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This site says:

Plants hybridize much more frequently and successfully than animals do. [...] Chromosomal doubling (polyploidy) occurs more frequently in plants and facilitates the fertility of the hybrid offspring.

Outcomes of the successful hybridization of different species of plants (i.e. yelding fertile offspring) can be easily observed in agriculture - for instance, Triticum aestivum is 6n, while Triticum durum is 4n. The latter comes from the hybridization of two plants from different genera (!). So it seems to me that not only can plants hybridize more easily, but also that the evolutionary distance between the parents can be greater than in animals.

As far as I know, the preferred animal strategy to have fertile hybrids is to go partheno/androgenic (for example in Phasmida).

My question is:

Why can plants produce fertile hybrids more often than animals? What constraints are present in animals and absent in plants?

To my knowledge, polyploidization is the main mechanism by which this is achieved. If this is true, then my previous question can be rephrased as why does animal polyploidization occur more rarely?

I'm not entirely sure about my assumptions, so feel free to correct me, of course with references.

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While I do not know if there is a definitive answer to this question, I suspect that at least part of the answer can be found in the fact that animals typically have much more complex and delicate mechanical interactions in their bodies than plants.

From a mechanical perspective, plants are pretty simple. They move, but generally quite slowly and via very simple mechanical principles, and the interconnection between different tissues and organs is mostly via chemical and fluid flow. Many plants are also highly flexible in their size and also change their size by orders of magnitude even after sexually mature.

Animals, by contrast, are often ferociously complex and intricate systems of joints and complex and highly differentiated organs. They also tend to have a well-defined typical size of mature individuals, which doesn't vary all that much compared to plants.

When you have a change in ploidy, a major effect is to multiply or divid the levels of gene expression, based on the change in number of copies. Where that interacts with the processes of morphogenesis, it will thus often have radical effects on the size or growth patterns of the effected tissues or organs.

With a more intricately connected and scale-sensitive system like an animal, it seems then unsurprising that such changes might be much more difficult to survive.

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