Energetics of the Lizard Cnemidophorus Tigris and Life History Consequences of Food‐Acquisition Mode

Abstract

Energy budgets for the wide-foraging "arthropodivorous" lizard Cnemidophorus tigris were constructed for the reproductive season using doubly labeled water measurements of field metabolic rate (FMR). Rates ofbody mass change, clutch sizes, and clutch intervals were also investigated. FMRs ofboth sexes (males, 298 J ·g-1 ·d-1 ; females, 24 7 J · g-1 • d -1 ) were greater in the reproductive season than during the postreproductive season. This was not due to differences in resting metabolism, but, instead, was due to higher activity costs during the reproductive season. Although males had signficantly higher FMR than females, males and females had similar feeding rates (as reflected by water influx rates). The ratio of energy intake to expenditure was higher in females than in males. Females produced eggs but did not grow. Large males did not grow, but smalllst-yr males similar in size to females did grow. Females laid at least two consecutive clutches during a single reproductive season; clutch interval was ~25 d. Clutch size varied with time of laying (first or second clutch), female body size, and year.We compare the reproductive energetics of C. tigris and other wide-foraging Cnemidophorus with the energetics of ambush iguanids. The wide forager C. tigris and the ambusher Uta stansburiana apparently do not differ in the proportion of the energy budget devoted to reproductive production (reproductive effort, REP). But total reproductive effort, RE., which includes metabolism associated with reproduction, is much lower in Cnemidophorus tigris.Review of the literature indicates Cnemidophorus tend to lay smaller clutches and larger eggs than iguanids, but the number of eggs laid per unit time generally equals that of most iguanids. Cnemidophorus also deposit energy into their eggs at rates almost 60% higher than ambush iguanids. We consider higher rates of production in wide foragers to be permitted by their higher rates of net energy intake while foraging, compared with most ambushers. These higher rates of production in Cnemidophorus apparently allow them either to reach a larger size than iguanids of similar age at first reproduction or to be younger than iguanids of the same size at first reproduction. Life history characters may be influenced by differences in rates of production associated with different food-acquisition modes.

Tail loss reduces mating success in the Iberian rock-lizard, Lacerta monticola

“…monticola in the field (but see P6rez-Mellado et al 1987, for the postreproductive period), but we have observed increased male activity and movements during the reproductive period (unpublished data). Also iguanid and teiid males maintain high activity levels during the entire breeding season, because re-peated searches of home range establish an encounter rate of males with prospective mates (Rose 1981;McCloskey et al 1987;Anderson and Karasov 1988). Lizards that maintain territories in the field commonly develop hierarchies in captivity (Stamps 1977;Deslippe et al 1990).…”

The Physiology of Life History Trade-Offs in Animals

“…A few studies have focused on variation in energy reserves, growth, and metabolism within populations, especially in the context of the cost of reproduction. For example, metabolic rates measured in the fi eld were higher in reproductive versus nonreproductive females of several species (Nagy 1983, Anderson & Karasov 1988. A number of correlational and experimental studies indicate that a common effect of current reproduction may be the reduction of internal reserves, which impacts future reproduction either by reducing survivorship or by reducing nutrients required for future reproduction (Landwer 1994, Schwarzkopf 1994, Doughty & Shine 1997, 1998, Wilson & Booth 1998.…”

The concentration of plasma metabolites varies throughout reproduction and affects offspring number in wild brown trout (Salmo trutta)

“…In many species, food intake is reduced during the reproduction because animals allocate preferentially their time and energy to different activities such as looking for mates or territorial defense (Doucett et al, n.d;Cherel et al, 1988;Anderson and Karasov, 1988;Barboza and Jorde, 2001;Esteve, 2005). Thus, during reproduction the energetic demand is expected to be high whereas feeding is reduced.…”