CROCODYLUS INTERMEDIUS (Orinoco Crocodile). HATCHING SYNCHRONY.

RAFEL ANTELO; PABLO SIROSKI

HERPETOLOGICAL REVIEW

SOCIETY FOR THE STUDY OF AMPHIBIANS AND REPTILES

Lugar: Califormia; Año: 2020 vol. 51

0018-084X

The Orinoco Crocodile is critically endangered throughout its range (https://www.iucnredlist.org/ species/5661/3044743. Accessed 20 July 2020). In Colombia, Palmarito Foundation bred this species from 2012 to 2020. Eggs were collected at Wisirare Biopark (4.910397°N, 71.433817°W, WGS 84; 139 m elev.), Orocué, Casanare, Colombia, as a part of a captive-breeding and release conservation program.From 2012 to 2015, eggs were incubated indoors in an incubator room, and from 2017 to 2020, they were incubated outdoors. In both cases, a hole similar in size and depth to wild nests was dug into sand. Each clutch was buried with 50 cm of separation between them. In the incubator room, eggs were heated with infrared lamps and temperature was controlled with a thermostat programmed at 31°C. Outdoor clutch temperatures were not recorded or controlled and the sun was the only heat source.At Wisirare, Orinoco Crocodiles nest once annually, usually from late December to mid-late January (time lapse of between 2?18 days). In the first four seasons all clutches hatched indoors in the same order in which they were laid (time lapse of between 4?16 days). However, in the reproductive seasons of 2017?2020 when eggs were outdoors, clutches hatched almost simultaneously (time lapse of between 0?2 days). We found differences (t = 2.535; p = 0.02; a = 0.05) in incubation period from indoor (mean = 83.8 days;N=14;SD=2.9)tooutdoor(mean=88.5days;N=19;SD = 6.3).Despite the environmental influence of temperature on incubation length, many reptilian embryos may alter their development and hatching time (Du. et al. 2011. PLoS ONE 6:e29027). Intra-nest hatching synchrony has been reported in several reptile species including snakes (Aubret et al. 2016. Sci. Rep. 6[23519]:1?5), sea turtles (Santos et. al. 2016. Proc. R. Soc. B 283:1?7) and freshwater turtles (McGlashan et al. 2012. Proc. R. Soc. B 279:1709?1715). Our data suggests hatching synchrony among C. intermedius eggs from independent nests incubated outdoors.Moreover, there is evidence that some embryos are able to metabolically compensate and catch up to more advanced embryos (McGlashan et al., op. cit.; Aubret et al., op. cit.). In our case, despite the lack of synchronicity patterns described for crocodilians, the process seems to be a deceleration of the metabolic rates of the early embryos, as evidenced by increased incubation period (Fig. 1).There are several reports of intra- and inter-specific communal nesting with different hypotheses suggested, but the lack of nesting sites with optimal conditions and the benefits of proximity among embryos are the most relevant (Radder and Shine. 2007. J. Anim. Ecol. 76:881?887). To our knowledge, there are no reports of communal nesting of wild Orinoco Crocodiles.A variety of methods of communicating hatching synchronicity within nests have been proposed: the production of sound, the vibration of the egg, an increase in heart rate, and odors or carbon dioxide levels within the nest, among others (Webster et al. 2015. PLoS ONE 10: e0116345). Our findings show that synchronicity occurs among eggs not in physical contact with each other. Based on our observations, we hypothesize that the sand may be transmitting some form of signal among nests that is promoted by environmental factors not available in the indoor incubators, possibly related to the natural cycle of heating and cooling.Intra-nest hatching synchronicity has previously been described for reptile species. However, to our knowledge, this is the first report to document inter-nest hatching synchronicity where it is driven by nearby conspecific nests and not eggs within the same nest.