The ecology of the Cape grass lizard, Chamaesaura anguina

Du Toit, Annemarie
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Stellenbosch : Stellenbosch University
ENGLISH ABSTRACT: The foraging mode of the Cape grass lizard, Chamaesaura anguina, was determined by using three criteria: 1) the number of movements per minute (MPM) and the percentage of time spent moving (PTM) during periods of activity; 2) the amount of tongueflicking directed at cotton applicators labelled with prey chemicals as a measure of prey chemical discrimination; 3) the stomach contents of the lizards as an indication of the natural diet. Observations were made by means of binoculars from an observation tower using a seminatural outdoor enclosure, and through a one-way glass panel using a seminatural indoor enclosure. Each lizard was observed for aIO minute period during peak activity and the times it was moving and the times it was stationary were recorded. Data obtained in the indoor- and outdoor enclosures did not differ significantly and were pooled. "MPM(0.37 ± 0.21 SD) and PTM (1.92 % ± 0.93 SD) values recorded for C. anguina (N = 10) fall within the range given as characteristic for sit-and-wait foragers. Nine C. anguina individuals were habituated in glass terraria to accept mealworms offered to them. When all lizards accepted food without hesitation, they were tested for their ability to discriminate among three different odours presented to them in a randomized block design: prey odours consisting of mealworm surface odours, distilled water as an odourless control stimulus, and cologne as a pungency control. The number of tongue-flicks directed at the cotton applicator containing the stimulus odour during 60 s was recorded. No statistically significant differences were found among the responses to the three treatment odours (Kruskal-Wallis, H = 2.41, dj = 2, P = 0.30). An analysis of the stomach contents of21 C. anguina specimens revealed a diet of mostly diurnally active arthropod prey species. The preferred body temperatures selected by 12 grass lizards in a thermal gradient were measured six times during a 48 hour period, using a copper-constantan thermocouple inserted into the cloaca. The measured body temperatures (N = 72) ranged from 22.62 oe - 27.07 oe with a mean of24.82 oe ± 2.27 SD. The low preferred body temperature exhibited by C. anguina as compared to other cordylids may be attributed to the combined influence of vegetative cover, high altitude, and high surface-volume ratio. To determine movement patterns and microhabitat use, six lizards were observed in a seminatural outdoor enclosure (4 x 4 m). The location of the grass tufts in the enclosure was mapped, and the position of each lizard within the enclosure was noted on 17 mornings. Observations of lizard behaviour during periods of activity were made by means of binoculars from an observation tower. Although C. anguina did not show reliance on a specific shelter site, the taller, broader tufts were generally preferred as refuges during inactivity. There were significant differences between the heights (student's z-test; P < 0.001) and the diameters (Mann-Whitney; P < O.00 1) of the preferred grass tufts, and those grass tufts that were not preferred as refuges, respectively. The lizards usually sheltered in a coiled-up position in the middle of the grass tufts close to the ground. During active periods, the lizards perched in an elevated position in the vegetation by entangling their elongated bodies and tails in the grass for efficient weight distribution. Locomotion was mainly restricted to the strike action when attacking prey. Fynbos and grassland, which are the main habitat of grass lizards of the genus Chamaesaura, are fire-prone. With their serpentiform morphology, grass lizards differ markedly from other cordylids, the majority of which are rock-dwelling. One aim of this study was to determine whether grass lizards make use of refuges like burrows or crevices within their grasslrestioid habitat during periods of inactivity or when threatened by fire. Refuge selection during inactivity was determined experimentally. Twelve lizards were offered different refuge options, namely grass tufts, crevices, burrows and loose sand. All twelve lizards preferred to shelter in the grass tufts. When the grass tufts were removed, only two lizards made use of the burrows and crevices provided, the other 10 not sheltering at all. Refuge selection when threatened by fire was tested by placing the 12 lizards in an enclosure provided with grass tufts and two types of refuges, burrows and crevices. The grass was set alight at one end of the enclosure and the fire was fanned on towards the other end with the aid of a high-speed fan. Precautions were taken to ensure the safety of all the lizards and to intervene when they were in direct danger. Only two of the 12 lizards sought shelter in the refuges provided. Of the remaining 10, six fled and four were trapped by the flames, requiring intervention. The results of these experiments, as well as field observations, suggest that C. anguina seldom makes use of shelter options other than grass and restio tufts, even when threatened by fire. In the case of fire, it flees by 'grass-swimming'. Field observations also suggest that mortality during and after a fire is considerably higher than in the case of rock-dwelling cordylids. The reproductive status of adult females (N = 85) were determined on the basis of the developmental stage of ovarian follicles and the presence or absence of oviductal eggs. Females were grouped into four reproductive categories: pre-vitellogenic, early vitellogenic, pre-ovulatory and gravid. To determine the reproductive cycle exhibited by the males (N = 46), testicular volume and seminiferous tube diameter were measured, as well as the spermatogenic activity assessed qualitatively. Spermatogenic activity was assessed by using Licht's (1967) classification system. The snout-vent length (SVL) of 144 specimens was measured. Sexual size dimorphism (SSD) recorded for C. anguina was quantified by a size dimorphism index (SDI). Reproductive activity was asynchronous among females, differing from the normal cordylid cycle of autumn/winter vitello genic activity, followed by winter/spring ovulation and gestation in late summer to autumn. The significant seasonal variation that existed in testes volume (ANOVA; F (7,22) = 3.70; P < 0.05) and seminiferous tubule diameter (ANOVA; F (10,25) = 4.90; P < 0.05), as well as sermatogenic activity as observed by histological examination, indicated that C. anguina males follow an annual spermatogenic cycle that can be described as post-nuptial. The cycle is characterized by summer/autumn spermiogenesis, associated with sperm storage throughout winter. Chamaesaura anguina males differ from other cordylids following a post-nuptial cycle, by starting with spermatogenesis in spring. The mean SVL of female grass lizards (109.51 mm ± 20.60 SD) was significantly larger (Mann-Whitney; P < 0.001) than that of males (84.77 mm ± 9.39 SD). A positive SDI of 1.29 and a SDImax of lAO were determined. Female-biased dimorphism in SVL recorded for C. anguina corresponds with the general pattern recorded for terrestrial cordylids, but contrasts with male-biased dimorphism in rupicolous forms. The longer SVL of C. anguina females facilitates higher fecundity. This, in turn, might be an adaptive survival strategy for this lizard species in the fire-prone environment where it occurs, because successful recruitment is facilitated by high fecundity. KEYWORDS: Chamaesaura anguina; serpentiform body; cryptic colouration; grass/restio habitats; undulatory locomotion; foraging mode; preferred body temperature; movement patterns; microhabitat use; fire susceptibility; refuge selection; reproductive cycle; sexual size dimorphism. 4
AFRIKAANSE OPSOMMING: Die voedingswyse van Chamaesaura anguina is bepaal deur drie kriteria: 1) die getal bewegings per minuut (BPM) en die persentasie tyd wat aan beweging bestee word (PTB) tydens aktiewe periodes; 2) die hoeveelheid tongskiete wat gerig word na wattepluisies bedek met prooi chemikalieë as 'n maatstaf van prooi chemiese diskriminasie; 3) die maaginhoud van die akkedisse as 'n indikasie van hul natuurlike diëet. Waarnemings is met 'n verkyker vanaf 'n waarnemingstoring langs 'n buitemuurse kampie gemaak, terwyl dit deur 'n eenrigting glaspaneel in die geval van 'n binnemuurse opstelling gemaak is. Elke akkedis is vir 'n periode van 10 minute tydens piek-aktiwiteit dopgehou, en die tye wat dit beweeg het en nie beweeg het nie, is aangeteken. Data verkry in die binnemuurse - en buitemuurse opstellings het nie statisties van mekaar verskil nie en is saamgevoeg. BPM (0.37 ± 0.21 SD) en PTB (1.92 % ± 0.93 SD) waardes aangeteken vir C. anguina (N = 10) val binne die reeks waardes wat as kenmerkend vir sit-en-wag voeders beskou word. Nege C. anguina individue is in glas terraria gewoond gemaak om meelwurms te aanvaar wat hul aangebied is. Toe al die akkedisse die kos sonder huiwering aanvaar het, is hul vermoë getoets om tussen drie verskillende geure wat hul aangebied is in 'n ewekansige blokontwerp, te diskrimineer: prooigeur bestaande uit die reuk van meelwurms, gedistilleerde water as 'n geurlose kontrole stimulus, en reukwater as 'n skerp kontrole. Die hoeveelheid tongskiete gerig na die gegeurde wattepluisie gedurende 'n 60 s periode, is aangeteken. Geen statisties-beduidende verskille is gevind tussen die reaksies tot die drie geure nie (Kruskal-Wallis, H = 2.41, df= 2, P = 0.30). 'n Analise van die maaginhoude van 21 C. anguina individue het meestal dag-aktiewe arthropoda prooispesies onthul. Die voorkeur liggaamstemperature wat deur 12 akkedisse in 'n termiese gradiënt geselekteer is, is ses maal gemeet gedurende 'n 48 uur periode, deur van 'n termo-koppel wat in die kloaka geplaas is, gebruik te maak. Die bepaalde liggaamstemperature (N = 72) het gevariëer van 22.62 oe - 27.07 oe met 'n gemiddeld van 24.82 oe ± 2.27 SA. Die lae voorkeur liggaamstemperatuur van C. anguina mag dalk toegeskryf word aan die gekombineerde invloed van plantbedekkingskadu, hoë hoogte bo seevlak, en hoë oppervlakte-volume verhouding. Die bewegingspatrone en mikrohabitat-gebruik van C. anguina is bestudeer deur ses akkedisse in 'n buitemuurse kampie aan te hou. Die ligging van die graspolle binne die kampie is op 'n kaart aangeteken, en die posisie van elke akkedis binne in die kampie is op 17 oggende aangeteken. Verdere waarnemings is gemaak met 'n verkyker vanaf 'n waarnemingstoring terwyl die akkedisse aktief was. Alhoewel die C. anguina individue nie herhaaldelik 'n spesifieke skuilplek gebruik het nie, het hul die langer, breër graspolle as skuilplek gedurende onaktiwiteit verkies. Daar was 'n hoogs beduidende verskil tussen onderskeidelik die hoogtes (studente z-toets; P < 0.001) en die deursnitte (studente I-toets; P < 0.001) van die verkose graspolle, en die graspolle wat nie gekies is as skuilplekke nie. Hulle het gewoonlik in 'n opgerolde wyse, in die middel en na aan die bodem van die graspolle, geskuil. Daar is gevind dat C. anguina vanaf 'n verhewe posisie voed deur sy verlengde liggaam en stert in die grass te vervleg om doeltreffende gewigsverspreiding te verseker. Beweging was hoofsaaklik tot die vangaksie van prooi beperk. Vuur is 'n algemene verskynsel in fynbos en graslande, wat die hoof habitat van grasakkedisse van die genus Chamaesaura uitmaak. Met hulle slangagtige morfologie, verskil grasakkedisse drasties van ander lede van die Cordylidae, waarvan meeste rotsbewonend is. Die doelwit van hierdie studie was om te bepaal of die grasakkedisse gebruik sal maak van skuilplekke, soos gate en klipskeure binne die grashabitat, gedurende periodes van onaktiwiteit of wanneer bedreig word deur vuur. Twaalf akkedisse is verskillende skuilopsies aangebied, naamlik graspolle, klipskeure, gate en los sand. Al twaalf het verkies om in die graspolle te skuil. Toe die graspolle verwyder is, het slegs twee akkdisse die klipskeure en die gate benut, terwyl die ander 10 nie geskuil het nie. Skuilplek-seleksie wanneer bedreig word deur vuur, is getoets deur 12 akkedisse in In afskorting te plaas wat met graspolle en twee tipes skuilplekke, gate en klipskeure, voorsien is. Die gras aan die een kant van die afskorting is aan die brand gesteek en is aangehelp m.b.v. 'n hoë-spoed waaier. Voorsorgmaatreëls om die veiligheid van al die akkedisse te verseker en om in te gryp as hulle in direkte gevaar sou verkeer, is getref. In twee van die 12 gevalle het die akkedisse skuiling gesoek in die beskikbare skuilings. In die oorblywende 10 gevalle het ses akkedisse gevlug, terwyl vier deur die vlamme vasgevang was en daar ingegryp moes word. Die resultate van hierdie eksperimente, sowel as waarnemings wat in die veld gemaak is, dui daarop dat C. anguina selde van skuilopsies, anders as graspolle en restio's, gebruik maak as hulle deur vuur bedreig word. In die geval van vuur, vlug hulle deur te "swem" deur die gras. Veldwaarnemings dui ook daarop dat mortaliteit gedurende en na die vuur heelwat hoër is as in die geval van rotsbewonende gordelakkedisse. Die reproduktiewe status van volwasse wyfies (N = 85) is bepaal deur die ontwikkelingsfase van ovarium follikels te ondersoek en deur die teenwoordigheid of afwesigheid van eiers in die oviduk. Wyfies is in vier reproduktiewe kategorieë gegroepeer: pre-vitellogenies, vroeg vitellogenies, pre-ovulatories en dragtig. Testikulêre volume en saadbuisdeursnit is gemeet, en spermatogeniese aktiwiteite soos histologies vasgestel, is gebruik om die reproduktiewe siklus van die mannetjies (N = 46) te bepaal. Spermatogeniese aktiwiteit is bepaal deur van Licht (1976) se klassifikasie sisteem gebruik te maak. Die snoet-kloaak lengte (SKL) van 144 individue is gemeet en die seksuele grootte-dimorfisme (SGD) soos bepaal vir C. anguina, is gekwantifiseer deur middel van In grootte-dimorfisme-indeks (GDI). Voortplantingsaktiwiteit in die wyfies was nie gesinchroniseerd nie, en verskil dus van die normale gordelakkedissiklus met herfs/winter vitellogeniese aktiwiteit, winter/lente ovulasie en swangerskap in die volgende laat somer tot herfs. Die beduidende seisoenale verskil wat bestaan het in die testesvolume (ANOV A; F (7.22) = 3.70; P < 0.05) en die saadbuisdeursnit (ANOVA; F (10,25) = 4.90; P < 0.05), asook testis histologie, het aangedui dat C. anguina mannetjies 'n jaarlikse spermatogeniese siklus volg, beskryf as "post-nuptial". Hierdie siklus word gekenmerk deur somer/herfs spermiogenese, geassosieer met spermstoring gedurende die winter. In teenstelling met ander gordelakkedisse wat hierdie siklus volg, begin spermatogenese in C. anguina alreeds in die lente. Die gemiddelde SVL van die wyfies (109.51 mm ± 20.60 SA) was beduidend groter (Mann-Whitney; P < 0.001) as dié van die mannetjies (84.77 mm ± 9.39 SA). In Positiewe GDI van 1.29 en In GDImax van 1.40 is gemeet. Wyfie-plus dimorfisme in SKL bepaal vir C. anguina, stem ooreen met die algemene patroon waargeneem by terrestriële gordelakkedisse, maar is in kontras met mannetjie-plus dimorfisme by rotsbewonende vorme. Die langer SKL by wyfies van C. anguina kan In hoër fekunditeit fasiliteer. Dit mag dalk In oorlewingstrategie vir die species wees wat in In vuurgeteisterde omgewing voorkom, omdat suksesvolle rekolonisering deur In hoë fekunditeit aangehelp word. TREFWOORDE: Chamaesaura anguina, slangagtige liggaam; kriptiese kleuring; graslrestio habitatte; kronkel beweging; voedingsrnetode; voorkeurtemperatuur; bewegingspatrone; mikrohabitat-gebruik; vatbaarheid vir vuur; skuilplekseleksie; voortplantingsiklus; seksuele dimorfisme.
Thesis (MSc)--University of Stellenbosch, 2001.
Lizards -- Ecology -- South Africa -- Western Cape