Short- and long-term effects of chronic cold exposure during youth in Japanese quail (Coturnix japonica)

Abstract

After hatching, bird chicks are inevitably exposed to the thermal conditions of their environment. For the first stage of development chicks are not yet fully capable of maintaining a stable body temperature. During this time, their thermal environment can cause morphological and physiological priming. The plasticity of these responses and the extent to which they persist in the long-term is not well understood. Given the stochastic nature of climate change, it is important to understand whether priming to one set of thermally challenging conditions during youth could hinder responses to the opposite thermally challenging conditions in the long term.
In this study, Japanese quail (Coturnix japonica) were raised in either cold (10°C) or mild (20°) conditions until the birds reached three weeks of age, from which point they were all raised in the mild conditions. Development was monitored regularly throughout the experiment. Physiological responses to temperatures of 10, 20, 30 and 40 °C were first tested at peak growth at the age of three weeks (to assess short-term effects) and again after reaching full maturity at eight weeks of age (to assess long-term effects) using a flow-through respirometry setup contained inside a climate chamber.
Cold-raised birds of both sexes had a significantly higher resting metabolic rate across all four testing temperatures and also a significantly higher evaporative water loss at the lower three temperatures. In the short term, cold-raised males had a higher thermal conductance than mild-raised males. Furthermore, growth models for the entire eight-week period point to sex-specific effects, with cold-raised males having a boost in growth in the final weeks resulting in a larger final size. In the short term, body mass did not differ between treatment groups; however, cold-raised males did have significantly shorter bills at 3w. At 8w, their bill size was not significantly different to their counterparts. In addition, far fewer eggs were laid by females in the cold-raised birds’ pen.
The absence of differences for most physiological parameters at 40°C both in the short and long term is encouraging from a conservation perspective because it suggests that the physiological development of the cold-raised group was resilient and did not impede heat tolerance. The study also suggests that males have a greater sensitivity to the thermal conditions of their environment. Future studies could investigate the mechanisms behind sex-specific effects and whether the changes in the duration and temperature of acclimation have different effects. Finally, studies on reproductive investment are warranted to understand whether the differences in the number of eggs laid are the result of reproductive constraints or alterations in reproductive investment favouring egg quality over quantity.

Popular Abstract

Investigating the effects of growing up cold

Birds can regulate their body temperature irrespective of environmental temperature. However, when they are newly hatched, the environmental temperature can have a major effect on physiological and morphological development. Little is known about the permanence of these effects. It is important to understand this because it is becoming ever more likely that many types of animals, including birds will face extreme temperatures as a result of climate change.

To this end, I studied the effects that early-life exposure to cold (10°C) and mild (20°C) environments in quail. Respirometry was used at three and eight weeks of age to assess physiological responses to a variety of temperatures (10 – 40 °C). Morphological effects were assessed by monitoring body mass and bill size over an eight week growth period. The number of eggs laid by the birds in each group was tracked to see if treatment could affect reproduction.

At three weeks of age, the birds raised in the cold had a higher metabolism, meaning that they expended more energy. Some additional minor physiological differences were found at this age in the birds’ responses between 10 – 30 °C. Cold-raised males also had smaller beaks at this age than mild-raised males and both groups of females, indicating the treatment affected males differently to females. This may have been an adaptive response since smaller bills reduce heat loss.

No physiological differences in temperature responses were found between the treatment groups at eight weeks of age. Although birds from both groups had similar weights at 8w, cold-raised birds reached peak growth slightly later and had a lower growth rate. Over the course of the entire experiment, cold-raised females laid far fewer eggs than mild-raised females, possibly indicating reduced or strategically altered reproductive investment.

The similar results between the two treatment groups at the hottest 40°C testing temperature are encouraging since they indicate that they developed a normal physiological tolerance for heat despite initially growing up in cold conditions. Future studies should investigate the mechanisms involved in plastic thermal responses. Doing so could reveal why each sex was affected differently in some cases and whether this makes either one more susceptible. Lastly, the results on egg laying highlight the need for detailed studies on the effects of thermal conditions during youth on reproduction later on in life, due to the potential effect on evolutionary fitness.

Master’s Degree Project in Animal Ecology 45 credits, 2022

Supervisor: Andreas Nord
Department of Biology

• author: Ó Cuív, Ciarán
• supervisor: Andreas Nord
• organization: Degree Projects in Biology
• course: BION02 20212
• year: 2022
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 9102910
• date added to LUP: 2022-11-07 14:52:07
• date last changed: 2022-11-07 14:52:07