Effects of two different incubation media on hatching success, body mass, and length in Caiman latirostris

Since 1990, Proyecto Yacaré (Min. Prod./MUPCN) is developing new technologies and improving/adapting old ones to reduce the production costs for the ranching programs in South America. Previous work evaluated growth rates of Caiman latirostris, the effect of time of collection on hatching success, depredation and temperature effects on incubation, but there is no information about incubation media for the species. In this experiment, we test the effects of two incubation media, vermiculite and grasses ('nesting material'), on hatching success, and hatchling size. We collected nine nests (350 eggs) from natural C. latirostris populations in Santa Fe, Argentina soon after oviposition. In Proyecto Yacaré facilities, each nest was divided in two groups and each one received one of two incubation treatments (vermiculite or nesting material as incubation media). We found no difference in hatching success among the treatments (89% for vermiculite and 87% for nesting material). We observed, but did not measure, that incubation with vermiculite tended to be longer and that hatchlings from this treatment had more unabsorbed abdominal yolk in all the nests used in the experiment. Hatchlings from nesting material treatment were longer (p<0.001) than those incubated in vermiculite, but we found no differences between treatments in body mass. As we found similar hatching success in both treatments (but possibly overestimated in vermiculite), a larger size of hatchlings (which could enhance survivorship as was reported in lizards and turtles) and lower cost, we consider that there is no advantage to the use of vermiculite over nesting material. We recommended nesting material (natural grasses) as incubation media. Future investigations should address how incubation media might modify hatchling performance.