Variable Production of Annual Growth Rings by Juvenile Chelonians WILLIAM R
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Turtle and Tortoise Newsletter, Issue 11 Variable Production of Annual Growth Rings by Juvenile Chelonians WILLIAM R. BELZER[ AND SUSAN SEIBERT' 'Box Turtle Consen-ation Trust, 304 East Bissell Ave. Oil City. Pennsylvania 16301 USA {[email protected]] Corresponding author. 2AA Forestry and Wildlife Sen-ice, Inc, 2270 Raymilton Road, Utica, Pennsylvania 16362 USA {[email protected]] The production of 1 annual growth ring (major growth (38 d'd'; 22 QQ) head-started box turtles. We divided each mark in nomenclature of Zug, 1991; cf. Wilson et al. 2003) juvenile's major ring count by its age (R = 1-2.5 years; s in a turtle's scute is a disputed assertion. The accuracy of us = 2 years) at the time when it was transferred from head ing growth mark (ring) counts to estimate the age of turtles start conditions into wild habitat and obtained a mean of 2.5 has been assessed in many species and debated extensively rings added per year (R = 1-7; SD = 0.8). in articles such as Germano and Bury (1998), Litzgus and We initiated head-start studies in 2000 in connection Brooks (1998), and Zug (1991). Many field workers (e.g.. with our eastern box turtle repatriation studies (Belzer Germano 1998) report a reliable scute ring:age correlation, 1999) after our work in the 1990s found that use of translo whereas others (e.g., Wilson et al. 2003) do not. Discern cated adults, nest protection, and short-term head starting ing narrow or shallow growth rings produced during low (Belzer 2002; Belzer et aJ. 2002) were inadequate strate growth years. especially as turtles become adults, is often gies for rebuilding extirpated populations. We therefore difficult, and deciding which rings are truly major annual began an assessment of potential success with 2-year-old marks (contrast Zug 1991; Tracy and Tracy 1995: Berry juveniles, head started by the Michell protocol (Michell 2002; Germano 1998; and Wilson et al. 2003) can be sub and Michell 1999). Our modified Michell regimen features jective and uncertain. 2 years of a 22°-25°C temperature range, moist peat moss Figure 1 documents a case of an eastern box turtle (Ter substrate in an 84-L Sterilite plastic box, 14 hId of light rapene carolina carolina Linneaus) conforming to the ideal from a 45.75-cm Lumichrome lXX 15-watt full-spectrum ized production of 1 ring per year. This juvenile female was plus fluorescent bulb, and twice-daily offerings of Repto rescued from a construction site near Washington. Pennsyl min aquatic turtle food sticks for the first 20 months or so vania in May 2001. Because the turtle could not be returned of life. This protocol generally produces large (250-300 to her native habitat, she was donated to our repatriation g, but sometimes exceeding 400 g or even 500 g) juvenile study (Belzer and Steisslinger 1999) in June 2001 with a eastern box turtles in less than 2 years. They are free of body weight of 170 g and a growth ring count of about 7, anatomic abnormalities sometimes seen by veterinarians as shown in Fig. lao During the next 4 years she lived and in pets grown rapidly on unbalanced diets. The health of foraged in an enclosure in wild habitat at the Buttermilk our 5 dozen Michell head-started animals appears excel Hill Nature Sanctuary (BHNS) near Utica, Pennsylvania. lent. Some are now 7 years old and have lived at large in and gained 67 g. Her 2005 photograph in Fig. Ib shows wild habitat at the 200-ha BHNS for 5 years. None has yet about 4 new rings added during that confinement, match contracted the common ailments of wild box turtle popu ing Germano's (1998) findings of annual ring production lations, such as aural abscesses (Brown et al 2003; Dodd in penned juvenile desert tortoises (Gopherus agassizii) in and Griffey 2004), or respiratory and eye infections (Evans natural habitat. 1993: Willer et aJ. 2003), whereas some of the adults who More than I ring per year, however, is often produced range among them have. by juvenile desert tortoises (Tracy and Tracy 1995; cf. Ger Because there are obvious differences in depth among mano 1998), as well as by wood turtles, Glyptemys insculpta the rings produced by our head-started animals, and because (formerly Clemmys insculpta) (Harding and Bloomer 1979) shallow rings are generally fine, closely packed, and diffi when they are reared in artificial conditions. Our findings cult to count, we counted only the deeper scute indentations with head-started hatchlings add the eastern box turtle to as major growth marks. and regard their shallow ones as that list. We counted the major growth rings on all of our 60 minor marks even when they formed complete rings. Our Figure 1. (a) Wild juvenile female, 2001, 170 g body weight; 7-8 growth rings in second right pleural scute. (b) Same female as (a). 2005, 237 g; 11-12 rings in second right pleural scute. 10 ... r December, 2007 Figure 3. Twenty-three-month-old head-started 237-g male. Three deep, and a few additional minor. growth rings in first right pleural scute. Figure 2. Epoxy cast of third left pleural scute of a 23-month-old head-started 396-g male. conservative counting standard is therefore a departure from the method that counts any complete ring as major (Tracy and Tracy 1995). Although subjectivity, involved in decid ing which rings are "deep enough" to count as major, can introduce some error into our ring counts, the prevalence of supernumerary annual growth rings was obvious. Wilson et Figure 4. Eleven-month-old head-started 299-g male. Two deep, plus al. (2003) instructively reviewed the confusion existing in multiple minor, rings in third left pleural scute. even the most basic biology and nomenclature of chelonian growth rings. Figure 2 is an example of one of our many head-started juvenile Box Turtles that display more than I major annual scute ring. The image is a negative epoxy impression of rings from a 23-month-old male (body weight 396 g). The five or six deepest rings are complete, as are many of the additional finer rings. Multiples of those finer rings are pro duced even by the rare individual among our head-started juveniles that added fewer than 2 major growth marks dur ing a year's rapid indoor growth (Fig. 3). Figure 5, Twenty-four-month-old head-started 523-g female. Before they reach the 250-g size sufficient to carry a ra Indeterminate major, but numerous minor, rings in first right pleural. compared to marginal, scute. diotransmitter and safely be released for field study (Yahner 1974; Murphy 1976; Belzer et al. 2002), our head-started animals display so much variation in numbers of major and chell head-starting regimen, and are often larger than their minor growth marks that considerable error would exist in mother within 2 years. age estimates made from counting their rings. Figures 4-8 The 3 turtles in Figs. 6-8 were slower-growing head-start provide a sample that illustrates that variety, the subjectivity ed juveniles from other mothers. The female in Fig. 6, at only required to decide which rings are major, and the conserva 12 months and 170 g, has 2 or 3 major rings and additional tive leaning in the ring counts reported in this article. minor rings. The 22-month-old juveniles in Figs. 7 and 8 are The male in Fig. 4 was only 11 months old at the time of each about 275 g, with mUltiple major, plus minor, rings. the photograph. He weighed 299 g (unusually fast growth The supernumerary annuli we see in our head-started box for our head-start regimen) and had already produced at least turtles extend the findings of Harding and Bloomer (1979) 2 deep major, as well as numerous minor, growth marks. and Tracy and Tracy (1995) for (respectively) artificially The female in Fig. 5 was 24 months old and weighed reared juvenile wood turtles and desert tortoises. Germano 523 g with numerous shallow growth marks. The rings on (1998) regarded such supernumeraries as peculiar to artifi the pleural scutes are not deeply indented and so appear to cial rearing conditions. However, juvenile chelonians in na include perhaps only 1, or maybe no, major rings. whereas tive habitats have produced multiple major marks in a year. her marginal scutes display as many as 5 major (deep) rings. Liztgus and Brooks (1998) found juvenile spotted turtles Most offspring from the 425-g mother of this female (who (Chlemmys guttata) that produced more (as well as fewer) also produced the large II-month-old male of Fig. 4 in a than the expected 1 ringly in native Canadian habitat. Berry previous season's clutch) grow unusually fast with the Mi (1998) found juvenile native desert tortoises that produced 11 .-------------------------- Turtle and Tortoise Newsletter, issue 11 ever, indicate that even the juvenile stages of various spe cies, living in native habitat, can deviate from the expected 1 annulus per year of age. Those field observations suggest that the occurrence of supernumerary annuli that we find among our head-started box turtles is not a deviation that occurs only under artificial rearing conditions, a recogni tion that recommends that an allowance for error be given to age estimates of native juvenile chelonians that are based on growth ring counts. Figure 6. Twelve-month-old head-started 170-g female with at least 2 major, and mUltiple minor, rings in first right pleural scute. Acknowledgments We are grateful to 1.