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Growth rates of neonate red cornsnakes, pantheropms guttatus (colubridae), when fed in mutually exclusive mass-ratio feeding categories

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Herpetological Review 43(4), 2012
HERPETOCULTURE 605
Herpetological Review, 2012, 43(4), 605–607.
© 2012 by Society for the Study of Amphibians and Reptiles
Growth Rates of Neonate Red Cornsnakes, Pantherophis
guttatus (Colubridae), When Fed in Mutually Exclusive
Mass-Ratio Feeding Categories
Studies on growth rates of snakes have long been investigated
(Barnard et al. 1979; Carpenter 1952; Ford 1974; Kauffeld 1943)
and are still ongoing (Boback 2003; Hill and Beaupre 2008; Mad-
sen and Shine 2001). There are two growth measurements that
are generally recorded when measuring snakes: length and mass
(Charland and Gregory 1989; Franz 1977; Kauffeld 1943; Myer
and Kowell 1973). A third and easily acquired measurement is
girth at mid-body but this is rarely reported. Straight-line length
is occasionally used but the most commonly reported length
measurement is snout to vent length (SVL; Seigel and Ford 1988).
It is important to state which measurement technique is being
used (Fowler and Salamao 1995).
In a study on Nerodia sipedon, Brown and Weatherhead
(1999) reported two variables that are likely to affect snake growth
rates: energy intake and climate. Laboratory investigations allow
for control of both of these variables. Many studies hold tem-
perature constant and investigate feeding regimes (Barnard et
al. 1979; Dmi’el 1967; Ford and Seigel 1994). Myer and Kowell
(1973) showed that frequency of feeding and food mass can af-
fect growth in Thamnophis sirtalis. As a snake consumes more
food its total body mass usually increases but this phenomenon
may not accurately relate the size (mass) of a snake to its age be-
cause body mass can be impacted by multiple variables. Snake
mass has been shown to fluctuate with feeding regimes (Myer
and Kowell 1973) and varying reproductive efforts (Charland and
Gregory 1989). Neonate Pantherophis guttatus have been shown
to convert up to one-third of their food weight into added body
mass (Love and Love 2005). However, age can be predicted based
upon SVL if the sampling period of the growth model is large
enough and the specimen collected is in close regional proxim-
ity to the growth model sample (Brown and Weatherhead 1999).
Individual marine iguanas total length has been shown to shrink
during times of low food availability (Wikelski and Thom 2000)
but this growth reduction phenomenon has not been shown in
snakes (Madsen and Shine 2001).
In an early field growth study, Kaufman and Gibbons (1975)
evaluated the relationship of SVL and mass of thirteen species
of snakes that were primarily road collected and reported a cor-
relation coefficient between SVL and mass of 0.82 with P. gutta-
tus being 0.97. Barnard et al. (1979) investigated the growth rates
of ten sibling P. guttatus for ca. 2 years in a laboratory setting.
Snakes were fed weekly meals of mice and were measured (total
length and mass) monthly. A correlation coefficient of 0.978 was
reported between total length and mass. They found that growth
is more dependent on food consumed rather than age, length
is logarithmically related to body weight, and weight gain and
length are related to the amount of food ingested.
Many investigators have evaluated snake growth at differ-
ent feeding frequencies (Dmi’el 1967; Wharton 1966) but to
our knowledge, none have evaluated snake growth when fed
in a mass-ratio feeding category with a constant frequency. A
mass-ratio (MR) feeding category is a mutually exclusive feed-
ing category calculated as the percent of prey mass to snake
mass (Mehta 2003). The objective of this study is to evaluate the
growth (length, girth, mass, and shedding rates) of neonate P.
guttatus when fed in mutually exclusive MR feeding categories.
We collected data on the growth rates and shedding frequencies
of captive P. guttatus.
Materials and Methods.—The 18 hatchling snakes used in
this study came from the personal collection of David Penning.
Parents of the offspring were originally obtained from Miles of
Exotics in Kansas City, Missouri. All snakes shared the same fa-
ther and came from one of two mothers. All hatchlings displayed
phenotypically normal traits but carried various non-expressed
alleles that their mothers displayed but they did not. The first
clutch of snakes began hatching on 8 June 2010 and all snakes
hatched by 15 June 2010. All snake eggs were incubated in the
same type of incubator (Little Giant® Still Air Incubator) with the
same average temperature (28°C) and humidity (80%).
Each neonate was held individually in a cage internally
measuring 27.9 × 27.9 × 15.2 cm. A sliding, clear piece of glass
was used for the lid. Multiple 5-mm holes were drilled into the
backs and fronts of the cages for proper air exchange. This al-
lowed proper ventilation without exposing each snakes to the
visual cues of the other snakes. Ambient room temperature aver-
aged 27.9°C. Each cage was spot cleaned daily and bedding was
changed pro re nata. No mites or parasites of any kind were ob-
served during the experiment. Water was available at all times.
Hatchlings were then checked once per week for their first
shed. The feeding trials began the following scheduled feeding
day upon the discovery of each snake’s first shed. The order in
which the snakes were placed into each category was deter-
mined by a random number generator. House Mice (Mus muscu-
lus) were the only food given to snakes in the experiment. Each
snake was put into a feeding schedule of one meal per week.
The two feeding categories were labeled as small and large. The
small feeding category had a prey mass-ratio of 20–40% of the
snake’s mass while the large category had a ratio of 41–60% of
the snake’s mass. The original categories followed the format of
Mehta (2003) but hatchlings were born at a small size (mean =
4.4 ± 0.68 g) that prohibited the narrower ranges. Snakes were
weighed using an AWS high capacity precision pocket scale (0.1
g) the day prior to each feeding trial and prey mass range was
calculated for them. A prey item within the snake’s range was
chosen ca. one hour before trials began. Mice were transported
to the university in containers in which all individuals of similar
mass were grouped together. Mice were then chosen at random
and weighed to match the appropriate snake. Snakes that failed
DAVID A. PENNING
e-mail: Davidapenning@gmail.com
STEFAN CAIRNS
e-mail: cairns@ucmo.edu
University of Central Missouri, Department of Biology and Earth Science,
WCM 306, Warrensburg, Missouri 64093, USA
Herpetological Review 43(4), 2012
606 HERPETOCULTURE
to eat for four weeks in a row were removed from the study. A
failed feeding trial was considered a period of 40 minutes at any
point of the feeding trial in which the snake did not engage the
prey.
Although previous studies measured snake length using
snout to vent length (Fowler and Salamao 1995), we used snout
to tail length for two reasons: the measurement data attained
from this study came from a larger project requiring minimal
handling; and to compare our data to that of Barnard et al.
(1979). Because of this, snakes were digitally and not manually
measured. Snakes were placed on a piece of 0.5 cm graph pa-
per and photographed directly overhead approximately 100 cm
above the snake. Pictures were then entered into the SnakeMea-
surer© program to get total length. This allowed for the snake
to orient its body in a natural position without being manually
manipulated. Snake length was recorded to the 0.1 cm. Girth (in
cm) was measured using a flexible measuring tape and wrapped
around the snake at midbody and measured to 0.1 cm. Shedding
events were recorded pro re nata. All statistical analysis was con-
ducted on Minitab 14.
Results.—Snake mass is significantly related to the amount
of food consumed in the small and large MR feeding categories
(P < 0.05, small r² = 0.974, large r2 = 0.949) and expressed by the
following simple linear regression models: Small snake mass =
3.85 + 0.419 (total food consumed), Large snake mass = 4.84 +
0.395 (total food consumed). The intercepts and slopes of the
two regression models are not significantly different (General
Linear Model, P > 0.05).
Snake length is significantly related to the amount of food
consumed in the small and large MR feeding categories (P <
0.05, small r² = 0.795, large r2 = 0.810) and expressed by the fol-
lowing simple linear regression models: Small snake length =
33.3 + 0.263 (total food consumed), Large snake length = 32.7
+ 0.244 (total food consumed). The intercepts and slopes of the
regression models are not significantly different (General Linear
Model, P > 0.05).
Snake girth is significantly related to the amount of food con-
sumed in the small and large MR feeding categories (P < 0.05,
small r² = 0.807, large r2 = 0.839) and expressed by the following
simple linear regression models: Small snake girth = 2.23 + 0.0180
(total food consumed), Large snake girth = 2.21 + 0.0183 (total
food consumed). The intercepts and slopes of the regression
models are not significantly different (General Linear Model, P >
0.05). Regression models can be seen in Fig. 1.
Correlations were run among all three growth forms. All cor-
relations are significant at P < 0.05. Mass and girth Pearson corre-
lation coefficients are 0.912 for the small MR category and 0.934
for the large MR category. Mass and length Pearson correlation
coefficients are 0.881 for the small MR category and 0.889 for the
large MR category. Girth and length Pearson correlation coeffi-
cients are 0.853 for the small MR category and 0.922 for the large
MR category.
Snake shed cycles from this experiment are presented in the
same format as that of Myer and Kowell (1973) in Fig. 2.
Discussion.—In both the small and large MR feeding catego-
ries, growth in mass, length, and girth was significantly related
to total food consumed. There was no significant difference
Fig. 1. Rate of growth increase for weight (A), length (B), and girth (C)
based upon the growth rates of 18 individual Red Cornsnakes (Panthe-
rophis guttatus) in two feeding categories over a 22-week feeding trial.
Fig. 2. Age of snakes at sequential shedding periods for both MR
feeding categories. Blue fill indicates the small MR feeding category,
red outline indicates the large MR feeding category.
Fig. 3. Relationship between weight (mass) of individual snakes and
age (in days). Blue lines represent snakes in the small MR feeding cat-
egory and red lines represent snakes in the large MR feeding category.
Herpetological Review 43(4), 2012
HERPETOCULTURE 607
between the regression slopes of the small and large MR feeding
categories for all three growth forms. This statistically supports
the concept that food ingested (regardless of how it is ingested)
will result in similar growth. Snakes in the larger MR category at-
tained a larger mass, girth, and length by the end of the feeding
trials but the overall growth models were not significantly differ-
ent. It took the snakes in the small MR category longer to attain
similar size in all growth forms but arrived at similar sizes as the
large MR category per total food consumed. Mass, length, and
girth gained by the snakes in this study depended upon the to-
tal amount of prey ingested. This supports the idea that snake
mass is not dependent upon age alone. These findings agree with
Barnard et al. (1979) in that snake mass is not an accurate esti-
mation of snake age. These findings also support Barnard et al.
(1979) in that variation (in mass) among individuals increased as
amount of food increased and is presented in a similar format in
Fig. 3. Snake size (mass) should not be used as an estimator of
age beyond reproductive status (which generally accompanies a
minimum age bracket).
We report a similar correlation coefficient as Barnard et al.
(1979) between snake length and body weight (mass) in P. gutta-
tus. A longer study is needed to specifically examine the growth
associations in mutually exclusive MR feeding categories as
Barnard et al. (1979) was a much longer study than the 22-week
length of this experiment. In both the small and large MR feed-
ing categories the correlation coefficients were similar for mass
and length, mass and girth, and length and girth. These correla-
tion coefficients suggest that there is a close association between
the two MR feeding categories growth forms. Length, girth, and
mass all covary with one another in a similar manner.
Cornsnakes had a variable % mass gain [(current pre-feeding
snake mass previous pre-feeding snake mass) / (prey mass
from previous week)*100] in body weight per feeding event.
Love and Love (2005) stated that neonate P. guttatus can convert
up to 33% of their food (prey) weight into body mass. Snakes in
this study had a percent mass gain range of -15% to 93% mass
gain per feeding event. The average percent gain for the small
MR feeding category was 40 ± 19.3%. The average percent gain
for the large MR feeding category was 45 ± 22.4%. The averages
suggest that it is more advantageous to eat larger prey (if the
goal is mass gained) but when accompanied by the standard de-
viations there is no discernible difference between the percent
mass gains of the two MR feeding categories. This observation
is a much more variable number than the percentage presented
by Love and Love (2005). There may be varying metabolic fac-
tors impacting mass gain that were not addressed in this study.
A mass gain ratio does not appear to be a reliable measure of
energetic (body mass) gain.
Acknowledgments.We thank the Department of Biology and
Earth Science’s faculty, staff, and graduate students, more specifi-
cally S. Wilson, K. Dean, and J. Mittelhauser. We also thank A. Brass,
M. Perkins, and A. Bossert for their guidance and editorial reviews.
This research was conducted under IACUC protocol #10-3212.
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... The somatic growth rate of snakes may be defined by feeding frequency and the amount of food intake (Barnard et al. 1979;Taylor and Denardo 2005;Penning and Cairns 2012). In studies where snakes were separated into different feeding groups, treatment groups that ate more frequently (Myer and Kowell 1973;Taylor and Denardo 2005) or consumed larger amounts of food in the same time interval (Forsman and Lindell 1996; Penning and Cairns 2012) grew more rapidly and were larger than snakes in groups fed with a lower frequency or at a lower prey mass to snake body mass ratio. ...
... In studies where snakes were separated into different feeding groups, treatment groups that ate more frequently (Myer and Kowell 1973;Taylor and Denardo 2005) or consumed larger amounts of food in the same time interval (Forsman and Lindell 1996; Penning and Cairns 2012) grew more rapidly and were larger than snakes in groups fed with a lower frequency or at a lower prey mass to snake body mass ratio. However, studies on growth rates in snakes have generally focused on feeding frequency (Taylor and Denardo 2005) or the amount of food ingested (Barnard et al. 1979;Forsman and Lindell 1996;Penning and Cairns 2012), with few relating these two variables (Myer and Kowell 1973). Furthermore, in these studies, the amount of food and frequency of the feedings were not controlled in relation to each other or to body size (but see Penning and Cairns 2012). ...
... However, studies on growth rates in snakes have generally focused on feeding frequency (Taylor and Denardo 2005) or the amount of food ingested (Barnard et al. 1979;Forsman and Lindell 1996;Penning and Cairns 2012), with few relating these two variables (Myer and Kowell 1973). Furthermore, in these studies, the amount of food and frequency of the feedings were not controlled in relation to each other or to body size (but see Penning and Cairns 2012). Thus, it is difficult to accurately infer the effects of feeding frequency and food intake based on these results because animals eating weekly ingest a greater amount of food (twice as much) than individuals eating biweekly if individual meal size remains constant. ...
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... Seigel and Ford (1988) reported the three most common measurements of snakes to be SVL, total length (TL), and mass. While SVL is the standard length measurement used for snakes today, TL is still occasionally used (Penning and Cairns, 2012). Typically SVL measurements are recorded using the methodologies of Fitch (1987) due to its time and cost effectiveness in the field. ...
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