Effect of Relative Clutch Mass on Sprint Speed in the Lizard Lacerta vivipara

Abstract

Relative clutch mass (RCM; the ratio of clutch to female body mass), a measure of the physical burden imposed on gravid females, is considered an important life history trait in reptiles. Several authors (Vitt and Congdon, 1978; Vitt, 1981; Vitt and Price, 1982; Seigel and Fitch, 1984) have hypothesized that RCM has evolved through differential mortality resulting from decreased locomotor ability and increased energetic costs of locomotion associated with transporting the added mass of the clutch. Three lines of evidence support this hypothesis or its assumptions. First, comparative studies (Vitt and Congdon, 1978; Vitt and Price, 1982; Seigel and Fitch, 1984) have shown that high RCM values are found in lizards that do not rely on fast movement for foraging and escaping (sit-and-wait foraging, cryptic escape behavior), and in oviparous snakes; low RCM is associated with active foraging and fleeing escape behavior in lizards, and with viviparity in snakes. Secondly, intraspecific studies have shown a reduction of sprint speed (Shine, 1980; Bauwens and Thoen, 1981; Garland, 1985; Seigel et al., 1987) or endurance (Seigel et al., 1987) in gravid lizards and snakes. Thirdly, differences among individuals in sprint speed and RCM have been identified in four scincid lizards (Shine, 1980) and one snake (Seigel et al., 1987). The latter studies strongly suggest that the added clutch mass exerts a direct negative effect on the locomotor performance of gravid females. In this note we document the relation between sprint velocity and RCM in gravid females of the lizard Lacerta vivipara. Lacerta vivipara is a small (adult body length: 45-65 mm) viviparous lizard that reproduces once a year. It is an agile lizard that forages actively on insects and other invertebrates (Avery, 1966; Itamies and Koskela, 1971; Koponen and Hietakangas, 1972; Pilorge, 1982), behaves like a typical heliotherm (Avery, 1976; Van Damme et al., 1987), and uses crypsis, flight and tail autotomy to escape from predators (Bauwens and Thoen, 1981). At parturition, this species has a remarkably high RCM (=clutch mass/female body mass after parturition). Mean values observed in different populations/years are: 0.81 (Bauwens and Thoen, 1981), 0.41-1.02 (Pilorge et al., 1983), 0.45-0.56 (Pilorge 1987) and 0.63 (this study). These values are among the highest reported for lizards in general (x = 0.29; range 0.05-0.68) as well as in live-bearing species (x = 0.31; range 0.13-0.48; recalculated from table 1 in Vitt and Price, 1982). During April 1984, we captured adult female lizards in the Belgian national nature reserve de Kalmthoutse heide (51?25'N, 4?25'E, Province of Antwerp, Belgium). They were mated in the laboratory and maintained individually in outdoor enclosures until parturition. About two weeks (x = 14.9 days, range: 8-25) before parturition, we determined sprint speeds of 17 gravid and 6 nongravid adult females by chasing them by hand down a 2 m racetrack (Huey et al., 1981). The t ack was constructed of plywood with walls 30 cm high positioned 15 cm apart; its floor was covered with carpet that provided excellent traction. Nine pairs of photocells measured the time the lizards needed to cover 8 consecutive intervals of 25 cm. Before test-