Minimum size at maturation in the mud snake, Farancia abacura (Serpentes: Colubridae) from the southeastern United States.
The age and size at which a species becomes reproductive is one of its most important natural history traits. This trait is often more influential to a species' fitness than any other natural history trait (Sterns 1992). Species that become reproductive earlier in life have a greater probability of survival to reproductive age and the potential for greater fecundity. Although there are costs associated with this life history strategy, for many species the benefits of early reproduction are much greater than the potential costs.
Constraints on the age at maturation include phylogeny and body size. In squamates, researchers have demonstrated a positive correlation between adult body size and age at maturation (e.g., Dunham & Miles 1985). Although there may be exceptions, this relationship is conserved among most reptiles.
There is limited information on the reproductive life history of mud snakes, Farancia abacura (see Fitch 1970; Mitchell 1982). Quantifying the reproductive traits in this species is difficult due to its secretive habits. There are several reports of oviposition and subsequent hatching (Meade 1935; 1937; 1940a; 1940b; Goldstein 1941; Reynolds & Solberg 1942; Meade 1945), but little is known about the minimum body size at which this species becomes reproductive. More recently, Robinette & Trauth (1992) investigated both female (n = 22) and male (n = 22) reproductive cycles from F. abacura collected throughout Arkansas. The smallest female with follicles was approximately 56.0 cm snout-vent length (SVL). This female is only 29.0 to 40.1 cm larger than the reported 15.9 to 27.0 cm hatching size of F. abacura (Conant & Collins 1998).
METHODS AND MATERIALS
A total of 129 female F. abacura museum specimens from throughout their range were examined to determine the minimum body size at maturation. Seventy-six of the 129 specimens provided reproductive data that could be used in the analyses; 53 female specimens had damaged follicles (e.g., road killed specimens) or were dissected previously. Specimens were sampled primarily from Louisiana and Texas, with some adults from Florida, Mississippi, Oklahoma, South Carolina, and Tennessee. Ovarian follicles and oviductal tissue samples were removed through a ventral incision and stored in 70% ethanol. Follicles were measured with a Fowler dial caliper and classified based on length according to Betz's (1963) system (Class I = 0.1-5.0 mm; Class II = 5.1-10.0 mm; Class III = 10.1-20.0 mm; and Class IV = 20.1-46.0 mm). This system allows for grouping follicles into one of four distinct size classes and is commonly used in studies investigating follicle size and development (e.g., Kofron 1979; Kofron 1983; Holycross & Goldberg 2001; Goldberg 2002; Rosen & Goldberg 2002).
Material examined.--Specimens of Farancia abacura examined. Standard museum symbolic codes for institutional resource collections follow Leviton et al. (1985).
Florida: DADE CO.: TNHC 50103, LAKE CO.: OMNH 18993, PUTNAM CO.: OMNH 34414.
Louisiana: AVOYELLES CO.: LSUMZ 2724, LSUMZ 75894, LSUMZ 75914, BEAUREGARD CO.: LSUMZ 22552, BOSSIER CO.: LSUMZ 24247, CADDO CO.: LSUMZ 4838, CAMERON CO.: TCWC 17417, EAST BATON ROUGE CO.: LSUMZ 2723, LSUMZ 5959, LSUMZ 11895, LSUMZ 20331, LSUMZ 20332, LSUMZ 24248, LSUMZ 24249, LSUMZ 31246, LSUMZ 38093, LSUMZ 38959, LSUMZ 39191, LSUMZ 44913, LSUMZ 65908, LSUMZ 83190, LSUMZ 83386, LSUMZ 83390, LSUMZ 84521, EAST FELICIANA CO.: LSUMZ 2725, LSUMZ 6109, LSUMZ 9121, LSUMZ 18296, LSUMZ 34306, EVANGELINE CO.: LSUMZ 29097, LSUMZ 58466, LSUMZ 58467, LSUMZ 74846, LSUMZ 75895, FRANKLIN CO.: LSUMZ 43537, GRANT CO.: LSUMZ 74849, IBERBVILLE CO.: LSUMZ 18770, LSUMZ 46868, LSUMZ 75888, LSUMZ 75889, JEFFERSON CO.: LSUMZ 9163, LSUMZ 9164, LSUMZ 18282, LSUMZ 58389, LSUMZ 58454, LSUMZ 58455, JEFFERSON DAVIS CO.: LSUMZ 59063, LAFAYETTE CO.: LSUMZ 74848, LSUMZ 75909, LAFOUCHE CO.: LSUMZ 19178, LIVINGSTON CO.: LSUMZ 12884, LSUMZ 13008, LSUMZ 55927, LSUMZ 79283, LSUMZ 80501, LSUMZ 80503, NATCHITOCHES CO.: LSUMZ 75896, LSUMZ 83451, LSUMZ 83485, LSUMZ 83504, LSUMZ 84597, LSUMZ 84674, ORLEANS CO.: LSUMZ 9162, LSUMZ 14154, PLAQUEMINES CO.: LSUMZ 75900, POINTE COUPEE CO.: LSUMZ 4149, LSUMZ 18295, RAPIDES CO.: LSUMZ 74853, LSUMZ 75869, LSUMZ 75893, RICHLAND CO.: LSUMZ 42524, ST. LANDRY CO.: LSUMZ 20330, LSUMZ 74850, LSUMZ 75862, LSUMZ 75868, TCWC 38241, ST. JOHN THE BAPTIST CO.: LSUMZ 39805, LSUMZ 58438, LSUMZ 59624, LSUMZ 80948, ST. MARTIN CO.: LSUMZ 74843, LSUMZ 74844, LSUMZ 74845, LSUMZ 74847, LSUMZ 74851, LSUMZ 75866, LSUMZ 75891, LSUMZ 75892, LSUMZ 75897, LSUMZ 75898, LSUMZ 75907, LSUMZ 75913, LSUMZ 75915, LSUMZ 75916, LSUMZ 75917, LSUMZ 75910, LSUMZ 75911, LSUMZ 75912, LSUMZ 79053, ST. MARY CO.: LSUMZ 75890, LSUMZ 75899, ST. TAMMANY CO.: LSUMZ 24098, LSUMZ 24099, LSUMZ 28816, LSUMZ 58518, LSUMZ 80255, LSUMZ 80898, LSUMZ 81207, TANGIPAHOA CO.: LSUMZ 17674, LSUMZ 23175, LSUMZ 47458, LSUMZ 57956, LSUMZ 57959, LSUMZ 57960, LSUMZ 80507, LSUMZ 80508, LSUMZ 80509, LSUMZ 80510, LSUMZ 80511, TERREBORNE CO.: TCWC 74150, TERREBORNE CO.: TCWC 71458, VERNON CO.: LSUMZ 20174, WASHINGTON CO.: LSUMZ 21026, WEST CARROLL CO.: LSUMZ 20333.
Mississippi: ATTALA CO.: LSUMZ 75989, HANCOCK CO.: LSUMZ 41368, LSUMZ 19176, JACKSON CO.: LSUMZ 57957, SHARKEY CO.: LSUMZ 47883.
Oklahoma: MCCURTAIN CO.: OMNH 30111, OMNH 38351, OMNH 24380, OMNH 30706.
South Carolina: CHARLESTON CO.: LSUMZ 36919, JASPER CO.: LSUMZ 74432.
Tennessee: LAKE CO.: LSUMZ 74856.
Texas: ANDERSON CO.: TCWC 64992, TCWC 81207, ANGELINA CO.: SFA 654, ARANSAS CO.: TCWC 81205, AUSTIN CO.: TCWC 4583, TCWC 6453, BURLESON CO.: TCWC 18279, BRAZORIA CO.: TCWC 53155, BRAZOS CO.: TCWC 5164, TCWC 13838, TCWC 45620, CHAMBERS CO.: TCWC 60707, COLORADO CO.: TCWC 64322, DEWITT CO.: TCWC 82477, FORT BEND CO.: TCWC 81641, GALVESTON CO.: TCWC 27368, GRIMES CO.: TCWC 64991, TNHC 36319, HARDIN CO.: TNHC 4534, TNHC 19800, TNHC 21940, TNHC 28728, HARRIS CO.: TCWC 183, TCWC 8711, TCWC 18278, HARRISON CO.: TCWC 79273, HOUSTON CO.: TCWC 67299, JACKSON CO.: TCWC 29467, JASPER CO.: SFA 2896, TCWC 48425, TCWC 78732, JEFFERSON CO.: TCWC 8710, TCWC 16178, LEON CO.: TCWC 2614, TCWC 5158, TCWC 5159, TCWC 5160, TCWC 5161, TCWC 5162, TCWC 5163, TCWC 5177, TCWC 8709, TCWC 8712, LIBERTY CO.: TNHC 21846, MADISON CO.: TCWC 17389, TCWC 49322, MORRIS CO.: TCWC 78731, MONTGOMERY CO.: TCWC 57916, TCWC 68233, TCWC 68237, TCWC 81209, TCWC 82476, NACODOCHES CO.: SFA, SFA 1216, SFA 1233, SFA 2033, SFA 2291, SFA 2309, NEWTON CO.: TCWC 48426, ORANGE CO.: TCWC 33646, TNHC 21963, REFUGIO CO.: TNHC 20583, TNHC 32202, SAN JACINTO CO.: LSUMZ 34289, TYLER CO.: TCWC 78730, TCWC 81204, VICTORIA CO.: TCWC 70080, WALKER CO.: TCWC 67234, TCWC 82818, WHARTON CO.: TCWC 4757, TCWC 81206.
Unknown Locality: SFA, SFA, TCWC 31956.
RESULTS AND DISCUSSION
Snout-vent length (SVL) of the 76 females examined ranged from 42.0-191.0 cm ([bar.x] = 92.4, SE = 3.53, n = 75); six individuals (TCWC-81206 = 42.0 cm; LSUMZ-75890 = 43.0 cm; LSUMZ-75913 = 43.0 cm; LSUMZ-75891 = 44.0 cm; TCWC-82477 =53.5 cm; LSUMZ-17674 = 55.0 cm) had a smaller SVL than the 56.0 cm SVL reported by Robinette & Trauth (1992). All six of these individuals had either Class I or II follicles. The smallest individual (TCWC-81206 = 42.0 cm) was 14.0 cm smaller than the female reported by Robinette & Trauth (1992) and had Class I follicles (4.08 mm). This individual represents a significant finding for this species' minimum size at maturation. All other reproductive females examined fell within the range of adult body size reported by Conant & Collins (1998). A frequency distribution of body size for 75 of the 76 specimens examined showed a normal distribution (Kolmogorov-Smirnov Distribution = 0.078, P > 0.20) for female reproductive size (Fig. 1). No relationship was found between female body size (SVL) and mean follicle length (Fig. 2). This is because follicular development is mostly dependent on time of year and not body size (Lutterschmidt et al. 2005). Snout-vent length explained only 2% ([r.sup.2] = 0.0203) of the variation in the mean follicle size (F = 1.51; df = 1, 74; P = 0.223). However, what may be of interest is the sequential increase in variation among Class I (SE = 0.149, n = 17), Class II (SE = 0.302, n = 44), and Class III (SE = 0.636, n = 14) follicle lengths (Fig. 2). These increases in variation among classes may be due to differences among females and their rates of follicular development through the reproductive season.
[FIGURE 1 OMITTED]
This report provides important information regarding minimum body size at maturation in a Colubrid that typically reaches 137 cm as an adult with hatchlings ranging from 15.9 to 27.0 cm (Conant & Collins 1998). As discussed by Sterns (1992), there are potential reproductive advantages in having a moderately large body size at hatching. The 42.0 cm female with Class I follicles (TCWC-81206) observed in this study was only 15 cm larger than the reported 27 cm maximum hatchling size. Unfortunately, there appears to be no information regarding growth rate of Farancia under field conditions and how long it may take an individual female to reach reproductive size.
[FIGURE 2 OMITTED]
Growth rates for Crotalus (a large-bodied snake in the family Viperidae) have been documented under field conditions. Prival et al (2002) reported that Crotalus pricei may grow 0.726 cm/shed or 0.0063 cm/day (i.e. 2.3 cm/year). Conversely, growth rates for immature female Crotalus viridus are considerably faster and have been reported as 10cm/year (see Fig. 1 in Diller & Wallace 2002). Himes et al. (2002) studied a large-bodied Colubrid (Pituophis ruthveni) from Louisiana and Texas using radio telemetry and reported a growth rate of 12.0 cm/19.4 months (i.e., 7.4 cm/year). Gibbons & Dorcus (2004) also report growth rates within species accounts of North American watersnakes (Colubridae: Nerodia). For example, Trauth (1990) in Gibbons & Dorcus (2004) estimated the growth rate in an Arkansas population of N. cyclopion (10.2-26.5 cm/year, n = 72) from size classes representing presumed age. Faster growth rates were reported for N. erythrogaster (0.77-1.63 mm/day or 28.1-59.5 cm/year) from three recaptures (Preston 1970 in Gibbons & Dorcus 2004). However, a slower rate of growth (9.5 cm/year) was observed for 20 newborn snakes raised in captivity (Conant & Downs 1940 in Gibbons & Dorcus 2004). Because Farancia is also a Colubrid snake and may experience similar lengths of seasonal activity as P. ruthveni, N. cyclopion, and N. erythrogaster due to similar geographic distributions, F. abacura may also demonstrate similar growth rates. Thus, a female could conservatively grow 10-20 cm in SVL and reach reproductive size within its second activity season.
Sterns (1992) discusses the evolutionary advantage of early reproduction and its most important limiting factors, minimum adult body size at maturation. However, as for other larger-bodied snakes, large hatchling size of F. abacura may allow this species to demonstrate early reproduction resulting in an overall increase in fitness.
This information on the natural history of Farancia may help future researchers studying the reproductive strategy and evolutionary ecology of this fully aquatic and secretive snake species.
We thank curators and staff of the Texas Cooperative Wildlife Collection at Texas A & M University, Louisiana State University Museum of Zoology, Sam Noble Oklahoma Museum of Natural History at the University of Oklahoma, Stephen F. Austin Vertebrate Museum at Stephen F. Austin State University, and Texas Natural History Collection at the University of Texas for access and use of all specimens of F. abacura. We sincerely thank Robert R. Fleet for comments upon reviewing this manuscript.
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WIL at: email@example.com
William I. Lutterschmidt, Sara B. Turk and Everett D. Wilson
Department of Biological Sciences
Sam Houston State University
Huntsville, Texas 77341
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|Author:||Lutterschmidt, William I.; Turk, Sara B.; Wilson, Everett D.|
|Publication:||The Texas Journal of Science|
|Date:||Aug 1, 2006|
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