Biology subjects

Tabh, J. K. R.

Publications and source records attributed to Tabh, J. K. R..

5 recordsLinked to original sources

bioRxiv2026

Allometric correlates of heat tolerance in birds: A test using quail breeds with extreme size variation

Birds and mammals are shrinking and shapeshifting as global temperatures rise. Ecogeographic rules predict that such changes should ease heat stress by increasing surface-area-to-volume ratios, and thus, the capacity for heat exchange. This has led to the hypothesis that body size reductions are driven by thermoregulatory selection or adaptive plasticity, although recent syntheses point to more complex, multifactorial causes. Crucially, recent theoretical models predict that thermoregulatory benefits of smaller body size only emerge at extreme deviations from average phenotypes. Here, we exploit agricultural selection in Japanese quail to directly test this hypothesis, using three breeds spanning extreme differences in body mass, surface area, and relative appendage lengths. Evaporative cooling capacity and the scope for evaporative water loss broadly followed allometric predictions when contrasting small and larger breeds. As expected, this allowed the smallest breed to tolerate higher air temperatures. However, differences in heat tolerance limits between breeds were consistently much smaller than predicted. Additionally, the breadth of thermoneutral zones overlapped in full, and upper critical temperatures were remarkably similar, between breeds. Together, these results show that heat tolerance is only weakly linked to surface-area-to-volume relationships and cannot be explained by size alone. Thus, although smaller bodies may modestly enhance heat dissipation when size variation in a population is substantial, our findings suggest that recent body size reductions and morphological shifts are unlikely to be driven primarily by thermoregulatory benefits.

evolutionary biology↗

bioRxiv2025

Rising role of phenotypic plasticity explains changes in avian body size distributions

Natural selection widely favours the largest within animal species. Why body sizes are declining in the worlds temperate birds is therefore mechanistically confusing and ecologically worrying. We argue that understanding the causes of these declines requires knowledge of how complete, body mass probability distributions - not just averages - are moving. Using data from 159 North American bird species - spanning 26 families, 53{degrees} of latitude, and 25 years - we show that body mass distributions are not only downgrading, but also narrowing, and losing their upper tails (the heaviest individuals), with the largest changes occurring at southern range limits. Combining fitness models with a novel, distributional Price equation revealed that these changes are increasingly driven by phenotypic plasticity, not selection or genetic drift, and may yet be reversible.

evolutionary biology↗

bioRxiv2024

No evidence that shrinking and shapeshifting meaningfully affect how birds respond to warming and cooling

Across the globe, birds and mammals are becoming smaller and longer-limbed. Although the cause of these changes is unclear, many argue that each provide thermoregulatory benefits in a warmer world by easing heat dissipation. Here, we show that neither body size nor limb length in a model species (the Japanese quail) influenced metabolic costs of warming during a cold challenge. In the heat, larger body sizes increased metabolic costs of thermoregulation, however, this effect was moderate and almost always negated by cooling from the limbs (>97% of cases). Rearing in the warmth (30{degrees}C) relative to the cold (10{degrees}C) reduced body sizes and increased limb lengths at adulthood but thermoregulatory benefits of these changes in later heat exposures were absent. Our findings demonstrate that shrinking and shape-shifting are unlikely to ease thermoregulation in contemporary birds or reflect selection for such. Alternative contributors, including neutral or non-adaptive plasticity, should be further investigated. TeaserUsing experimental data, we show for the first time that shrinking and shape-shifting - which has been described as the third general response to climate change in animals - does not inherently provide thermoregulatory benefits to birds in a warming world. Further research evaluating the drivers of shape-shifts (including neutral plasticity and temporal reductions in resource abundance) is needed before we can determine why animals shrink under climate change.

physiology↗

bioRxiv2023

Terrestrial endotherms trade body temperature regulation for the stress response when energy is limited

Responding to perceived threats is energetically expensive and can require animals to curtail somatic repair, immunity, and even reproduction to balance energy ledgers. Among birds and mammals, energetic demands of thermoregulation are often immense, yet whether homeostatic body temperatures are also compromised to aid the stress response is unknown. Using data sourced from over 60 years of literature and 24 endotherm species, we show that exposure to non-thermal challenges (e.g. human interaction, social threats) caused body temperatures to decrease in the cold and increase in the warmth, but particularly when species-specific costs of thermoregulation were high and surplus energy low. Biophysical models revealed that allowing body temperature to change in this way liberated up to 24% (mean = 5%) of resting energy expenditure for use toward coping. While useful to avoid energetic overload, such responses nevertheless heighten risks of cold- or heat-induced damage, particularly when coincident with cold- or heat-waves.

physiology↗

bioRxiv2021

Within- and transgenerational plasticity of a temperate salmonid in response to thermal acclimation and acute temperature stress

Environmental temperatures associated with climate change are rising too rapidly for many species to adapt, threatening the persistence of taxa with limited capacities for thermal acclimation. We investigated the capacity for within- and transgenerational responses to increasing environmental temperatures in brook trout (Salvelinus fontinalis), a cold-adapted salmonid. Adult fish were acclimated to temperatures within (10{square}) and above (21{square}) their thermal optimum for six months before spawning, then mated in a full factorial breeding design to produce offspring from cold- and warm-acclimated parents as well as bidirectional crosses between parents from both temperature treatments. Offspring families were subdivided and reared at two acclimation temperatures (15{square} and 19{square}) representing their current environment and a projected climate change scenario. Offspring thermal physiology was measured as the rate of oxygen consumption (MO2) during an acute change in temperature (+2{square} h-1) to observe their MO2-temperature relationship. We also recorded resting MO2, the highest achieved (peak) MO2, and critical thermal maximum (CTM) as performance metrics. Within-generation plasticity was greater than transgenerational plasticity, with offspring acclimation temperature having demonstrable effects on peak MO2 and CTM. Transgenerational plasticity was evident as an elevated resting MO2 and the MO2-temperature relationship in offspring from warm-acclimated parents. Both parents contributed to offspring thermal responses, although the paternal effect was stronger. Although brook trout exhibit both within- and transgenerational plasticity for thermal physiology, it is unlikely that these will be sufficient for coping with long-term changes to environmental temperatures resulting from climate change. SummaryBrook trout (Salvelinus fontinalis) exhibit within-generation and transgenerational plasticity for thermal performance, although neither response appears sufficient to cope with long-term climate change effects.

physiology↗