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Herpetologists' League

Ecology, Reproduction, and Reproductive Effort of the Iguanid Lizard Urosaurus graciosus onthe Lower Colorado RiverAuthor(s): Laurie J. Vitt and Robert D. OhmartSource: Herpetologica, Vol. 31, No. 1 (Mar., 1975), pp. 56-65Published by: Herpetologists' LeagueStable URL: http://www.jstor.org/stable/3891986Accessed: 22/09/2008 16:37

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ECOLOGY, REPRODUCTION, AND REPRODUCTIVE EFFORTOF THE IGUANID LIZARD UROSAURUS GRACIOSUSON THE LOWER COLORADO RIVER

LAURIE J. VITT AND ROBERT D. OHMARTABSTRACT: Urosaurusgraciosuswas studied from March through November 1973 on the lower Colo-rado River, primarilyYuma and Mohave counties, Arizona. Limited reproductiveinformationfrom thesame population in 1974 was also evaluated. The species is strictly arboreal, nhabiting primarilymes-quite, ironwood, and smoke trees. Foraging occurredin the outer canopy of trees and stomach contentsshowed a high incidence of arborealinsects. Seasonal shifts were apparent in the diet, probably reflect-ing seasonal differences in insect abundance. Reproductiveseason extended from May through August.Clutch size for 23 9 9 averaged 5.3 (range, 3-10) and there was the potential for two clutches perseason. In d 8, spermiogenesiscommencedin April and sperm were present in the testes and epididymisfrom April through July. Fat body cycle in 8 8 appearedto be a function of food supply. Fat bodycycle in 9 9 was inversely related to reproductive cycle early in the season but did not show this trendlater in the season.Tail break incidence was low as comparedto other species and observationson foraging and climbing

suggest that the tail serves a balance function, with autotomyfor predatorescape and intrasexual ightingsecondary.Reproductive effort, defined as the ratio of total clutch calories of ash-free dry weight (AFDW):total body calories (AFDW), averaged0.640 (range, 0.474-0.725). Mean caloriccontent per gramof egg(AFDW) was 6,612 compared to 5,492 calories per gram of body (AFDW). The wet ratio of clutchweight: body weight was 0.313 (range, 0.271-0.399) whereas the dry ratio was 0.531 (range, 0.403-0.604). In terms of reproductive and other attributes, U. graciosusfits the r strategy.

UROSAURUS graciosus inhabits smallshrubs in sparsely vegetated desert regionsof western North America (Stebbins, 1954),but it is common in larger vegetation inriparian situations in Arizona and south-eastern California. Thermal ecology ofthis species was studied by Gates (1963)on the Hassayampa River near Wicken-burg, Arizona, and Brattstrom (1965) in-cluded this species in a study of reptilebody temperatures. Norris and Lowe (1964)studied color matching in U. graciosus fromthe Mohave Desert, and Pianka (1965, 1967)included this species in studies of lizardspecies diversity in flatland deserts of NorthAmerica. Our study presents new informa-tion on reproduction and ecology of U.graciosus in riparian habitats on the lowerColorado River, in combination with esti-mates of reproductive effort based oncaloric content of eggs and bodies.

MATERIALS AND METHODS

Description of Study Area.-The studyarea was located between 320 30' and 350 15'HERPETOLOGICA 31:56-65. March 1975

N and 114?-115? W, extending from nearTopock, Mohave County, Arizona in thenorth, to the Mexican-American Interna-tional Boundary in the south. The desert inthis region falls into the "Lower ColoradoDesert Subregion" (Shreve, 1951) and ageneral description of the habitat appearselsewhere (Vitt and Ohmart, 1974).Samples of U. graciosus were collectedfrom March through November of 1973. Inaddition, data from 9 9 collected in thesame localities during June, July, and Au-gust of 1974 were included. Lizards werecollected by hand, noose, and BB rifle. Atthe time of collection, snout-vent length(SVL), total tail length, and length of re-generated tail portion (if any) were re-corded to the nearest millimeter. Data onmicrohabitat included vegetation typewhere lizard was first sighted, time of day,position of lizard, and whether the animalwas basking, foraging, or attempting escape.For analysis of diet, contents of stomachswere identified. Volume of excised stomachwas determined by liquid volume displace-ment in a narrow graduated cylinder. The

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March 1975] HERPETOLOGICA 57stomach was then emptied and the volumeof the lining was determined in the samemanner. The difference between the twovalues yielded stomach content volume. Therelative proportion of each type of food itemwas determined visually with the aid of agridded petri dish, taking into account dif-ferences in thickness of prey items. The vol-ume of any given food item could then bedetermined by multiplying the proportiontaken up by that item by the stomach con-tent volume. All food items were identifiedto at least family where possible. Incidenceof parasites and non-food material such asrocks, sand, and miscellaneous vegetationwas also recorded. Food items were thengrouped into broad categories related toprobable spatial location within the habitatin order to gain insight into foraging pat-terns of U. graciosus. These data were thencoupled with observations on foraging andfeeding behavior.Lizards used for reproductive informationwere fixed in 10%buffered Formalin withinone hour of collection. After 24-48 hoursfixation, lizards were stored in 50% isopro-pyl alcohol. Laboratory measurements ontestes and fat bodies of 8 S included length,width, and weight. Since shape of fatbodies was variable, only weight data wereused. Fat bodies were apparently not af-fected by storage in isopropanol since theywere solid and intact when measured. Lefttestis and attached epididymis of each 8were embedded in paraffin and sectionedat 10 jum after standard dehydration. Sec-tions were doubly stained with Harris' hema-toxylin and eosin. For each Y, clutch size,egg length and width (ovarian and ovi-ducal), and weight of fat bodies were re-corded. Weights were to the nearest 0.001g and linear measurements were to thenearest 0.1 mm.

Lizards used for estimating reproductiveeffort were fresh frozen in the field usingdry ice (solid CO2). Only 9 9 with freshlyovulated (oviducal) eggs were used. Wetweights of body and total clutch were re-corded to the nearest 0.1 mg. In addition,

number, size, and location of oviducal eggswere recorded. Bodies were then ovendried at 700 C and eggs freeze-dried to con-stant weights (unsatisfactory drying ofbodies resulted from attempts to freeze-drythem). These weights were also recordedto the nearest 0.1 mg. Bodies were groundin a Wiley Mill and eggs were ground bymortar and pestle. Samples of each bodyand clutch were ashed at 5500 C for 24 hfor correction of caloric determinations.This was necessary since ash content ofbodies and eggs are quite different. Threealiquant samples (9-14 mg) per lizard bodyand per individual (eggs pooled) clutchwere burned in a Phillipson microbombcalorimeter (Phillipson, 1965). Calories ofash free dry weight (AFDW) were thencalculated in the standard fashion, utilizingknown calories per unit weight of benzoicacid as a standard. The ratio of total clutchcalories to total body calories was utilizedas the best estimate of reproductive effort.

RESULTSAND DIsCUSSIONOn the lower Colorado River, U. graciosuswas strictly arboreal, inhabiting mesquite(Prosopis juliflora and P. pubescens), smoketrees (Dalea spinosa), and ironwood trees(Olneya tesota). A few adults were foundin cottonwood trees (Populus fremontii) andseveral juveniles were found on creosote(Larrea divaricata) and other small shrubs.During spring and fall, lizards were activefrom late morning to late afternoon. During

late spring, summer, and early fall therewas a shift toward early morning (0530-0800) and late afternoon (1800-2000) activ-ity. Few were seen during midday at thistime, and those observed were not foragingbut rather positioned on tree trunks in theshade. During warmer months, individualswere found at night, apparently sleeping inhorizontal positions on branches. Duringspring and late fall, lizards did not spendthe nights in trees, but could be found earlyin the morning beneath bark and in packratnests.Feeding and Foraging.-Foraging activity

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58 HERPETOLOGICA [Vol. 31, No. 1TABLE 1.-Summary of stomach contents of 87 Urosaurus graciosus collected between March and No-vember, 1973 from the lower Colorado River. Thirty families of insects were present in lizard stomachsin addition to mixed larvae, spiders, and miscellaneous matter. Insects were grouped according to theplace they occur in the habitat in orderto gain insight into foraging place for U. graciosus.

% Total Volume % TotalPrey category Number number (cm3) volume Frequency*Arboreal invertebratesHomopterans 36 2.64 0.93 9.51 15Hymenopterans (not 12 0.88 0.33 3.30 10including ants)Hemipterans 219 16.08 1.11 11.36 28Orthopterans 3 0.22 0.59 5.98 3Dipterans 43 3.15 0.62 6.44 11Neuropterans 3 0.22 0.13 1.29 3Coleopterans 79 5.79 1.20 12.11 30Trichopterans 6 0.44 0.07 0.86 5Odonata 2 0.15 0.32 3.22 2Lepidopterans (parts) 0.07 0.71 1Terrestrial nvertebratesOrthopterans 5 0.36 0.50 5.14 5Neuropterans 1 0.07 0.01 0.15 1Mixed invertebrates (including families with both arboreal and terrestrial species and larval forms)Coleopterans (FamilyTenebrionidae) 18 1.32 0.32 3.24 9Ants (Formicidae) 842 61.82 1.15 11.75 37Unidentified insect parts 0.27 2.80 11Insect eggs 31 2.28 0.15 1.55 7Larvae

Eruciform 21 1.54 0.52 5.26 14Scarabaeiform 14 1.03 0.13 1.31 1Elateriform 7 0.51 0.05 0.55 2Unidentified 6 0.44 0.15 1.53 6Spiders 13 0.95 0.34 3.47 10MiscellaneousLizard (shed skin) 0.05 0.47 1ImmatureU. graciosus 1 0.07 0.19 1.94 1Sand, gravel, andvegetation parts 0.58 5.93 55

TOTALS 1362 99.96% 9.78 99.87% 268* Number of stomachs containing the specific item indicated.

occurred in the morning with seasonalshifts as mentioned earlier. Lizards foragedin the outer canopy of the vegetation. Oneindividual descended a smoke tree, crossed10 m of a sandy wash, ascended a mesquite,climbed to an outer branch tip, and de-voured a small vespid wasp. The actionswere so deliberate that it appeared the liz-ard observed the wasp from its originalperch in the smoke tree. Both the "sit andwait" and "widely foraging" strategies

(Pianka, 1974) were observed. Here,"widely foraging" is somewhat restricted,referring to active searching from branchtip to branch tip. Individual lizards, whileapparently basking, would take any insectsthat moved in front of them.Information on food habits (Table 1) in-dicates that U. graciosus is restricted in dietonly by the microhabitat that it utilizes.The wide variety (over 30 insect familiesin addition to other arthropods) suggests

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Alarch 1975] HERPETOLOGICA 59

5012A

w8~~~40 o Ants1 #14O *I ~~~~~~~~A> 30 l .4 20 z rtotrn0 2~~~~~'00

T/ O,tntopteransZ /~~~~~~0 20 1~"

A ~ ~ ~ ~ ~ A10 - Homopterans

At 'A- , AAll Larvaeb .... ..A Hemipterans

MAR-APR1MAY JUN 'JUL AUG SEP OCT-NOVMONTH

FIG. 1.-Seasonal variation in the diet of Urosaurus graciosus from the lower Colorado River. Onlythe most common items in terms of %volume (see Table 1) are shown. Seasonal differences in theutilization of prey items suggest differences in seasonal relative abundanceof prey in view of observa-tions on foraging (see text).that this species is a very generalized feeder.Seasonal shifts were apparent in the com-position of the diet (Fig. 1) and probablyreflect seasonal abundance of potential preyitems. Overall, arboreal families of the fol-lowing orders comprised a majority of thediet; hemiptera, coleoptera, homoptera,orthoptera, and hymenoptera. Comparedto the sympatric semiarboreal speciesSceloporus magister (Parker and Pianka,1973; Vitt and Ohmart, 1974), U. graciosusutilizes more insects occurring in the outercanopy of the vegetation than S. magisterand the latter utilizes more terrestrial in-sects. Barnes (1974) found that these twospecies even utilize different ant species.Since the foraging patterns of the differentant species were similar to the foraging pat-terns of the lizard species feeding on them,the data of Barnes (1974) is in full supportof the above discussion.Body form of U. graciosus is slender ascompared to either S. magister or U. ornatus,both of which occur in sympatry with U.

graciosus in areas along the lower ColoradoRiver (Table 2). The slender body formcoupled with small body size of U. graciosusis advantageous in terms of agility and abil-ity to forage in the outer canopy of vegeta-tion where branches are thin. In addition,this body form is adaptive in terms of pred-ator escape in that the lizards become cryp-tic in form and color (Norris and Lowe,1964) when pressed against a thin branch.The long tail appears to serve a balancingfunction, similar to the lizard Anolis caro-linensis (Ballinger, 1973). Lizards observedforaging extended the tail, apparently forbalance, while positioned in a perpendicularstance on small limbs. Since tail retentionwould be at a premium if in fact balancewere important, incidence of tail break asevidenced by regenerated tails would beexpected to be low as compared to specieswith tail adaptations primarily for predatorescape. In fact, tail break in U. graciosus(Fig. 2) is quite low as compared to eitherU. ornatus (Vitt, 1974a; Barnes, 1974) or S.

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60 HERPETOLOGICA [Vol. 31, No. 1TABLE 2.-Comparison of body proportions n threearboreal or semiarboreal lizards from the lowerColorado River. All figures represent mean ratiosof adult d 8 (N = 10/species). Data on 9 9were also collected but were not different fromthose of d . In terms of tail length and bodywidth, U. graciosus was significantly differentfromU. ornatus. U. graciosuswas significantly differentin all ratios from S. magister. Overall,U. graciosusis more slender in body form than the two otherarboreal forms.

Tail Head Head Bodylength/ width/ length/ width/Species SVL SVL SVL SVLUrosaurus graciosus 2.24* 0.18** 0.21** 0.22*Urosaurusornatus 1.69 0.19 0.22 0.25Sceloporus magister 1.30 0.23 0.18 0.32

* Indicates significant difference (P < .05) from Uornatus and S. magister.** Indicates significant difference (P < .05) from S.magister, but not from U. ornatus.

magister (Parker and Pianka, 1973; Vitt etal., 1974; Vitt and Ohmart, 1974). It mustbe kept in mind that U. graciosus is capableof tail autotomy and some tails are undoubt-edly lost from intrasexual fighting andpredation. In view of work by Congdon etal. (1974), the tail adaptation in U. gracio-sus most likely represents an adaptive com-

u 03005 ~~~~~~~~~~~0L20 \ 0- 0--,* - --1000 *--e--@ -0---020

15 Urosaurus graciosusN=88m

n 0-5-

20-35 35-40 141-45 145-50 51 5556 50 5155Snout vent Length (mm)FiG. 2.-Composition of samples of Urosaurusgraciosus from the lower Colorado River showingsexual dimorphismin size and relative tail break.In view of other studies on tail breaks in iguanidlizards, the high incidence noted in 20-40 mm S 8is probably a result of sampling error.

W .02

.00 -_ _ _ __C)) 3F-.03-(D

02F-) ol f3

4 --r OC Urosaurus graciosus

MAR APR MAY JUN JUL AUG SEP NOVFIG. 3.-Seasonal changes in weights (in grams)of testes and fat bodies of adult Urosaurusgracio-sus d d from the lower ColoradoRiver. Horizon-tal line representsthe mean and bars representone

standard error of the mean.* Sample size for testes was 2 here since one lizardhad been shot through the testes.

promisewhereretention or balancing unc-tionis important,but autotomy orpredatorescapeandescapein intrasexual ncountersis also important.MaleReproduction ndFatBodyCycling.-The breeding season for d d extendedfrom April through July. Mating was ob-servedand spermwerepresent n the testesand epididymis during this time. Testesremainedat maximum ize (Fig. 3) duringthis period. Testes in Marchwere inactiveand no spermiogenesiswas observed. Apriltestes were muchlargerand spermatogonialcell proliferation, spermatogenesis, andspermiogenesis were occurring. The epi-didymal lining was regressed during March,but by mid April, the epididymal epithe-lium increased in height with the cell nucleimigrating toward the basal membrane.Sperm were present in the epididymis at

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March 1975] HERPETOLOGICA 61

E 2z

0

40-uU 0

30-

w20-

F-

10-

0

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DECMONTH

FIG. 4.-Seasonal high (upper line) and low (lower line) temperatures and rainfall data from theYuma substation of the National Weather Service. The study area is characterizedby little fluctuationbetween daytime high and nighttime low temperatures n addition to little rainfall.

this time. Spermiogenesis was not occurringin July testes but sperm remained in boththe testes and epididymis. Regression wasnot yet apparent. By August, regressionwas apparent and cellular debris was pres-ent in the testes and epididymis. At thistime, the epididymal epithelium was re-duced in height and the nuclei were posi-tioned away from the basal membrane.September and November testes were veryregressed and sperm were absent from thetestes and epididymis. In terms of testessize, Gates (1963) reported a similar cyclefor both U. graciosus and U. ornatus nearWickenburg, Maricopa County, Arizona.Near Phoenix, however, Parker (1973)noted that U. ornatus showed increases intestes size during February and March butin southern New Mexico and west Texas,U. ornatus displayed a testicular cycle simi-lar to that reported here for U. graciosus onthe lower Colorado River.Fat bodies of g U. graciosus were large

upon emergence from overwintering anddisplayed a marked size decrease with theonset of the reproductive season (Fig. 3).Shortly after breeding season began, andduring a period when insect abundance ap-peared high (indirect observation based onvegetation blooms in the area), weights offat bodies increased. During July, fatbodies showed a distinct decrease in size,possibly reflecting a food shortage. Sincesummer rains did not occur at this time(Fig. 4), food shortage as the result of lo-calized drought could have occurred. Fol-lowing rains in August, fat bodies of MSincreased in size and remained largethroughout the remainder of the season, atime when orthopterans became abundantin the stomachs (Fig. 1). Although the fatbody cycle of 8 S appears to be inverselyrelated to the testicular cycle (see Fig. 3),correlation of testes and fat bodies was low(r =-.035) and insignificant (F = 0.05, df= 1/40).

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62 HERPETOLOGICA [Vol. 31, No. 1TABLE 3.-Female reproductive data for three arboreal or semiarboreal lizard species from Arizona.Figures in some instances are interpolations from the data presented by the cited authors. Also, theinformation on Sceloporus magister is not limited to Arizonasince the study included data from through-out the species' range.

x Clutch No. clutches Reproductive Minimum SVLSpecies size per season season at maturity Source

Urosaurus graciosus 5.3 (3-10) 1-2 May-Aug 47 This paperUrosauruis raciosus 4.6 (2-7) 1-2 May-Aug Gates (1963)Urosaurus ornatus 7.6 (6-10) 1-2 May-Aug Gates (1963)Urosaurus ornatus 4.8 (2-7) 1 or more Mar-Aug 44 Parker (1973)Sceloporus magister 8.4 (3-12) 1-2 May-Aug 80 Parker and Pianka(1973)

The fat body cycle of U. graciosus wasquite different from that of a sympatricsemiarboreal species, S. magister (Vitt andOhmart, 1974) even though collections weremade simultaneously. S. magister had rela-tively small fat bodies from March throughJune with a marked increase during Julyand August, followed by a decrease in Sep-tember. Perhaps differences in the relativeseasonal abundance of insects within themicrohabitats where foraging occurs ac-counts for the observed fat body cycle dif-ferences. Current studies by the authors onthe same species in another riparian habitat,utilizing large samples, may bear this out.Although there are no fat body data on U.ornatus, differences in the foraging micro-

10- aw 8N

6-D 0U 4- *0 * *

02- n =23r =0.39

I~~~~~ I50 55 60SNOUT-VENT LENGTH(mm)FIG. 5.-Clutch size data as related to body size(SVL) for 23 Urosaurus graciosus 9 9 collectedalong the lower Colorado River during 1973-74.

habitat (Barnes, 1974) between this speciesand U. graciosus and S. magister would beexpected to influence fat body cycles rela-tive to insect abundance as discussed above.Female Reproduction and Fat BodyCycling.-Deposition of lipids in follicleswas apparent by the first of May during1973. The first 9 containing oviducal eggswas collected on 28 May. 9 9 with oviducaleggs were found from the end of Maythrough the end of August, suggesting anextended breeding season. In addition, twodifferent size groups of juveniles were ob-served in late fall indicating success of earlyand late clutches. Shaw (1952) reportedincubation times of 62 and 78 days for eggsof this species under laboratory conditions.9 9 producing early clutches had the poten-tial of producing a second clutch in view ofthe above information, even though we donot have mark recapture data to verify this.It is not uncommon for deserticolous insec-tivorous lizards to produce multiple clutcheswithin a season (Table 3). Mean clutchsize for 23 9 9 was 5.3 (range, 3-10) andthere was very little difference betweenclutch size of 12 9 9 in spring (X = 5.1,range = 4-9) and that of 11 9 9 in latesummer (X = 5.6, range = 3-10). Therewas a low and insignificant correlation (r= 0.39, F = 3.783, df = 1/21) betweenclutch size and SVL, an indicator of relativeage (Fig. 5). Gates (1963) reported a meanclutch size in 12 9 9 from the HassayampaRiver of 4.6 (range, 2-7). The breedingseason for U. graciosus firom he lower Colo-

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AMarch 975] HERPETOLOGICA 63TABLE 4.-Fat body weights of adult 9 9 of Urosaurusgraciosus from the lower Colorado River. In-cluded are only those 9 9 collected during 1973. Reproductiveand nonreproductive9 9 have been sepa-rated to facilitate comparisons. Reproductive 9 9 include only those with enlarged yolked follicles oroviducal eggs, and those with large corpora lutea, indicative of having just laid. Fat body weights(FBW) are in gramsand snout-vent lengths (SVL) are in millimeters.Month N x SVL (range) Reproductive condition xi FBW (range)April 1 48 nonreproductive 0.051May 3 51.7 (49-54) reproductive 0.000June 1 52 nonreproductive 0.0376 50.7 (47-54) reproductive 0.006 (0-0.034)July 1 57 reproductive 0.028August 5 52.6 (49-57) nonreproductive 0.012 (0-0.044)4 53.3 (51-55) reproductive 0.055 (0-0.119)September 6 50.7 (47-55) nonreproductive 0.091 (0-0.300)

rado River was shorter but clutch size waslarger than for U. ornatus from near Phoenix(Parker, 1973). Gates (1963) indicated nodifference in length of breeding season be-tween the two Urosaurus species but notedsignificant differences (although no actualstatistics were presented) in clutch size be-tween the two (see Table 3 for actual data).Comparisons of reproductive attributes of9 9 of three arboreal desert lizards of Ari-zona appear in Table 3.Although sample size is too small for sta-tistical comparisons, fat body weights of9 9 (Table 4) do exhibit certain trends.Reproductive 9 9 from spring and earlysummer had smaller fat bodies than nonre-productive 9 9 from the same season. Inview of Derickson's (1974) work on lipiddeposition and utilization in Sceloporusgraciosus, it is likely that the differencesnoted in U. graciosus result from fat bodymobilization for egg production. Late sum-mer 9 9 were much more variable in fatbody weights (Table 4) most likely result-ing from differences in number of clutchesproduced in that particular season by eachindividual 9 (for example, one 9 may haveproduced a spring clutch, and then a fallclutch, whereas another may have only pro-duced a fall clutch).

Reproductive Effort.-Reproductive ef-fort, defined by Williams (1966) as thetotal amount of energy that is available toorganisms that goes into reproductive re-

lated activities (mating, additionalcost as-sociated with carryingeggs, and egg andshell production,etc.), is a centralconcernof evolutionary cologists. The conceptwasinitiallydiscussedby Fisher (1930). In thepast, the measurementof reproductiveef-fort has been crude,involvingsimpleratiosof clutch weights to body weights (Clark,1970;ParkerandPianka,1973;and others).Recentstudiesby Tinkle andHadley (1973)and Vitt (1974b) indicatethat interspecificdifferences in the amount of calories perunit weight of egg may exist. Since dis-tinct differencesare apparentbetween eggcaloriesper unit weight and body caloriesper unit weight (eggs being the energyrichest life history stage), simple use ofwet or dry weight ratios as suggested byBallingerand Clark(1973) underestimatesthe energetic cost of reproduction.Caloriccontent of eggs and bodies wasdeterminedon four U. graciosus9 9 whichcontainedoviducaleggs. Although he sam-ple is small, all studies thus far utilizingmicrobomb calorimetry for reproductiveeffortestimationshaveshownno significantintraclutch variation in calories per unitweight, and no significant interclutch(within a population) variation n caloriesper unit weight (see Tinkle and Hadley,

1973; Ballingerand Clark,1973; and Vitt,1974b). Table 5 presents informationoncalories,percentash, and watercontentforthis sample. Mean caloriesper gram egg

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64 HERPETOLOGICA [Vol. 31, No. 1TABLE 5.-Energy (calories of ash-free dry weight, AFDW), ash content, and water content of bodiesand eggs of the iguanid lizard Urosaurusgraciosus from the lower Colorado River. Only lizards withoviducal eggs were utilized for caloricdeterminations (see text). F-tests representcomparisonsof caloricdeterminationswithin each sample (3 determinations/pooled sample) to comparisonsbetween each sam-ple (4 samples, 3 determinations/sample). As shown, no significantdifferenceswere found in calories pergram within and between samples.

No. of caloric x % X calories Range of x % waterCategory N determinations ash per gram individual means F-test (.05) contentBodies 4 12 19.38 5492 5384-5620 F = 2.10, 3/8 df 70.50Eggs 4 12 6.95 6612 6347-6770 F= 2.06, 3/8 df 56.20

weight (AFDW) of U. graciosus were higherthan any species studied by Ballinger andClark (1973), higher than the viviparoushigh latitude species Gerrhonotus coeruleusprincipis (Vitt, 1974b), and lower than thehigh elevation viviparous montane speciesSceloporus jarrovi (Tinkle and Hadley,1973).Reproductive effort (total clutch caloriestotal body calories ratio) averaged 0.640(range, 0.474-0.725) in U. graciosus andthe total calories per egg averaged 638(range, 438-771). Of the four experimentalclutches, two contained four eggs and twocontained five. The two larger clutches con-tained smaller eggs (in weight and totalcalories) than the two smaller clutches. Al-though these data were very limited, theremay be a negative feedback between clutchsize and egg size in this species. This couldaccount for the lack in correlation between9 size and clutch size. The wet ratio ofclutch: body weight averaged 0.313 (range,0.271-0.399) whereas the dry ratio was

0.531 (range, 0.403-0.604). In view of thedifferences in body and egg energy, bodyand egg ash, and caloric ratios and weightratios, the ratio of clutch calories to bodycalories corrected for ash content serves tobest estimate reproductive effort in speciesexhibiting no post-ovulatory contributionto eggs and no parental care.Reproductive Strategy.-Reproductive at-tributes of U. graciosus and growth rateinformation (Gates, 1963) suggest that U.graciosus conforms to the early maturing,short lived species presented by Tinkle et al.(1970). The production of many (3-10)

small eggs once or more per season, smalladult body size (as compared to manyiguanids) adds support to this and placesU. graciosus in the r category of Pianka(1970) and MacArthur and Wilson (1967).Clutch weight to body weight (wet anddry) ratios are high as is the clutch caloriesto body calories ratio (reproductive effort)especially when number of clutches perseason is considered, suggesting an r strat-egy. Data on survivorship would probablyalso indicate an r strategy but such data arenot yet available.

Acknowledgments.-This study was supportedby Bureau of Reclamation Grant No. 4-01-01-10-310. The ColoradoRiver Indian Reservation,Cali-fornia Department of Fish and Game, ArizonaDe-partment of Game and Fish, and the U. S. Fishand Wildlife Service supplied scientific collectingpermitsnecessaryfor completionof this study. Wethank Mike Walker and Harry Shankeman of Ari-zona State University for technical assistance andJustin D. Congdon (ASU) for critically reviewingthe manuscript. In addition, criticisms by W. S.Parker,MississippiUniversity for Women, and twoanonymous reviewers enabled us to clarify manyaspects of the discussion of our data.

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of western North America. McGraw-Hill BookCo., New York.TINKLE, D. W., AND N. F. HADLEY. 1973. Re-productive effort and winter activity in the vi-viparous montane lizard Sceloporus jarrovi.Copeia 1973:272-277.TINKLE, D. W., H. M. WILBER, AND S. G. TILLEY.1970. Evolutionary strategies in lizard repro-duction. Evolution 24:55-74.ViTT, L. J. 1974a. Winter aggregations, sizeclasses, and relative tail breaks in the tree lizard,Urosaurus ornatus (Sauria: Iguanidae). Her-petologica 30:182-183.

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Department of Zoology, Arizona StateUniversity, Tempe, Arizona 85281, USA

REPRODUCTION IN GUATEMALAN ANOLIS BIPORCATUS(SAURIA: IGUANIDAE)C. J. McCoy

HENDERSON (1972) noted the scarcity ofinformation on reproduction in larger spe-cies of Anolis, and reported observations onegg-laying by a captive Anolis biporcatus.Henderson's anole laid two eggs within 7HERPETOLOGICA31:65-66. March 1975

hours, suggesting the unlikely possibilitythat A. biporcatus may have a normal clutchsize of two eggs in parts of its range. ACarnegie Museum (CM) series of Anolisbiporcatus from southeastern Guatemala