Lambir gecko project
From BiodivBorneo09
Sexual size-dimorphism and weight-length relationships in two species of geckos from Lambir Hills, Malaysia
Contents |
Abstract
The weight – length relationships and morphometric patterns in two allopatric species of geckos, a common South-East Asian House Gecko Hemidactylus frenatus and a Borneon endemic Cyrtodactylus pubisulcus were studied in Lambir Hills National Park, Malaysia. In both species, snout-vent length has a strong and positive correlation to the weight and tail length. Sexual dimorphism in terms of tail length is evident in both species. The difference of A-G distance between the two species might be related to the their different movement style. Long-term study and greater sampling effort are needed to give a more persistent result.
(See summary of argument)
Introduction
Within reptiles, body size is an important life history trait that influences microhabitat type, diet, vulnerability to predators and reproductive success (Calder, 1984; Blueweiss et al., 1978; Lobo et al., 2004). Weight – length relationships have been demonstrated in many species of snakes (Kaufman & Gibbons, 1975; Guyer & Donnelly, 1990; Das, 1991) and it is studied that in two thirds of the snake species for which data are available, female snakes grow longer and consequently weigh more than males (Shine, 1993) and differences in mean body size can result in interspecific variation in ecology (Shine, 1994). There have been very little study done on the weight-length relationships and morphometric patterns in geckos and it is not clearly known if the information obtained from snakes applies to geckos. In this paper, we examine the weight – length relationships, the difference between sexes, and the influence of axilla-groin distance in the pattern of movement in H. Frenatus and C. pubisulcus, encountered in Lambir Hills National Park.
Methods
Study area
The study was undertaken around the headquarters and in the forests of Lambir Hills National Park, located on the north coast of Borneo, Malaysia at 4° 11’ 90 N and 114° 02′ 75 E. It has an area of 6,949 hectares of sandstone hills with some very rugged forest terrain.
Field methods
Geckos were collected between 14 June 2009 to 18 June 2009 in six different sites in the forest and on the edges using visual encounter survey. The geckos were measured, sexed within 5 minutes at the site of capture and released at the same location. Sex of the juveniles remains unknown as it is hard to differentiate their sexes when using live specimens as a subject of study. Morphometric data were recorded from 20 and 18 individuals of H. frenatus and C. pubisculus respectively that were measured in the National Park. Snout to vent length (SVL), tail length (TaL), axilla-groin distance (A-G) and weight (Wt) of all geckos were measured using a measuring tape (in mm) and a pesola weighing scale (in gm).
Data Analyses
Scatter plots were made to depict the relationships between snout-vent length to tail length and weight in the case of H. frenatus and C. pubisulcus. The standard deviation (SD) were computed for each morphometric measurements. The statistical analysis was carried out using R 2.9. Linear models were used to look at the combined effect of sex and species. The Sexual Size Dimorphism (SSD), a measure of degree of sex difference in body size, was quantified by dividing the mean size of the smaller sex by the mean size of the larger sex (Gibbons and Lovich, 1990).
Results
In total 9, 8 and 2 in Hemidactylus frenatus, and 9, 5 and 3 in Cyrtodactylus pubisulcus were males, females and juveniles respectively. In H. Frenatus and C. Pubisulcus, it was observed that the SVL explains most of the variation in Wt and TL (figure 1). There was no obvious sexual dimorphism observed in the species. However, sexual dimorphism in terms of tail length is evident in both species (p < 0.05). The Sexual Size Dimorphism (SSD) value calculated was 0.92 in H. frenatus and 0.91 in C. pubisulcus. The sex ratios are highly biased towards males in H. frenatus and towards females in C. pubisulcus. However, the values were not significantly different in males and females of both species (linear model: p > 0.05). The A-G distance is comparatively greater in H. frenatus to C. pubisulcus but does not show a significant difference.
Discussion
Our data does not conform to the broad body size-weight relationship as observed in snake species (Das, 1991; Kaufman & Gibbons, 1975; Guyer & Donnelly, 1990). However, it is very interesting to note that the males in H. frenatus are bigger and weigh more than the females, and the males in C. pubisulcus are smaller and weigh less than the females of the same species (Table 1; Figure 1). This is probably because of the fierce fighting habits of male H. frenatus and this study throws a light on the natural history of C. pubisulcus, which may have a different sexual selection that remains unstudied. It would be very difficult to draw conclusion on their sexual dimorphism without long-term studies but this short-term study can lay a platform to study the regional variations relating it to the habitat, prey availability, and behavioral pattern.
Tail length difference between sexes of both species was evident. The males of each species have longer tail length compared to females (Figure 2). This difference might be related to the important role of tail in reproduction and fights for females (Sreekar, pers. obs.). The smaller A-G distance in C. pubisulcus (Figure 3) might be accounted for by its hopping style during movement that is significantly different from the crawling style of H. frenatus which comparatively has a greater A-G distance. Greater sample size and including more species in the study can give significant results to the given predictions.
References
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