Reproductive modes and patterns of egg and clutch size among anurans in Eastern Amazonia, Brazil

Because of limited resources and the physical constraints of reproducing females, there is an inherent trade-off between the number of eggs produced and their individual size within a clutch. This trade-off typically leads to an inverse correlation between egg size and clutch size, a pattern consistently documented across amphibia. However, relatively few studies have explored how this relationship is influenced by life-history characteristics such as reproductive modes. We investigated reproductive modes and patterns of eggs and clutch size variation among amphibians in eastern Amazon. Our data on reproductive modes comprise field observations of the opposition sites of 37 species of anurans from Amapá, eastern Amazon. Parameters of egg and clutch size were obtained from 92 dissected gravid females. We registered 11 reproductive modes including aquatic, arboreal, semiterrestrial and terrestrial, of which aquatic deposition of eggs in lentic water was the most common. The trade-off between egg and clutch size and female size differed between reproductive modes. In aquatic ovipositing species, clutch size was associated with female size. For species that oviposit terrestrially and exhibit parental care, we found a greater egg investment. In addition, species with parental care had larger clutch sizes indicating a K-selection scenario. The inverse relationship between clutch and egg size was similar to the pattern observed in other neotropical biomes and world regions. We provide evidence that oviposition site, female body size, and the presence of parental care are key factors shaping the trade-off between egg and clutch size in Amazonian anuran assemblages.