Short Notes Lamellaand scansor numbers in Thecadactylus rapicauda (Gekkonidae): Patternsrevealed through correlational analysis and implicationsfor systematicand functional studies PhilipJ. Bergmann,Anthony P .Russell Vertebrate MorphologyResearch Group,Department ofBiologicalSciences, Universityof Calgary,2500 UniversityDr. N.W .,Calgary,Alberta, Canada T2N1N4 e-mail: [email protected],[email protected] Manytaxa of lizardsbear transversely enlarged subdigital scales that are often a source ofsystematic characters. Among gekkonid and polychrotid lizards, elaborations of such scales,called lamellae and scansors, are employed in adhesivelocomotion (Colette, 1961; Hiller,1968; Russell, 1975). Subdigital lamellae and scansors are derivativesof scales, the form, shapeand number of whichare thought to re ect function (Russell, 1981) as well asindicatepatterns of relationship(Couper et al. ; 1993 Raxworthyand Nussbaum, 1993; I Grismer etal. ; 1994/.Whilelamellae in the loose sense encompass all subdigital scales thatare transverselyenlarged, they can be divided into two subsets ( g. 1): scansors, thedistal lamellae most closely involved in adhesion and therefore occurring on the hyperextensibleportion of adigit(Russell, 1981, 1986); and basal lamellae, which differ morphologicallyfrom scansors(Russell, 1981), and are situated more proximally. Scale patternsin squamatesare generally regarded as being genetically determined and discrete (Hecht,1952). Counts of total lamellae feature in both systematic (Grismer etal. ; 1994, etc.)and functional (Hecht, 1952; Peterson, 1983a, b; Mayerin Losos, 1990; Glossip and Losos,1997) studies. Numbersof totallamellae vary both within and between digits and, as a consequence, mostauthors choose to countthese structures on asmallerset of digits,on theassumption © KoninklijkeBrill NV ,Leiden,2003 Amphibia-Reptilia24: 379-385 Alsoavailable online - www.brill.nl 380 Short Notes Figure 1. Ventralview of digitIV ,left pes of Thecadactylusrapicauda ,showingthe location of thetotal lamella numberand its subsets: scansors andbasal lamellae, theformer beingpositioned beneath the hyperextensible regionof the digit. thatthese digits will be representativeor maximallyinformative (e.g. Digit IV :Broadley, 1977;King, 1962. Digits I, III, andIV :Otaet al., 1995). Although such selectivity is pragmaticand potentially justi able, we areunaware of any studies that have formally addressedthe questionsof whichdigits are maximally informative, and which are the most appropriatefor aparticulartaxon. As boththe manus and pes of lizardsgenerally exhibit asymmetryof digitallength, digits three and four are often chosen for totallamella counts (Hecht,1952; Colette, 1961). This has been justi ed because, being the largest, these digitsare assumed to be most load-bearing (Hecht, 1952), and the easiest to distinguish andcount (Colette, 1961). However, asymmetry of the length of digits varies markedly acrosstaxa (Russell et al., 1997), even when phalangeal counts are identical. Given that discrepancyexists between the differential length of digitsin different taxa, the question ofhowrepresentative or informativeselected total lamella counts are of a particulartaxon remains,and should be assessed before a selectionis made of which data to record and employ. Short Notes 381 Hereinwe investigatethe variation within and between total lamella, scansor, and basal lamella( g. 1)countson manualand pedal digits of thegekkonid Thecadactylusrapicauda asan exemplar .Stemmingfrom this,we outlinea methodby whichmaximally informative datafor systematicand functional studies might be selected. W eexaminethe question ofwhether there are high levels of correlation between total lamella, scansor, and basal lamellacounts on all digits of the manus and pes and explore ways to determine, on asmallersubsample, which of these counts are ofmost interest in the context of the question(systematic, functional, or both)at hand.W ealsoaddress the question of whether correlationalpatterns exhibited by scansor and basal lamella counts mirror thoseof total lamellacounts, or ifthesetwo component counts exhibit independent patterns. Byundertakingsuch a correlationalstudy of theseiterative homologues, we investigate whetherdifferent digits provide new or merely repeated information, and which, if any, digitsare most representative (being most highly correlated) of the other digits on the limbin question. Both highly representative and poorly representative counts form valid charactersfor systematicstudies and focal points for functionalconsiderations. The inclusionof theformer isjusti ed asaproxyfor theother digits, while the inclusion of the latteris justi ed as anindicator of theuniqueness of aparticulardigit, which may be of particularimportance in functional studies. Totallamella number( g. 1) was recordedfor all digitsof the right manus and pes of40 specimens of Thecadactylusrapicauda fromacross itsbroad range (see Appendix1 fora listof specimens andtheir localities). Asample size of40was selected arbitrarilyas atrade-offbetween time involvedin data collectionand a sufcient sample. We suggestthat twenty would be a minimumsample size forthis methodology. Additionally, the scansor numberwas recordedby countingthose enlarged plates thatoccur only beneath the hyperextensible portion of each digit(Russell, 1981). This was achievedby re ecting the distal portion of each digitwith an entomological pinto determine thepoint of in ection at whichhyperextension occurs (Russell and Bels, 2001).Due tothe intimateinvolvement of scansors inadhesion, they may bemore constrainedby selection than the more extensive totallamellar series (as countedby Hecht, 1952). Finally, basal lamella numberwas calculated bysubtracting scansor numberfrom the total lamella count( g. 1).These twogroups of ‘subset’counts are includedhere as potentiallyuseful, albeit neglected (but see Russell,1981; Russell and Bels, 2001),characters forsystematic and functionalstudies. Theresulting data (table1 forsummary) were tested fornormality using the Kolmogorov-Smirnov test and were foundto be highlynon-normal for total lamella, scansor,and basal lamella counts.For this reason, and due totheirdiscontinuous nature, Spearman correlations(Sokal and Rohlf, 1995) were usedin the analysis. Six sets ofcorrelationswere conducted:one for each combinationof total lamella, scansor,and basal lamella countsfor thefore and hindlimb. For each digitin each set, Spearman correlationcoef cients withthe remaining four digits were averaged.This resulted in a singleAverage Spearman CorrelationCoef cient for each digit.Although this doesnot represent arigorousstatistic, we believethat it does give a goodidea ofhowrepresentative a countis of othersuch counts, and is easier tointerpret than a correlationof a particulardigital count with the total respective countfor the entire limb (which would eliminate theuse ofaverages). These average Spearman’s correlation coefcients were thenused to determine howrepresentative a particularcount was ofall othercounts in a set (withoutaccounting for differential digital lengths). AverageSpearman correlation coef cients for totallamella, scansor, and basal lamella countsof fore andhindlimbs follow several patterns ( g. 2).Similar general patterns are evidentfor bothtotal lamella and scansor counts for theforelimb, with digit I beingleast representativeof theothers (see Russelland Bauer, 1990: 464-466 for possiblereasons), 382 Short Notes Table 1. Summaryof statistics forcounts of totallamellae, scansors,and basal lamellae onall digitsof themanus andpes for40 specimens of Thecadactylusrapicauda .Allvalues are mean standarddeviation. § Digit I II III IV V Totallamellae 15 :7 2:0 18:6 1:6 20:1 1:7 20:6 1:6 18:8 2:2 § § § § § ManusScansors 8:3 1:3 11:0 1:1 11:5 1:0 11:8 0:9 10:9 0:9 § § § § § Basal lamellae 7 :4 1:5 7:7 1:2 8:6 1:3 8:7 1:4 7:9 1:7 § § § § § Totallamellae 17 :6 2:0 19:7 1:9 21:1 1:9 21:6 1:8 20:3 1:4 § § § § § Pes Scansors 9:5 1:3 11:6 0:8 12:1 1:1 12:3 0:9 11:5 0:9 § § § § § Basal lamellae 8 :3 2:2 8:1 1:5 9:1 1:4 9:3 1:5 8:9 1:0 § § § § § Figure 2. Average Spearman correlationcoef cients foreach digitwith all otherdigits for total lamella (a, d), scansor (b,e), andbasal lamella (c, f) countsfor fore (a, b,c) andhindlimbs (d, e, f) for Thecadactylusrapicauda (n 40). D digitsII, III andIV beingincreasingly representative of theother digits, and digit V being lessrepresentative ( g. 2a,b). A similarpattern is revealed for thetotal lamella counts for thehindlimb ( g. 2d),except that digit V istheleast representative. The pattern changes, however,when the scansor counts for thehindlimb and basal lamella counts for bothlimbs areconsidered ( g. 2e,c, f, respectively).For hindlimbscansor counts, digit II isthe least representativewhile digit V isthe most representative. When basal lamella counts are analyzed,digit III ismostrepresentative on both limbs ( g. 2c,f). Theleast representative digitsfor frontand hindlimbs are I andV (g. 2c, f), respectively,corresponding to the leastrepresentative digits for totallamella counts ( g. 2a,d). Short Notes 383 Theseresults suggest that for Thecadactylusrapicauda ,atotallamella count for the forelimbwould best be representedby digitsI andIV ,whilefor thehindlimb it would be bestrepresented by digitsIV andV .Representativescansor counts for theforelimb would mirror thesituation for thetotal lamella counts of that limb, but the hindlimb would be mosteffectively represented by countsof scansorson digitsII andV .Basallamella counts wouldbe