Biology subjects

Shipley, J. R.

Publications and source records attributed to Shipley, J. R..

5 recordsLinked to original sources

bioRxiv2026

Developmental cold exposure increases the ability to maintain body temperature during future cold challenges in a free-living altricial bird

Developing in suboptimal temperatures can have widespread negative effects in organisms, but early exposure to thermal challenges can also trigger increased investment in thermoregulatory capacity. Within birds, the effects of cold exposure during incubation may differ between precocial and altricial species due to differences in the ontogeny of thermoregulation. To date, most of the evidence showing that embryonic cold exposure shapes future thermoregulatory capacity comes from a few precocial species in laboratory settings. Less is known about sensitivity to low-temperature incubation in altricial species which only become fully endothermic after hatching. In this study, we tested the effects of cold temperatures during embryonic development by temporarily cooling the nest boxes of free-living tree swallows (Tachycineta bicolor) during late incubation and subsequently exposing nestlings to an acute cold challenge. Cold exposure during early development made nestlings better at maintaining their body temperatures during the acute challenge. Developmentally cold-exposed birds also had higher thyroxine (T4) levels when sampled at lower ambient temperatures, whereas control birds showed the opposite relationship. Among nestlings that failed to maintain their body temperature during the acute cold challenge, developmentally cold-exposed nestlings secreted more corticosterone during the acute cold challenge than control nestlings. Despite these changes, cold-exposed birds did not differ from controls in cold-induced metabolic rates, body mass, or bacteria killing ability. These results are, to our knowledge, the first to show that developmental cold exposure increases the capacity to maintain body temperature during future cold challenges in a songbird. These findings suggest that experiencing even a mild decline in ambient temperatures during embryonic development could prime birds to cope more effectively with harsh or variable environmental conditions later in life.

ecology↗

bioRxiv2025

Organismal robustness and resilience influence the ability to cope with cold snaps

Coping with challenges often requires maintaining performance during poor conditions (robustness) and reestablishing normal performance following disturbance (resilience). Trade-offs between performance under normal and challenging conditions may generate variation in stress coping capacity, but there is little empirical data from wild populations. We studied robustness and resilience to temperature in tree swallows (Tachycineta bicolor) using a 39-year dataset that included >75,000 hours of behavioral data. Cold snaps had profound and sustained impacts on fitness; effects on nestlings were mediated by the behavioral robustness and resilience of parents. Parental robustness was predicted by developmental cold exposure and current endocrine state. As expected, trade-offs between peak performance and behavioral robustness influenced susceptibility. Selection on trade-offs may generate population differences in vulnerability to changing temperature regimes.

ecology↗

bioRxiv2025

Divergent climate impacts despite similar response to temperature in a widespread aerial insectivore

Climate change is shifting when animals breed1,2, but it is still not clear why some populations keep pace with warming while others fall behind3,4. Differences could arise from variation in sensitivity to temperature3 or constraints on the ability to respond to temperature. Without knowing whether populations differ in sensitivity--or in their ability to act on that sensitivity--we cannot identify which are most at risk. Using 1,555 population-years from 123 populations of tree swallows (Tachycineta bicolor), we show that populations have similar sensitivity to local temperature, advancing breeding by about one day per degree of warming. However, northern populations face tighter time constraints and greater exposure to recent warming. Northern populations have advanced laying dates the most, but still experience stronger selection for earlier breeding, especially in warm years; they have also declined most in breeding abundance. These findings show that vulnerability to climate change can arise not just from different sensitivity to warming, but from when and where populations can respond effectively. By disentangling sensitivity from timing constraints, our results support a general mechanism by which even uniformly responsive species can show uneven impacts of climate change across their ranges.

ecology↗

bioRxiv2023

Inconsistent shifts in warming and temperature variability negatively impact avian fitness

Climate change can create challenging conditions for reproduction by creating mismatches between breeding activity, resource availability, and favorable weather. Phenological advancement may mitigate some of these effects, but it can also result in exposing developing offspring to greater temperature variability during reproduction. We combined >300,000 community science breeding records with data on historical temperature to understand how exposure to extreme climatic events (ECEs) has changed for 24 North American songbirds during breeding. More specifically, we wanted to understand if changes in average spring temperature were associated with when the latest cold-snap or earliest heat-wave occurred across the breeding range and the relationship to individual fitness. While average spring temperature increased universally across North America since 1950, the change in timing of ECEs was inconsistent in both direction and magnitude. Moreover, increase in average temperature did not predict the amount of change in average cold-snap and heat-wave timing. Thus, the current relationships between temperature and temperature variability differ from those experienced historically during breeding. After accounting for covariates, we found that 16 of 24 species had reduced reproductive success when a cold-snap occurred during the breeding attempt and 11 of 24 had reduced success when a heat-wave occurred. Four of the five aerial insectivores included showed marked sensitivity to ECEs, as did all the sallying insectivores. For three widespread species, we found evidence for latitudinal differences in susceptibility to temperature extremes. However, the pattern of sensitivity differed for each species, suggesting that life history details might play an important role in species responses to ECEs. Large-scale patterns and consequences of climate change on breeding birds ultimately result from the accumulated effects of individual susceptibility. Our results add to evidence demonstrating that understanding individual and species level sensitivity and linking them to population level processes is critical for predicting vulnerability to changing climates.

ecology↗

bioRxiv2022

Molecular early burst associated with the diversification of birds at the K-Pg boundary

Complex patterns of genome and life-history evolution associated with the end-Cretaceous (K- Pg) mass extinction event limit our understanding of the early evolutionary history of crown group birds [1-9]. Here, we assess molecular heterogeneity across living birds using a technique enabling inferred sequence substitution models to transition across the history of a clade [10]. Our approach identifies distinct and contrasting regimes of molecular evolution across exons, introns, untranslated regions, and mitochondrial genomes. Up to fifteen shifts in the mode of avian molecular evolution map to rapidly diversifying clades near the Cretaceous-Palaeogene boundary, demonstrating a burst of genomic disparity early in the evolutionary history of crown birds [11-13]. Using simulation and machine learning techniques, we show that shifts in developmental mode [14] or adult body mass [4] best explain transitions in the mode of nucleotide substitution. These patterns are related, in turn, to macroevolutionary shifts in the allometric scaling relationship between basal metabolic rate and body mass [15, 16]. In agreement with theoretical predictions, this scaling relationship appears to have weakened across the end-Cretaceous transition. Overall, our study provides evidence that the Chicxulub bolide impact [17] triggered integrated patterns of evolution across avian genomes, physiology, and life history that structured the evolutionary potential of modern birds.

evolutionary biology↗