Poison Arrow Frogs

How do families resolve conflicts over resources – and what consequences does any resolution have for the individuals involved?

We have recently been awarded a Royal Society Research grant to establish a globally unique laboratory population of the strawberry poison arrow frog (Oophaga pumilio), in order to conduct pilot experiments investigating its remarkable system of parental care.

O. pumilio is a tiny (<1cm) South American rainforest frog. Unusual for a frog, mothers care for their tadpoles: they deposit single tadpoles in pools of water held by the leaves of bromeliads, returning to feed them with unfertilised eggs. Mothers care for multiple tadpoles, travelling between pools to feed each in turn. This creates a dispersed nursery, where each tadpole is only in contact with the mother, but where they still compete for food by begging. This enables us to manipulate each individual (mother or single tadpoles) independently, and quantify the effects on everyone else. This will be the first study of family dynamics ever conducted able to do this, and as such promises to answer fundamental questions which have been attracting attention and controversy for over 40 years.

We aim to:

1. Set up 20 breeding pairs in tanks, and confirm that they will deposit tadpoles in artificial pools (plastic cups).

2. Obtain basic information about breeding behaviour, including conditions most favourable to breeding; duration of parental care period; frequency of visits by mother to each tadpole; frequency of feeding; and the timing of tadpole development.

3. Conduct preliminary experiments manipulating tadpole food supply, in order to assess how tadpoles react to changes in hunger, and how they communicate these changes to their mothers; how mothers react to these changes; and how variation in the behaviour of one tadpole affects the food provided to its siblings.

PhD project: The cost of flexible parenting: measuring the later life consequences of plasticity in parental care.

In species with parental care, offspring commonly compete over the distribution of parental resources, and parents must make decisions about the allocation of limited resources which balance the current needs of their offspring against their own survival and future reproductive potential.  Parents often make these decisions in the presence of pronounced differences in offspring competitive ability and unpredictable fluctuations in resource availability. This requires parents to monitor offspring state closely, and to react flexibly to both social and environmental variation.

Such flexibility in response to social and ecological variability may impose substantial costs on parents. In particular, there may be physiological damage incurred when monitoring and correcting large asymmetries in offspring development while subjected to unpredictable resource availability. Such damage may degrade a parents capacity to care for future offspring, in particular reducing the extent of future flexibility in decision making.   

This project will ask whether there are costs to parents associated with plasticity in parental care and the cognitive abilities underlying such flexibility (Buchanan et al., 2013). The project will use a novel model species, Oophaga pumilio, a frog with obligate parental care. Females feed tadpoles on unfertilised, trophic eggs, and flexibly adjust their provisioning in relation to tadpole behaviour and development (Stynoski, 2009).  However, offspring in the same brood are spatially separated within their own bromeliad pool, which provides two advantages in this study: (i) it removes the possibility of direct sibling conflict, meaning that parental decision-making is the only factor that maintains or alleviates asymmetries; and (ii) it allows individual offspring to be manipulated independently.

We will manipulate individual tadpoles to either exaggerate or equilibrate asymmetries within broods, while simultaneously manipulating resources available to the parent (both abundance and predictability).  Of specific interest will be whether parents exposed to exaggerated brood asymmetries in the presence of unpredictable resources suffer a decline in their subsequent capacity to care for offspring. This will be tested using periodic performance assays and physiological tests, as well as reproductive success over subsequent breeding attempts.

The student will receive training in: (i) relevant evolutionary theory, with specific reference to theories of adaptive senescence; (ii) data collection techniques, including videography, to capture variation and link biological processes through to phenotypic traits; (iii) experimental design and implementation in a laboratory environment; (iv) modern analytical techniques and multivariate statistical analysis; (v) care and husbandry of captive amphibians.

Buchanan, K.L., Grindstaff, J.L., & Pravosudov, V.V. (2013) Condition dependence, developmental plasticity, and cognition: implications for ecology and evolution. Trends in Ecology & Evolution 28: 290–296.

Stenning, M. J. (1996) Hatching asynchrony, brood reduction and other rapidly reproducing hypotheses. Trends in Ecology & Evolution 11: 243–246.

Stynoski, J.L. (2009) Discrimination of offspring by indirect recognition in an egg-feeding dendrobatid frog, Oophaga pumilio. Animal Behaviour 78: 1351–1356.