Biology subjects

Safran, R. J.

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

6 recordsLinked to original sources

bioRxiv2025

The effects of temperature on nestling growth in a songbird depend on developmental and social context

Climate change can adversely impact animals, especially those that cannot independently thermoregulate or avoid exposure. Cold, hot, and variable temperatures may impede nestling songbird growth due to increased thermoregulatory costs and reduced food delivery by parents. At a broad scale, temperature effects on nestling growth vary across climatic zones, but how temperature effects vary with early-life developmental constraints imposed by the timing of thermoregulatory development, competition with siblings, and the amount of parental care has received less attention. We investigated whether the effect of temperature on the mass of wild barn swallow (Hirundo rustica erythrogaster) nestlings (n = 113 nestlings, 31 nests) in Boulder County, CO depends on timing of exposure during development, relative size within the brood, or level of parental feeding. We found that the effect of minimum temperature differed in early and late development (before versus after putative development of thermoregulatory independence) and may be less pronounced for nestlings that received more parental feeding. We did not find evidence that the smallest nestling in the brood differs from other nestlings in vulnerability to temperature. These findings indicate the existence of fine-scale heterogeneity in which the effects of temperature on nestling development are sensitive to metabolic constraints and early-life social environment, providing key insight into the factors that may ameliorate or exacerbate climate impacts on individual birds.

ecology↗

bioRxiv2025

Testing the mediating role of female-male social interactions on the relationship between age and reproductive success.

Differential reproduction is a key driver of evolution that is determined by individual characteristics and mating opportunities, including mate choice. Social interactions between conspecifics are hypothesized to be important in facilitating mate choice and reproductive success but are difficult to measure. Using data from 52 adult barn swallows (Hirundo rustica erythrogaster), whose social interactions were measured via proximity tags, we tested the hypothesis that social interactions mediate the relationship between age (a proxy for experience) and condition-dependent plumage traits, and their associations with reproductive success. We found that older female barn swallows had higher fecundity and that older males have higher paternity. Older males achieved higher paternity through extra pair copulations, not by greater paternity with their social mate. Longer tail streamers were associated with greater fecundity/paternity in both sexes, but this effect was independent of age only among females. Darker ventral plumage coloration was not associated with higher reproductive success in either sex. We also observed that older birds appear to be less social with conspecifics, as indicated by fewer numbers of social interactions, though these associations were only marginally significant in males. Interestingly, females with fewer social interactions had higher fecundity. Finally, we found no evidence of mediation by the number of social interactions. Taken together, our results suggest that older, more experienced birds can produce more offspring while being less social.

animal behavior and cognition↗

bioRxiv2024

Parental care modifies the role of early-life size and growth in shaping future physiology

Size and growth early in life are associated with physiological development and these traits influence fitness. Life history theory predicts that the relationship between traits reflect constraints involving allocation and acquisition of resources. Using longitudinal data from 113 wild nestling barn swallows (Hirundo rustica erythrogaster), we first characterized developmental changes in glucose metabolism, a physiological trait involved in energy mobilization and response to stress. Next, we used these data to test hypotheses from life history theory about allocation and acquisition of resources based on associations of nestling size and growth with glucose physiology and assessed whether these relationships are modified by parental care. We found that larger nestlings had higher baseline blood glucose and larger magnitude of change in glucose in response to a stressor. Further, this relationship was most pronounced among birds in nests that received the lowest amount of parental care. Given that glucose metabolism fuels activity and is critical in the vertebrate stress response, these results suggest that physiological constraints may contribute to the early-life disadvantage of being smaller, especially in the context of lower parental care. While these findings are inconsistent with a trade-off involving differential allocation of resources between life history traits, they align with the differential acquisition hypothesis.

evolutionary biology↗

bioRxiv2022

An Experimental Analysis of the Fine-Scale Effects of Nest Ectoparasites on Incubation Behavior

Avian incubation is a highly complex, adjustable behavior essential to embryo development and survival. When incubating, parents face a tradeoff between investing in incubation to maintain optimal temperatures for egg development or in self-maintenance behaviors to ensure their own survival and future reproduction. Because nest ectoparasites are costly and can reduce nestling quality and survival, infections could shift parental investment in current vs. future offspring. However, it is not well understood whether birds change investment in incubation in response to nest ectoparasitism, particularly in the context of other factors that are known to influence incubation behavior, such as ambient temperature, clutch size, and embryo development. We hypothesized that parents could respond to nest parasites by 1) investing more in incubation to promote the development of high-quality offspring to help offset the cost of parasites, 2) investing less in incubation or even abandoning their nest during incubation to save resources for future reproduction, or 3) being unresponsive to parasite infections, as incubation is more constrained by other factors. We tested these hypotheses by experimentally removing and adding mites in barn swallow nests at the start of incubation and deploying thermocouple eggs to measure egg temperatures at one-minute intervals until hatching. We found that while ambient temperature, clutch initiation date, embryo age, and clutch size were the main factors driving variation in egg conditions and parental incubation behavior, parasitized nests had higher mean egg temperatures, which could aid in nestling immune development. However, despite more optimal developmental temperatures, eggs in parasitized nests also had lower hatching success. Our results indicate that incubation is a dynamic behavior that is largely driven by the constraints of maintaining appropriate egg temperatures for development. Although quite costly upon hatching, ectoparasites appear to play a relatively minor role in driving variation in parental incubation investment. LAY SUMMARYO_LIIncubation is a complex behavior shaped by both internal and external factors. C_LIO_LIEctoparasites often decrease quality and survival of nestlings and could influence investment in incubation because of tradeoffs in how parents spend energy. C_LIO_LIWe manipulated parasites in barn swallow nests and used fake eggs with temperature sensors to collect data on egg temperatures and parental behavior throughout incubation. C_LIO_LIWe found that other factors were the main drivers of variation in incubation behavior, but that eggs in parasite nests were warmer on average, which could help nestlings better cope with parasites upon hatching. C_LIO_LIDespite more optimal developmental temperatures, eggs in parasitized nests had lower hatching success. C_LIO_LIAlthough quite costly to nestlings, ectoparasites played a minor role in shaping parental incubation behavior. C_LI

animal behavior and cognition↗

bioRxiv2020

Analysis of female song provides insight into the evolution of dimorphism in a widely studied songbird

ABSTRACTUnderstanding the patterns and processes related to sexual dimorphism and sex differences in diverse animal taxa is a foundational research topic in ecology and evolution. Within the realm of animal communication, studies have traditionally focused on male signals, assuming that female choice and male-male competition have promoted sex differences via elaboration of male traits, but selection on females also has the potential to drive sexual differentiation in signals. Here, we describe female song in barn swallows (Hirundo rustica erythrogaster) for the first time, report rates of female song production, and couple song data with plumage data to explore the relative degree to which sex differences in phenotypic traits are consistent with contemporary selection on males versus females. During previous intensive study of male song over two years, we opportunistically recorded songs for 15 females, with matched phenotypic and fitness data. We randomly selected 15 high-quality samples from our larger male dataset to test whether sex differences in song and plumage are more strongly associated with fledgling success for females or genetic paternity for males. Analyses included 35 potential sexual signals including 22 song parameters and 13 plumage traits. Outcomes indicate that: female songs were used in multiple contexts, restricted primarily to the beginning of the breeding season; song traits showed greater sexual differentiation than visual plumage traits; and trait correlations with reproductive success in females, rather than males, predicted sex-based differences in song and plumage. These results are consistent with phylogenetic studies showing that sex-based phenotypic differences are driven by changes in females, highlighting the potential role of female trait evolution in explaining patterns of sexual differentiation. To achieve a better understanding of sex differences and dimorphism, we require comprehensive studies that measure the same traits in males and females and their fitness consequences.Competing Interest StatementThe authors have declared no competing interest.View Full Text

animal behavior and cognition↗

bioRxiv2019

Migratory divides coincide with species barriers across replicated avian hybrid zones above the Tibetan Plateau

Migratory divides are proposed to be catalysts for speciation across a diversity of taxa. However, the relative contribution of migratory behavior to reproductive isolation is difficult to test. Comparing reproductive isolation in hybrid zones with and without migratory divides offers a rare opportunity to directly examine the contribution of divergent migratory behavior to reproductive barriers. We show that across replicate sampling transects of two pairs of barn swallow (Hirundo rustica) subspecies, strong reproductive isolation coincided with an apparent migratory divide spanning 20 degrees of latitude. A third subspecies pair exhibited no evidence for a migratory divide and hybridized extensively. Within migratory divides, migratory phenotype was associated with assortative mating, implicating a central contribution of divergent migratory behavior to reproductive barriers. The remarkable geographic coincidence between migratory divides and genetic breaks supports a longstanding hypothesis that the Tibetan Plateau is a substantial barrier contributing to the diversity of Siberian avifauna.

evolutionary biology↗