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Are there any examples of two species taxonomically classified in different biological families that have successfully hybridized and produced viable offspring? If not, is there an example of where reproduction occured with non-viable offspring?

To be clear, I mean regular sexual reproduction that could occur in the natural world outside a lab. Even so, I'd be curious to know if it could even occur in a lab without direct genetic manipulation.

For example, grolar bears which are ursid hybrids between different species in the Ursus genus are known to exist. Also ursid hybrids between bear species in different genuses have been produced in captivity (sloth bear Melursus ursinus x Malayan sun bear Ursus malayanus and sloth bear x Asiatic black bear Ursus thibetanus). Would an extra-familial hybridisation be possible? Would this be more likely in the plant kingdom?

This question is inspired by a separate question on the Gardening SE which hints at a general lack of understanding of the genetic similarity required for cross-pollination in plants. It made me wonder whether there are any exceptions to the general assumption that extra-familial hybridisation is impossible.

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  • $\begingroup$ Following the definitions of hybrid and of sexual reproduction, one could consider Horizontal Gene Transfer and answer YES to your question with the case of the photosynthetic sea slug for example. $\endgroup$
    – Remi.b
    Oct 28, 2013 at 17:17
  • $\begingroup$ I should have been more specific to limit this to gene transfer/recombination occurring by sexual reproduction (i.e. vertical gene transfer) but thanks for the point. $\endgroup$
    – Lisa
    Oct 28, 2013 at 23:46
  • $\begingroup$ One of the problems is that "Family" and really any taxonomic designation are fuzzy. We often don't even really know where to draw the line between two species, even in animals, where such things are relatively easy. Since none of the taxonomic designations tell us anything about genetic distance except "the two taxa are genetically different from each other", any examples of inter-familial hybridization won't tell you anything about the general likelihood of such an occurrence... $\endgroup$
    – Chinmay Kanchi
    Oct 29, 2013 at 0:50
  • $\begingroup$ A more valuable question might be "What is the maximum genetic distance at which hybridization by sexual reproduction has been observed?" And of course, the answer to that is, "I don't know" :P. Which is why this is a comment and not an answer. $\endgroup$
    – Chinmay Kanchi
    Oct 29, 2013 at 0:51
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    $\begingroup$ @Lisa My point is that even when you say hybrid via sexual reproduction you do not exclude Horizontal gene transfer. There are so many different way of reproducing sexually that our definitions are usually quite broad. But your question is interesting, I just thought it was worth stating horizontal gene transfer as this process fits in the definitions of sexual reproduction. $\endgroup$
    – Remi.b
    Oct 29, 2013 at 6:06

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Interfamilial hybrids have never, to my knowledge, been recorded occurring naturally (without human intervention).

In plants, somatic inter-familial hybrids have been produced for a wide variety of species pairs in the lab (e.g. between carrot and barley; Kisaka et al. 1997).

In animals, there are some historical reports of hybrids between chickens (Mathis & MacDougald 1987) or peafowl (Serebrovsky 1929), both in Phasianidae, and guineafowl (in Numididae). The animal example meets your condition of being outside the lab, although they were produced by breeders.

Refs

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