Captive breeding, embryonic and larval development of Ranitomeya variabilis (Zimmermann & Zimmermann, 1988), (Anura, Dendrobatidae)

**Background:** Amphibians are the most threatened vertebrate group globally, and knowledge of their reproductive biology is critical for conservation. The genus Ranitomeya (poison dart frogs) includes small, brightly colored species with complex reproductive behaviors. Ranitomeya variabilis (Zimmermann's Poison Frog) has a disjunct distribution in eastern French Guiana/Brazil and western Peru/Ecuador, and its taxonomic status is under revision. Detailed developmental data are lacking for this species, which is listed as Data Deficient by the IUCN. This study aimed to describe embryonic and larval development of R. variabilis from French Guiana under captive conditions, providing growth measurements, staging, and captive-breeding observations.

**Methods:** Adult R. variabilis (5 females, 4 males) were obtained from the pet trade (captive-bred F2 from French Guiana) and housed at the LIB, Bonn, Germany. Species identity was confirmed by DNA barcoding (12s rRNA) and morphology. Frogs were kept in a terrarium (100×40×60 cm) with artificial daylight (12 h), misting, and natural and artificial phytotelmata (bromeliads, film containers). They were fed collembolans, fruit flies, and crickets enriched with vitamins/minerals. Clutches were removed and embryos kept individually in petri dishes in an environmental chamber (80% humidity, 24°C, 12-h photoperiod). After hatching, tadpoles were housed individually in containers with osmosis water, leaf litter, and plants, fed Repashy gel ad libitum. Development was staged using Gosner (1960) and categorized into embryo (stages 1–19), hatchling (20–25), larva (26–41), and metamorph (42–46). Photographs were taken daily (embryos) or twice weekly (later stages). Total length (TL) and surface area of silhouette were measured using ImageJ and SAISAQ software. Growth curves were fitted using local polynomial regression (Loess) with 95% confidence intervals.

**Key Results:** Thirteen embryos from four spawnings were obtained. Seven individuals were followed in detail; six completed metamorphosis. Survival to metamorphosis was 46% (6/13). Four tadpoles had limb malformations (thin limbs, missing digits) and died; two died as embryos. One individual developed slowly (117 days to stage 41, TL=24 mm) and died before forelimb emergence. For the six successful individuals, development from stage 8 to stage 46 took 79–91 days (mean 81.8±4.6 d). TL peaked at stage 40 (mean 32.0 mm, range 29–34 mm) at 58–65 days. Surface area peaked at stage 43 (mean 1.35 cm², range 1.13–1.56 cm²) at 69–72 days. TL and surface area were strongly correlated (R²=0.9441). Embryonic stages: At stage 8 (day 0), capsule diameter 2.2 mm; stage 19 (day 4), larval shape with heartbeat. Hatchling stages: Stage 20 (day 5), TL 7.66 mm; stage 25 (day 10–11), TL 14.61 mm, free-swimming at day 16. Larval stages: Stage 26 (day 21–25), TL 17.78 mm, hind limb buds visible; stage 41 (day 58–68), TL 31.7 mm, hind limbs complete. Metamorphic stages: Stage 42 (day 67–70), TL 31.0 mm, forelimbs emerge; stage 46 (day 79–91), TL 11.5 mm, tail resorbed. Deviations from Gosner (1960): labia/teeth differentiation occurred at stage 24 (one stage later), and oral apparatus atrophy began at stage 40 (one stage earlier) in two tadpoles. Compared to other Ranitomeya species, R. variabilis tadpoles were larger at given stages than R. amazonica (e.g., stage 26: 17.8 vs 15.5 mm; stage 41: 31.7 vs 27.7 mm) and larger than R. imitator, R. reticulata, R. sirensis, and R. vanzolinii at peak size, but smaller than R. benedicta. Development time was shorter than R. amazonica (81.8 vs 96 days).

**Clinical Implications:** This study provides the first comprehensive developmental staging for R. variabilis, facilitating identification of tadpoles in the wild and supporting taxonomic and biogeographic studies. The captive-breeding protocol (adapted from Klein et al. 2020) yielded 46% survival, which is considered satisfactory given that mortality rates up to 80% are reported for captive amphibians. The observed limb malformations may be related to Spiny Leg Syndrome, a common captive-breeding anomaly. The preference for bromeliads over artificial containers for egg deposition suggests that captive setups should prioritize natural phytotelmata. The larger size of French Guiana tadpoles compared to Peruvian conspecifics and other Ranitomeya species may be a population-specific trait, but caution is needed as captive conditions (constant temperature, ad libitum food) differ from natural environments. These data contribute to ex situ conservation programs and help clarify the species' distribution and taxonomy.