A hybrid in the making? Attempted mating between Sanderling and Broad-billed Sandpiper

Could this mating result in a hybrid?

It is always nice to receive pictures from readers (see for example here and here). Mostly, the pictures contain a peculiar hybrid, but this week another kind of picture ended up in my mailbox. Jaysukh Parekh Suman from India send me a photograph of a Sanderling (Calidris alba) mounting a Broad-billed Sandpiper (Calidris falcinellus). Could this unexpected mating result in a hybrid?

A Sanderling (Calidris alba) mounting a Broad-billed Sandpiper (Calidris falcinellus). Picture taken in Great Rann of Kutch,Gujarat, India on 6 October 2019. © Jaysukh Parekh Suman

 

No Reports

To my knowledge, no hybrids between these two species have been documented. In fact, no hybrids with Broad-billed Sandpiper have been reported so far. But that doesn’t mean they don’t occur. Hybrids between Sanderling and Broad-billed Sandpiper might be rare or they are difficult to identify (see Randler 2004 for more on hybrid detectability).

 

Viable or Not?

Alternatively, hybrids between these waders might not be viable. TimeTree dates the divergence between these species to about 26 million years ago (range: 18.8 – 38.3). Benjamin Fitzpatrick estimated that birds can still hybridize after an average of 21 million years of divergence. So, in theory, Sanderling and Broad-billed Sandpiper could produce viable offspring.

However, things can go awry at an earlier stage. Possibly, the sperm and egg cells of these species are not compatible. Hence, the Sanderling sperm will not be able to fertilize the Broad-billed Sandpiper egg. But we can only guess about the compatibility of their gametes. For more about these so-called postcopulatory prezygotic barriers to hybridization, I can recommend this review by Tim Birkhead and Jean-Pierre Brillard.

 

Conclusion

All in all, we cannot make a confident statement about the possible outcome of this unusual mating attempt. It seems unlikely that this copulation will result in a hybrid. First, the sperm and egg have to be compatible (and fertilization has to occur). Then, the hybrid embryo will need to develop properly. And finally, it will have to be viable and crawl out of the egg. Never say never, though…

 

References

Birkhead, T. R., & Brillard, J. P. (2007). Reproductive isolation in birds: postcopulatory prezygotic barriers. Trends in Ecology & Evolution, 22(5), 266-272.

Fitzpatrick, B. M. (2004). Rates of evolution of hybrid inviability in birds and mammals. Evolution, 58(8), 1865-1870.

Randler, C. (2004). Frequency of bird hybrids: does detectability make all the difference? Journal of Ornithology, 145(2), 123-128.