The Effects of Egg Incubation Temperature on Post-Hatching Growth of American Alligators

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1 CHAPTER 51 The Effects f Egg ncubatin Temperature n Pst-Hatching Grwth f American Alligatrs Ted janen ', Larry Mclvease ' and Mark W. J. Fergusn''

2 CHAPTER 51 r\ The Effects f Egg ncubatin Temperature n Pst-Hatching Grwth f American Alligatrs Ted janen ', Larry McNease l and Mark W.]. Fergusn/ " NFORMATON n incubatin techniques fr crcdilian eggs has been prvided by Pley (1971), Yangprapakrn et al. (1971), Blake and Lveridge (1975), janen and McNease (1976), Chabreck (1978), Whitaker (1979), Fergusn (1981), and De Vs (1982). Hatchlings prduced by these techniques have varied cnsiderably in grwth and survivrship, and mst researchers reprt a percentage f animals which are nticeably inferir t thers (Pley 1971; Yangprapakrn et al. 1971; Whitaker and Whitaker 1977; janen and McNease 1977; De Vs 1982; Webb et al. 1983). Grwth rates have als been reprted t vary with stcking rates, "grw-ut" temperatures, hygiene and diet. Recent studies have demnstrated that embrynic grwth and sex determinatin f Alligatr mississippiensis are affected by incubatin temperature (Fergusn and janen 1982, 1983). Exclusively females hatch frm eggs incubated at 86 F (3 C), and they weigh Significantly mre than the exclusively males that hatch frm eggs incubated at 93 F (33.9 C). This weight difference is a cnsequence f the females having mre abdminal ylk than the males (Fergusn and anen 1982, 1983). Only a few studies have reprted n the psthatching grwth f alligatrs frm artificially incubated eggs cllected very sn after being laid (anen and McNease 1977, 1981a), and in these, nly a single incubatin temperature (85 F; 29.4 C) was used. The study reprted here evaluates the effects f fur different incubatin temperatures n hatching success, size at hatching, survival, sex determinatin and grwth f alligatrs t 18 mnths f age. t was carried ut at Rckefeller Refuge, Luisiana. METHODS Alligatr mississippiensis eggs were cllected frm eleven nests n Rckefeller Refuge. Each egg was marked t maintain egg rientatin, packed in nesting media and transprted t the labratry n June 21, Fergusn's (1981) paque banding prcedure was used t bth identify infertile eggs (which were discarded) and t age fertile eggs, which were set in incubatrs and incubated thrugh t hatching using the techniques described by janen and McNease (1977). A ttal f 357 fertile eggs were incubated at fur different temperatures; 91 F (32.8 C), 89 F (31.7 C), 87 F (3.6 C) and 85 F (29.4 C). Eggs frm each clutch were mixed and randmly allcated t the fur temperature treatments, and all eggs were less that seven days ld (mstly 1-3 days) when artificial incubatin started. At hatching, each individual was weighed (BWT) t the nearest.1 g and had its ttal length (TL) measured t the nearest millimetre. Fr individual identificatin, tw serially numbered web tags were attached t each animal. All animals were measured and weighed each three mnths until the eighteenth mnth f study. Alligatrs were raised in cntrlled envirnment chambers at 86 F (3 C) and were fed a mixture f grund nutria and vitamin premix (McNease and janen 1981b). All alligatrs, regardless f hatching temperature, were raised under identical cnditins. Excess fd was always prvided s that all animals had an adequate pprtunity t eat. Feeding schedules, cleaning prcedures and stcking rates were as described by janen and McNease (1976) [seejanen and McNease Chapter 32). After eighteen mnths, all animals were sexed by inserting a nasal speculum int the claca and viewing the mrphlgy f the clitris r penis. The results were analyzed by the Department f Experimental Statistics at Luisiana State University, utilizing the General Linear Mdels Prcedure in SAS.ANOVAs were perfrmed n length and weight using the main effects f treatment and sex, and 'Luisiana Department f Wildlife and Fisheries, Grand Chenier, Luisiana 7643, USA "Turner Dental Schl, University f Manchester, Higher Cambridge Street, Manchester, Ml S 6FH, England. Pages in WllLlFE MANAGEMENT CROCODlLESAND AlllGATORS ed by Grahame). W. Webb, S. Charlie Manlis and Peter). Whitehead. Surrey Beatrv and Sns Pry Limited in assciatin with the Cnservatin Cmmissin f the Nrthern Territry.

3 534 WLDLFE MAlAGEMENT: CROCODLES Al\lD ALLGATORS varius interactins where apprpriate. A t-test was used fr cmparing means and regressin line slpes where apprpriate. RESULTS Of the 357 fertile eggs incubated, 289 (81.%) hatched. Hatching success between the fur temperature treatments ranged frm 76.2% t 83.% (mean f all eggs = 81.%) (Table 1). ncubatin temperatures had a prfund effect n the sex ratis (Table 1; F = 228.4, p<.1), as was fund previusly (Fergusn and janen 1982,1983). Ttal incubatin time varied inversely with incubatin temperature: 91 F (32.8 C), 66 days; 89 F (31.7 C), 69 days; 87 F (36 C), 72 days; and, 85 F (29.4 C), 74 days. Likewise, the range in days between first and last pipping fr all eggs hatched at anyne temperature was inversely prprtinal t incubatin temperature: 91 F (32.8 C), 6 days; 89 F (31.7 C), 9 days; 87 F (3 6 C), 9 days; and, 85 F (29.4 C), 14 days. The mean size f hatchlings prduced frm different incubatin temperatures did nt vary greatly (Table 2). Mean T shwed n cnsistent relatinship with temperature, but mean BWTs were slightly greater at the highest and lwest incubatin temperatures, and the ratis f BWT:T indicated this was reflecting a tendency fr hatchlings t be slightly heavier per unit length at the tw extreme temperatures. Ttal survival thrugh the first seven days was 96.9% per treatment, with all lsses being restricted t the lwest (85 F; 29.4 C) and highest (91 F; 32.8 C) incubatin temperatures (Table 1). Survival frm hatching t the end f the study, eighteen mnths later, was nly marginally less (95.8%; Table 1).! Table 1. The hatching success, sex rati and pst-hatching survival fr 357 fertile Alligatr mississipiensis eggs, frm 11 clutches, that were used t quantify the relatinship between egg incubatin temperature and pst-hatching grwth and survival. Numbers in brackets are ttals and percentages f ttals. Temperature N. f % Survival % Survival OF (OC) Eggs % Hatch % Males t 7 days t 18 mnths 91 (328) (317) (36) (294) (357) (81) (969) (95.8) Table 2. The relatinship between hatchling size (ttal length and bdy weight) and incubatin temperature fr Alligatr mississippiensis used in the grwth experiments. Rati WL refers t the mean weight divided by the mean length. ncubatin Temperature Length (rnrn) Weight (g) Rati OFCC) Sex Mean Range Mean Range WL J!' 91 (32.8) Males (317) Males ' (31.7) Females (36) Males (36) Females (294) Females Table 3. Mean bdyweights (BWT; g) and ttal lengths (Tl., mm) (with 1 SE) f Alligatr mississippiensis hatchlings after incubatin at different temperatures, at hatching, after 12 mnths and after 18 mnths. At hatching 12 mnths f age 18 mnths f age Temperature OF (OC) Sex N BWT SE rt SE N BWT SE rt SE N BWT SE rt. SE 85 (294) F (36) M ' (36) F H9 (317) M O.H (317) F (328) M {1

4 JOANEN, McNEASE and FERGUSON EFFECTS OF EGG NCUBATON TEMPERATURE ON AMERCAN ALLGATORS g.9 - Z W -1 <i ' SON i J F M A M J J A SON i J F M 1981: 1982 : 1983 TME Fig. 1. The relatinship between ttal length, egg incubatin temperature and time fr Alligairrnississippiensis raised under identical cnditins. Sexes are cmbined, and data are means, standard deviatins and ranges fr incubatin temperatures f: 91 F (32.8 C) (pen squares); 89 F (31.rC) (pen Circles); 8rF (3.6 C) (clsed circles); and 85 F (29.4 C) (clsed squares). Sample sizes decreased marginally thrugh the time perid. f [ Althugh there was cnsiderable variatin in the size f individuals frm all incubatin temperatures ver time (Fig. 1), the effect f incubatin temperature n final size (Figs 2 and 3; Table 3) was highly significant [T (F = 12.31, p<.1); BWT (F = 6.92, p<.1)).!l i 3 TME (mnths) g. Fig. 2. The relatinship between mean bdy weight. egg incubatin temperature and time fr Alligatr mississippiensis raised under identical cnditins. Sexes are cmbined, and data are fr incubatin temperatures f: 91 F (32.8 C) (pen squares); 89 F (317 C) (pen circles); 8rF (3. 6 C) (clsed circles); and 85 F (29.4 C) (clsed squares). The crsses signify where weights fr all incubatin temperatures verlap. Alligatrs incubated at 89 F (3l. 7 C) attained the largest sizes (mean = 1.16 m T; 5.32 kg BWT), and were fllwed by thse incubated at 87 F (3.6 C) (1.13 m T; 4.98 kg BWT); differences between the tw were nt Significant. The prest grwth was w ';; --' >- >-.. b 2 l CD 3 k x [J,,,,,, J TME (mnths) Fig. 3. The relatinship between mean ttal length. egg incubatin temperature and time fr Alligatr mississippiensis raised under identical cnditins. Sexes are cmbined, and data are fr incubatin temperatures f: 91 F (32.8 C) (pen squares); 89 F (31. rc) (pen circles); 8rF (3.6 C) (clsed circles); and, WiF (29.4 C) (clsed squares). The crss signifies where ttal lengths fr all incubatin temperatures verlap. 1/

5 536 WLDLFE MANAGEMENT: CROCODLES AND ALLGATORS exhibited by animals frm the tw extreme temperatures [91 F (32.8 C) and 85 F (29.4 C)] and the differences between them were nt significant. When the tw "gd" and tw "pr" incubatin temperature treatments were each pled, the differences between the tw were significant fr bth T (F = 15.49, p<.1) and BWT (F = 7.94, p<.1) U ':J -' ;! c:. a>-- l TME (mnths) i Fig. 4. The relatinship between mean ttal length and time fr male (pen circles) and female (clsed Circles) Alligatr mississippiensis incubated at 89 F (31. 7 C) and raised under identical cnditins. E 4 >-- W 3 :;; >- 2' a <l i TME (mnths) Fig. 5. The relatinship between mean bdy weight and time fr male (pen circles) and female (clsed circles) Alligatr mississippiensis incubated at 89 F (3l.rC) and raised under identical cnditins ] L.6L ':J -' ;! a>-- l TME (mnths) C» c:. 18 Fig. 6. The relatinship between mean ttal length and time fr male (pen circles) and female (clsed circles) Alligatr mississippiensis incubated at 8rF (3.6 C) and raised under identical cnditins. g >-- UJ :;; 15 2 a <l t,, , 15, 18 TME (mnths) Fig 7. The relatinship between mean bdy weight and time fr male (pen circles) and female (clsed circles) Alligatr mississippiensis incubated at 87 F (3.6 C) and raised under identical cnditins. 18 Within these same tw incubatin treatments, males incubated at 89 F (31. rc) attained a mean size f 1.18 m T and 5.54 kg BWT, which was higher than the mean fr females incubated at 87 F (3.6 C) (1.13 m Tand 5.19 kgbwt) (Table 3). Hwever, the females frm 87 F (3.6 C) incubatin were larger than the females frm 89 F (31.7 C) incubatin (Figs 4 t 7; Table 3). Within the data fr the better grwing animals [89 F (31.7 C) and 8rF (3.6 C)], there were bth males and females at each temperature (Table 1). Analysis f incubatin temperature treatments and sex n T and BWT after 18 mnths revealed a signficant difference attributable t sex fr T (F = 2.9, p<.4), but nt fr BWT (F = 1.8, P >.14). At 89 F (31.7 C), the males grew faster than the females and attained larger sizes in bth T (Fig. 4) and BWT (Fig. 5), and at 87 F (3.7 C), there were marginal differences between the sexes in T (Fig. 6), and the females exceeded the males in BWT (Fig. 7). These differences match the sex rati bias at bth temperatures; males predminated at 89 F (31.rC) and females at 87 F (3.6 C) (Table 1). Table 4 The percentage f "runt" Alligatr mississippiensis after eighteen mnths raising, as a functin f incubatin temperature. The size limits fr runts were determined frm the bttm 1% f animals at the incubatin temperature that gave the best grwth [89 F (31.rC)j. ncubatin Percent Percent Temp.F(OC) by Length by Weight 91 (328) (31.7) (3.6) (29.4) After eighteen mnths, there was cnsiderable variatin between the largest and smallest animals frm all treatments (Fig. 1). T determine the extent t which "inferir" r "runt" animals culd be ;

6 JOANEN, McNEASE and FERGUSON: EFFEC;TS OF EGG NCUBATON TEMPERATURE ON AMERCAN ALLGATORS 537 attributed t incubatin temperature, the 11. and BWf which bunded the smallest 1% f animals within the best treatment [89 F (31.7 C)) was delineated, and the prprtin belw this line was determined fr each f the ther three treatments (Table 4). These results are cnsistent with thse discussed abve, in that the percentage f runts is appreciably greater in the rw extreme temperatures. Hwever, it als indicates that althugh n significant difference in mean size ccurred between the animals incubated at 89 F (31.7 C) and 87 F (3.6 C), there were twice as many runts frm 87 F (3.6 C) incubatin as there were frm 89 F (31. 7 C) incubatin. DSCUSSON The grwth rates and survivrship reprted fr Alligatr mississippiensis frm all treatments within this study are cmparable t thse reprted previusly by Culsn et at. (1973) and janen and McNease (1976) fr animals raised in cntrlled envirnmental chambers. ncubatin temperature was inversely prprtinal t bth the ttal mean incubatin time, and the range f incubatin times at anyne temperature. t did nt greatly influence hatchling length, but the highest and lwest temperatures prduced hatchlings that were slightly heavier than thse frm the middle temperatures. The study demnstrates that 89 F (31.rC) and 87 F (3.6 C) incubatin prduces hatchlings that are marginally lighter than thse prduced at 91 F (32.7 C) and 85 F (29.4 C), but which nevertheless survive better as bth embrys and hatchlings, grw faster, attain larger mean sizes and have a smaller prprtin f runts. ncubatin at 89 F (31.7 C) results in a high male:female sex rati and the least number f runts f any temperature treatment tested. The males prduced at this temperature grew faster and attained larger sizes than any ther sex-temperature cmbinatin. ncubatin at 87 F (3.6 C) prduced a high female-male sex rati and the largest females f any treatment, althugh they were nt as large as the 89 F (31.7 C) males; furthermre, incubatin at 87 F (3.6 C) resulted in twice the number f runts as did incubatin at 89 F (31. 7 C). ncubatin at 85 F (29.4 C) prduced heavy hatchlings which were all females, but they had slw grwth rates and abut five times the number f runts as did incubatin at 89 F (31.7 C). Similarly, incubatin at 91 F (32.7 C) prduced the heaviest hatchlings, which were all males, and which grew slwly and had arund fur times the number f runts as animals incubated at 89 F (31.7 C). Taken tgether, the results indicate that incubatin temperature can have a prfund effect n the pst-hatching grwth f Alligatr mississippiensis, which wuld nt be apparent frm hatchling dimensins alne. Given that similar relatinships prbably ccur with ther species f crcdilians, incubatin at "ptimal" temperatures shuld imprve prductin n crcdile and alligatr farms. Althugh nt discussed here, the relatinship berween incubatin temperature and pst-hatchling grwth pens a number f avenues thrugh which temperature-dependent sex determinatin culd functin t assign sexes t the embrys mst likely t benefit frm enhanced grwth, r least likely t be cmprmised by retarded grwth. REFERENCES BlAKF.D. L. ANDLOVERDGE,].P., The rle f cmmercial crcdile farming in crcdile cnservatin. Bi. Cnseru. 8: CHABRECK, R H., Cllectin f American alligatr eggs fr artificial incubatin. Wildl. Sc. Bull. 6: COULSON,T. D., COlJL<;ON,R A ANDHERNANDEZ, T, Sme bservatins n grwth f captive alligatrs. Zlgica (New Yrk) 58: DE VOS, A, A manual n crcdile cnservatin and management in ndia. FAO Prject Dcument ND174/46, ndia - Crcdile breeding and management prject. 69pp. FERGUSON, M. W.J., The applicatin f embrylgical studies t alligatr farming. Alligatr Prd. Cn! (Gainesville, Flrida) 1: FERGUSON, M. W.].AND]OANEN,T, 1982.Temperature f egg incubatin determines sex in Alligatr mississippiensis. Nature Lnd. 296: FERGUSON, M. W.]. AND]OANEN,T, Temperature-dependent sex determinatin in Alligatr mississippiensis.j. Zl. Lnd. 2: ]OANEN,T. ANDMcNEASE,L., Culture f immature American alligatrs in cntrlled envirnmental chambers. Prc. Wrld MaricultureSc. 7: ]OANEN,T ANDMcNEASE,L., Artificial incubatin f alligatr eggs and pst-hatching culture in cntrlled envirnmental chambers. Prc. Wrld Mariculture Sc. 8: ]OANEN,T ANDMcNEASE,L., 1981a. ncubatin f alligatr eggs. Alligatr Prd. Cni (Gainesville, Flrida) 1: McNEA';E,L. AND]OANEN,T., 1981b. Nutritin f alligatrs. Alligatr Prd. Cnf. (Gainesville, Flrida) 1: POOLEY, A C, Crcdile rearing and restcking. Pp in "Crcdiles" UCN Publ New. Ser. Suppl, Paper N. 32. UCN: Gland, Switzerland. WEBB,G. J. W., BUCKWORT, R ANDMANus,S. C, Crcdylus jbnstni in a cntrlled-envirnment chamber: a raising rrial.aust Wi/dl. Res. 1: WHTAKER,R, Crcdile egg cllectin in Tamil Nadu. ndian frester 15: WHTAKER,R. ANDWlTAKER,Z., Grwth rate f Crcdylus palustris.]. BmbavNat. Hist. Sc. 75: YANG'RAPAKORN, U., McNEELEY,].A ANDCHONN,E. W., Captive breeding f crcdiles in Thailand. Pp in "Crcdiles" UCN Publ. New Ser. Suppl. Paper N. 32. UCN: Gland, Switzerland.

Effects of incubation temperature on growth and development of embryos of Alligator mississippiensis

Effects of incubation temperature on growth and development of embryos of Alligator mississippiensis J Cmp Physil B (1989) 159 : 183-193 Jurnal f Cmparative Systemic, ~.m,... and nvirn~ Physilgy B ~"' Physilgy (~ Springer-Verlag 1989 ffects f incubatin temperature n grwth and develpment f embrys f Alligatr