Radiata2010(4)e

Ewald Roddewig next

Ewald Roddewig next oviposition period (comp. Hertwig 2001). Males have a much lower food intake, which is not surprising considering their smaller body sizes. They are fed only every two to three days. I also do without supplementing the food for both sexes with vitamins, as I deem this measure unnecessary if their diet is composed properly. The menu for my Graptemys nigrinoda nigrinoda includes crickets, roaches, grasshoppers, a wide range of beetles, caterpillars, worms, frosted and freeze-dried shrimps and Gammarus, furthermore small fish (frozen rudd, smelt, topmouth gudgeon; freeze-dried fish from the Asian supermarket), octopus, fowl meat, beef heart, giant mealworms (Zophobas), mealworms, flies and spiders, woodlice, snails and slugs, frozen pink mice, and many others more. When I go out to hunt native invertebrates, I always have an eye on not collecting protected species, and native amphibians are never collected for feeding, not at least because they are protected as well. I prefer to offer live feeder animals, but also use freeze-dried and frozen foods, the latter are of course first defrosted. Turtle jelly is a possible substitute, provided it is made after a thought-through, balanced recipe (e.g., Schulz 2001). The females always have cuttlefish shell at their disposal, which serves to satisfy their great need for calcium. It continues to amaze me just how much of the cuttlefish shell they consume. Besides dietary considerations, matching pairs is the next important factor, and it is not always easily resolved. Sometimes, the male shows intentions to mount, but the female will not permit him to do so. At other times, the male specimens show no interest in their potential mating partners. It is typical for the females in my care that they will agree to copulation only once every year. This almost exclusively happens in unheated water and usually shortly after hibernation. However, I have also developed a routine that appears to be safer in my view and that can be applied prior to hibernation: In October, the water in the males’ tank is exchanged, using cold tap water for refilling. The same is then done in the tank of the females. Following a waiting period of a few hours, the males are placed with the females, where they will immediately start courting them. The male turtles will swim in circles around their chosen females, occasionally emphasizing their intentions with vibrating claws. Copulation then involves a rather “solid” connection between the male and the female that persists for some 20 minutes. Initially, the female will remain lying quietly on the bottom, permitting the male to mount. After a while, however, the female will start swimming through the aquaterrarium, towing the attached male with her, and force the connection to break by fast and agitated movements. Now, something unusual can be seen: the exposed penis looks like the flower of a field bindweed, save for its dark blue to dark greyish black colour, and shows elegant movements that resemble a jellyfish in the current of the sea. This display does not last long, though, and ends when the penis is eventually retracted into the cloaca of the male’s tail. Provided the sawbacks were awakened from their hibernation around mid-February, my two females produce eggs between March and July. Oviposition events are heralded two or three days prior when the female moves from the water to the terrestrial section. A potential laying spot is first examined and rechecked once or twice or even up to six times. Oviposition eventually takes place in the early morning or late in the afternoon. If the sand is not moist enough and therefore not in an optimum condition for excavating a nest pit, the female will moisten the selected spot with fluid from her anal bladder. She will then excavate a pit of 12-15 cm in depth with her hind legs. Once she has laid her eggs, she will reuse the excavated sand to refill the pit with her front and hind legs. The surface is finally smoothed by the female sliding on her 14 RADIATA 19 (4), 2010

Black-knobbed Sawback, Graptemys nigrinoda nigrinoda Cagle, 1954 ventral shell over the closed pit. The entire process of oviposition, including closing the nest pit, does not even take an hour in the females in my care. However, no person may be present in the room, which makes observing these events rather challenging. The soft-shelled eggs are then recovered and carefully freed of adhering substrate. They weigh about 14-16 g and are some 35-40 mm long. One of the two incubators used is set to a temperature of 26 and the other to 30 °C. Incubated at 26 °C, the hatchlings emerge after 78-83 days and are certainly of the male sex. Eggs that are incubated at 30 °C hatch after only 58-62 days and yield female turtles. These incubation temperatures are a failsafe method of determining the sex of the offspring. I cannot, however, as yet state where exactly the vertex point lies; as far as other species of Graptemys are concerned, Bull et al. (1982) and Ewert & Nelson (1991) suggested 29.0-29.5 °C. I always incubate these eggs at a constant temperature, i.e., without decreasing nightly values. Vermiculite is used as a substrate. It is soaked in water and then squeezed out so that it forms a moist mass. It is then filled into a rectangular freezer tubs until these are about four fifths full. I take care that tub and filling make up quite exactly 450 g so that the subsequent loss of moisture can be quantified and compensated by remoistening. A small depression is made into the surface of the vermiculite so that every egg can be placed there, without changing its original positions, and be buried for about one third. This is done by handling every egg individually. A small paintbrush is used to carefully plane and slightly compact the surface of the vermiculite so that the eggs have proper contact with it. It just takes a day or two for a white blotch to appear on the upper side of the egg and subsequently spread all over it, which indicates that it is fertile. The originally translucent egg so turns into a truly white opaque one. Infertile eggs take on a glassy amber colouration, start collapsing, and need to be removed. The incubator is checked every five days. The vermiculite is remoistened if and when necessary, and the water in the designated bowl in the incubator is replenished to guarantee a constantly high level of humidity. A number of experiments have shown that the procedure described afore works best for me. I have noted, however, that not every clutch of eggs develops exactly in the same manner, even if the conditions are identical. The eggs from the smaller female are much easier to incubate successfully than those from the larger female. For example, some clutches from the latter consist of eggs that are prone to inflating. While soft-shelled eggs are supposed to absorb moisture, i.e., water, they are certainly not supposed to balloon in the process. If this happens nevertheless, I found you could prick them carefully with a very sharp pin, which will reduce the pressure inside. I have used this method with success on several occasions, but it does obviously not remedy the actual cause, i.e., the excess moisture. Hatching of the baby turtles begins with a cut appearing in one of the tips of the egg, which the hatchling makes with its egg tooth. It may now take several days until the baby turtles actually leave their eggs. I let them take their time and do not manipulate the eggs. Ideally, the yolk sac sticking out from the plastron of the hatchling will be almost fully used up. If the yolk sac is still too large, the affected hatchlings may die. To me, oversized yolk sacs are an indication of inadequately high moisture levels during incubation, which caused the hatchlings to emerge prematurely from their eggs. In such a case, it helps to bury the babies slightly in vermiculite and leave them in the incubator until they have resorbed the remaining yolk. This point of time has come when the baby turtles begin to walk about. RADIATA 19 (4), 2010 15