Field of Science

Evolution and pleiotropy

ResearchBlogging.orgPleiotropy is the effect of one gene affecting multiple traits, as when Drosophila genes are expressed in more than one place during embryogenesis. For a bunch of examples of that, see
Repression and loss of gene expression outpaces activation and gain in recently duplicated fly genes, Oakley, Østman, and Wilson, 2006, PNAS, 103, 11637.

In my own work on computer simulations of epistatic interactions, it is clear that pleiotropy has the effect of changing the phenotype more per mutation than withoput pleiotropy. With pleiotropy, more than one trait gets affected by each mutation. And each trait can potentially be affected by the same amount (i.e. numerical value), so if a mutation affects five instead of one trait, it can change the fitness five times as much. Admittedly, this is a result from simulating a very simple model, but that it has biological relevance is suggested (among other considerations) in a recent Nature paper by Günter Wagner et al. where they measure pleiotropy in mice. They show that a substitution at a QTL has an effect on each trait that increases with the total number of traits affected. While mutations in many genes produces only a small effect on a few traits, those that affect many traits does so with higher effect.
Pleiotropic scaling of gene effects and the ‘cost of complexity’, Wagner, Kenney-Hunt, Pavlicev, Peck, Waxman, Cheverud, 2008, Nature, 452, 27.

The significance of this observation is that once the environment changes, and the population is forced to adapt, those organisms that exhibit much pleiotropy in the genomes can adapt really fast. And that organisms can adapt way faster than we normally imagine became increasingly clear when a paper came out this year about a lizard, Podarcis sicula. This lizard evolved differences in head morphology, bite strength, and digestive tract structure in a very, very short period of time. How short? Ten thousand years? That would be short by evolutionary standards. But no, it took just 36 years! In about 30 generations the lizards evolved larger heads, stronger bites, and cecal valves - a structure in the gut that can constrict, slowing down the passage of food, giving more time for digestion. Behaviorally the lizards changed their diet to include much more plant material, and the morphological changes were adaptations to this new lifestyle. Clearly the lizards became a new species, as they moved into a new niche. You can read more about that all over the web - it deservedly got a ton of coverage - but I recommend Science Daily for this one.
Herrel, Huyghe, Vanhooydonck, Backeljau, Breugelmans, Grbac, Van Damme, and Irschick (2008). Rapid large-scale evolutionary divergence in morphology and performance associated with exploitation of a different dietary resource PNAS, 105 (12)


  1. None of this is evidence of evolutionism;

  2. AP, thanks for pushing these videos. Thanks a lot.

    In the beginning of the first one NephilimFree (I assume) says "morphology does not change." (1:38)

    The Croatian lizards in the third paper above is an example of exactly that: "changes in morphology and performance parallel those typically documented among species and even families of lizards in both the type and extent of their specialization."

    Morphometric data describing head size and shape show that both males and females of the two populations differ significantly in head morphology [MANOVA; males: Wilks's λ = 0.463, F 9,115 = 14.81, P < 0.001; females: Wilks's λ = 0.425, F 9,123 = 18.45, P < 0.001 (Table 1 and Fig. 1)] with lizards on Pod Mrčaru having longer, wider, and taller heads than lizards on Pod Kopište (Table 1 and Fig. 1).


    This shift to a predominantly plant-based diet has resulted in the dramatic evolution of intestinal morphology. Morphological analysis of preserved specimens shows the presence of cecal valves (Fig. 4) in all individuals, including a hatchling (26.4-mm snout-vent length, umbilical scar present) and a very young juvenile (33.11-mm snout-vent length) examined from Pod Mrčaru. These valves are similar in overall appearance and structure to those found in herbivorous lacertid, agamid, and iguanid lizards (13, 14) and are not found in other populations of P. sicula (13) or in P. melisellensis. Cecal valves slow down food passage and provide for fermenting chambers, allowing commensal microorganisms to convert cellulose to volatile fatty acids (15, 16).

    Thus, I conclude that NephilimFree doesn't know what he is talking about. (The fact that he doesn't know the plural of 'phylum' and 'genus' backs that up as well.)


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