend to be lower than max T levels for most of the day 89 , and the bloodstream is the interface between parasite and host, additional work investigating the impact of chronic and experimental Plasmodium infection on circulating T is warranted.…”

Section: Discussionmentioning

confidence: 99%

Physiological impacts of chronic and experimental Plasmodium infection on breeding-condition male songbirds

Talbott

Ketterson

2023

Sci Rep

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While Plasmodium parasitism is common in songbirds, its impact on avian reproduction is unclear owing to conflicting reports in the existing literature. Particularly understudied is the impact of phase of infection on variation in host reproductive physiology in wild, breeding-condition birds. However, assessing the full impact of Plasmodium on reproductive success in the wild can be difficult because individuals experiencing severe effects of parasitism may not enter the breeding population and may be less likely to be captured during field studies. To address these factors, we quantified metrics of health and reproductive physiology in wild-caught, breeding-condition male dark-eyed juncos (Junco hyemalis hyemalis) before and after experimental Plasmodium inoculation in a captive setting. Metrics of health and reproductive physiology included activity rate, hematocrit, scaled body mass, testosterone and sperm production. Individuals already infected at capture (i.e., chronically infected) had higher levels of hematocrit than males without chronic infections. Experimentally infected males showed a larger reduction in hematocrit and activity rate as compared to controls. However, chronic infection status did not influence the extent of metric decline. Testosterone production did not vary by treatment and most birds produced sperm following inoculation. Broadly, our results suggest that male juncos exposed to Plasmodium during the breeding season likely experience declines in general health, but Plasmodium infections do not negatively impact reproductive physiology. We conclude that physiological tradeoffs in males may favor maintenance of reproductive function despite infection.

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Section: Discussionmentioning

confidence: 99%

Physiological impacts of chronic and experimental Plasmodium infection on breeding-condition male songbirds

Talbott

Ketterson

2023

Sci Rep

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“…at high latitudes, but it undergoes seasonal modulation [39][40][41]. Sex steroids, such as circulating testosterone and estradiol concentrations, also exhibit distinct circadian rhythms [42,43] royalsocietypublishing.org/journal/rstb Phil. Trans.…”

Section: Endocrine-clock Interactions In Avian Physiologymentioning

confidence: 99%

“…at high latitudes, but it undergoes seasonal modulation [ 39 – 41 ]. Sex steroids, such as circulating testosterone and estradiol concentrations, also exhibit distinct circadian rhythms [ 42 , 43 ], and in turn, can exert powerful effects on the circadian system [ 44 , 45 ]. Some of the pathways that interact with biological rhythms are summarized in figure 2 .…”

Section: Endocrine–clock Interactions In Avian Physiologymentioning

confidence: 99%

Endocrine–circadian interactions in birds: implications when nights are no longer dark

Helm,

Greives,

Zeman

2024

Phil. Trans. R. Soc. B

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Biological clocks are evolved time-keeping systems by which organisms rhythmically coordinate physiology within the body, and align it with rhythms in their environment. Clocks are highly sensitive to light and are at the interface of several major endocrine pathways. Worryingly, exposure to artificial-light-at-night (ALAN) is rapidly increasing in ever more extensive parts of the world, with likely impact on wild organisms mediated by endocrine–circadian pathways. In this overview, we first give a broad-brush introduction to biological rhythms. Then, we outline interactions between the avian clock, endocrine pathways, and environmental and internal modifiers. The main focus of this review is on the circadian hormone, melatonin. We summarize information from avian field and laboratory studies on melatonin and its relationships with behaviour and physiology, including often neglected developmental aspects. When exposed to ALAN, birds are highly vulnerable to disruption of behavioural rhythms and of physiological systems under rhythmic control. Several studies suggest that melatonin is likely a key mediator for a broad range of effects. We encourage further observational and experimental studies of ALAN impact on melatonin, across the full functional range of this versatile signalling molecule, as well as on other candidate compounds at the endocrine–circadian interface. This article is part of the theme issue ‘Endocrine responses to environmental variation: conceptual approaches and recent developments’.

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“…For example, testosterone in many temperate bird species peaks seasonally during territorial establishment and mating, but decreases to basal, non-detectable levels during the non-breeding season, when gonads regress ( Wingfield et al 2019 ). Within an individual, testosterone levels vary substantially throughout the day ( Panico et al 1990 ; Brambilla et al 2009 ; Greives et al 2021 ). Given their daily, seasonal, and cross-species variation, hormone levels are not a binary indicator of sex.…”

Section: Sex At the Endocrine Levelmentioning

confidence: 99%

Multivariate Models of Animal Sex: Breaking Binaries Leads to a Better Understanding of Ecology and Evolution

McLaughlin

Brock

Gates

et al. 2023

Integrative and Comparative Biology

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‘Sex’ is often used to describe a suite of phenotypic and genotypic traits of an organism related to reproduction. However, these traits – gamete type, chromosomal inheritance, physiology, morphology, behavior, etc. – are not necessarily coupled, and the rhetorical collapse of variation into a single term elides much of the complexity inherent in sexual phenotypes. We argue that consideration of ‘sex’ as a constructed category operating at multiple biological levels opens up new avenues for inquiry in our study of biological variation. We apply this framework to three case studies that illustrate the diversity of sex variation, from decoupling sexual phenotypes to the evolutionary and ecological consequences of intrasexual polymorphisms. We argue that instead of assuming binary sex in these systems, some may be better categorized as multivariate and nonbinary. Finally, we conduct a meta-analysis of terms used to describe diversity in sexual phenotypes in the scientific literature to highlight how a multivariate model of sex can clarify, rather than cloud, studies of sexual diversity within and across species. We argue that such an expanded framework of ‘sex’ better equips us to understand evolutionary processes, and that as biologists it is incumbent upon us to push back against misunderstandings of the biology of sexual phenotypes that enact harm on marginalized communities.

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Early nighttime testosterone peaks are correlated with GnRH-induced testosterone in a diurnal songbird

Cited by 6 publications

References 72 publications

Physiological impacts of chronic and experimental Plasmodium infection on breeding-condition male songbirds

Physiological impacts of chronic and experimental Plasmodium infection on breeding-condition male songbirds

Endocrine–circadian interactions in birds: implications when nights are no longer dark

Multivariate Models of Animal Sex: Breaking Binaries Leads to a Better Understanding of Ecology and Evolution

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