The Ripple Effect: Hidden Costs of Courtship Cues

The one fundamental quality shared unwaveringly among all living species is the commitment to reproduction. Thus, remarkable courtship behaviors have evolved among species dedicated to attracting a promising mate. These include distinctive songs, conspicuous display of plumage, bright colors, and bioluminescence and offering of shelter and food. Needless to say, every advertised mating cue poses a certain cost to the individual. The costs can become monumental when these cues inadvertently tip-off competitors as well as life-threatening predators and parasites.

This principle has been elegantly demonstrated in a recent study published in Science by W. Halfwerk et al (2014). The subjects of the study are male tungara frogs, which produce distinct sounds to attract a female mate. The ritual takes place in shallow ponds of water where several male frogs gather at night and try their best at winning a date.  A byproduct of these mating calls is the production of discernible ripples in the water, begging the question-are these ripples perceived as additional mating cues?

Thus, Halfwerk and team tested the effect of ripples on male-male competition as well as on predation by frog-eating bats.  To test the effect on competition, the team created an experimental set up where a male frog was exposed to either a combination of call sound and ripples or ripples alone or sound alone. The resulting observation was that male frogs responded aggressively to the combination of sound and ripples by more than doubling their own call rate, when compared to their call rate with sound alone. Moreover, males did not respond to ripples alone, implying that the ripples had to be associated with a call sound in order to be perceived as a rival cue.

Frogs prevent predation during courtship by ceasing mate calling in response to any sign of predators such as bats. However, the ripples from their calls linger in the water for a few seconds even after call cessation. Thus, to test the effect of these ripples on predation, Halfwerk and team used two pools of shallow water, each fitted with a robotic frog and acoustic sound, mimicking mating calls. The experimental pool also generated ripples, while the control did not. In this scenario, the team observed that bats strongly preferred to prey on frogs that displayed sound and ripples, in comparison to frogs with sound alone, rendering the defense strategy of frogs of ceasing mating calls ineffective against predation.

The study highlights the selective pressure imposed by competition and predation on the evolution of elaborate courtship behavior. The individuals seem to need to strike a healthy balance between being highly elaborate and conspicuous to provoke attraction in a suitable mate, while remaining subtle enough to avoid getting noticed by predators.

It would be interesting to also test the effect of the ripples on female frogs in this system. Do they prefer frogs associated with sound and ripples more than the ones with sounds alone? Does this preference hold up even in the presence of predator cues? These follow-up questions would provide even more insights into the complexity of intra and interspecies interactions in nature.


W. Halfwerk et al. (2014) Risky Ripples Allow Bats and Frogs to Eavesdrop on a Multisensory Sexual Display. Science 343: 413-416

Breakthrough in Science’s Price: Life Sciences Breakthrough Prize

Without a doubt, the most coveted honor in any academic field, including life sciences, is the Nobel Prize. At a lavish ceremony held annually at Stockholm, the laureate receives a regal gold medal, an exclusive diploma and a hefty cash prize-currently amounting to USD1.2 million.  In addition, the laureate also receives the ultimate worldwide validation of his or her achievement-an accolade on its own.

Established as a result of the will written by Alfred Nobel, the Prize is intended to recognize people who have made significant contributions to the fields of physics, chemistry, medicine or physiology, literature, peace and economics. A prolific chemist and engineer himself, Alfred Nobel built his fortune through copious inventions. In an attempt to be remembered favorably by the world, he left his fortune for the recognition of innovators who produced knowledge yielding the “greatest benefit to mankind.”

Yuri Milner, a modern-day magnate, seems to have a similar vision. An entrepreneur and venture capitalist by profession, Milner started out studying theoretical physics, but gave it up to pursue business. The result: a billion dollar fortune.

Perhaps to commemorate his first love for Physics, Milner, in 2012, established the Fundamental Physics Prize-given annually to a significant contributor to the field of physics. The laureate receives USD 3 million as part of the recognition- more than double the amount given for the Nobel Prize. What’s more? Milner did not stop with Physics.

In 2013, he teamed up with other opulent giants of our times, including Arthur Levinson, chairman of Apple Inc. and Genetech, Sergey Brin, co-founder of Google, Anne Wojcicki, a biologist and an entrepreneur, Mark Zuckerberg, founder of Facebook with wife Priscilla Chan, to establish the Life Sciences Breakthrough Prize, awarded annually to six life science researchers. The prize also includes USD 3 million given to each of the six recipients.

These awards and the large sums of money they carry have received mixed reviews. Some welcome such monetary support to brilliant minds (considering that the Nobel prize money is split even further among multiple laureates); others scorn at the prizes, accusing them of attempting to buy the prestige of a Nobel Prize.

I wonder how Alfred Nobel would feel about these prizes. Seeing as how he wanted his own money to be given to discoverers who benefited mankind, I can’t help but believe that he would indeed welcome these upcoming prizes. And let’s face it. Research is expensive. USD 3 million sounds like a big amount at first but is nothing that a handful of genome-sequencing projects cannot exhaust!


Scent of a Hymenopteron

Division of labor to maximize fitness is a phenomenon seen in several insects of the order Hymenoptera, including bees, ants and wasps. The extraordinary system entails a single queen responsible solely for reproduction; and the rest for all other tasks; building the nest, protecting against predators, gathering food. The queen ensures authority over reproduction by releasing pheromones that render the worker females sterile, a fascinating fact known for a long time.

The true identify and nature of these pheromones, however, has remained largely elusive, till the recent publication of a new study in Science. Through their work, Oystaeyen et al. (2014) have identified for the first time a conserved class of chemicals that are used to induce sterility in worker population of bumblebees, desert ants and wasps.

The study started with a simple question-is a conserved compound responsible for worker sterility in multiple Eusocial species? The suspect was long-chain hydrocarbons, shown previously to act as pheromones in one species of ants. To answer this question, Oystaeyen et al. used gas chromatography mass spectrometry to identify various chemicals on the cuticles of queens and workers and used deductive reasoning to identify chemicals unique to queens. Synthetic versions of these were used to test the chemical’s effects on worker ovary development in the absence of the queen. In addition, previous data from 64 other eusocial insects was synthesized. The conclusion-in three species, the bumblebee, the desert ant and the common wasp-saturated hydrocarbons are indeed responsible for worker sterility.

This finding sheds light on the evolution of eusocial species. Turns out these hydrocarbons are also used to attract mates in some species and thus it is proposed that their primary objective was in fact to attract a mate and not to suppress worker sexual development.

It will be interesting to look out for studies that identify more of these chemicals used for sexual selection in these species.


Oystaeyen et al. (2014) Conserved class of queen pheromones stops social insect workers from reproducing. Science. 343 (6168): 287-290.