Biology subjects

Noiret, A.

Publications and source records attributed to Noiret, A..

5 recordsLinked to original sources

bioRxiv2024

Mind the polar sun: Solar radiations trigger frequent heat stress in breeding king penguins, despite relatively cool air temperatures.

Polar and sub-polar animals evolved to thrive in cold climates and may thus be particularly sensitive to rising temperatures associated with climate change. Penguins may be especially vulnerable, due to their dual habitat, alternating between foraging in cold waters and breeding/moulting on an increasingly warm land. Here, we characterized heat stress occurrence in breeding king penguins through behavioural observations (e.g. panting occurrence) and body temperature measurements. We observed that behavioural signs of heat stress are frequent in king penguins breeding in the sub-Antarctic region (> 20% of observations at mid-day), and that subcutaneous temperatures increase under high heat load, especially in penguins observed panting. Subcutaneous and core body temperatures were moderately correlated and both increased with heat load. Yet, their responses were not parallel since core body temperature is markedly less sensitive to heat load than subcutaneous temperature. Air temperature alone was a poor predictor of heat stress occurrence, whereas the combination of high solar radiation, low wind speed and high air temperatures provided the strongest predictive power. Finally, reproductive failures were more likely to occur on warmer days, suggesting that heat stress may have significant sublethal effects on adults that could ultimately affect population dynamics. O_FIG O_LINKSMALLFIG WIDTH=150 HEIGHT=200 SRC="FIGDIR/small/611977v3_ufig1.gif" ALT="Figure 1"> View larger version (95K): org.highwire.dtl.DTLVardef@26db91org.highwire.dtl.DTLVardef@119461dorg.highwire.dtl.DTLVardef@4a1d8forg.highwire.dtl.DTLVardef@1da9d96_HPS_FORMAT_FIGEXP M_FIG C_FIG

evolutionary biology↗

bioRxiv2023

Sex-specific central regulation of reproductive activity revealed by the use of deslorelin in the grey mouse lemur, Microcebus murinus.

Deslorelin is a GnRH agonist used in veterinary medicine to temporarily inhibit reproduction in domestic animals and is sometimes tested in captive species in zoo to control population or tame aggressive behaviours in males. However, some studies have revealed the inefficacy of deslorelin specifically in males, contrary to females that follow a classic long-term inhibition of the reproductive hypothalamic-pituitary axis through sexual steroid negative feedback. We implanted 5 males and 6 females grey mouse lemurs (Microcebus murinus), long-day breeders that display a complete inhibition of the reproductive system during winter, at the end of the short-day period, a few weeks before the breeding season. Contrary to females, which exhibited a classic inhibitory response to deslorelin, males testosterone levels increased as well as their testis size, which suggests a sex-specific sensitivity to the negative feedback of sexual steroids before the mating period. We propose that this sex-imbalance is related to the different life-history of males as opposed to females concerning reproductive tasks and behaviour.

physiology↗

bioRxiv2023

Grey Mouse Lemurs' response to acute caloric restriction before reproduction supports the Thrifty Female Hypothesis

The thrifty female hypothesis states that females would preserve more of their energy reserves during winter than males, because of a sex specific time-frame of energy allocation to reproduction. As males reactivate their reproductive axis before the mating period, while females mainly allocate energy in gestation and lactation, we make the hypothesis that males would have to use shorter torpor bouts and longer periods of normothermic activity in order to promote spermatogenesis during winter, a period of low food availability. Here we applied an acute two-week 80%CR in males and females grey mouse lemurs, shortly before the mating period. We show evidence of thriftier phenotypes in wintering females, which performed deeper and longer torpor bouts than males, and ultimately lost less body mass. Our results thus support the thrifty female hypothesis in a seasonally breeding primate, and reinforce the concept of a sex-biased trade-off in using torpor, which might ultimately benefit to reproduction and survival.

evolutionary biology↗

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

Why be thrifty? Sex-specific heterothermic patterns in wintering captive Microcebus murinus do not translate into differences in energy balance.

The physiological mechanisms of the responses toward stressors are the core of ecophysiology studies to understand the limits of an organisms flexibility and better predict the impact of environmental degradation on natural populations. However, little information is available when we question inter-individual variability of these physiological responses, even though they can be particularly important. Some observations of intersexual differences in heterothermy raised the question of a difference in energy management between sexes. Here we assess male and female differences in a mouse lemur model (Microcebus murinus), a highly seasonal Malagasy primate, studying their physiological flexibility toward caloric restriction, and examining the impact on their reproductive success. These animals are adapted for naturally changing food availability and climate conditions, and can express deep torpor, allowing them to spare their energy expenses over the dry and cold season. We monitored body mass and body temperature on 12 males and 12 females over winter, applying a chronic 40% caloric restriction to 6 individuals of each group. Our results showed variability of Tb modulations throughout winter and in response to caloric treatment depending on the sex, as females entered deep torpor regardless of food restriction, while only CR males had a similar response. The use of deep torpor, however, did not translate into better body condition either in females, or in response to CR, and did not clearly affect reproductive success. The favorable captive context potentially buffered the depth of torpor and minimized the positive effects of using torpor on energy savings. However, our results may emphasize the existence of other benefits of heterothermic responses than fat reserves.

physiology↗