Radiata2010(4)e

Ewald Roddewig My

Ewald Roddewig My Experiences with the Keeping and Propagation of the Black-knobbed Sawback, Graptemys nigrinoda nigrinoda Cagle, 1954 Introduction With the Back-knobbed Sawback (Graptemys nigrinoda), we look at one of the smaller species of Graptemys – a fact that triggers the fancy of many a friend of aquatic turtles. These turtles furthermore require only a relatively small investment at present, which is something that cannot be said about the other small-sized species such as the ringed (Graptemys oculifera) and yellow-blotched map turtle (Graptemys flavimaculata). There are large-headed species of Graptemys like Barbour’s map turtle (Graptemys barbouri) in which adult females have heads the size of a child’s fist. Graptemys nigrinoda, in contrast, belongs to the Sawback map turtles that have small heads. What is noteworthy in all species of this genus, though, is the distinct difference in size and weight between the sexes. My observations indicate that large female Graptemys barbouri may weigh more than twenty times as much as their male counterparts. In Graptemys nigrinoda nigrinoda, this difference is not quite as extreme. The largest female in my care weighs just about six to seven times as much as one of my males. Over millions of years of evolution, Nature has here created perfect “egg-laying machines”, whereas males just have to contribute a drop of sperm every now and then, so why should they grow to the same size as a female? The German pet trade offers mainly the false (Graptemys pseudogeographica pseudogeographica), the Mississippi (Graptemys pseudogeographica kohnii), and the Ouachita map turtle (Graptemys ouachitensis) to the enthusiast. These forms are commercially propagated in American turtle farms. A major disadvantage of these imported juveniles is that there are no indications yet which sex they might be. This results in beginners in turtle keeping acquiring specimens that, Fig. 1. Juvenile Graptemys nigrinoda nigrinoda. 2 RADIATA 19 (4), 2010

Black-knobbed Sawback, Graptemys nigrinoda nigrinoda Cagle, 1954 years later, turn out to be females and grow to sizes that by far exceed the expectations of the inexperienced buyer. They often do not know how to handle this situation, or have lost interest in the meantime anyway. The respective turtles are then dumped, for example, at reptile rescue stations. This scenario provides so-called animal activists with ammunition to demand that the private keeping of wild animals be banned in general, ignoring entirely the fact that serious terrarium keepers contribute substantially to the knowledge of wild animals in the sectors of ecology, ethology, reproductive biology, life expectancy etc. in particular, which is information that would not be available if it were not for turtles in responsible human care. Without these major realizations and data collections, our knowledge of the biology of numerous animal species would still be very deficient, and effectively protecting threatened species would not be possible in many cases. In the countries of the European Union, Graptemys nigrinoda nigrinoda is usually available only in the shape of captive-bred specimens. Prices are typically in a range that prohibits purchases on the spur of the moment and motivates a potential beginner in turtle keeping to first acquire detailed information and the required basic knowledge. Personally, I know only of less than a dozen breeders of this subspecies in Europe so that newcomers will usually be placed on a waiting list. I also have so many requests that I can select those applicants who appear to be the most qualified ones. Appearance The presence of conspicuous black protuberances (“knobs”) on the medial keel of the dorsal shell formed the basis of the name when Cagle first described Graptemys nigrinoda nigrinoda in 1954, both for the scientific specific and its vernacular name in most languages. In females, these black elevations become increasingly pale and inconspicuous with age. Another eye-catching trait is the weakly orange loops on the scutes of the carapace. Hatchlings are initially light grey dorsally, but darken visibly within a few weeks. Over the years, the dorsal shell becomes even darker, until it shows a blackish grey that appears “dirty”, often with a hint of olive. The ventral shell is cream in colour, sometimes slightly pinkish yellow. The transversal sutures of the plastral scutes are marked with black bars, which fade with age in females. Males instead often develop greyish black plastral scutes as they grow older. The soft parts (limbs, head and tail) often exhibit a bright white to yellowish pattern of lines. The upper side of the head is marked with a Y-shaped figure. A light-coloured dot is often present posterior to the eye. Secondary sexual differences typically become recognizable at an age of about two years. From this point of time on, the females (which become sexually mature at an age of five to seven years; [Glaser pers. comm., own obs.]) start growing ever larger while male specimens continue to add only very little to their size; they already mature at about three years of age (own obs.). Males have long claws on the front feet, and their Systematic position Class: Reptilia (Reptiles) Order: Testudines (Turtles) Suborder: Cryptodira (Hidden-necked turtles) Family: Emydidae (New World pond turtles) Genus: Graptemys (Map turtles) Species: Graptemys nigrinoda (Black-knobbed Sawback) Subspecies: Graptemys nigrinoda nigrinoda (Northern Black-knobbed Sawback) RADIATA 19 (4), 2010 3