Bone histology of a lowland and montane species from the family Cordylidae (Reptilia : Squamata)

Curtin, Amanda (1999)

Thesis (M.Sc.) -- University of Stellenbosch, 1999.

Some figures are missing and were not present in the original hard copy which was digitized.

Thesis

ENGLISH ABSTRACT: Ecological adaptations, size and longevity, are known to be reflected as histological variations within vertebrate skeletons. To obtain baseline information on bone histology in the lizard family Cordylidae, two species, which differ considerably in general morphology and biology, were selected as representatives of the family. These were Cordy/us cataphractus, a lowland lizard found along the western districts of South Africa, and Pseudocordylus capensis, a montane lizard occurring in the Cape Fold Mountains of South Africa. Cross-sections of the femora from an ontogenetic range of individuals were examined for each species. In the smallest juveniles of both species, the compacta consisted of typical embryonic bone, while in adults it consisted of parallel-fibred bone. In general, the compacta was poorly vascularized. Endosteally formed lamellar and parallel-fibred bone, lined the medullary cavity in most adults and juveniles of C. cataphractus, but was limited in P. capensis. Bone remodeling, which incorporates the removal of old bone as new bone is added, produced distinctive featiires in both species. Endosteal resorption was intensive but irregular in both species. In C. cataphractus, however, resorption was more widespread along the medullary cavity margin, while in P. capensis, it was more localized. This observation was supported by the presence of embryonic bone remnants in most juveniles and some adults of P. capensis, as well as the shape of the medullary cavity area and number of lines of arrested growth (LAGs) resorped in both species. In C. cataphractus, up to four LAGs were estimated to have been resorped, and in P. capensis, up to three LAGs were estimated to have been resorped. Endosteal bone was present in 80 % of the C. cataphractus sample, but in only 68 % of the P. capensis sample. When it occurred in P. capensis individuals, it was thinner than the endosteal deposits of C. cataphractus individuals. In general, therefore, the relative bone thickness (RBT) of P. capensis was thin (9 - 39 %), compared to the RBT of C. cataphractus (18 - 49 %). Genetic and epigenetic processes can explain the differences and variations observed between these two species. P. capensis bone morphology, resulting in a lighter skeleton, could possibly be due to the need for speed and agility. C. cataphractus, on the other hand, is a heavily armoured, sluggish lizard with a lower basal metabolic rate than any other cordylid species studied to date. A heavier skeleton would, therefore, be an advantage in supporting a heavily armoured body. It is suggested that the intensive, widespread resorption in C. cataphractus could be due to food shortages as a result of group-living behaviour and apparent lack of active foraging. Growth was periodic in both species and growth marks were represented by zones and LAGs. Most P. capensis juveniles and even some adults had a clearly defined birth line. A birth line was visible in only one C. cataphractus juvenile. LAGs varied in distinctness and spatial arrangement within and between the two species, possibly due to a variety of factors, including altitudinal differences, climatic conditions and individual variation. C. cataphractus possessed more double LAGs than P. capensis, a feature usually related to cold climates and high altitudes. This phenomenon is suggested to be mainly due to food shortages rather than climatic conditions, as C. cataphractus occurs in a warm temperate climate. Skeletochronology was used to provide information on age, longevity, growth rates and age at sexua! maturity for both species. Individual ages were estimated by calculating the number of LAGs resorped and adding them to the number of visible LA Gs. The maximum estimated age was 13 years in C. cataphractus and 11 years in P. capensis. Sexual maturity, assessed through the analysis of femoral microstructure, occurred around six to seven years in C. cataphractus and four to six years in P. capensis. This estimate corresponded favourably with macroscopic and microscopic assessments of the gonads. Log-transformed variables regressed against log number of LA Gs, were used to assess growth rates and sexual dimorphism. In general, there was considerable variation in all variables within age classes among the juvenile cohort, but less variation was noted among adults of both species. In C. cataphractus, males and females exhibited different growth rates when snout-vent length (SVL), femoral length (FL) and bone wall area (BWA) were regresses against the number of LAGs (age). In P. capensis, sexual dimorphism in growth rate was only observed between BW A and age. Evidence suggests that both species have the potential for long life-spans.

AFRIKAANSE OPSOMMING: Dit is bekend dat ekologiese adaptasies, grootte en lewensverwagting as histologiese veranderlikes in die weweldierskelet waameembaar is. Basiese inligting oor die beenhistologie van die Cordylidae is verkry deur twee spesies, wat grootliks in algemene morfologie en biologie van mekaar verskil, as verteenwoordigend van hierdie familie te kies. Cordy/us cataphractus is 'n laagland-akkedis wat in die westelike gebiede van Suid-Afrika voorkom en Pseudocordylus capensis 'n bergakkedis wat in die Kaapse Plooiberge hou. 'n Ontogenetiese reeks dwarssnitte van die femora is vir elke spesies ondersoek. Die beenkorteks van die kleinste onvolwassenes van beide spesies het tipiese embrioniese been vertoon terwyl die beenweefsel van volwassenes, parallelgerigte vesels vertoon het. Die korteks was oor die algemeen swak gevaskulariseer. Die medulere holte is by die meeste volwassenes en onvolwassenes van C. cataphractus·uitgevoer met endosteale gelamineerde been en been met paralelle vesels in terwyl dit in P. capensis beperk was. In beide spesies het die hermodulering van beenweefsel, wat die verwydering van ou been en die toevoeging van nuwe been insluit, kenmerkende eienskappe vertoon. In beide spesies was endosteale resorpsie intensief maar oneweredig. By C. cataphractus was die resorpsie meer wydverspreid langs die rand van die medulere holte terwyl dit by in P. capensis meer gelokaliseer was. Hierdie waameming word ondersteun deur die teenwoordigheid van embrioniese beenoorblyfsels by die meeste onvolwassenes en sommige volwassenes van P capensis, tesame met die vorm van die area van die medulere holte en die aantal minimale groeilyne (MR Ge) wat in beide spesies geresorpeer is. Daar is geskat dat tot vier MGRe by C. cataphractus en drie MGRe in P. capensis geresorbeer is. Endosteale been was by 80% van die C. cataphractus monster teenwoordig maar slegs by 68% van die P. capensis monster. W aar dit voorgekom het in P. capensis individue, was dit dunner as die endosteale neerlae van C. cataphractus individue. Die relatiewe beendikte van P. capensis was dus oor die algemeen dun (9 - 39 %) in vergelyking met C. cataphractus (18 - 49 %). Genetiese en epigenetiese prosesse kan die histologiese verskille en variasies tussen hierdie spesies verklaar. Die beenmorfologie van P. capensis, wat 'n ligte skelet veroorsaak kan moontlik as gevolg van die behoefte van speod en ratsheid wees. In teenstelling hiermee is C. cataphractus 'n swaar gepantserde, lomp akkedis, wat 'n laer basale metaboliese tempo het as enige ander Cordy/us spesie wat tot op datum bestudeeer is. Dit is voorgestel dat die intesiewe wydverspreide resorpsie in C. cataphractus moontlik die gevolg is van voedseltekorte wat gepaard gaan met groeplewende gedrag en die waarskynlike afwesigheid van die aktiewe voeding. Beide spesies het 'n periodieke groei getoon en groeimerke is verteenwoordig deur sones en MGR Die meeste onvolwasse eksemplare van P. capensis asook sommige volwassenes, het'n duidelik afgebakende geboortelyn getoon. 'n Geboortelyn was slegs in een onvolwasse C. cataphractus sigbaar. MGR het in duidelikheid en spasierering binne en tussen die twee spesies gewissel, waarskynlik as gevolg van 'n verskeidenheid faktore wat verskille in hoogte bo seesppieel, klimaatsomstandighede en individuele variasie insluit. C. cataphractus vertoon meer dubbele MGR as P. capensis, 'n kenmerk wat gewoonlik verband hou met 'n koue klimaat en groot hoogtes bo seespieel. Die stelling word gemaak dat hierdie verskynsel hoofsaaklik te wyte is aan voel. .... seltekorte eerder as klimaatstoestande aangesien C. cataphractus in 'n warm, gematigde klimaatstreek voorkom. Skeletokronologie is aangewend om inligting t.o.v. ouderdom, lewensverwagting, groeitempo en ouderdom met geslagsrypheid in beide spesies te bepaal. Individuele ouderdomme is geskat deur die aantal geresorpeerde MGRe te bereken en dit by die aantal waameembare MGRe te tel. Die maksimum geskatte ouderdom vir C. cataphractus was 13 jaar en vir P. capensis 11 jaar. Geslagsrypheid is bepaal deur die analise van femorale mikrostruktuur en vind plaas vanaf 6 tot 7 jaar by in C. cataphractus en 4-6 jaar by P. capensis. Dit vergelyk gunstig met beide makroskopiese en mikroskopiese data van die gonades. Die regressielyn van logaritmies-getransformeerde veranderlikes teenoor die logaritme van die getal MGRe is bepaal om groeitempo en geslagsdimorfisme te evalueer. Oor die algemeen was daar groot variasie binne ouderdomskalsse tussen onvolwassenes, maar minder variasie is waargeneem tussen volwassenes van beide spesies. In C. cataphractus, het mannetjies en wyfies verskillende groeiptempos getoon, wanneer snoet-kloaak lengte (SKL), femorale lengte (FL) en beenwand area (BW A) teen die getal MGRe ( ouderdom) geregreseer was. By P. capensis is geslagsdimorfisme en groeitempo net tussen BWA en ouderdom waargeneem. Dit suggereer dat beide spesies die potensiaal besit om 'n hoe oe ouderdom beriek.

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