Toads jump on to the cross mating bandwagon

November 14th, 2007 - 10:24 am ICT by admin  

The two species of toads that are involved in this cross mating procedure are Spea bombifrons and S. multiplicata. Though they look quite similar, the major difference that sets them apart is the structure of their nose.

“While S. bombifrons has more of a pug nose and a bump between its eyes, S. multiplicata lacks the bump and has a more of a cartoon like nose,” the journal Nature quoted Karen Pfennig, a biologist at the University of North Carolina at Chapel Hill.

According to the new study, under some conditions, the females of these toad types will chose a partner of another species from the puddle of possible mates .

“This extreme mating measure is undertaken to ensure that the offspring of the toads have the best chance of survival, even if it means that those offspring will themselves have a lower chance of reproducing successfully,” said Pfennig.

Generally, when cross-species mating occurs, fertile offspring are not produced.

When these two toads get together, they sometimes yield males that are sterile. Even their female offspring is only about to produce about half the numbers of eggs as a purebred. That’s enough for scientists to label them as different species, and for the two to usually avoid interbreeding.

For investigating this particular cross breeding, researchers played recordings of songs from the males of each species to the females. Surprisingly, it was found out that the female S. bombifrons responded to the call of an S. multiplicata male.

But it was also found out that this response by the female was only possible when the waters were shallow. This suggests that S. bombifrons might benefit in some way from cross-species hybridization when waters are shallow.

One possible reason for this is that the toads need their offspring to develop more quickly when water is in short supply, so that the tadpoles turn to toads before the shallow puddles run dry. The fact that S. bombifrons are slower to develop and S. multiplicata are faster, only confirms this scenario.

This is the first time that harsh environmental conditions have been shown to drive an animal across the species barrier.

“It’s quite spectacular,” said Maurice Sabelis of the University of Amsterdam. “You have an example of one species relying on another to produce viable offspring,” he added.

According to Sabelis, this type of dependence on another species could have implications for researchers trying to preserve toads. “Researchers should take heed that things may be more complicated than they have assumed, he said.” It’s a warning that such complexities might play a crucial role for species conservation,” he added.

Researchers say that the results emphasize that mate selection isn’t just a matter of sizing up male ornamentation. “Females are probably assessing a lot more out there than just how long the male’s tail is,” said Pfennig. “They are probably more sensitive to their own condition and environment when choosing a male,” she added. (ANI)

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