Ronald & Ronny Bakowskie bastards. These include Phrynops geoffroanus × Mesoclemmys gibba and a hybrid Phrynops geoffroanus × Phrynops williamsi, which had been collected in Paraguay and thus was not of captive origin. Hybrids resulting from Phrynops geoffroanus mating with Phrynops hilarii were not mentioned by Fritz & Baur (1995), though. Distribution According to Vetter (2005), Phrynops geoffroanus is distributed from the southern parts of Venezuela via Colombia, parts of Brazil and Bolivia, to Uruguay and Argentina, in other words throughout a large part of northern South America. The distribution range of Phrynops hilarii, on the other hand, is much smaller, covering Uruguay, parts of Brazil, Paraguay and Argentina. This means that the ranges of both species overlap in southern Brazil, Paraguay and Argentina, possibly creating opportunities for natural hybridisation. However, we are not aware of hybrids between these two species having been reported from the wild. exhibits a few dark, obscure markings on a dirty yellow background. In Phrynops tuberosus (see the contribution by Stephan Böhm in the current issue), which was formerly regarded as a subspecies of Phrynops geoffroanus, the dots are more contrasting with a ground colour that may even be a shade of orange. In Phrynops hilarii, there are several dark dots on a “clean”, light background. Most noteworthy are the different markings covering the limbs and the head of juveniles of these two species. The upper half of the neck and head of Phrynops geoffroanus is almost black and shows lighter, symmetrical patches and spots in places. The dark upper portion borders the white lower half separated by a black stripe, with the lower half being marked Descriptions Juvenile Phrynops geoffroanus have a dark brown to black, flat carapace without any markings. In both Phrynops hilarii and the hybrids, the dorsal shell is altogether lighter, with a tendency towards light brown, sometimes olive colouration. In Phrynops hilarii and the hybrids, the marginals of the posterior portion lend the shell a slightly serrated appearance when viewed from above, whereas it appears entirely smooth-margined in Phrynops geoffroanus. The plastron of juvenile Phrynops geoffroanus Fig. 3. Phrynops hilarii, the plastron of the male. 70 RADIATA 17 (3), 2008
Hybrids of Phrynops geoffroanus and Phrynops hilarii with several black stripes along the neck. The snout region is also white. The mentioned black borderline splits into two in the temporal region, with one fork continuing through the eye and the other extending along the upper jaw, creating the likeness of a moustache. The limbs are also dark dorsally and greyish white below, with the transitional region appearing obscure. In Phrynops hilarii, on the other hand, the dorsal portions of head and neck are uniform greyish green and clearly separated from the white ventral parts by a narrow black stripe. This stripe runs via the temporal region through the otherwise yellowish green iris of the eye and thus takes a higher course than is the case with Phrynops geoffroanus. It is also more contrasting. The white portion of the neck is marked in an irregular manner with black dots of various sizes. Dots like these are also evident on the lower sides of the front and hind legs. The upper sides of the limbs are greyish green like the head and sharply delimited from the white ventral surfaces. The juveniles resulting from the accidental crossbreeding described here exhibit a mix of some of the above mentioned characteristics and have some that are unique to them. They resemble Phrynops hilarii with regard to their rather light brown colouration of the carapace and also show the serrated marginals of this parent (see above). They furthermore resemble this species more than the other in the separation of dark dorsal and light ventral colours on the limbs and head/neck, but the dorsal side of the head shows a pretty marbled pattern of black and greyish green elements. While the black temporal stripe also crosses through the iris, it is distinctly broader, less contrasting, and less sharply defined than in Phrynops hilarii. The dark spots on the white neck and the white portions of the limbs once more resemble the markings of Phrynops hilarii. The plastral pattern, on the other hand, is similar to that of Phrynops geoffroanus, but shows a greater contrast between the orange/light brown ground colour and the interlinked, irregular, dark markings than would be typical of Phrynops geoffroanus, and thus resembles that of Phrynops tuberosus (comp. Böhm 2008). In general the hybrids present themselves as much more agile and inquisitive than juveniles of Geoffroy’s side-necked turtle. They furthermore grow more rapidly than our offspring of Phrynops geoffroanus even though both are raised in the same manner. The hybrids hatched from the second clutch of the mentioned female in 2005 and are thus about half a year younger than their “pure-bred” half siblings. Nevertheless they are already larger and heavier than these at the time of this manuscript. As of May 2008, the largest hybrid juvenile weighs 780 g at a carapace length of 19.0 cm and is only insignificantly larger than its siblings. By comparison, the largest Phrynops geoffroanus juvenile measures 15.2 cm in carapace length and weighs a mere 390 g. Besides these differences in growth rates, it must be mentioned that the pure-bred Phrynops geoffroanus juveniles prove much more susceptible to shell necroses than their half siblings even though both are kept under identical conditions. While isolated necrotic patches on the carapaces have affected almost all baby Phrynops geoffroanus, none of the bastards have so far been affected. We were unable to include juveniles of Phrynops hilarii in a direct comparison here simply because we have as yet not managed to propagate this species and have no access to juveniles. Comparisons with Phrynops hilarii were therefore limited to evaluations of photographs taken of the babies bred by Stephan Böhm (comp. his paper in this issue). Conclusions In summary we can conclude that even very brief periods of time are sufficient to facilitate mating between these turtles; it is likely that this does not only apply to the two RADIATA 17 (3), 2008 71
