Dissertation Research

More specifics about some of the my dissertation research at the National University of Singapore and Sakaerat Station (Thailand). 
Parental care

 

The arboreal frog, Chiromantis hansenae (Family: Rhacophoridae) is one of only a handful of Southeast Asian amphibian species reported with parental care. I present the first systematic observational and experimental study confirming offspring benefits as a result of this care, which has a number of unusual life-history characteristics. Eggs are unusually small, breeding takes place in large pools, and females attend the eggs. Field observations and an adult removal experiment demonstrated a critical contribution of egg attendance to offspring survivorship. Harsh environmental conditions for offspring appeared to be the prime mover of parental care in this species, with desiccation as the main source of mortality when attending adults are absent. Results confirm females to be the care-givers, making C. hansenae a rare case of maternal egg attendance in a non-directly developing anuran. (Study published in Ethology 199(8), 671-679)

 
Anti-predator defense

 

Predator and prey relationships are dynamic and interrelated. Thus, any offensive behavior will vary according to differing defensive behaviors, or vice versa, within each species in any predator-prey system. However, most studies are one-sided as they focus on just one behavior, either that of the predator or prey. With this in mind, I examine both predatory behavior of an oophagus katydid and anti-predator behavior by a frog with egg-stage parental care. 

 

Katydid offensive behavior and predation success increased with predator maturity and size and was greater in females. Frog defensive behavior was sex-specific, likely because only mothers provide parental care. Defensive behavior could be active, such as charging predators, or passive, such as sheltering eggs, with greater active defense against larger predators. Further, maternal defense was not influenced by offspring age. These results are contrary to existing theory, which suggests parental investment ought to be negatively correlated with parental predation risks and affected by offspring age. This study highlights the use of anti-predator behavior to test predictions of parental investment theories in amphibians and illustrates the need to consider factors influencing both species concurrently when examining the complex interaction between predators and parents. (Manuscript submitted)

 
Environmentally-cued hatching 

 

Hatching, the life-history switch-point between embryonic and larval stages, has traditionally been regarded as a fixed event in an organism’s development. This notion has been challenged by reports of environmentally-cued hatching in recent years, which show embryos improve fitness by hatching in response to mortality risks. Here, I present evidence of accelerated hatching due predation cues at two points during embryonic development in Chiromantis hansenae. Young embryos (0 day old) exposed to simulated predation hatched earlier compared to undisturbed clutches. Old embryos (4 day old) subjected to direct predation had more immediate responses, hatching <1 hour after predation on average. Hatching time was not correlated with female frog size, egg attendance time, or other predator cues. Results confirm predator-cued hatching in a new family of amphibians and support hatching plasticity being a widespread and potentially basal condition. (Study published in Behavioral Ecology and Sociobiology 68:1733–1740)

 

In addition, studies revealed C. hansenae embryos are able to respond to other environmental cues in order to maximize survival when transitioning between life stages. (Manuscipt in prep  

 

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