Journal of Herpetology, Vol. 38, No. 1, pp. 1–8, 2004 Copyright 2004 Society for the Study of Amphibians and Reptiles Cross-Breeding of Distinct Color Morphs of the Strawberry Poison Frog (Dendrobates pumilio) from the Bocas del Toro Archipelago, Panama 1,2,3 4 5 K. SUMMERS, T. W. CRONIN, AND T. KENNEDY 1Department of Biology, East Carolina University, Greenville, North Carolina 27858, USA 2Smithsonian Tropical Research Institute, Apartado 2072, Balboa, Republic of Panama 4Department of Biology, University of Maryland at Baltimore County, Hilltop Circle, Baltimore, Maryland 21250, USA 5Department of Biology, McGill University, Montreal, Quebec H3A 2K6, Canada ABSTRACT.—Populations ascribed to Dendrobates pumilio, the Strawberry Poison Frog, show extreme variation in color and color pattern among island and mainland locations in the Bocas del Toro Archipelago in Panama. Previous analyses indicate that these different populations are probably members of a single species. Here we present data on crosses between several different color and color pattern morphs. Successful crosses were made between different morphs from seven populations: Bocas Island, Nancy Cay, Pope Island, Bastimentos Island, and Almirante, Rambala and the Aguacate Peninsula on the mainland. The resulting offspring were characterized for color and color pattern. Our study indicates that different color morphs can interbreed to produce viable offspring. The offspring typically displayed a mixture of colors but always showed color pattern if one parent showed color pattern. This suggests that color pattern is under single locus control with dominance, whereas coloration may be under polygenic control, or may represent a single locus system with incomplete dominance. One of the most dramatic examples of color a preliminary investigation of the inheritance of and color pattern polymorphism within a puta- color and color pattern in these populations. tive single species occurs in the Bocas del Toro Color polymorphisms are found in many differ- Archipelago, in Panama (Daly and Myers, 1967; ent species of anurans (Hoffman and Blouin, Myers and Daly, 1983). Populations ascribed to 2000). Color in anurans typically results from Dendrobates pumilio, the Strawberry Poison Frog, pigments contained in chromatophores, whereas display extreme variation in color and color color pattern (hereafter referred to as ‘‘melanistic pattern among island and mainland locations in pattern’’) is usually caused by melanin contained this archipelago (Daly and Myers, 1967; Myers in melanophores (Hoffman and Blouin, 2000). and Daly, 1983). Recent analysis of the spectral The inheritance of color or melanistic pattern reflectances of individuals from different popu- (or both) has been investigated in a number of lations quantitatively documents the extent of the species of anurans (Hoffman and Blouin, 2000). divergence among these populations (Summers In most cases, evidence from single generation et al., 2003). In spite of these extreme differences crosses suggests that melanistic pattern is con- in color and color pattern among populations, trolled by simple Mendelian single-locus inher- evidence from both acoustic analysis of call itance (e.g., Lantz, 1947; Goin, 1960; Browder et similarity (Myers and Daly, 1976) and genetic al., 1966). Similar investigations of the inheri- analysis of DNA sequence similarity (Summers tance of color have been done in a smaller et al., 1997) suggests that the different popula- number of cases. In some studies, inheritance of tions are closely related and probably members color appears to be under single locus control of the same species. However, the most impor- with a dominant and recessive allele (e.g., tant criterion for determining species status Fogelman et al., 1980; Blouin, 1989), whereas in under the biological species concept is ability to other cases, multiple loci are involved (e.g., interbreed and produce viable offspring (Mayr, Mattews and Pettus, 1966). Multiple generation 1942). One goal of this study was to demonstrate studies using F2 or backcrosses (which are that different color and color pattern morphs can necessary to conclusively determine modes of interbreed and produce viable offspring. inheritance) have been done with only a few Another goal of this study was to make species (Hoffman and Blouin, 2000). Studies of the inheritance of color and mela- nistic pattern provide basic information impor- 3 Corresponding Author. E-mail: summersk@mail. tant to investigations of the evolutionary forces ecu.edu producing and maintaining color and melanistic 2 K. SUMMERS ET AL. pattern polymorphisms in anurans, which are PVC pipe, and then feed the tadpoles infertile currently poorly understood (Hoffman and eggs for approximately six weeks (Weygoldt, Blouin, 2000). Both the genetic control of color 1980; Brust, 1993). Some offspring were aban- and melanistic pattern, and the evolutionary doned by their mother, and we attempted to feed mechanisms that have generated the diversity of these tadpoles with chicken egg yolk and frogs color and melanistic pattern among populations eggs gathered from the field. However, none of of D. pumilio, are unknown. In fact, the genetic these tadpoles survived to metamorphosis. basis of color and melanistic pattern polymor- The six offspring that survived transport to the phisms in tropical frogs in general is poorly United States were taken to the University of understood, and relatively few studies have been Maryland at Baltimore County, and their spectral done on tropical species (Hoffman and Blouin, reflectance was measured. The spectral reflec- 2000). tance of a sample of adults from each of the Several of the different Bocas del Toro color populations used in the cross-breeding experi- morphs have been bred in captivity at the United ments was taken in Panama (before the pro- States National Aquarium in Baltimore. These duction of the offspring), to characterize the morphs breed true under uniform environments parental color morphs for each cross. Measure- (R. Gagliardo, pers. comm.), suggesting that ments of spectral reflectance were made with color and melanistic pattern are under genetic a portable spectrometer (Ocean Optics 2000), control. We used cross-breeding between differ- attached to a portable computer (BiLink), at the ent color and melanistic pattern morphs and STRI field laboratory on Bocas Island. Adult spectrometric analysis of color, to investigate the frogs in the laboratory were illuminated with inheritance of color and melanistic pattern in a single halogen lamp (250 watts). The spectrom- these populations. eter was calibrated before measuring each in- dividual, using a white diffuse reflectance MATERIALS AND METHODS standard (Spectralon). Measurements were taken Cross-breeding experiments were carried out with either a 50 lm 3 2 m or 400 lm 3 2 m optic at the Smithsonian Tropical Research Institute’s fiber. Three measurements in separate locations (STRI) research station on Bocas Island, Bocas del were taken from the dorsum of each frog, and Toro, Panama, and took place from 15 May to 7 three from the venter. The offspring from crosses September 2000. Adult frogs were caught in the were measured in the laboratory at the Univer- field in the Bocas del Toro Archipelago. Research sity of Maryland at Baltimore County, using the and collection permits were obtained from the same type of spectrometer used in the field, and Panamanian authorities (ANAM), via the Smith- ambient illumination. For both adults and off- sonian Tropical Research Institute, before the spring, the source of illumination provided onset of collecting. ample light across the full spectrum during all Frogs were caught by hand and kept in plastic reflectance measurements. bags until they were measured. The sex and population of the morphs used, the number of RESULTS pairs maintained, and the total number of The majority of pairs did not produce surviv- offspring produced are shown in Table 1. ing offspring, and only two pairs produced more Terrariums were set up at the Smithsonian than a single surviving offspring. Approximately Tropical Research Institute’s Bocas del Toro half of the offspring produced (i.e., observed as Research Station, on Bocas Island. Each of a total embryos or tadpoles) did not survive to meta- of 35 terraria was prepared for the cross-breeding morphosis. A total of 16 offspring survived experiments by placing a single pair of frogs from through metamorphosis during the four months distinct populations in the terrarium. Each of the study. Unfortunately, 10 of these juveniles terrarium was also provided with leaf litter, died in transit or as a result of stresses induced a bromeliad, a leafy plant, two pools of water during transport from Panama to the United (one in a plastic cup and one in a six-inch piece of States. Three juveniles died in the United States, PVC pipe), and a piece of bamboo as a hiding and three survived the juvenile period in place. The frogs were fed with fruit flies captivity. (Drosophila) grown in cultures or collected from Color was determined for the 16 juveniles that the field. Flies were coated with vitamin powder survived beyond metamorphosis (Table 1). The before being placed in the terrariums. Terrariums offspring showed distinctive color and pattern were misted with water daily to keep the even before metamorphosis. The color of juve- humidity level high. niles in the field appears identical to that of Eggs were laid on leaves (typically bromeliad adults, indicating that there is