Biology subjects

STIER, A.

Publications and source records attributed to STIER, A..

8 recordsLinked to original sources

bioRxiv2026

Early-life optimization of mitochondrial aerobic metabolism: high efficiency to grow fast, yet at no oxidative cost

Variation in mitochondrial aerobic metabolism has been suggested to underlie variation in interindividual performance. Mitochondrial efficiency quantifies, directly or indirectly, the amount of adenosine triphosphate (ATP) produced relative to O2 consumption. High mitochondrial efficiency is theoretically beneficial by providing more ATP per amount of resource consumed, but may come at the cost of increased reactive oxygen species (ROS) production damaging tissues through oxidative stress. Mitochondrial efficiency is a plastic trait but how it changes through postnatal development remains unknown. We hypothesized that strong selective pressure could lead to an increased mitochondrial efficiency to support fast growth but incur an oxidative cost. We tested this hypothesis by quantifying mitochondrial aerobic metabolism, efficiency and ROS production through postnatal growth in Japanese quail (Coturnix japonica), in two highly aerobic tissues: skeletal and cardiac muscles. Mitochondrial efficiency was indeed higher during peak growth in both tissues, but this was surprisingly associated with markedly lower ROS production. This high efficiency was likely achieved via both a lower proton leak and a higher contribution of complex I to respiration. These results show that enhancing mitochondrial efficiency may be important to support growth, but suggest the presence of unexpected ROS mitigation processes during early-life growth.

physiology↗

bioRxiv2025

Warm and cool temperatures decrease early-life telomere length in wild pied flycatchers

Climate change represents a major challenge for avian species. It is characterized by an increase in average ambient temperatures, but also in occurrence of extreme weather events, such as heat weaves and cold snaps. These abrupt temperature changes can modify the immediate and long-term survival prospects of nestling birds, when their thermoregulatory capacities are still not fully developed. While immediate nestling survival can easily be measured, long-term survival is more challenging to evaluate. Early-life telomere length has been suggested as a potential biomarker of future fitness prospects. To evaluate the potential impact of changes in early-life temperature, we thus experimentally increased (ca. +2.8{degrees}C) and decreased (ca. -1.7{degrees}C) average nestbox temperatures in wild pied flycatchers (Ficedula hypoleuca) during nestling postnatal growth, and measured nestling telomere length before fledging. Shorter telomeres were observed in individuals exposed both to an experimental heating or cooling during growth. Our results suggest that long-term survival prospects or long-term performances of individuals exposed to abrupt changes in early-life temperature may be decreased. O_FIG O_LINKSMALLFIG WIDTH=197 HEIGHT=200 SRC="FIGDIR/small/651824v2_ufig1.gif" ALT="Figure 1"> View larger version (118K): org.highwire.dtl.DTLVardef@2ec526org.highwire.dtl.DTLVardef@915e9borg.highwire.dtl.DTLVardef@1da157borg.highwire.dtl.DTLVardef@b857ce_HPS_FORMAT_FIGEXP M_FIG C_FIG

zoology↗

bioRxiv2023

Surface temperatures are influenced by handling stress independently of glucocorticoid levels in wild king penguins

Assessing the physiological stress responses of wild animals opens a window for understanding how organisms cope with environmental challenges. Since stress response is associated with changes in body temperature, the use of body surface temperature through thermal imaging could help to measure acute and chronic stress responses non-invasively. We used thermal imaging, acute handling-stress protocol and an experimental manipulation of corticosterone (the main glucocorticoid hormone in birds) levels in breeding king penguins (Aptenodytes patagonicus), to assess: 1. the potential contribution of the Hypothalamo-Pituitary-Adrenal (HPA) axis in mediating chronic and acute stress-induced changes in adult surface temperature, 2. the influence of HPA axis manipulation on parental investment through thermal imaging of eggs and brooded chicks, and 3. the impact of parental treatment on offspring thermals response to acute handling. Maximum eye temperature (Teye) increased and minimum beak temperature (Tbeak) decreased in response to handling stress in adults, but neither basal nor stress-induced surface temperatures were significantly affected by corticosterone implant. While egg temperature was not significantly influenced by parental treatment, we found a surprising pattern for chicks: chicks brooded by the (non-implanted) partner of corticosterone-implanted individuals exhibited higher surface temperature (both Teye and Tbeak) than those brooded by glucocorticoid-implanted or control parents. Chicks response to handling in terms of surface temperature was characterized by a drop in both Teye and Tbeak independently of parental treatment. We conclude that the HPA axis seems unlikely to play a major role in determining chronic or acute changes in surface temperature in king penguins. Changes in surface temperature may primarily be mediated by the Sympathetic-Adrenal-Medullary (SAM) axis in response to stressful situations. Our experiment did not reveal a direct impact of parental HPA axis manipulation on parental investment (egg or chick temperature), but a potential influence on the partners brooding behaviour. HighlightsO_LIExperimental increase in corticosterone does not affect king penguins surface temperature C_LIO_LIAcute handling stress increases eye but decreases beak surface temperature in adults C_LIO_LIAcute handling decreases both eye and beak surface temperatures in young chicks C_LIO_LIParental corticosterone treatment does not affect egg surface temperature during incubation C_LIO_LIChicks brooded by non-implanted partners of corticosterone parents are warmer than chicks brooded by others adults. C_LI

zoology↗

bioRxiv2021

From climate warming to accelerated cellular ageing: an experimental study in wild birds

Climate change is increasing both the average ambient temperature and the frequency and severity of heat waves. While direct mortality induced by heat waves is increasingly reported, sub-lethal effects are also likely to impact wild populations. We hypothesized that accelerated ageing could be a cost of being exposed to higher ambient temperature, especially in early-life when thermoregulatory capacities are not fully developed. We tested this hypothesis in wild great tits (Parus major) by experimentally increasing nest box temperature by ca. 2{degrees}C during postnatal growth and measuring telomere length, a biomarker of cellular ageing predictive of survival prospects in many bird species. While increasing early-life temperature had no detectable effect on growth or survival to fledging, it accelerated telomere shortening, and although non-significantly, reduced medium-term survival from 34% to 19%. Heat-induced telomere shortening was not explained by oxidative stress, but more likely by an increase in energy demand (i.e. higher thyroid hormones levels, increased expression of glucocorticoid receptor, increased mitochondrial density) leading to a reduction in telomere maintenance mechanisms (i.e. non-significant decrease in the gene expression of telomerase and protective shelterin). Our results thus suggest that climate warming can affect rate of ageing in wild birds, with potential impact on population dynamics and persistence.

physiology↗

bioRxiv2021

Altricial bird early-stage embryos express the molecular "machinery" to respond to maternal thyroid hormone cues

Maternal hormones, such as thyroid hormones transferred to embryos and eggs, are key signalling pathways to mediate maternal effects. To be able to respond to maternal cues, embryos must express key molecular machinery of the hormone pathways, such as enzymes and receptors. While altricial birds begin thyroid hormone (TH) production only at/after hatching, experimental evidence suggests that their phenotype can be influenced by maternal THs deposited in the egg. However, it is not understood, how and when altricial birds express genes in the TH-pathway. For the first time, we measured the expression of key TH-pathway genes in altricial embryos, using two common altricial ecological model species (pied flycatcher, Ficedula hypoleuca and blue tit Cyanistes caeruleus). Deiodinase DIO1 gene expression could not be reliably confirmed in either species, but deiodinase enzyme DIO2 and DIO3 genes were expressed in both species. Given that DIO2 coverts T4 to biologically active T3, and DIO3 mostly T3 to inactive forms of thyroid hormones, our results suggest that embryos may modulate maternal signals. Thyroid hormone receptor (THRA and THRB) and monocarboxyl membrane transporter gene (SLC15A2) were also expressed, enabling TH-responses. Our results suggest that early altricial embryos may be able to respond and potentially modulate maternal signals conveyed by thyroid hormones.

developmental biology↗

bioRxiv2021

Experimental demonstration of prenatal programming of mitochondrial aerobic metabolism lasting until adulthood

It is increasingly being postulated that among-individual variation in mitochondrial function underlies variation in individual performance (e.g. growth rate) and state of health. It has been suggested (but not adequately tested) that environmental conditions experienced before birth have been suggested to programme postnatal mitochondrial function, with persistent effects potentially lasting into adulthood. We tested this hypothesis in an avian model by experimentally manipulating prenatal conditions (incubation temperature and stability), then measuring mitochondrial aerobic metabolism in blood cells from the same individuals during the middle of the growth period and at adulthood. Mitochondrial aerobic metabolism changed markedly across life stages, and part of these age-related changes were influenced by the prenatal temperature conditions. A high incubation temperature induced a consistent and long-lasting increase in mitochondrial aerobic metabolism. Postnatal mitochondrial aerobic metabolism was positively associated with oxidative damage on DNA but not telomere length. While we detected significant within-individual consistency in mitochondrial aerobic metabolism across life-stages, the prenatal temperature regime only accounted for a relatively small proportion (<20%) of the consistent among-individual differences we observed. Our results demonstrate that prenatal conditions can program consistent and long-lasting differences in mitochondrial function, which could potentially underlie among-individual variation in performance and health state.

physiology↗

bioRxiv2021

Population differences in the length, early-life dynamics, and heritability of telomeres among European pied flycatchers

Telomere length and shortening rate are increasingly used as biomarkers for long-term costs in ecological and evolutionary studies because of their relationships with survival and fitness. Both early-life conditions and growth, and later-life stressors can create variation in telomere shortening rate. Studies on between- population telomere length and dynamics are scarce, despite the expectation that populations exposed to varying environmental constraints would present divergent telomere length patterns. The pied flycatcher (Ficedula hypoleuca) is a passerine bird breeding across Eurasia (from Spain to western Siberia) and migrating through the Iberian Peninsula to spend the non-breeding period in sub-Saharan Africa. Thus, different populations show marked differences in migration distance. We studied the large-scale variation of telomere length and early-life dynamics in the pied flycatcher by comparing six European populations across a north- south gradient (Finland, Estonia, England, and Spain) predicting negative effect of migration distance on adult telomere length, and of nestling growth on nestling telomere dynamics. There were clear population differences in telomere length, with English birds from mid-latitudes having the longest telomeres. Telomere length did not thus show consistent latitudinal variation and was not linearly linked to differences in migration distance. Early-life telomere shortening rate tended to vary between populations. Fast growth was associated with shorter telomeres in the early life, but faster nestling growth affected telomeres more negatively in northern than southern populations. While the sources of between-population differences in telomere-related biology remain to be more intensively studied, our study illustrates the need to expand telomere studies at the between-population level.

zoology↗

bioRxiv2020

Testing for context-dependent effects of maternal thyroid hormones on offspring survival and physiology: an experimental approach manipulating temperature in a wild bird species

Maternal effects via hormonal transfer from the mother to the offspring provide a tool to translate environmental cues to the offspring. Experimental manipulations of maternally transferred hormones have yielded increasingly contradictory results, which may be explained by environment-dependent effects of hormones. Yet context-dependent effects have rarely been experimentally tested. We therefore studied whether maternally transferred thyroid hormones (THs) exert context-dependent effects on offspring survival and physiology by manipulating both egg TH levels and post-hatching nest temperature in wild pied flycatchers (Ficedula hypoleuca) using a full factorial design. We found no clear evidence for context-dependent effects of prenatal THs related to postnatal temperature on growth, survival and potential underlying physiological responses (plasma TH levels, oxidative stress and mitochondrial density). We conclude that future studies should test for other key environmental conditions, such as food availability, to understand potential context-dependent effects of maternally transmitted hormones on offspring, and their role in adapting to changing environments.

ecology↗