Biology subjects

Ketterson, E.

Publications and source records attributed to Ketterson, E..

4 recordsLinked to original sources

bioRxiv2025

Male songbirds show higher coccidia oocyst burdens than femalesfollowing anthelmintic treatment

In wildlife research, wild-caught vertebrates are often given anti-parasitic drugs when brought into captivity to protect animal health and reduce confounding effects of parasitic infection on research outcomes. However, the impacts of antiparasitic drugs on non-target parasite taxa are understudied, especially regarding host sex. To help address this gap, we investigated the impact of an anthelmintic medication on a protozoan gut parasite by quantifying coccidia oocyst burden in the feces of wild-caught dark-eyed juncos (Junco hyemalis) before and after two oral doses of ivermectin. Prior to treatment, males showed higher oocyst burdens than females. Following treatment, ivermectin-treated males showed larger increases in oocyst burden compared to both control males and ivermectin-treated females, while there was no difference in baseline and post-treatment oocyst burden in treated females. Our results suggest that wild-caught songbirds should be housed separately by sex during ivermectin treatment and that male enclosures should be cleaned at a relatively higher frequency due to excessive oocyst shedding. It is unclear whether increases in oocyst burden among males were attributable to helminth removal or a direct impact of ivermectin on host immune function. Further work investigating sex differences in the impact of antiparasitic drugs on non-target parasite taxa is warranted.

ecology↗

bioRxiv2025

Fitness impacts of Plasmodium vary by host age and sex in a North American songbird

Birds infected with the malaria-causing parasite Plasmodium comprise a popular model in evolutionary ecology, yet Plasmodiums impact on host survival and reproduction remains unclear in wild bird populations where Plasmodium is historically endemic. Recent research in endemic host populations shows that Plasmodium reduces survival in juveniles, but not adults. Additional research is needed to understand 1) age-based variation in the impact of Plasmodium on host reproduction, and 2) sex-based variation in the impact of Plasmodium on survival and reproduction. To this end, we leveraged a long-term dataset from a dark-eyed junco (Junco hyemalis carolinensis) population with a high prevalence of Plasmodium. Juvenile males had lower probability of Plasmodium infection than juvenile females, indicating either elevated resistance or mortality in young males before the juvenile stage. Second year females had a lower probability of infection than females of other age classes, which suggests elevated mortality in infected yearling females after their first breeding season. Model comparison did not identify a direct relationship between Plasmodium infection and adult return (a proxy of survival), yet surprisingly, females paired with infected males in the previous breeding season had a higher probability of return. There was no relationship between Plasmodium infection and juvenile return, but returners with relatively higher parasite loads as juveniles had shorter lifespans than those without juvenile infections. Among adults, Plasmodium infection did not predict fledging success or fledgling number. However, returning juncos with relatively heavier bodies and higher parasite loads as juveniles had an increased probability of breeding in their first adult year. Combined with the shorter lifespans observed in infected juveniles, this suggests a terminal investment strategy for juncos contracting Plasmodium early in life. Our results indicate that the impact of Plasmodium on host fitness likely varies by host age at first infection and may exacerbate physiologically stressful life stages.

ecology↗

bioRxiv2018

A role for differential gene regulation in the rapid diversification of melanic plumage coloration in the dark-eyed junco (Junco hyemalis)

Color plays a prominent role in reproductive isolation, therefore understanding the proximal basis of pigmentation can provide insight into speciation. Subspecies of the dark-eyed junco (Junco hyemalis) have evolved marked differences in plumage coloration since the Last Glacial Maximum, yet whether color differences are caused by mutations in coding regions of expressed genes or are instead the result of regulatory differences remains unknown. To address this question, we studied the pigment composition and the genetic basis of coloration in two divergent subspecies, the slate-colored and Oregon juncos. We used HPLC and light microscopy to investigate pigment composition and deposition in feathers from four body areas. We then used RNAseq to compare the relative roles of differential gene expression in developing feathers and sequence divergence in transcribed loci under common garden conditions. Junco feathers differed in eumelanin and pheomelanin content and distribution. Within subspecies, in lighter feathers melanin synthesis genes were downregulated (including PMEL, TYR, TYRP1, OCA2, MLANA), ASIP was upregulated. Feathers from different body regions also showed differential expression of HOX and Wnt genes. Feathers from the same body regions that differed in color between the two subspecies showed differential expression of ASIP and three other genes (MFSD12, KCNJ13, HAND2) associated with pigmentation in other taxa. Sequence variation in the expressed genes was not related to color differences. Our findings support the hypothesis that differential regulation of a few genes can account for marked differences in coloration, a mechanism that may underlie the rapid diversification of juncos.

evolutionary biology↗

bioRxiv2017

The effect of chronic and acute stressors, and their interaction, on gonadal function: an experimental test during gonadal recrudescence

Organisms are expected to invest less in reproduction in response to a stressor, but theory predicts that this effect should depend on the frequency of stressors in the environment. Here we investigated how an acute stressor affected gonadal function in a songbird, and how long-term differences in the stress environment influenced these acute stress responses. We exposed male Dark-eyed Juncos (Junco hyemalis) either to chronic or minimal (control) disturbance during gonadal recrudescence, after which we measured baseline testosterone, testosterone after an acute handling stressor, and the ability to elevate testosterone in response to hormonal stimulation. In a 2x2 design, we then euthanized males from the two chronic treatment groups either immediately or after an acute stressor to investigate the effect of these treatments on the gonadal transcriptome. We found that chronically disturbed birds had marginally lower testosterone. The acute stressor suppressed testosterone in control birds, but not in the chronic disturbance group. The ability to elevate testosterone did not differ between the chronic treatments. Surprisingly, chronic disturbance had a weak effect on the testicular transcriptome, and did not affect transcriptomic response to the acute stressor. The acute stressor, on the other hand, upregulated cellular stress response, and affected expression of genes associated with hormonal stress-response. Overall, we show that both chronic and acute stressors affect reproductive function, and that chronic stress changes how acute stressors affect testosterone physiology. Our findings also suggest that acute and chronic stressors affect testes differently, and that gonadal function is relatively robust to long-term stressors.\n\nSummary statementAn acute stressor downregulated testosterone production, but this effect was absent in chronically disturbed birds. The acute stressor had a strong effect on the gonadal transcriptome, whereas chronic disturbance had a negligible effect.

physiology↗