Thursday, May 1, 2014

Deadbeat Dads: Hatching Plasticity in Glassfrog Embryos

I have recently emerged from the all-enveloping cocoon that is data analysis and presentation writing. Powerpoint, Photoshop, and JMP have been in charge of my waking hours for the past couple of weeks. But now I am free! Is that daylight and springtime I see? If you’ve been following the Facebook page then you will still have received the occasional sciency goodness, but now it’s time for me to get back to blogging.

This week a new paper published in Proceedings of The Royal Society B about baby glassfrogs caught my eye. There are more than 100 species of neotropical glassfrogs (Centrolenidae) and more are being regularly discovered. Glassfrogs are so called because of the transparent skin on their venters which allow for the observation of their internal organs. Dorsally, they tend to be green with various yellow, white, blue or red markings, with some species even reflecting light in the infrared spectrum. These frogs live high in the trees that overhang mountain streams in Mexico, Central, and South America. They make high peeps or whistles, and in some species, a single individual will initiate a chorus.

Glassfrogs are also known for their parenting skills, which seems ubiquitous across the taxon. Females lay small clutches of eggs several meters above the water on rocks or vegetation. The male will then take charge of egg maintenance, sometimes caring for multiple clutches. The male will hydrate the eggs (“hydric brooding”) in order to moderate water balance and prevent dehydration, modifying this behavior in response to weather conditions. When the eggs hatch, the tadpoles fall into the water. But sometimes a new female will show up and the male glassfrog will forget all about his clutches and he’ll take off with her. So what happens to all of his abandoned eggs?

The behavior exhibited by the males offers an excellent opportunity to study parent-embryo interactions. Early life stages in most animals are often the most vulnerable and, as such, parental care of eggs has evolved independently in many species. The term “hatching plasticity” can encompass a wide variety of these survival methods employed by embryos to increase their survivorship such as hatching early to escape danger or delaying hatching to remain in safety. Embryos can alter their rate or sequence of development. The environment and/or parental care than have both direct and indirect effects on these processes.

The authors looked at the brooding behaviors of male Fleischmann’s Glassfrogs (Hyalinobatrachium fleischmanni), specifically how embryos respond when their fathers are no longer around to hydrate them. Nightly, the researchers monitored male territories and egg clutches along stream transects near San Gabriel Mixtepec in Oaxaca, Mexico. They conducted a male-removal experiment where they displaced 40 males from their clutches and then monitored embryo survival, development and hatching time compared to the clutches of 50 attending males.

The researchers found that removing fathers significantly reduced the amount of time until hatching, with no effect on embryo survival. They found that, on average, there was a 21.2% reduction in the duration of the embryonic period for the male-removal group. This early hatching appeared to be a response to the deteriorating conditions without the fathers rather than the parent directly altering hatching time. These unmaintained eggs lost thickness (a measure of hydration) but not integrity (the egg capsules did not degrade over time) or rate of development. The neglected embryos simply hatched at a less mature stage of development. However, hatchlings from the male-removal group were significantly smaller and had fewer, less developed gut coils, the latter illustrating that age had a significant effect on development. The observed hatching plasticity was found to be due to embryos actively hatching at different developmental stages; the neglected embryos hatched at a less mature stage.

This is one of the first studies to demonstrate that embryos can time hatching to cope with variation in parental care, employing adaptive strategies to cope with these variations. The embryos are responding to their deteriorating egg environment, a dehydration-induced hatching if you will. They increase their likelihood of surviving by responding to their changing environment. A nice example of within-species coevolution.

ResearchBlogging.orgDelia, J., Ramirez-Bautista, A., & Summers, K. (2014). Glassfrog embryos hatch early after parental desertion Proceedings of the Royal Society B: Biological Sciences, 281 (1785), 20133237-20133237 DOI: 10.1098/rspb.2013.3237

And a nice little write-up over at Science called "When Dads Go Missing, Frogs Start Hatching"

(image via Tropical Herping)

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