Terrestrial reproduction and parental care drive rapid evolution in the trade-off between offspring size and number across amphibians

The trade-off between offspring size and number is central to life history strategies. Both the evolutionary gain of parental care or more favorable habitats for offspring development are predicted to result in fewer, larger offspring. However, despite much research, it remains unclear whether and how different forms of care and habitats drive the evolution of the trade-off. Using data for over 800 amphibian species, we demonstrate that, after controlling for allometry, amphibians with direct development and those that lay eggs in terrestrial environments have larger eggs and smaller clutches, while different care behaviors and adaptations vary in their effects on the trade-off. Specifically, among the 11 care forms we considered at the egg, tadpole and juvenile stage, egg brooding, male egg attendance, and female egg attendance increase egg size; female tadpole attendance and tadpole feeding decrease egg size, while egg brooding, tadpole feeding, male tadpole attendance, and male tadpole transport decrease clutch size. Unlike egg size that shows exceptionally high rates of phenotypic change in just 19 branches of the amphibian phylogeny, clutch size has evolved at exceptionally high rates in 135 branches, indicating episodes of strong selection; egg and tadpole environment, direct development, egg brooding, tadpole feeding, male tadpole attendance, and tadpole transport explain 80% of these events. By explicitly considering diversity in parental care and offspring habitat by stage of offspring development, this study demonstrates that more favorable conditions for offspring development promote the evolution of larger offspring in smaller broods and reveals that the diversity of parental care forms influences the trade-off in more nuanced ways than previously appreciated.

Relying on known or exploring for new? Movement patterns and reproductive resource use in a tadpole-transporting frog

Animals relying on uncertain, ephemeral and patchy resources have to regularly update their information about profitable sites. For many tropical amphibians, widespread, scattered breeding pools constitute such fluctuating resources. Among tropical amphibians, poison frogs (Dendrobatidae) exhibit some of the most complex spatial and parental behaviors—including territoriality and tadpole transport from terrestrial clutches to ephemeral aquatic deposition sites. Recent studies have revealed that poison frogs rely on spatial memory to successfully navigate through their environment. This raises the question of when and how these frogs gain information about the area and suitable reproductive resources. To investigate the spatial patterns of pool use and to reveal potential explorative behavior, we used telemetry to follow males of the territorial dendrobatid frog Allobates femoralis during tadpole transport and subsequent homing. To elicit exploration, we reduced resource availability experimentally by simulating desiccated deposition sites. We found that tadpole transport is strongly directed towards known deposition sites and that frogs take similar direct paths when returning to their home territory. Frogs move faster during tadpole transport than when homing after the deposition, which probably reflects different risks and costs during these two movement phases. We found no evidence for exploration, neither during transport nor homing, and independent of the availability of deposition sites. We suggest that prospecting during tadpole transport is too risky for the transported offspring as well as for the transporting male. Relying on spatial memory of multiple previously discovered pools appears to be the predominant and successful strategy for the exploitation of reproductive resources in A. femoralis. Our study provides for the first time a detailed description of poison frog movement patterns during tadpole transport and corroborates recent findings on the significance of spatial memory in poison frogs. When these frogs explore and discover new reproductive resources remains unknown.

Female activity patterns and aggressiveness in the strawberry poison frog Dendrobates pumilio (Anura: Dendrobatidae)

Female strawberry poison frogs (Dendrobates pumilio) exhibit highly evolved maternal care, including tadpole transport and tadpole provisioning with unfertilized eggs. We observed that tadpole-rearing and mating activity are mutually exclusive behavioural states in a Costa Rican population. Tadpole-rearing females did not engage in courtship activity. Only non-rearing females courted. Non-rearing females occupied larger home ranges than tadpole-rearing females, which may be related to female selection of mates. For the first time aggressive female-female interactions were observed in the field. Tadpole-rearing females were significantly more aggressive than non-rearing females, especially in the vicinity of their offspring-rearing sites. Las hembras de la ranita roja Dendrobates pumilio ejecutan cuidado parental altamente desarrollado que incluye el transporte y la alimentación de los renacuajos. En una población costaricense encontramos que el cuido materno y la actvidad sexual son comportamientos mutualmente exclusivos: Las hembras que estan cuidando a su cría son sexualmente inactivas, solamente las hembras sin renacuajos se aparean. Las hembras sexualmente activas poseian un rango de actividad más grande que las hembras cuidando a renacuajos. Los rangos de actividad en el primer grupo de hembras eran más grandes probablemente porque ellas visitan los territorios de varios machos con el fin de seleccionar una pareja. Además, por la primera vez interacciones aggressivas entre las hembras de la ranita roja fueron observados en el campo, siendo más aggressivas las hembras con rencuajos, particularmente en la vencidad de los hábitats de su cría.

Tadpole transport in relation to rainfall, fecundity and body size in five species of poison-dart frogs from Amazonian Peru

During a study on annual activity patterns of anurans at a neotropical study site (Aichinger, 1987a) additional observations on tadpole carrying poison-dart frogs were made. Seventy-four individuals representing five species, Colostethus marchesianus, Dendrobates quinquevittatus, Epipedobates femoralis, E. pictus, and E. trivittatus (generic names follow Myers, 1987), were observed during larval transport. Eighty-nine percent transported their larvae immediately after rain showers. In 1981 and 1985 seventy-eight percent of the observations were made on two days at the beginning of the rainy season. There was no relation between snout-vent length (SVL) of adults and number of tadpoles carried. In Colostethus marchesianus and Epipedobates pictus the number of ovarian eggs increased significantly with increasing SVL. The number of ovarian eggs is compared with the number of tadpoles carried. In Epipedobates spp. the remarkably lower number of tadpoles carried (X = 25.9 % ) may be due to the mortality rate of the larvae. The number of transported tadpoles in C. marchesianus exceeded the number of ovarian eggs by up to 89 % . It is supposed that C. marchesianus may carry the hatched tadpoles of two clutches.