Ranitomeya sirensis ( Aichinger, 1991 )

Klein, Benjamin, Regnet, Ruth Anastasia, Krings, Markus & Rödder, Dennis, 2020, Larval development and morphology of six Neotropical poison-dart frogs of the genus Ranitomeya (Anura: Dendrobatidae) based on captive-raised specimens, Bonn zoological Bulletin 69 (2), pp. 191-223 : 214-216

Ranitomeya sirensis ( Aichinger, 1991)

Breeding behavior in captivity. The breeding pairs among the four specimens deposited clutches of up to two eggs in the bromeliad phytotelm. Reproduction occurred occasionally.

Larval morphology. The description is based on lateral and dorsal pictures of one specimen at stage 29. Thus, no voucher specimen is available. According to McDiarmid & Altig (1999), the tadpole belongs to the exotrophic, lentic, benthic and arboreal larval type. All measurements that were used to calculate the following proportions and its comparison with the other species of this study, can be found in Appendix III.

Dorsal view: Body shape is oval and slightly elongated (MBW/BL = 0.86). The snout is short and round (RED/ BL= 0.24, BWN/BWE = 0.88). Nares are oval in dorsal view. The eyes are large (ED/BL = 0.09), located dorsally and oriented dorsolaterally. Internarial distance in small- er than interorbital distance (IND/IOD = 0.48). Sinistral spiracle is clearly visible in dorsal view.

Lateral view: The body is depressed (MBH/ MBW= 0.71), the snout is moderately pointed. Nares are almost round. Sinistral spiracle is situated below the longitudinal axis, at the second half of the body (RSD/ BL= 0.53), oriented laterally with an elliptical opening, whereas the inner wall of the spiracle is free from the body wall. The maximum body height is situated posterior to the spiracle. The tail is long and broadly rounded (TAL/BL= 1.90, TAL/TL = 0.66). The tail musculature is well developed (TMH/MTH = 0.51), “V”-shaped myo- septa are visible at the first two thirds of the tail. Both fins are equal in height and originate at the tail body junction. The ventral tube is situated dextrally, the emergence from the abdomen is sagittal and the opening is oval. Hind- limb development is not completed (length ≥ 150% of the diameter). Upper and lower labia are clearly visible in lateral view.

Oral Apparatus: The oral disc is emarginated, elliptical, positioned ventrally and covers more than one third of the maximum body width (ODW/MBW= 0.39). Mar- ginal papillae are present at the posterior labium and at the outermost parts of the anterior labium. The anterior labium contains two tooth rows of the same width (A1, A2), with a large gap in the second row (A2-GAP). The posterior labium contains three tooth rows (P1, P2, P3), of which the first has a moderate medial gap (P1-GAP). The first two rows (P1, P2) have the same width, while the third one (P3) is slightly shorter. The tooth row formula is 2(2)/3(1).

Coloration of living tadpole of R. sirensis . The basic color is beige, densely coverered with dark dots. Two light blue spots anterior to the nares, fused medially ( Fig. 12A ). The first half of the dorsum is brighter than the second half, additionally slightly transparent below the longitudinal axis ( Fig. 12B ). Inner organs are visible in ventral and lateral view ( Fig. 12C ). The hindlimb buds are white, slightly pigmented at the base. The tail has the same coloration as the dorsum, the color density of the dark pigmentation wanes to the posterior end. The tip of the tail lacks any pigmentation. Fins are transparent and spotted with brown dots. The density of those dots decreases to the tip.

Larval staging. During the stages 25 to 27, before the hindlimb buds were clearly discernible, the larvae had a mean surface area of 0.29 ± 0.13 cm ² ( Table 11). After 24 to 39 days, half of the tadpoles reached stage 28 (median= 31 days). At this time, the hindlimb buds were almost equal in width and length and the surface area increased to 0.58 ± 0.11 cm ². In between the stages 29 to 40, the hindlimb development was completed and the larvae had a mean surface area of 0.86 ± 0.23 cm ². After 47 to 56 days, 50% of the individuals reached stage 41 (median = 52 days). The forelimb buds were perceptible and the tadpoles had a surface area of 1.15 ± 0.17 cm ². While the forelimbs grew inside the dorsum, the larval growth rate decreased. After 56 to 65 days, half of the tadpoles reached stage 42 and the forelimbs emerged through the body wall (median = 60 days). At this time, the tadpoles reached their peak of growth with a surface area of 1.20 ± 0.16 cm ². Afterwards, between day 60 and 71 (median = 63 days), the resorption of the tail was initiated. Close to the end of the metamorphosis, when the froglets had just a short remnant of the tail, the metamorphs had a surface area of 1.01 ± 0.16 cm ² ( Fig. 6 , Table 11).

The development was observed under constant conditions with a temperature of 24 °C, while the annual mean temperature within the natural distribution area of R. sirensis is slightly higher (T Mean = 24.7 °C, T Max = 29.1 °C, T Min = 18.8 °C: Karger et al. 2017a,b; Fig. 7 ).

Figures

Fig. 12. Illustrations of the tadpole of Ranitomeya sirensis, stage 29 of Gosner (1960). A. Frontolateral view. B. Lateral view. C. Ventral view. Photo credit: Morris Flecks.

Fig. 6. Developmental series of six Ranitomeya species during the transition from a hatchling to a froglet. The upper panel illustrates the increase of surface area over time, whereby the surface area [cm²] is highly correlated with the body mass. Warmer colors indicate a higher sample density; each circle represents one data point. Loess function represented by the red lines, whereby the outer lines display the 95% confidence interval. The lower panel illustrates the temporal occurrence of the following traits: 1=no limb bud discernible; 2=hindlimb bud discernible; 3=forelimb pouches discernible; 4=forelimbs emerged; 5=initiation of tail resorption.

Fig. 7. Climatic characteristics within the geographic ranges of six Ranitomeya species in terms of annual mean temperature, minimum and maximum temperature of the coldest / warmest month. Boxplots show the 95% range, lower and upper hinge enclosing 50% of the samples and the median based on a random sample per 10 km2.