Transgenerational epigenetic inheritance of sexual orientation
News & Opinion
Reversible marks on the genome allow honeybees to swap between lives as nurses and foragers.
By Ed Yong | September 16, 2012
Excerpt: “Bees start off as nurses and then become foragers,” said Gro Amdam of Arizona State University, who co-authored the study. “It’s as different as being a scientist or journalist. It’s really amazing that they can sculpt themselves into these two roles that require very specialist skills.”
My comment: Actually, it may be as different as being a heterosexual or homosexual organism. The adaptive plastic behavior that allows organisms such as bees to respond to their immediate environment with epigenetically-determined changes in their behavior was predicted by what is known about the adaptive evolution of sexual reproduction in microbes. Sex differences in behavior (e.g., in yeasts) appear to result from gene duplications driven by the need for genomic adaptation to a changing nutrient chemical environment, as evidenced in paralogues of genes that enhance the ability to use glucose.
Cellular metabolism of nutrient chemicals to pheromones allows conspecifics to recognize and to learn and to remember what evolved to become the epigenetic effects of what we call sex pheromones that control reproduction in all species — as pheromones also do in asexual microbes prior to the evolutionary advent of sexual reproduction. The difference in behaviors that adaptive evolution has established via ecological, social, neurogenic, and socio-cognitive niche construction in the honeybee model organism are simply an extension of the epigenetic effects of nutrient chemicals and pheromones that were transgenerationally inherited via the behavior of species from microbes to man.
“The concept that is extended is the epigenetic tweaking of immense gene networks in ‘superorganisms’ (Lockett, Kucharski, & Maleszka, 2012) that ‘solve problems through the exchange and the selective cancellation and modification of signals (Bear, 2004, p. 330)’. It is now clearer how an environmental drive probably evolved from that of food ingestion in unicellular organisms to that of socialization in insects. It is also clear that, in mammals, food odors and pheromones cause changes in hormones such as LH, which has developmental affects on sexual behavior in nutrient-dependent, reproductively fit individuals across species of vertebrates.” — Kohl (2012)
Oddly, what we presumed in 1996 to be a known established biological fact when we published our Hormones and Behavior review, titled: From fertilization to adult sexual behavior, may not have been fully considered and may not be now, in the light of new evidence that can be integrated across disciplines and across species in the context of transgenerational epigenetic inheritance of bee behavior. But the epigenetic effect on behavior in the honeybee can not truly be considered the first evidence that DNA methylation alters behavior, can it?
Sexual orientation in any species is epigenetically and transgenerationally linked to their survival despite wide variations in nutrient-dependent, stress-dependent, endocrine disruptor-dependent and pheromone-dependent sexual behaviors. We wrote: Parenthetically it is interesting to note even the yeast Saccharomyces cerevisiae has a gene-based equivalent of sexual orientation (i.e., a-factor and alpha-factor physiologies). These differences arise from different epigenetic modifications of an otherwise identical MAT locus (Runge and Zakian, 1996; Wu and Haber, 1995).
Since the epigenetic effects of these modifications on sexual orientation and associated behaviors in a unicellular organism were known 16 years ago, does anyone else wonder why they now appear to show up only in the behavior of the honeybee model organism?