Life-History Traits in a Population of the Dwarf Gecko, Sphaerodactylus vincenti ronaldi, from a Xerophytic Habitat in Martinique, West Indies
Leaf-litter geckos of the genus Sphaerodactylus are highly diversified but their small size and secretive habits have made them difficult to study. In 1972–1973, we conducted a demographic study on a population of S. vincenti ronaldi from a xerophytic forest in Martinique, with the prediction that seasonality in local climatic conditions, especially precipitation, should cyclically constrain food consumption, growth, and reproduction. We used a mark–recapture method to get basic data on population structure and density. We sacrificed 62 specimens to determine diet and reproductive conditions. Individual age, growth, and longevity were assessed by skeletochronology. Lizards were ubiquitous in the 900 m2 study area, with most found singly under humid rotten logs. Population density averaged 8220 geckos/ha. Individual movements were very limited over a six-month period. We noted a high incidence (62%) of tail autotomy. Diet included a diversity of small invertebrate prey (15 different orders) with collembolans being most abundant. However, food consumption (measured as stomach content and intestine masses) dropped to a minimum in late dry season, a cyclic pattern most likely responsible for the observed lines of arrested growth (LAGs) registered in the femoral bone cortex of these lizards. Sequences of LAG dimension and modal distributions of snout–vent lengths (SVL range: 13–32 mm) revealed a slow growth rate (0.66 mm/month) during the first year of life with both genders attaining sexual maturity at 25–26 mm SVL and 18–20 months of age. Longevity did not exceed 48 months. Reproduction appeared seasonal, with the geckos laying eggs at an undetermined frequency during a period lasting approximately seven months. Egg size and incubation time were similar to other Sphaerodactylus of comparable body size. These results indicate special constraints associated with body size in species of Sphaerodactylus living in xerophytic habitats. However, for S. vincenti, a species that extends its range to other mesic/humid habitats in Martinique and three other nearby island banks, it is not known if larger subspecies (up to 40 mm SVL) suffers the same constraints in food intake, growth, and reproduction as observed in this study for S. v. ronaldi.Abstract
Comparisons of three different parameters of food consumption (A–C) and an index of abdominal fat reserve (D) at five different sampling dates (15 December 1972 to 6 August 1973) for Sphaerodactylus vincenti ronaldi from the Presqu'île de la Caravelle. Numbers above mean values denote sample size.
Body size distributions of Sphaerodactylus vincenti ronaldi from the Presqu'île de la Caravelle caught during two different periods: late wet season (21 November 1972–4 January 1973; white columns; n = 121) and mid-dry season (7 February–31 March 1973; black columns; n = 88).
Sampling dates (15 December 1972 to 6 August 1973) versus (A) adjusted testis diameter and (B) follicular or oviductal egg diameter in a population of Sphaerodactylus vincenti ronaldi from Presqu'île de la Caravelle. Each symbol represents one specimen. In (A), open symbols are males with reticulated epididymides and well developed vasa deferentia; solid symbols are males with smooth epididymides and poorly developed vasa deferentia. In (B), diamonds are oviductal eggs; round symbols are follicles in females with well (open symbols) or poorly developed (solid symbols) oviducts.
Cross-sections of femoral diaphyses of Sphaerodactylus vincenti ronaldi of different body sizes, from neonate to large adults, showing the following structures from the medullary cavity towards the outer margin: endosteal bone (E), cementing line (CL), embryonic bone (EB), hatching line (HL), and periostic bone (PB) with different number of lines of arrested growth (LAGs, arrows). (A) 15-mm SVL neonate with only a ring of EB containing coarse osteocytes; (B) 1.5-yr, 26-mm SVL adult caught in August with partially eroded EB; LAG 1 confounded with HL; (C) 2.25-yr, 26.5-mm SVL adult caught in February with a distinguishable LAG 1 (white arrow) close to HL; (D) 3-yr, 30-mm SVL adult caught in February with LAG 1 merged with HL forming a thick line. Unstained outer margins in (B) and (D) correspond to osteoid, a peripheral bone matrix still in process of mineralization.
Frequency distributions of diameters of the hatching line (HL) and of other lines of arrested growth (LAG 1 to LAG 4) measured in femoral cross-sections of 58 specimens of Sphaerodactylus vincenti ronaldi. (A) The diameter of HL; (B) the bimodal distribution of diameters of the LAG immediately following the HL; the subset of smaller diameters (≤0.210 mm, gray columns) was assigned to LAGs 1 in lizards that benefited from a short period of growth before the dry season, the other subset (open columns) to LAGs 2 in lizards born during the dry season and for which LAG 1 merged indistinguishably with HL; (C) LAG 2 in lizards that showed the distinguishable LAG 1 seen in (B); (D) and (E) third and fourth LAGs, respectively, in older lizards.
Growth in body length (SVL) of Sphaerodactylus vincenti ronaldi. Age estimated by skeletochronology and data fitted to von Bertalanffy growth models. Neonates (solid squares) were used for both gender growth models. Males (solid circles): Lt = 31.01 [1−e−0.051 (t−12.07)]; females (open circles): Lt = 32.55 [1−e−0.049 (t−11.86)].
Contributor Notes
Associate Editor: S. E. Wise.