Biology subjects

Hallman, T. A.

Publications and source records attributed to Hallman, T. A..

2 recordsLinked to original sources

bioRxiv2020

Duck, duck, goose: Benchmark bird surveys help quantify counting errors and bias in a citizen-science database

The growth of biodiversity data sets generated by citizen scientists continues to accelerate. The availability of such data has greatly expanded the scale of questions researchers can address. Yet, error, bias, and noise continue to be serious concerns for analysts, particularly when data being contributed to these giant online data sets are difficult to verify. Counts of birds contributed to eBird, the worlds largest biodiversity online database, present a potentially useful resource for tracking trends over time and space in species abundances. We quantified counting errors in a sample of 1406 eBird checklists by comparing numbers contributed by birders (N=246) who visited a popular birding location in Oregon, USA, with numbers generated by a professional ornithologist engaged in a long-term study creating benchmark (reference) measurements of daily waterbird counts. We focused on waterbirds, which are easily visible at this site. We evaluated potential predictors of count differences, including characteristics of contributed checklists, of each species, and of time of day and year. Count differences were biased toward undercounts, with more than 75% of counts being below the daily benchmark value. When only checklists that actually reported a species known to be present were included, median count errors were -29.1% (range: 0 to -42.8 %; N=20 species). Model sets revealed an important influence of each species reference count, which varied seasonally as waterbird numbers fluctuated, and of percent of species known to be present each day that were included on each checklist. That is, checklists indicating a more thorough survey of the species richness at the site also had, on average, lower counting errors. However, even on checklists with the most thorough species lists, counts were biased low and exceptionally variable in their accuracy. To improve utility of such bird count data, we suggest three strategies to pursue in the future. One is to assess additional options for analytically determining how to select checklists that have the highest probability of including less biased count data, as well as exploring options for correcting bias during the analysis stage. Another is to add options for users to provide additional information that helps analysts choose checklists, such as an option for users to tag checklists where they focused on obtaining accurate counts. We also recommend exploration of opportunities to effectively calibrate citizen-science bird count data by establishing a formalized network of marquis sites where dedicated observers regularly contribute carefully collected benchmark data.

ecology↗

bioRxiv2020

Isolating the role of corticosterone in the hypothalamic-pituitary-gonadal genomic stress response

The negative impacts of stress on reproduction have long been studied. A large focus of investigation has centered around the effects of the adrenal steroid hormone corticosterone (CORT) on a system of tissues vital for reproduction, the hypothalamus of the brain, the pituitary gland, and the gonads (the HPG axis). Investigations of the role of CORT on the HPG axis have predominated the stress and reproductive biology literature, potentially overshadowing other influential mediators. To gain a more complete understanding of how elevated CORT, characteristic of the stress response, affects the activity of the HPG axis, we experimentally examined its role at the level of the genome in both male and female rock doves (Columba livia). We exogenously administrated CORT to mimic circulating levels during the stress response, specifically 30 min of restraint stress, an experimental paradigm known to increase circulating corticosterone in vertebrates. We examined all changes in genomic transcription within the HPG axis as compared to both restraint-stressed birds and vehicle-injected controls, as well as between the sexes. We report causal and sex-specific effects of CORT on the HPG stress response at the level of the transcriptome. Restraint stress caused 1567 genes to uniquely differentially express while elevated circulating CORT was responsible for the differential expression of 304 genes. Only 108 genes in females and 8 in males differentially expressed in subjects who underwent restraint stress and those who were given exogenous CORT. In response to CORT elevation characteristic of the stress response, both sexes shared the differential expression of 5 genes, KCNJ5, CISH, PTGER3, CEBPD, and ZBTB16, all located in the pituitary. The known functions of these genes suggest potential influence of elevated CORT on immune function and prolactin synthesis. Gene expression unique to each sex indicated that elevated CORT affected more gene transcription in females than males (78 genes versus 3 genes, respectively). To our knowledge, this is the first study to isolate the role of CORT in HPG genomic transcription during a stress response. These results provide novel targets for new lines of further investigation and therapy development. We present an extensive and openly accessible view of the role corticosterone in the HPG genomic stress response, offering novel gene targets to inspire new lines of investigation of stress-induced reproductive dysfunction. Because the HPG system is well-conserved across vertebrates, these data have the potential to inspire new therapeutic strategies for reproductive dysregulation in multiple vertebrate systems, including our own.

physiology↗