Ranitomeya imitator ( Schulte, 1986 )

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 : 207-211

Ranitomeya imitator ( Schulte, 1986)

Breeding behavior in captivity. The single breeding pair deposited the clutches of one to two whitish to beige eggs directly in the bromeliad phytotelm or in a horizontally orientated film container, which was attached to the side wall of the terrarium, which was kept moist by the misting system. Reproduction did not obey a standardized way.

Larval morphology. Description of the tadpole is based on two specimens at stage 41 ( ZFMK 97358 ). Further voucher specimens are ZFMK 97364 , 97368 and 97377. According to McDiarmid & Altig (1999), the larvae belong 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: The body is shaped elliptically and slightly elongated (MBW/BL= 0.75). The snout is short, rounded and moderately pointed (RED/BL= 0.26, BWN/ BWE = 0.65). The shape of the nares is not visible in dorsal view. A skin fold, which originates at the nares, ends close to the anterior margin of the eyes; the two landmarks are not connected. Nares are located closer to the snout than to the eyes (RND/RED= 0.39). Eyes are large (ED/BL = 0.09), situated dorsally and orientated laterally. Internarial distance is smaller than the interorbital distance (IND/IOD = 0.46). The single sinistral spiracle is not visible in dorsal view.

Lateral view: Body is depressed (MBH/MBW = 0.73), snout is pointed. Nares are round, positioned and orientated dorsally. The spiracle is positioned below the longitudinal axis, at the posterior part of the body (RSD/ BL = 0.56), the inner wall is free from the body and the opening is round, spiracle tube is short. The maximum body height is situated between the eyes and the tail-body junction. The tail is long and the tip is broadly round- ed (TAL/BL= 1.83, TAL/TL = 0.65). The musculature is well developed (TMH/MTH = 0.49; TMW/MBW = 0.34). The “V”- shaped myosepta are visible along the whole length of the tail, particularly in the first half. The up- per fin originates anterior, the lower posterior to the tail-body junction. Upper fin is slightly higher than lower fin. Ventral tube partially absorbed, dextral; emergence from the abdomen sagittal, the opening is triangular and has smooth edges. Hindlimb development is completed. Parts of the oral apparatus are visible in lateral view, particularly the margins.

Oral apparatus: The oral disc is shaped elliptically, positioned ventrally, emarginated and covers almost one third of the body width (ODW/MBW= 0.31). Two rows of marginal, ensiform, rounded and transparent papillae are present at the posterior labium (around 20 papillae) and except one short row at the most lateral part, absent at the anterior labium (three to five papillae). Submargin- al papillae are absent. The anterior labium contains two tooth rows of equal width (A1, A2) with a large medial gap in the second row (A2-GAP). The posterior labium contains three tooth rows (P1, P2, P3) with a moderate medial gap in the first tooth row (P1-GAP). Black jaw sheaths, both serrated. Upper jaw sheath is wider than the lower jaw sheath. Lateral processes are present, extending slightly past the lower jaw. Tooth row formula is 2(2)/3(1) ( Fig. 9D ).

Coloration of a living tadpole of R. imitator (ZFMK 97358). The basic color of the dorsum is beige, heavily covered with puce to black dots. Additionally, the first half of the body is strongly dotted with yellowish green spots, which are able to reflect the light and become gold- en yellow, while the second half is almost completely covered with black dots, except some single yellowish green spots. The hindlimbs are beige with dark spots. The

tail is dun and spotted with puce dots; the second half is brighter than the first one. Fins are transparent and spot- ted with beige dots.

Coloration of a preserved tadpole of R. imitator (ZFMK 97358). Dorsum is beige, densely spotted with gray dots, with some brighter areas at the forelimb pouches and the muscle structures at the tail-body junction. The hindlimbs and the tail are of the same color as the dorsum, spotted with gray dots. While the dots on the hindlimbs are evenly distributed along their length, the

pigmentation of the tail decreases towards the tip. The fins are transparent and spotted with gray dots. The ven- tral side is beige and spotted with gray dots, while the concentration of that pigmentation increases to the tail-body junction.

Larval staging. One egg with a diameter of around 1.2 mm was found within a bromeliad phytotelm, where it swam beneath the water surface. At this time, it was not pigmented, had a transparent egg integument and was encompassed by a highly glutinous layer ( Fig. 10A ).

n = 1 Day Stage Traits

After one day it reached stage 9, the coloration became paler and the number of discernible cells increased ( Table 6). At day three the egg reached stage 11 and the yolk plug was visible, followed by the neural fold at day four ( Fig. 10B ). A large yolk sack was discernible and the embryonic body assumed a larval shape at stage 19 ( Fig. 10D ). Thus, the head and tail region became visible and the gill buds were present. After six days of development the gills were discernible and the tail underwent several changes. The upper and lower tail fins together with the myosepta were slightly visible, while the whole tail was elongated ( Fig. 10E ). That elongation went on until day eight, as the hatchling reached stage 22.

The tail was pointed, the overall body size and the area of the gills increased, whereby the yolk sack atrophied. The pigmentation of the body and tail region became denser; the tail fins more transparent ( Fig. 10F ). At day nine, the hatchling was still at stage 22. The tail fins were higher, the nares discernible and the yolk sack was covered with blood vessels. When the larva reached stage 23, the transparent tail fins were spotted with beige dots, the oral apparatus was clearly visible and the yolk sack was almost completely atrophied. During day eleven and twelve, at stage 24, the dextral gill was reduced while the sinistral gill was still present ( Fig. 10G ). Additionally, the pigmentation of the body and tail region became denser and the anterior and posterior labia together with the papillae were discernible. At stage 25, both gills were absent while the sinistral spiracle was present. After 16 days of development the tadpole hatched from the jelly layer and swam free in the water body ( Fig. 10H ). At this time it had a surface area of 0.22 cm ² ( Table 7).

Between stages 25 to 27, where the hindlimb bud was slightly discernible, the larvae had a surface area of 0.39 ± 0.12 cm ² ( Table 7). After 24 to 43 days (median = 34 days), half of all individuals had a hindlimb bud that was equally in width and length and a surface area of 0.69 ± 0.11 cm ² ( Table 7). Between stages 28 to 40, the tadpoles had a surface area of 0.89 ± 0.16 cm ². During this development period, the hindlimbs grew, all toes became separated and the typical dorsal color pattern was discernible. After 48 to 53 days (median = 51 days), 50% of the tadpoles reached stage 41, with a surface area of 1.11 ± 0.04 cm ². The forelimb buds were clearly perceptible and the hindlimbs displayed their typical reticulated col- or pattern. The forelimbs emerged after around 63 days, while the larvae reached their peak of growth with a surface area of 1.20 ± 0.17 cm ², followed by the resorption of the tail after 67 days. During the transition to a young froglet, the surface area decreased to a mean value of 1.03 ± 0.10 cm ² ( Fig. 6 , Table 7). A more detailed staging table based on stereomicroscopic determinations of four specimens between stages 25 to 37 can be found within Table 8.

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. imitator is slightly higher (T Mean = 25.5 °C, T Max = 29.2 °C, T Min = 21.1 °C: Karger et al. 2017a,b; Fig. 7 ).

Figures

Fig. 9. Illustrations of the tadpole of Ranitomeya imitator, stage 41 of Gosner (1960). A1. Dorsal view, photograph. A2. Dorsal view, drawing.B1. Ventral view, photograph.B2. Ventral view, drawing. C1. Lateral view, photograph. C1. Lateral view, drawing. D. Drawing of the oral disc. LTRF = 2(2)/3(1).

Fig. 10. Embryos and hatchlings of Ranitomeya imitator. A. Isolated egg at stage 8. B. Embryo at stage 14–15. C. Embryo at stage 16–17. D. Embryo at stage 19. E. Embryo at stage 20. F. Hatchling at stage 21. G. Hatchling at stage 24. H. Free swimming larva at stage 25–26. Picture C is from a different clutch.

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.