TRANSACTIONS OF THE KANSAS Vol. 121, no. 3-4 ACADEMY OF SCIENCE p. 403-410 (2018) Ontogenetic changes in tail-length and the possible relation to caudal luring in northeast Kansas Copperheads, Agkistrodon contortrix GEORGE R. PISANI1 AND J. DAREN RIEDLE2 1. Kansas Biological Survey, Higuchi Hall, Lawrence, KS 66047 [email protected] 2. Wildlife Diversity Coordinator, Kansas Dept. of Wildlife, Parks, and Tourism, Pratt, KS Electronic data capture of the nearly 60 years of field data on northeast Kansas snake populations collected by Henry Fitch enabled review of ontogenetic changes in tail- length from birth through adult size in Agkistrodon contortrix. Data from 5084 northeast Kansas Copperhead (Agkistrodon contortrix) records collected by Fitch from 1948-2003 (2287F:2797M) were examined to assess the nature of ontogenetic changes in relative tail length of sexes. We suggest that the longer relative tail length of neonate and juvenile copperheads, combined with tail color, enhances the effectiveness of caudal luring, and offer suggestions for further study. INTRODUCTION for the possibility that one treatment group spent more time foraging and caudal luring,” or that “... Ontogenetic shifts in prey in the Crotalinae black-tailed snakes may have compensated for contribute to variation in morphology, reduced prey capture rates by spending more time physiology, and behavior between juveniles in ambush postures...” Ontogenetic tail coloration and adults (LaBonte 2008). Examples include in viperids merits more extensive study. ontogenetic shifts in foraging strategy, microhabitat use, activity period, and shifts in Similar to tail coloration, the influence of the chemical composition of venom (Mackessy ontogenetic and sex-specific differences in tail 1988; Andrade and Abe 2005; Eskew et al. 2009; length on foraging ability has yet to be fully Clark et al. 2016). One of the most obvious of explored. In his extensive documentation of these ontogenetic shifts is the brightly colored tail northeast Kansas Copperhead (Agkistrodon of juveniles of some species, which is used as a contortrix) ecology, Fitch (1960a, 1999) provided lure to attract frogs and lizards as prey (Carpenter an overview of ontogenetic changes in tail- and Gillingham 1990; Greene and Campbell length from birth through adult size, but did not 1972; Neill 1960). elaborate on the nature of the changes or their possible adaptive significance. He described the Juvenile tail coloration has been experimentally change as “... the ontogenetic change in each sex manipulated in other pit vipers, but with consists of shortening of the tail in relation to inconclusive results. Thus, Farrell, et al. (2011) snout-vent length...” (Fitch 1960b), and “sexual experimentally manipulated tail color in juvenile dimorphism is relatively slight and tends to be Pigmy Rattlesnakes (Sistrurus miliarius), obscured by ontogenetic changes” (Fitch 1960a) concluding that tail coloration did not affect and “as the young snakes grow the difference overall foraging success in this caudal-luring in proportions increases gradually… In both species. Though their findings are interesting, they sexes the tail becomes relatively shorter as size did not attempt to monitor foraging thereafter, increases” (Fitch 1960a). nor identify prey in subsequently recaptured snakes, and so no conclusions can be drawn To preserve the nearly 60 years of field data regarding the effectiveness of luring and tail color collected by Henry Fitch, his extensive field on any particular prey types. Additionally, they records on this and other species are being acknowledge that their model “...could not control migrated from paper to database format by one 404 Pisani and Riedle of us (GRP). This has provided an opportunity RESULTS to re-examine this ontogeny in detail with the addition of data collected after the original In all instances, outcomes were equivalent, and publications (Fitch 1960a, b and summarized in are consistent with (thus supporting as well as Fitch 1999), and to suggest a possible selective elaborating) the general conclusions of Fitch mechanism for the observed changes. (1960a, b). MATERIALS AND METHODS Summary statistics are presented in Table 1; distributions of the two tail ratios examined We used 5084 Fitch Copperhead records (of a were (male vs female) significantly different total of 5462) from 1948-2003 (2287F:2797M) (Table 2). A histogram of Log10-transformed that had complete data (in mm) for Snout-Vent TTLs (Fig. 1) shows the very slight sexual Length (SVL) and Tail Length (TL). Also dimorphism in relative tail length noted by omitted from this total were records (>10) of Fitch (1960a, b) in this species. When Log10 snakes with tails not noted as broken but that transformed data from sexes are examined resulted in greatly reduced TTL values were via OLS (Fig. 2), it becomes apparent that regarded as original recording errors. the smallest SVL snakes (e.g., neonates) are effectively indistinguishable (though Data Analysis: Data were analyzed in three significantly different at p=0.05 in large sample primary ways in an attempt to minimize (even sizes) in relative tail length (TTL), and that given the large data set) the potential for TTL remains noticeably greater in juveniles, inference error due to SVL being a component decreasing with size as the snakes grow. of the ratios examined (TTL, TL÷SVL). A similar regression of untransformed (e.g., raw) data (Fig. 3) indicates the absolute Raw, and thereafter transformed, values of TL values of the TL-SVL relationship. Results and TTL as varying with SVL were analyzed of ANCOVA (Fig. 4) and both OLS tests initially by Ordinary Least Squares (OLS) (absolute and relative TLs) support the regression. Additionally, one-way ANCOVA ontogenetic difference. TL residuals of both was performed using Log-transformed SVLs sexes are normally distributed (Fig. 5), and and TTLs within sexes as column-paired showed weak but definite negative correlation correlated x-y data. Also non-parametric (Pearson r: -0.30) with SVLs. Non-parametric evaluations (Kruskal-Wallis tests for equal Kruskal-Wallis tests for equal medians using medians) of TL÷SVL and thereafter TTL were both absolute and relative tail lengths with SVL done to compare with parametric ANOVAs. by sex showed significant difference between sample medians (Table 3). Also, raw data for TL was regressed on raw data for SVL; residuals for TL were calculated, Since absolute (and hence relative) tail length in and then examined for negative correlation A. contortrix across SVL sizes varies considerably (indicating an ontogenetic shift) with SVL. through the extensive range of the species (Gloyd and Conant 1990; Mitchell 1994), with broad In all tests, significance was set to p<0.05. areas of intergradation through states along the Lower and upper 95% confidence intervals Atlantic coast (Mitchell 1994:287) we did not were calculated using simple bootstrapping, attempt comparisons of this character with distant with 9,999 bootstrap replicates. All statistics populations. Table 4 is condensed from Gloyd and were performed using PAST 3.2 (Hammer, et. Conant (1990) and contrasts Kansas copperheads al. 2001) and Microsoft Excel-2010. (A. c. phaeogaster) with the northern populations. Transactions of the Kansas Academy of Science 121(3-4), 2018 405 Table 1. Summary statistics for male and female Snout-Vent Length (SVL), Tail Length (TL), Ratio of Tail to Total Length (TTL). SVL and TL in mm. DISCUSSION shown here (neonate Kansas copperhead sexes less distinct from each other than are adult) The decrease in relative tail length with resembles patterns found for four natricids by increased age (as inferred from size) in A. King, et al. (1999) in their review of general contortrix is accompanied by slight, but sexual dimorphism and ontogeny, e.g. neonates increasing, sexual dimorphism as male of both sexes have similar (but not identical) hemipenes and the associated musculatures absolute TLs. There is no indication that mature; this sexual dimorphism is typical of the genera examined by King, et al (1999) viperids in general (Bonnet, et al. 1998; Shine actually engage in caudal luring, and so their et al. 1999), though the dichromatic change in explanatory hypotheses did not consider this copperheads and some other tail-luring viperids behavior and its adaptive significance. is not. The untransformed tail length pattern Table 2. Epps-Singleton tests of distributions, tail length ratios. 406 Pisani and Riedle Figure 1. Distributions of relative tail-lengths (Log10 transformed) by sex, NE Kansas Agkistrodon contortrix. Magenta bars are areas of overlap; curved lines are fitted normal distributions for values. See Table 1 for untransformed data. Conclusions regarding diet of juvenile vs. adult squamates and anurans in the prey of neonates A. contortrix (Fitch 1960a, 1999; Lagesse and than in mid-size or adult snakes; the Fitch data Ford 1996) indicate the importance of small, relate to the population for which we here generally insect, prey to mid-sized copperheads. discuss caudal luring, and we hypothesize that However, both Fitch (1999, table 7) and Lagesse both these prey types MAY respond to caudal and Ford (1996) found a higher percentage of luring in natural circumstances. Our hypothesis Figure 2. Regressions (with 95% confidence bands) of log-transformed male and female relative tail lengths on snout-vent lengths, NE Kansas Agkistrodon contortrix. Transactions of the Kansas Academy of Science 121(3-4), 2018 407 Figure 3. Regressions (with 95% confidence bands) of untransformed male and female tail lengths on snout-vent lengths, NE Kansas Agkistrodon contortrix. is not de novo, and is similar to that of Eskew, in eliciting the tail-waving behavior...” in et al. (2009) regarding juvenile cottonmouths captive neonate and juvenile copperheads, that selectively prey upon salamanders. Though the behavior is well-documented, though not Fitch (1960a) stated that he never “succeeded as prominent a display as noted for juvenile Figure 4. Plot from ANCOVA. SVL vs TL÷SVL. 408 Pisani and Riedle Figure 5. Distribution of residuals from OLS, untransformed SVL and TL.