Analysis of Spotted Salamander (Ambystoma maculatum) Growth Rates Based on Long-Bone Growth Rings

—Amphibians experience indeterminate growth, but although factors affecting larval growth are relatively well studied, less is known about correlates of postmetamorphic growth. We measured areas between lines of arrested growth (inter-LAG) to determine yearly growth rates to test whether the postmetamorphic growth of 32 Spotted Salamanders (Ambystoma maculatum) was related to age, sex, or year of emergence. Growth decreased with age and was not associated with sex or year of emergence. Using interLAG area as a metric of growth provides growth information in the years before first capture and can be done using the toe-clips commonly taken for marking individuals. Growth rate and body size are important intraspecific characteristics for adult amphibians. First, rapid growth immediately following metamorphosis reduces the time to sexual maturity for anurans, allowing them to reproduce earlier (Turner, 1960). Second, reproductive output is often correlated with body size. For example, larger Spotted Salamanders (Ambystoma maculatum) and Wood Frogs (Rana sylvatica) produce significantly larger clutches than do smaller conspecifics (Woodward, 1982; Howard, 1988), and larger male Bullfrogs (Rana catesbeiana) mate more frequently each year than do smaller males (Howard, 1988). In some Ambystoma, larger individuals breed earlier in the season than do smaller individuals (Lowcock et al., 1992), perhaps offering a time advantage to their offspring in a rapidly fluctuating environment. Finally, larger male body size may be important in species where individuals defend territories (Howard, 1988; Regosin et al., in press). Amphibians exhibit indeterminate growth continuing to grow beyond reproductive maturity (Perrin and Sibley, 1993). Therefore, factors that affect growth and body size may act during the larval stage and continue well after metamorphosis. In contrast to amphibian postmetamorphic growth, larval growth has been well studied, and important correlates have been identified. Higher temperatures and greater food availability, for example, can increase larval growth (Duellman and Trueb, 1986), but increased density of conspecifics, regardless of prey density, decreases larval growth rates (Petranka, 1989; Scott, 1990; Van Buskirk and Smith, 1991). Also, some species of anurans produce a chemical that can inhibit growth of both conspecific larvae and larvae of other amphibian species (Richards, 1958; Rose, 1960; West, 1960). Larval growth rates can affect size at metamorphosis and, thus, can impact adult body size (Semlitsch et al., 1988; Scott, 1994); however, patterns and correlates of adult amphibian growth are relatively poorly known. Several early studies, however, have identified factors affecting postmetamorphic anuran growth (e.g., Raney and Ingram, 1941; Fitch, 1956; Martof, 1956; Turner, 1957), and there are a few studies specific to salamanders (Flageole and Leclair, 1992; Wake and Castenet, 1995; Caetano and Leclair, 1996; Castenet et al., 1996; Russell et al., 1996). An animal’s age is one factor often 2 Corresponding Author. E-mail: michael.reed@ tufts.edu SHORTER COMMUNICATIONS 617