Reproductive Investment of Female Green Toads (Bufo viridis)

Females of iteroparous species may compromise between contrasting reproductive strategies. They should balance the amount of energy devoted to reproduction against the energy saved for growth and survival, and they should compromise between the quantity versus the quality of offspring. In the present paper, we analyze these trade-offs in European Green Toads (Bufo viridis). We define reproductive investment in terms of clutch dry mass, number of eggs, and mean ovum dry mass, whereas we describe the amount of resources saved for growth and survival (somatic investment) with a fat index derived from the total body electrical conductivity (TOBEC) of postspawning females. Our results indicate that larger individuals produce larger clutches, both in the number and size of eggs. Females with higher reproductive effort, however, also show a larger somatic investment regardless of size. We show that females of similar size invest similar proportions of resources in reproduction, so that those in good condition not only show larger reproductive effort than lower-quality females but also store larger amounts of resources for growth, survival, and future reproduction.

Fig. 1.

Models of condition-dependent reproductive allocation strategies. Females with different amounts of available resources move along different diagonal lines. The horizontal dash line represents the minimum somatic investment compatible with survival, whereas the vertical dash line represents the minimum amount of resources necessary for reproduction. The stippled area represent potential reproductive production. Three strategies are presented, all resulting in a positive correlation between reproductive effort and female condition. According to the Hypothesis A, females invest most of their available resources in reproduction, and similar amounts of resources in growth and survival. According to Hypothesis B, females in poor condition save larger amounts of resources for growth and survival than those in better condition. According to Hypothesis C, females invest similar proportions of available energy to reproduction, those having invested more in reproduction saved also larger amounts of energy for growth

Fig. 2.

Relationship between female SVL and clutch size (r = 0.748; F = 30.464; df = 1, 24; P < 0.001)

Fig. 3.

Pattern of association among the variables employed to describe female state (SVL), somatic effort (postspawning fat index), and reproductive effort (number and mean size of eggs)

Contributor Notes

(SC, CG) Dipartimento di Biologia Animale e dell'Uomo, UniversitÀ di Torino, Via Accademia Albertina, 17, 10123 Torino, Italy; and (MC) Dipartimento di Scienze e Tecnologie Avanzate, UniversitÀ del Piemonte Orientale, via Cavour 84, 15100 Alessandria, Italy. (SC) sergio.castellano@unito.it; (MC) cucco@unipmn.it; and (CG) cristina.giacoma@unito.it Send reprint requests to SC.

Accepted: 24 Apr 2004