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Reproduction, growth, survivorship and activity patterns in the southwestern earless lizard (Cophosaurus texanus scitulus) (phrynosomatidae) from the Big Bend region of Texas.

Abstract. -- This study reports on various aspects of reproduction, growth and survivorship in a population of the southwestern earless lizard, Cophosaurus texanus scitulus, from Big Bend Ranch State Park in west Texas (U.S.A.) over a two year period. Testis enlargement began in mid-April. For females, the earliest presence of oviductal eggs was the first week of June. No females with oviductal eggs were found after 27 August. Yolked follicles were first observed in females collected on 10 April 1998 and 4 April 1999. Egg weight ranged from 13-35% of the total weight of a female with oviductal eggs. Mean clutch sizes ranged from 2.77-4.67 over the two year period. Females collected earlier in the season had larger fat bodies and higher levels of storage lipids. Males had higher growth rates than females in the juvenile-to-yearling age class and in the growth period between yearling and adult. Adult males were significantly larger than females. No bias in the sex ratio was found for any age class in 1998. In 1999, the sex ratio was skewed in favor of yearling males. Survivorship was low for males (juveniles, 12%; yearlings, 29%; adults, 24%) and females (14, 37 and 16%, respectively). Peak periods of activity were between 1000-1159 hr CST.

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Previous research on the reproductive biology and other aspects of the natural history of the southwestern earless lizard (Cophosaurus texanus scitulus) includes studies on feeding habits and diets (Engeling 1972; Smith et al. 1987; Maury 1995), reproductive biology (Ballinger et al. 1972; Shrank & Ballinger 1973; Vitt 1977; Smith et al. 1987; Sugg et al. 1995), and general life history traits (Howland 1992). However, relatively few populations of this species have been studied in any detail. Any information that will help to assess intraspecific geographical variation in life history traits is essential for a more complete understanding of the relationships between environmental conditions and lizard life histories.

Cophosaurus texanus scitulus is a small to medium-sized phrynosomatid lizard. It is found in far west Texas, west of the Pecos, and extends into southern New Mexico and eastern Arizona (Bartlett & Bartlett 1999). It prefers open areas with sand and exposed rocks (Engeling 1972; Garrett & Barker 1987). This species has a short life span, exhibits small clutch sizes, and produces a variable number of clutches during the breeding season (Sugg et al. 1995).

Field studies were conducted on the reproductive ecology, growth rates and survivorship in a population of C. texanus from west Texas in order to gather more information on these important parameters. The evolutionary processes that act on body size and growth rates have become increasingly interesting to evolutionary biologists (Stearns 1976; 1992; Roff 1992; Punzo 1998; 2000). In addition, differences in growth rates between the sexes have been shown to result in size dimorphism in many species of lizards which has been attributed to a variety of causes (Trivers 1976; Schoener & Schoener 1978; Anderson & Vitt 1990; Sugg 1992). These studies also argue that dimorphism in size is primarily the result of sexual selection. However, others have suggested that size dimorphism results from females having a higher investment in reproductive activities and as a result can allocate less energy toward growth (Downhower 1976; Carothers 1984).

The purpose of this paper is to describe studies on various aspects of the biology of Cophosaurus texanus scitulus from the Big Bend region of west Texas, including reproduction, growth, survivorship and activity patterns.

MATERIALS AND METHODS

The study site consisted of a sandy wash and surrounding flats at the bottom of Madera Canyon (MC) (29[degrees]7'30"N; 103[degrees]55'04"W). The entrance to this canyon is located directly off State Road 170, 5 km NW of Lajitas, Brewster County, Texas, at an elevation of approximately 900 m. This site, which is part of Big Bend Ranch State Park, is characterized by an abundance of exposed rocks, and lies within the creosote/lechuguilla/cactus association of the Chihuahuan Desert in the Big Bend region of Trans Pecos Texas (Punzo 1974; 1998). For a detailed description of the vegetation of this region the reader should consult Tinkham (1948), Warnock (1970) and Powell (1988). A 2.2 ha portion of the site was gridded with wooden stakes and thoroughly censused during March through September, in 1998 and 1999. Additional areas adjacent to the canyon walls were sampled at weekly intervals to assess the degree of migration into and out of the main study site. Voucher specimens have been deposited in the University of Tampa Vertebrate Collection.

Cophosaurus texanus were abundant at this study site. The animals were observed through the use of binoculars while walking slowly through the area. All animals were captured with a noose over the two year period and provided with a unique identification number via toe clipping as described by Punzo (1982). Each lizard was sexed and given a unique paint mark to facilitate identification at a distance as well as upon recapture. Each animal was weighed to the nearest 0.01g using an Ohaus Model 31677 Port-O-Gram electronic balance, and measured its snout-vent length (SVL) to the nearest 0.1 mm with vernier calipers. Cloacal temperatures were recorded with a Schultheis quick-reading thermometer. The microhabitat, soil type, air temperature and time of capture were also recorded for each lizard. Time of capture data were used to determine diel periodicity. All animals were released within 6 hr at the original capture site. Population density was estimated from data on yearling and adult lizards.

Lizards were aged according to SVL. Previous observations on this population indicated that juveniles could be reliably aged on the basis of their small body size, and that there was no overlap in size between yearlings and adults of known age. Lizards were classified as juveniles if their SVL was less than 45 mm. Snout-vent lengths for adult males and females were > 50 mm. Lizards of intermediate size were aged based on their size at first capture, date of first capture, or subsequent growth history if available.

Individual growth rates were calculated from the first capture of a lizard to its final capture in the same active season, based on the increase in SVL (in mm/day), and from the last capture of a lizard in 1998 to its first capture in 1999 (Howland 1992). SVL was chosen as the index of body size due to the high within-individual variation in mass attributed to the reproductive condition of females that has been previously reported for this lizard as well as other species (Ballinger et al. 1972; Vitt 1977; Dunham & Reznick 1987; Howland 1992).

Survivorship was measured for three age classes as described by Howland (1992): juveniles (lizards in their first season); yearlings (lizards in their second active season; approximately one year old); and adults (lizards two years or older). The number of animals of age x + 1 recaptured in 1999 that were initially marked at age x in 1998 divided by the total number of lizards marked at age x in 1998 was used to estimate survivorship. In this approach, the time of hatching is considered age 0, and mortality of eggs between oviposition and hatching is ignored.

Additional samples of males and females were collected weekly during the two year period for anatomical examination. A total of 160 males and 203 females were killed, frozen, returned to the laboratory, and autopsied for reproductive condition. This population is contiguous with several others which allowed for the migration of additional lizards into the study population over subsequent years. Testis weight and length were recorded for males. For females, data were recorded for the number, weight and size of vitellogenic follicles, oviductal eggs, corpora lutea and corpora adiposa. The simultaneous occurrence of vitellogenic follicles with either oviductal eggs or corpora lutea were taken as evidence for the production of multiple clutches by a single female (Vitt 1977). Since previous work has indicated that approximately four weeks are required to produce a clutch of eggs in this species (Ballinger et al. 1972), females that possess vitellogenic follicles or oviductal eggs on two capture dates separated by at least four weeks can provide further evidence for multiple clutches. These data were used to estimate clutch frequency, average clutch size, and age and size at first reproduction.

After removal of the eggs and follicles, the fat bodies were removed, and along with the remaining carcasses, weighed on a Sartorius 215 analytical balance to the nearest 1.0 mg. Fat bodies and carcasses were freeze dried and reweighed to the nearest 0.1 mg. Male and female lizards used for lipid analyses were collected from three sample periods during 1999 : early (19-25 June), middle (16-23 July) and late (19-23 August). Quantitative lipid extraction (total lipids) was conducted separately for vitellogenic follicles, individual oviductal eggs, fat bodies and carcasses according to the procedure described by Congdon & Gibbons (1989). Follicle and egg lipids were not included as a part of storage lipids for females (Ballinger et al. 1972; Howland 1992). The statistical tests used in the analysis of data follow the procedures described by Sokal & Rohlf (1995). For variables influenced by body size, analysis of covariance (ANCOVA) was employed with SVL as the covariate. Adjusted least squares means were then compared with t-tests.

RESULTS

In males, testis enlargement began in mid-April and regression was completed by mid-August in both years (Table 1). Males attain maturity at a size of 50-52 mm SVL, about 11 months after hatching. For females, the earliest presence of oviductal eggs was 5 June in 1998, and 3 June in 1999. No females with oviductal eggs were found after 27 August. The highest frequency of gravid females occurred during two periods in 1998, and three periods in 1999. In 1998, 23 females with oviductal eggs were collected between 11-17 June, and 19 females between 7-13 August. For 1999 the data were as follows: 29 females between 6-12 June, 33 between 6-15 July and 17 between 12-18 August. Thus, oviposition in C. texanus from this site occurs from early June to late August.

The smallest female in either year that contained oviductal eggs had a SVL of 51 mm. In 1998 and 1999, 14 and 9 females, respectively, were reproductive at body sizes ranging from 51.5-53.5 mm SVL. A total of 24 females were reproductive at approximately 11.5 months after the initial appearance of hatchlings. On the basis of body size (SVL) and dates of capture, females attain sexual maturity at a SVL of 51-53 mm, and an age of 11-11.5 months.

The mean clutch sizes for C. texanus ranged from 3.07-4.67 in 1998, and from 2.77-4.43 in 1999 (Table 2). It can be seen that clutch sizes decreased as the breeding season progressed, and this decrease was significant from July to August. Seventeen recaptured lizards showed evidence for multiple clutches in 1998, and 12 in 1999. The simultaneous presence of vitellogenic follicles and oviductal eggs suggested that these lizards would have produced two clutches.

With respect to the reproductive condition of the females, the ovaries of immature females contained 8-21 translucent white follicles ranging in size from 0.25-1.2 mm in diameter. Yolked follicles were first observed in females collected on 10 April in 1998, and on 4 April in 1999. It is possible that yolking could occur earlier at this site since oviductal eggs were present in some females as early as 17 and 20 April, in 1998 and 1999, respectively. Yolked follicles were found in females throughout the reproductive season. None were observed after 5 August in 1998, and 11 August in 1999.

Although the precise length of time required for follicular development is not known, it is most likely about 30 days, since the first large proportion of females containing oviductal eggs occurred in the May sample for both years, one month after the occurrence of a high proportion of females with yolked follicles. The occurrence of yolked follicles in females containing oviductal eggs occurred in 24 cases in 1998, and 18 cases in 1999. The size of the follicles ranged from 0.007-0.023g in weight, and from 2.1-3.2 mm in diameter. Since this represents only 12% of the maximum follicular size attained in this population, it is reasonable to conclude that follicular development was only recently initiated in these females.

Oviductal eggs were present in 31% (31 out of 100) and 49% (50 out of 103) of the reproductive females in 1998 and 1999, respectively. These eggs ranged from 9-14.3 mm in length, and 4.6-7.5 mm in width, with a mean weight of 0.307g (0.209-0.426g). The egg weight ranged from 13-35% of the total weight of a female with oviductal eggs. The smallest oviductal egg weight was less than the largest follicle weight. However, the largest egg weight recorded for females over the entire study period was markedly heavier than that for the largest follicle weight (0.248g). In smaller females (< 58 mm, SVL), the average weight of eggs deposited before June (0.265g [+ or -] .024 SD) was significantly smaller (p < 0.05) than the average egg weight (0.316g [+ or -] .017) laid by larger females (> 59 mm) during the same period. The difference in the average weight of eggs laid by smaller females (51-55 mm) after the middle of June (0.339g [+ or -] .021) did not differ significantly (P > 0.1) from the egg weight of larger females (0.331g [+ or -] .016).

The levels of storage lipids and lipid components (fat body and carcass lipids) for females (1999) showed significant differences among the sampling periods (ANCOVA: F = 12.13, P < 0.001; F = 10.76, P < 0.001; F = 11.84, P < 0.001, respectively) (Table 3). Larger fat bodies were observed in females earlier in the season perhaps attributable to the incomplete development of follicles. No significant differences in the variation of storage lipids or major lipid components were found for males between sampling periods (P > 0.05). Females collected during the early sampling period had significantly higher levels of storage lipids (F = 7.71, P < 0.03) and carcass lipids (ANCOVA: F = 8.06, P < 0.02) than males. No significant differences were found in the late sampling period (P > 0.05). Since yearlings and adults exhibited no significant differences in lipid levels for any sample period, they were lumped for all other lipid comparisons.

In females (1999), fat body wet mass was significantly correlated with carcass lipids (F = 37.22, P < 0.001, [r.sup.2] = 0.71), fat body lipids (F = 601.23, P < 0.001, [r.sup.2] = 0.88), and storage lipids (F = 506.67, P < 0.001, [r.sup.2] = 0.84). Similar patterns were observed for males (F = 29.66, P < 0.001, [r.sup.2] = 0.92; F = 544.76, P < 0.001, [r.sup.2] = 0.79; F = 447.21, P < 0.001, [r.sup.2] = 0.87, respectively). The correlations between egg lipids and egg wet mass (F = 3.99, P < 0.05, [r.sup.2] = 0.42), and dry mass (F = 33.84, P < 0.001, [r.sup.2] = 0.39), were significant. The carcass lipids accounted for 27% of the variation in total egg lipids within a clutch (F = 3.87, P < 0.05, [r.sup.2] = 0.27). Lipid levels in eggs were significantly higher during the early sample period than in the middle or late samples (ANCOVA, with SVL as covariate: P < 0.05). Egg dry mass from the late sample period was significantly lower than that of the early period (P < 0.01) or the middle period (P < 0.02).

The mean sex-specific growth rates (in mm/day) for the various age classes of C. texanus are shown in Table 4. In this population, males had higher growth rates than females in the juvenile-to-yearling age class in both 1998 and 1999 (ANOVA: F = 9.32, P < 0.01; F = 7.88, P < 0.02, respectively) and in the growth period between yearling and adult (F = 11.01, P < 0.01; F = 6.99, P < 0.02). The data also indicated that male growth rates were highest during the juvenile-to-yearling and yearling age classes. Growth rates typically declined with increasing age as well.

Adult males were significantly larger than females (Z = 12.07, P < 0.001). The mean SVL for females in August was 59.33 mm (1998) and 58.97 mm (1999) (Table 2), with a maximum of 64 mm. For males, the values were 63.72 mm ([+ or -] 3.01SD) in 1998, and 66.03 mm ([+ or -] 2.97) in 1999, respectively, with a maximum of 72 mm. No bias in the sex ratio was observed for adults and yearlings in 1998 ([X.sup.2] = 3.07, P > 0.05) and 1999 ([X.sup.2] = 5.36, P > 0.1).

No bias was found for the sex ratios of juveniles ([X.sup.2] = 1.93, P < 0.1), yearlings ([X.sup.2] = 3.01, P > 0.15), or adults ([X.sup.2] = 2.23, P > 0.1) in 1998. In 1999, the sex ratio was skewed in favor of yearling males (1.6 : 1; [X.sup.2] = 8.04, P < 0.01), but not in other age classes. Survivor-ship for males between 1998 and 1999 was 12% for juveniles, 29% for yearlings and 24% for adults. For females, the values were 14%, 37%, and 16%, respectively.

Only adults and yearlings were tabulated for density estimates. The gridded area encompassed 2.2 ha and contained 193 marked individuals (88 lizards/ha) in 1998.

Cophosaurus texanus was strongly diurnal in its diel periodicity (Table 5). The peak time of activity at this site was between 1000-1159 hr (Central Standard Time, CST). No lizards were collected between 1900-0759 hr. No significant differences in activity were found between the sexes or age classes. In addition, activity patterns showed no significant seasonal shifts (G = 1.87, P > 0.05).

Incidental observations indicated that only those lizards whose home ranges were located close to the boundaries of the gridded study site exhibited any movements into or out of this area. Twenty-one adult (12 males; 9 females) and 7 yearling lizards traveled in various directions over distances ranging from 35 to 90 m. No directional bias was noted in these movement patterns.

DISCUSSION

The Madera Canyon (MC) population of C. texanus exhibited similar clutch sizes and growth rates when compared to populations from Rosillos Ranch (RR) and Grapevine Hills (GVH), approximately 40 km further south, in Big Bend National Park (BBNP) as reported by Howland (1992), and from Elephant Butte (EB), New Mexico (Sugg et al. 1995). Body sizes were somewhat smaller and adult survivorship was lower. However, the MC population exhibited smaller clutch sizes, lower clutch frequencies, and delayed reproduction when compared to times reported for populations of this species from central and west-central Texas (Johnson 1960; Ballinger et al. 1972; Engeling 1972). Although Howland (1992) suggested that C. texanus from BBNP may lay up to three clutches per season, and Ballinger et al. (1972) suggested a maximum of five clutches for a population from San Angelo, Texas, additional studies are needed to determine the reproductive potential of C. texanus more precisely. Nonetheless, the data available for reproduction in C. texanus indicates that this species is characterized by early sexual maturation and reduced longevity. Selection should favor animals that expend a large amount of reproductive energy earlier in life (Congdon et al. 1982; Stearns 1992).

The smaller clutch size and growth rates exhibited by the MC, RR and GVH, and EB populations may be due to lower annual precipitation levels at these locations. The larger clutch sizes reported from central and west-central Texas are associated with habitats that experience 1.5-2.5 times the mean precipitation levels that characterize lowland habitats at BBNP (Medellin-Leal 1982; Punzo 1991) and MC (Punzo 1997). It is well known that precipitation has a pronounced effect on the amount of vegetation and the abundance of arthropods available as food to lizards (Dunham 1978; Pianka 1986; Fellers & Drost 1991). Increased food intake would increase the amount of energy available for reproduction and other activities.

At MC, the mean clutch sizes decreased significantly from July to August. Howland (1992) reported a significant decrease in clutch size for C. texanus from GVH (from a mean of 3.7 in early July, to 2.82 in mid-August). However, females from the RR population did not show any concomitant decrease. Ballinger et al. (1972) reported no significant difference in clutch size over the breeding season in C. texanus from San Angelo (SA), Texas.

The results of this study showed that males had higher growth rates than females in the juvenile-to-yearling age class. This is in agreement with studies on populations of C. texanus from other localities (Johnson 1960; Ballinger et al. 1972; Engeling 1972; Howland 1992) as well as other species of desert lizards (Pianka 1986). Females most likely begin to allocate increasing energy sources to reproduction as soon as they become sexually mature thereby decreasing the amount of energy allocated toward growth. Sugg et al. (1995) showed that female growth in the EB population of C. texanus decreases at an earlier age than males suggesting that females devote more energy to reproduction earlier in life. They found that the energy content of eggs accounted for 63-90% of the difference in adult size between the sexes.

At the MC site, females can attain sexual maturity at minimum body sizes (SVL) from 51-53 mm, and at an age of 11-11.5 months. At the GVH site, the smallest female with oviductal eggs was 52 mm SVL, and 6 females were reproductive at 53-55 mm (Howland 1992). Several females at the GVH and RR sites were reproductive at 12 months of age. Thus, the lizards at MC appear to reach maturity a little earlier in the season than those animals further south in BBNP. In the SA population, reproductive females ranged in size from 50-56 mm SVL (mean: 60 mm) (Ballinger et al. 1972). In view of the relatively short life span of C. texanus, sexual selection may have acted to increase male growth rates as well as size, resulting in sexual dimorphism (Sugg 1992; Sugg et al. 1995). Previous studies have shown a relationship between large size and the mating success of males in several species of lizards (Trivers 1976; Cooper & Vitt 1989; Anderson & Vitt 1990). The increased growth and size of males may also be related to their defense of territiories. It has been shown in other species of lizards that larger males are usually more successful at establishing and defending territories than smaller males (Clarke 1965; Stamps 1983).

The sum of fat body lipids and carcass lipids represents storage lipids (Shrank & Ballinger 1973; Derickson 1976). Females from MC collected early in the season exhibited significantly higher levels of storage lipids and carcass lipids when compared to males. These levels decreased later in the season when reproduction was complete. Schrank & Ballinger (1973) observed a depletion of the fat bodies of C. texanus females from central Texas during the early summer months and suggested that these lipids are used during early reproduction. Hahn & Tinkle (1965) were among the first to experimentally demonstrate the importance of stored lipids in corpora adiposa to the production of the first clutch of eggs in the side-blotched lizard, Uta stansburiana. Large corpora adiposa were present in females early in the season before follicular development, followed by a decrease during the middle of the summer, and another increase in post-reproductive females later in the season. Similar depletion patterns have been reported for other populations of C. texanus (Johnson 1960; Ballinger et al. 1972; Howland 1992) as well as other species of lizards (Vitt & Cooper 1985; Ramirez-Pinilla 1991; Flemming 1993; Van Wyk 1994).

The low values for survivorship in juveniles, yearlings and adult males and females indicates a high rate of mortality for these lizards. They are commonly preyed upon by roadrunners (Geococcyx californianus), long-nose leopard lizards (Gambelia wislizenii), and a number of snakes including the western coachwhip, (Masticophis flagellum), striped whipsnake (M. taeniatus), and long-nosed snake (Rhinocheilus lecontei) at the MC site. Even higher mortality rates were reported by Engeling (1972) for C. texanus from Comal County, Texas. The relatively low abundance of arthropods at this site may also contribute to mortality as well (Punzo 1997).

No bias in the sex ratio was observed for any age class of C. texanus in 1998 from MC. In 1999, the sex ratio was skewed in favor of yearling males (1.6:1). A bias toward juvenile females was reported for a population of C. texanus from GVH in 1981 but not from the RR site (Howland 1992). No bias was observed for any age class in 1982. Smith et al. (1987) reported a bias toward adult males in a population of C. texanus from Arizona and male : female sex ratios of 53:50 (1.6:1) and 42:40 (1.05:1) for yearlings and juveniles, respectively.

Cophosaurus texanus at the MC site were strongly diurnal which is in agreement with data from other populations (Cagle 1950; Degenhardt 1966; Smith et al. 1987). Between 0800-0859 hr, they begin to emerge from their shelter sites within rock crevices and under rocks and other surface debris. They prefer open sandy areas with scattered vegetation and occupy this habitat with other ground-dwelling species including two teiid lizards, the western whiptail, Cnemidophorus tigris and the little striped whiptail, C. inornatus. Future studies should analyze the types of interactions between these ground-dwelling lizard species to assess the degree of competition and resource partitioning.

In summary, C. texanus scitulus populations in west Texas exhibit short life spans, early maturity, relatively large clutch size, and low population densities. Their growth rates are lower than those reported for C. texanus from central Texas. Cophosaurus texanus scitulus exhibits a seasonal decline in clutch and egg size as well as in the depletion of storage lipids, suggesting that this population is limited by available resources.
Table 1. Testis weight (g) for Cophosaurus texanus males during the
reproductive season. Values represent means ([+ or -]SD). Numbers in
parentheses beneath the testes weights represent the sample size for
that year.

 Mean Testis Weight (g)
Month n 1998 1999

March 12 0.076 (.008) (7) 0.078 (.007) (5)
April 31 0.134 (.006) (18) 0.132 (.007) (13)
May 24 0.154 (.011) (10) 0.149 (.008) (14)
June 27 0.127 (.009) (16) 0.129 (.010) (11)
July 30 0.085 (.002) (17) 0.091 (.004) (13)
August 22 0.066 (.004) (10) 0.071 (.003) (12)
September 14 0.047 (.005) (7) 0.049 (.002) (7)

Table 2. Mean clutch sizes and snout-vent lengths (SVL) for females of
Cophosaurus texanus (1998 and 1999) from west Texas. Values in
parentheses represent ([+ or -]SD). Sample data with different
superscripts differ (Mann-Whitney-Wilcoxon Z-tests, P < 0.02); those
with the same superscripts do not differ (P > 0.05)

 Number Clutch Size SVL (mm)

1998
 June 34 4.67 (0.38) (a) 58.83 (2.92) (a)
 July 26 4.21 (0.18) (a) 59.53 (3.27) (a)
 August 43 3.07 (0.22) (b) 59.33 (2.79) (a)

1999
 June 47 4.43 (0.44) (a) 58.47 (3.04) (a)
 July 31 3.86 (0.31) (a) 58.89 (2.85) (a)
 August 29 2.77 (0.17) (b) 58.97 (2.68) (a)

Table 3. Total lipid levels and fat body wet masses for Cophosaurus
texanus during 1999. Adults and yearlings are lumped within each group.
Values represent means [+ or -]SD. Numbers in parentheses represent
sample sizes. Statistical analyses are based on comparisons of adjusted
least squares means on log-transformed data using t-tests with
significance level adjusted for multiple comparisons. For intrasexual
comparisons, values with different superscripts differ significantly
(P < 0.01) whereas others do not (P > 0.05). Sampling periods for
lizards used in these analyses: early (19-25 June); middle (16-23 July);
late (19-23 August).

 Fat body lipids (g)
Sample
period Females Males

Early 0.043 [+ or -] .03 (a) (21) 0.036 [+ or -] .01 (a) (8)
Middle 0.037 [+ or -] .01 (a) (36) 0.033 [+ or -] .02 (a) (21)
Late 0.018 [+ or -] .01 (b) (19) 0.025 [+ or -] .003 (b) (28)

 Carcass lipids (g)
Sample
period Females Males

Early 0.161 [+ or -] .03 (a) (21) 0.159 [+ or -] .01 (a) (8)
Middle 0.174 [+ or -] .04 (a) (36) 0.161 [+ or -] .02 (a) (21)
Late 0.067 [+ or -] .01 (b) (19) 0.158 [+ or -] .02 (a) (28)

Table 4. Mean sex-specific growth rates (in mm/day) for various age
classes of Cophosaurus texanus from west Texas. Values represent means
[+ or -] SD. Data pooled from 1998 and 1999. Sample sizes shown in
parentheses. For intrasexual comparisons of age classes, growth rates
with different superscripts indicate significant differences (Tukey's
HSD test: a - 0.05). Asterisks indicate age classes exhibiting
intersexual differences in growth rates (t-tests: all P < 0.05).

 Mean growth rates (mm/day)
Age class Females Males

Juvenile 0.149 [+ or -] .009 0.115 [+ or -] .011
 (15) (a) (11) (ab)
Juvenile-to-yearling* 0.134 [+ or -] .012 0.159 [+ or -] .015
 (22) (a) (9) (a)
Yearling* 0.073 [+ or -] .015 0.121 [+ or -] .008
 (35) (b) (19) (a)
Yearling-to-adult* 0.022 [+ or -] .005 0.063 [+ or -] .002
 (10) (c) (15) (bc)
Adult 0.010 [+ or -] .001 0.006 [+ or -] .003
 (20) (c) (27) (c)

Table 5. Daily activity patterns for Cophosaurus texanus from west
Texas. Time intervals represent CST.

 1998 1999
 Percent Percent
Time interval n frequency n frequency

0700-0759 0 0 0 0
0800-0859 7 4.9 2 0
0900-0959 13 9.0 10 8.8
1000-1059 42 29.2 31 27.4
1100-1159 31 21.6 29 25.8
1200-1259 19 13.1 11 9.7
1300-1359 11 7.6 7 6.2
1400-1459 4 2.8 9 8.0
1500-1559 6 4.2 8 7.1
1600-1659 3 2.1 0 0
1700-1759 6 4.2 3 2.7
1800-1859 2 1.3 3 2.7
1900-1959 0 0 0 0
2000-2059 0 0 0 0


ACKNOWLEDGMENTS

This study was supported by a Faculty Development Grant from the University of Tampa. I wish to thank T. Punzo, J. Bottrell, K. Smart, L. Henderson and T. Ferraioli for assistance in collection of specimens and field observations, B. Garman for consultation on statistical procedures, and R. Schleuter, C. Bradford, and two anonymous reviewers for commenting on earlier drafts of the manuscript. This research was conducted with the permission of the Texas Parks and Wildlife Department, Permit # 66-98.

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Fred Punzo

Box 5F, Department of Biology, University of Tampa

Tampa, Florida 33606

FP at: fpunzo@alpha.utampa.edu
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Publication:The Texas Journal of Science
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Date:Aug 1, 2000
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