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The sexual behaviors of irdividual leopard gcckos ftom dificrcnt hcubation tomperatures
varies in a systcmatic ma!.oer, witt thc rcsponses offomales to malc courtship stowing the greate,st
difercnce (Gutzke and Cre'; , 1988), FerMles ftom low ircubation tempratues readily cfibit
receptivity whetr courtod by a Balo. Or the oth€r hard, females fiom high hcubation tempcratures
r€spond more lile males tha! lite feEales fton low teEperatures. Ttey often lf,il aggessively reject
the malc or attack him as would occur in a dale-Ealo encouDter. This effect ofa Dale-ploducirg
temperature oD tbe feEalc phenotype is iemidscent of the well-tnown masculinizirg effecLs of
a.Dalrogen treatment ilr leonatal feEale mamDrals. In other wordE high i.ncubation teEperature Eay
be acring in a fashion aralogous to a.ldroge! duriDg developmeut in mamDrak.
Captive Ma&gement of Reptiles with TSD
Thc occurence of TSD io rBalry reptiles affords thc udque opportu.nity to artifici.lly codtJol
sex detcrmination lrithin a c.ptive populatioD" However, several basic questiols must be addlessed to
optid;ze thc captive DraDageEent ofrepdles qit[TSD. These questions include: (i) Whictr
temperaturcs produc€ a particular s€x? (ii) Do a[ temperatues producing a particular sex r€sult iD
iadividuals of equd sexual competeDce? (iii) Wlich sex ratios are best for a captive populatiotr?
The ftst questio! is b€giljlilg to bc arswered in a number of species. It is beaomiDg dear
tbat species which show sioila! patterDs of'ISD car bave different pivotal temperatures ( = idcubation
temperature p.oduciDg a Ll sex ratio) (Bull et al., 1982; Mrosoisky et al., 1984a; Wibb€ls et al., 1991).
Becausc of this variability i! tle patterns a.ud pivot3l temperatures of TSD, masipulatiry the sex ratio
of a given species qould r€quire ttrat a variety of incubation lcmperatures be studied simultaa€ously to
determine whid sFd6c teoipcratBro langes ploduce a giver sex ratio.
Are there ccrtair optimal temperatures for producirg sexually coDpetelt indrviduals? Itr the
leopard geckq the ocssional femalas resulting ftoru relatively high Eale-produciog hcubatron
temp€ratures are lrot reproductively c&petent (s€€ above). Futher, the "sexual poterq/ of alr
incubatiotr teEperature car vary (BDI et al., 1990; Wibbels et al., 191), For example, ia the red-eared
slider tlddtl (Tru.hemrs scliprd), shiftilg eggs to a higher (fenale-producing) or a lo*er (Draleproducilg)
tenperature wil rcsdt;n more stewed s€xratios. Such studies could prove difficult using
turdes becauso of thc length oI time sepa.rating ircubation and adult rcproductive success. However, a
liz-ard such as the leopard geckq wbich matures mpidly aDd adapt6 *€ll to captivity, could plove to be a
6odel species for such studies.
The ability to ma.!.ipulate sex dete.mjlatiotr by temperature nccessitates tle choosiag of ar
appropriate sex ratio for a g1vetr c:ptive reari.Dg progr6m. This issue car be approached using two
distinctly differert strategies. In the 6lst approach, one could attempt to duplicate the sex ratio of
naturally o..urring populatios. Thc sex ratios in natual populations of leptiles witl TSD do Dot
al*?ys conform to tle L1 ratio suggested by sex allocation tleory (reviewed by BuI ard Chanov, 1988;
see also Limpus, 1985; Mrosorsty and Provancha, 1989; Wibb€ls et al., 1991). In facl rnary feloa.lebiased
sex ratios have becn dotected as well as at least one Drale-biased sex ratio (Linpus, 198t, The
evolutionary basis of skewed sex ratios i6 ulkrcwq although Bu[ and Chamov (1989) have proposed
that factors such as tberEal envirooment prefererces and/or postLatchling groi+,tL rate,s could afiect
the fitoess of a particular sex ald thus selcct for biased 6e.( ratios. Regarau€ss, our presert knowledge
of TSD ard the resulting sex ratios pre!€nt us ftom .*ig"i"g a! evolutiorarily stable sex ratio to a
give! populatiod of reptiles *ith TSD.
Wlile lhe effects of sex ratio on the reproductive output of a population of reptiles witl TSD
has lot bee! empirically addrc,se4 it se€&s that h situatiols ir which reproductio! is female-limited,
an iocreased production of fenale offspring could signiEcardy i.ncrease the reproductive output of a
captive populatio& Thus, a.n altematirc 6trategt would simply be to disregard s€-r ratios that o€cur in
the wild a.rd Ea.oipulate the sex ratio of tle captive population i! order to msxiEize reproductive
sucacss.
If ole decides to generate a biased sex ratiq what ircubation temperahles should be used?
That is, should an iDcubatior teEperature that producls the desired sex ratio be utilizrd or should a
proportior of tbe eggs be incubated at a male-producing tempelature aDd lhe renfider incubated at a
female-ploducirg teEperafiirc? Thesc questiors ca! be addr€ssed by studies investigating t[€ effects
of hcubation temperature olt sexual colrpetence (as discuss€d above fo! lhe l€opard g€cko).