While marriage across racial and religious lines is frequently frowned upon, caste has largely been forgotten. More importantly, while the majority of the population came from what was then the United Provinces and Bihar, there was a substantial minority of Tamils, and a non-trivial scattering of others (though no one talks about it, there probably were more than a few Bengalis, given that the major port of departure was Calcutta). Given the shortage of (Indian) women in the first few decades in Trinidad, regional origin, caste and even religion was secondary to being able to find a wife at all. Even though the next generation may have been more particular about who they married, regional origin and caste were no longer meaningful – the first generation born in Trinidad was already outbred.

Couldn’t this just be regression to the mean?

#4 Chad – I assume the small starting size would cause inbreeding problems as well, but that rapid expansion doesn’t solve inbreeding either. Only many generations of gradually introduced mutations solves the problems. But I don’t really know.

Adapting to a new environment is what I’m calling outbreeding depression due to genes/gene combinations not starting off present in the right proportions for populations to grow. The alternative version that Razib outlines for outbreeding depression due to gene-gene interactions might make sense in the case you mention where individuals from very different populations are brought together to create a founding population that is genetically diverse in order to avoid inbreeding.

Kakutani, T., Jeddeloh, J. A., Flowers, S. K., Munakata, K. & Richards, E. J. Developmental abnormalities and epimutations associated with DNA hypomethylation mutations. Proc. Natl Acad. Sci. USA 93, 12406–12411 (1996).

Mathieu, O., Reinders, J., Caikovski, M., Smathajitt, C. & Paszkowski, J. Transgenerational stability of the Arabidopsis epigenome is coordinated by CG methylation. Cell 130, 851–862 (2007).

Of course this is Arabidopsis, which is typically self-pollinating and typically inbred. But it opens interesting possibilities.

I would not expect epigenetics to supplant other traditional explanations for inbreeding depression, but complement it to a certain extent and perhaps explain some unknowns.

Heres the papers:

Reinders, J. et al. Compromised stability of DNA methylation and transposon immobilization in mosaic Arabidopsis epigenomes. Genes Dev. 23, 939–950 (2009).

Johannes, F. et al. Assessing the impact of transgenerational epigenetic variation on complex traits. PLoS Genet. 5, e1000530 (2009).

Biémont, C. Inbreeding effects in the epigenetic era. Nature Rev. Genet. 11, 234 (2010).

Johannes, F. and Colomé-Tatché, M. Concerning epigenetics and inbreeding Nature Rev. Geneti. 12, 376 (2011).

can be both. for humans though i don’t think the latter applies. we’re not so well adapted to a particular ecology that there isn’t an appropriate in-between ecology. then again, i’m a genetics person

Do you have any thoughts on the possible contributions of epigenetics in inbreeding? There is recent evidence, primarily from Arabidopsis that there are epigenetic effects that contribute to inbreeding depression and that some of the effects of inbreeding depression are lost when epialleles revert to wild type.

can i get the cite for that paper? i’m curious. i think epigenetics has a role in everything, but probably a small (though not trivial) role. if epigenetics was so powerful i don’t think that analytical genetics would have made such initial progress.

Peter, in this circumstance, I would instead lean towards the possibility of Heterosis, aka Hybrid Vigor.

Unless you are assuming that the introduced populations are all unrelated individuals and that is the source of the outbreeding? I could understand such a scenario in the case of scientific introduction. Not so much in the case of unscientific introductions, especially the starlings which were introduced before the rediscovery of Genetics by crazy Shakespeare fans.

I’ve found it interesting that introduced populations of animals seem to do worse initially than after a number of years, whether it’s intentional introductions like lynx in Colorado and Mexican wolves in New Mexico, or unscientific introductions like starlings to the US. My assumption was that a version of outbreeding depression held the populations back for awhile until the poor-performing genes or gene assortments were removed. Maybe that’s not right.

Do you have any thoughts on the possible contributions of epigenetics in inbreeding? There is recent evidence, primarily from Arabidopsis that there are epigenetic effects that contribute to inbreeding depression and that some of the effects of inbreeding depression are lost when epialleles revert to wild type.