Frogs’ Porn is good for Monogamy

Last month, here in deepest Cornwall, we were lucky enough to have a talk given by Kyle Summers about his work on the evolution of monogamy in Peruvian poison frogs.

The talk was so good we decided to discuss a recent paper by the man himself at our weekly Journal Club. For me, the best part of the talk (and the paper) is the evidence of ecological factors driving biparental care and, in turn, monogamy. 

The topic appealed to us as it provides a neat example of how ecological factors can lead to the evolution of biparental care. The study system as close to perfect as an experimental ecologist could find for this question, and provides some great pictures. Nothing against experimental workhorses like cockroaches or fruit flies, but who doesn’t want to look at brightly coloured frogs from exotic locations?

The study tests the hypothesis that biparental care will be favoured when times are hard for offspring, either through a lack of resources, or predation, and that monogamy may follow as both parent s see a greater return for their investment, i.e. surviving offspring, if they don’t sneak off looking for other mating opportunities.

The system:

Closely related poison frogs, Ranitomeya variablilis and R.imitator are the species used for experimentation. They provide a perfect negative control- 2 very closely related species, with similar life histories except for the size of the breeding pool. R.variabilis use large pool, whereas R.imitator use small pools to rear their young and lay trophic eggs- essentially a lunchbox dropped into the pools to support the tadpoles.

Image

This team-effort in rearing young consists of the female depositing an egg on a leaf surface, the male retrieving the egg after 7 days and depositing it in a small pool. The male then surveys the tadpole and calls to the mother every few days for her to lay a trophic egg in the pool. By removing tadpoles and swapping the pools they inhabit, they find that, regardless of species and in the absence of trophic eggs, tadpoles grow bigger in larger pools, suggesting that they aren’t nutrient limited. As such, it seems a move into small pools, to avoid predation, included a loss of nutrients, making trophic egg deposition a must.

The study also finds genetic monogamy in R.imitator from molecular analysis, suggesting the parents really are bound to the small pool, and aren’t investing in looking for extra-pair matings. This process is crudely summed up below:

Image

Is this system specific? Well they find the same trend for lower parental care as pool size increases across multiple species and find a consistent trend-so it’s not just confined to R.imitator and R.variablis.

This work provides a comprehensive look at the mating system of two species and finds good evidence for the evolution of monogamy- and we enjoyed chatting about it.

As PhD students the nice thing about our journal club is that we can discuss papers way outside of our fields of study. The other nice thing is that we can include spurious Mark Twain quotations. So on that note I’ll paraphrase: ‘It’s better to write a short blog post and have people think you don’t know much about frogs, mating systems or ecology, than keep writing and prove it’.

Brown, J., Morales, V., & Summers, K. (2010). A Key Ecological Trait Drove the Evolution of Biparental Care and Monogamy in an Amphibian The American Naturalist, 175 (4), 436-446 DOI: 10.1086/650727

One thought on “Frogs’ Porn is good for Monogamy

  1. “trophic eggs- essentially a lunchbox dropped into the pools to support the tadpoles” don’t know about you but my lunch box wasn’t a unfertilised potential brother or sister….

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