Nature Made This Frog Fluorescent, And It’s One Of A Kind
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The present study adds to the growing list of documented cases of fluorescence in terrestrial animals. Bone fluorescence within the Brachycephalus genus appears to be associated with the loss of high-frequency hearing, raising the possibility that it represents an alternate communication channel. However, data are not available from enough species to be sure that this correlation is robust, and the functions of these fluorescent patterns remain speculative. Thorough in situ light spectra measurements and behavioural studies are needed in order to determine whether conspecifics and/or potential predators respond to fluorescent patterns in Brachycephalus toadlets, and in what way. The biochemical nature of this fluorescence remains to be investigated.
Combined with rapid extracellular perfusion and UV-flash photolysis of caged compounds, measurement of ICa variations was also used to estimate and compare the time course of [cAMP]i changes upon a sudden application of different cAMP-elevating agents. For instance, in guinea-pig (Yatani & Brown, 1989) and frog ventricular myocytes (Frace et al. 1993), the stimulatory effect of FSK on ICa develops with a 2- to 3-fold slower time scale than the effect of ISO at doses that are equipotent in their effects on ICa. While this difference was attributed to different kinetics in [cAMP]i changes (Jurevicius & Fischmeister, 1996), it could also result from some concomitant inhibitory effects of FSK on ICa (Boutjdir et al. 1990; Asai et al. 1996) or from the presence of an additional activatory mechanism in β-adrenergic stimulation such as a priming effect of the G protein Gs on PKA phosphorylation of the Ca2+ channel (Cavaliéet al. 1991). Clearly, the indirect assay of [cAMP]i changes via the measurement of ICa has reached its limits in trying to distinguish between these hypotheses. For this and many other applications, a direct assessment of [cAMP]i in an intact isolated cardiac myocyte is required. However, to our knowledge, this has not been technically feasible until now.
Here, we developed a novel approach which combines electrophysiological measurement of ICa and simultaneous detection of [cAMP]i changes by the fluorescent probe FlCRhR in intact single frog ventricular myocytes. While this probe has already been used in several non-excitable cells (Adams et al. 1991) and in giant invertebrate neurones (Bacskai et al. 1993; Hempel et al. 1996), it has never been used in native excitable vertebrate cells. Combined measurements of [cAMP]i and ICa allowed us to compare the time course of the responses of these parameters to a challenge of the myocyte with ISO or FSK.
Since FlCRhR is made of active PKA, we first examined whether intracellular dialysis with FlCRhR generated spontaneous PKA enzymatic activity which could possibly affect ICa. In the absence of FlCRhR in the patch pipette, application of the non-selective β-adrenergic agonist isoprenaline (ISO, 1 μm) strongly increased ICa. When the cell was exposed only briefly (10 s) to ISO, the stimulation of ICa was transient and the current returned to a basal level within 20 min (Fig. 1A and C). Pressure ejection of FlCRhR at the tip of the patch pipette led to diffusion of the probe in the cytosol, as evidenced by the increase in fluorescence intensity (Fig. 1B). Following FlCRhR ejection, a clear increase in ICa was observed (Fig. 1A and C). However, this rise in ICa did not prevent a second response of ICa to ISO (Fig. 1A and C), although its amplitude was somewhat diminished.
The Cuban treefrog, Osteopilus septentrionalis (Figure 1), is native to Cuba, the Isle of Youth (an island province of Cuba also known as Isle of Pines), the Cayman Islands, and the Bahamas. It is an introduced species in Florida, and the earliest confirmed records date to the 1920s in the Florida Keys. The first Cuban treefrogs in Florida likely arrived as stowaways in shipping crates originating from the Caribbean. By the mid-1970s, they had dispersed throughout most of southern Florida. As of 2017, there are established breeding populations as far north as Cedar Key on Florida's Gulf Coast, Jacksonville on the Atlantic Coast, and Gainesville in north-central Florida (Figure 2). This species certainly has the potential to expand its range in Florida and the Southeast, and isolated individuals have been documented in coastal South Carolina, Georgia, Alabama, Mississippi, Lousiana, and Texas. The number of reports of Cuban treefrogs from the Florida panhandle continue to increase, and this invasive frog may already have small populations established in this region of the state. Cuban treefrogs spread by hitchhiking on ornamental plants, motorized vehicles, boats, etc. The Cuban treefrog is considered an invasive species in Florida.
The ultimate distribution of Cuban treefrogs in Florida and the southeastern United States will likely be dictated by climate. A scientific paper published by German biologists in 2009 suggested that human-caused climate change may create conditions suitable for Cuban treefrog colonization and breeding and allow this frog to become established across much of the southeastern US. An unusually long period of cold temperatures in January of 2010 appears to have killed many Cuban treefrogs in peninsular Florida, but the population decline was only a temporary setback for this invasive frog. Cuban treefrog populations have rebounded throughout the peninsula and are likely to continue to expand their range into Florida's panhandle and beyond.
Several of Florida's native treefrogs superficially resemble Cuban treefrogs. These frogs, like Cuban treefrogs, also show considerable variation in colors and markings, but generally are smaller and have smaller eyes. Therefore, it can be difficult to distinguish native treefrogs from invasive Cuban treefrogs. However, there are ways to confidently identify all of Florida's treefrogs, and with a little bit of practice anyone can tell them apart. The three native species most likely to be found with Cuban treefrogs are the squirrel treefrog, barking treefrog, and Cope's gray treefrog. Adult squirrel treefrogs are small, and only grow to 1.5 inches. Their color varies a lot, and they may be bright green, dull green, grayish, or brown. They may or may not have a pattern on their back, but their skin is smooth and lacks warts. Barking treefrogs are much bigger and plump, growing to 2.5 inches long. Their overall color varies from yellowish-green, to dark green, to brown. On rare occasions they have a lot of white or their backs. They almost always have numerous round spots on their back and a white upper lip. Their back skin lacks distinct warts, but appears granular or slightly rough. Cope's gray treefrogs closely resemble Cuban treefrogs; both have a yellow-colored wash in their groin and armpits, and both have warts on their back. They also often have obvious, dark wavy bands on their back and sides. The best way to identify a Cope's gray treefrog is by the light-colored blotch below each eye. For details and images of Florida's treefrogs, and to learn how to differentiate them, please visit the UF/IFAS Wildlife website at and follow the "Florida Frogs" link in the left hand column. Also visit the websites listed at the end of this document to find additional digital images of Cuban and native treefrogs.
Male Cuban treefrogs have a fairly distinct call that sounds like a squeaking door and has also been described as a "snoring rasp". Visit the websites listed at the end of this document to find links to recordings of Cuban treefrog calls. In addition to their breeding calls, individual males will also call from daytime retreat sites to advertise their presence. This "rain call," as it is sometimes called, can be triggered by light rainfall during the day.
An invasive species is generally defined as a plant, animal, or microbe that is found outside of its native range, where it negatively impacts the ecology, economy, or quality of human life. Cuban treefrogs fit this definition of an invasive species because they were introduced to Florida by the activities of people and they are causing harm to Florida's natural ecosystems and the quality of life of Floridians. They are also causing economic impacts in some places.
Cuban treefrogs are having negative impacts on Florida's native species and ecosystems. Although they predominately occur around human development, such as urban neighborhoods, Cuban treefrogs are also able to invade natural areas. In both natural and urbanized settings, Cuban treefrogs are known predators of Florida's native treefrogs (Figure 4) and appear to be responsible for declines of some native treefrog species. They also are known to eat several additional species of native frogs, lizards, and many types of invertebrates. Many homeowners in Florida report that Cuban treefrogs appear to have replaced native treefrogs as the dominant frog found around their homes. These same people say that they no longer see native species, such as squirrel treefrogs or green treefrogs, but only Cuban treefrogs. Furthermore, lab experiments (conducted by herpetologist Dr. Kevin Smith) have shown that Cuban treefrog tadpoles are superior competitors with at least two species of native frog tadpoles. Tadpoles of the invasive Cuban treefrog inhibited the growth and development of native southern toad and green treefrog tadpoles. Additional experiments by ecologist Dr. Michael Knight and colleagues showed that survivorship of native squirrel treefrog tadpoles declined significantly in the presence of Cuban treefrog tadpoles. As scientists continue to conduct research on the ecological impacts of Cuban treefrogs, we will develop a better understanding of the effects that this invasive frog is having on Florida's environment.
Unlike many invasive insect pests and invasive plants, Cuban treefrogs do not currently appear to be having any large-scale negative effects on Florida's economy. Nonetheless, they are known to get into transformer boxes and electrical switches (Figure 7) and occasionally cause short-circuits. This increases maintenance costs for electrical utility companies, and power to some customers in central Florida has been interrupted as a result of short-circuits in disconnect switches caused by Cuban treefrogs. They may also invade electric water pump housings and AC compressor units around residential homes, potentially causing damage. As Cuban treefrog populations continue to expand, this may eventually become a large-scale issue. 2b1af7f3a8