Hair type, intake, and detection method influence Rhodamine B detectability

Abstract

Rhodamine B (RB) is a popular bait-marking tool in wildlife research, although its use has required many assumptions about marking reliability. These assumptions have limited dosage ranges and detection methods in research applications. Identification of alternate detection methods, hair types, and dosage rates could create new opportunities for RB use and potentially reduce adverse effects on target animals. We examined the relationship between hair types, dosage rate, and detection method for RB applications using black rats (Rattus rattus) in laboratory settings. We gave study animals varying doses of RB, and examined vibrissae and guard hairs for the detection of RB bands using ambient light, ultraviolet (UV) light, and fluorescence microscopy techniques. Fluorescence microscopy detected more RB marked hairs than UV light or ambient light. Fluorescence microscopy was more sensitive to RB dose rate detection; with receiver operating characteristic curves suggesting that the minimum dose rates at which RB intake can be correctly detected are 3.9 and 33 mg/kg for vibrissae and guard hairs, respectively. Guard hair RB detection was less reliable under ambient light and UV lamps, but equally detectable as vibrissae under fluorescence microscopy. Our results confirmed the interrelationship between dosage and detection methods in the efficacy of bait markers. We demonstrated that guard hairs can be a reliable hair type for the detection of RB. This application is less invasive than sampling animal tissues to detect bait uptake. ß 2012 The Wildlife Society.

Tracking invasive rat movements with a systemic biomarker

“…This finding is consistent with laboratory rat trials by Purdey et al (2003) (R. norvegicus) and Weerakoon et al (2013) (R. rattus) in which 50% and 51% (respectively) of sampled vibrissae tested positive for RB under fluorescence microscopy. These percentages reflect the fact that not all vibrissae are growing at the same time and rate thus not incorporating the RB in the hair shaft (Purdey et al 2003).…”

“…Upon ingestion, RB can stain a variety of tissues and excretory products, including the gastrointestinal (GI) tract, systemic and internal tissues (Weerakoon et al 2013). RB can be detected as a maroon colour in ambient light and bright orange under ultraviolet (UV) light in hair and gut (Weerakoon et al 2013), with keratinous tissue (hair) staining having superior persistence compared with gut and excreta staining (Fisher 1999). Fluorescence microscopy techniques have shown higher sensitivity, detecting smaller doses of RB in hair than detected under ambient or UV light (Fisher 1999;Weerakoon et al 2013).…”

“…RB can be detected as a maroon colour in ambient light and bright orange under ultraviolet (UV) light in hair and gut (Weerakoon et al 2013), with keratinous tissue (hair) staining having superior persistence compared with gut and excreta staining (Fisher 1999). Fluorescence microscopy techniques have shown higher sensitivity, detecting smaller doses of RB in hair than detected under ambient or UV light (Fisher 1999;Weerakoon et al 2013). Vibrissae (whiskers) are useful because they are highly vascularised, thus exposed to circulating RB, and they have a shorter resting phase than other hair types which allows RB marking to grow out of the bulb, facilitating detection (Purdey et al 2003;Weerakoon et al 2013).…”

“…Fluorescence microscopy techniques have shown higher sensitivity, detecting smaller doses of RB in hair than detected under ambient or UV light (Fisher 1999;Weerakoon et al 2013). Vibrissae (whiskers) are useful because they are highly vascularised, thus exposed to circulating RB, and they have a shorter resting phase than other hair types which allows RB marking to grow out of the bulb, facilitating detection (Purdey et al 2003;Weerakoon et al 2013). RB marking is seen as a bright, orange fluorescent band or series of bands along the shaft of the whisker (Fisher 1999;Purdey et al 2003).…”

“…RB marking is seen as a bright, orange fluorescent band or series of bands along the shaft of the whisker (Fisher 1999;Purdey et al 2003). Persistence of RB in the animal's system depends on the dose, species, size and tissue marked (Weerakoon et al 2013). In small mammals comparable to rats, a dose over 15mg/kg has been shown to persist in vibrissae at least 10 weeks post-ingestion (Fisher 1999).…”