Matthew R. Robinson, AJ Wilson, JG Pilkington TH Clutton-Brock, JM Pemberton and LEB Kruuk.
Genetics 181: 1639-1648
Finally a paper in Genetics that I can understand, and it presents an intriguing idea. It caught my eye, because a friend of mine recently asked me if I knew of any examples of sexual dimorphism driven by natural selection. I couldn't think of any, at that time, and also was wondering how that could work. Well... this is perhaps how. From the giant database of the Soay sheep on that cold and windswept island of St Kilda. Be aware of complicated stats...
This work demonstrates that environmental conditions experienced by individuals can shape their development and affect the stability of genetic associations. The implication of this observation is that the environmental response may influence the evolution of traits in the wild. Here, we examined how the genetic architecture of a suite of sexually dimorphic traits changed as a function of environmental conditions in an unmanaged population of Soay sheep (Ovis aries) on the island of Hirta, St. Kilda, northwest Scotland. We examined the stability of phenotypic, genetic, and environmental (residual) covariance in males during the first year of life between horn length, body weight, and parasite load in environments of different quality. We then examined the same covariance structures across environments within and between the adult sexes. We found significant genotype-by-environment interactions for lamb male body weight and parasite load, leading to a change in the genetic correlation among environments. Horn length was genetically correlated with body weight in males but not females and the genetic correlation among traits within and between the sexes was dependent upon the environmental conditions experienced during adulthood. Genetic correlations were smaller in more favorable environmental conditions, suggesting that in good environments, loci are expressed that have sex-specific effects. The reduction in genetic correlation between the sexes may allow independent evolutionary trajectories for each sex. This study demonstrates that the genetic architecture of traits is not stable under temporally varying environments and highlights the fact that evolutionary processes may depend largely upon ecological conditions.
Monday, April 27, 2009
Tuesday, April 21, 2009
Alternative mating strategies may favour the persistence of a genetically based colour polymorphism in a pentamorphic fish
Jorge L. Hurtado-Gonzales and J. Albert C. Uy
Males of the pentamorphic fish, Poecilia parae, show a striking colour polymorphism that ranges from drab coloration resembling females to brilliant black and red stripes. We tested the hypothesis that the observed polymorphism may persist because each morph uses a unique but equally successful mating strategy. We quantified the mating behaviour, testes investment and sperm morphometrics of each morph. We found that the smallest morph (immaculata), which resembles drab females, used a ‘sneaker’ tactic (i.e. forgoing courtship and mostly ‘stealing’ copulations) as a mating strategy. Immaculata males also had larger testes, and produced larger ejaculates and sperm with longer flagella, which should provide advantages during sperm competition. The largest morph (parae) and the coloured blue, red and yellow morphs used a combination of courtship and sneaker tactics. However, they achieved greater copulation success as a result of courtships. The testes investment of parae and yellow morphs were similar but larger than those of the blue and red males. Our results suggest that male morphs of the pentamorphic Poecilia parae use unique mating strategies that exploit different aspects of pre- and postcopulatory sexual selection, which, in turn, may help maintain their relatively stable frequencies in the wild.
Keywords: alternative mating strategy; frequency-dependent selection; genetic polymorphism; Poecilia parae; sperm competition
link from campus
Males of the pentamorphic fish, Poecilia parae, show a striking colour polymorphism that ranges from drab coloration resembling females to brilliant black and red stripes. We tested the hypothesis that the observed polymorphism may persist because each morph uses a unique but equally successful mating strategy. We quantified the mating behaviour, testes investment and sperm morphometrics of each morph. We found that the smallest morph (immaculata), which resembles drab females, used a ‘sneaker’ tactic (i.e. forgoing courtship and mostly ‘stealing’ copulations) as a mating strategy. Immaculata males also had larger testes, and produced larger ejaculates and sperm with longer flagella, which should provide advantages during sperm competition. The largest morph (parae) and the coloured blue, red and yellow morphs used a combination of courtship and sneaker tactics. However, they achieved greater copulation success as a result of courtships. The testes investment of parae and yellow morphs were similar but larger than those of the blue and red males. Our results suggest that male morphs of the pentamorphic Poecilia parae use unique mating strategies that exploit different aspects of pre- and postcopulatory sexual selection, which, in turn, may help maintain their relatively stable frequencies in the wild.
Keywords: alternative mating strategy; frequency-dependent selection; genetic polymorphism; Poecilia parae; sperm competition
link from campus
Wednesday, April 15, 2009
Sex chromosome evolution
Accelerated Adaptive Evolution on a Newly Formed X Chromosome Bachtrog D, Jensen JD, Zhang Z PLoS Biology Vol. 7, No. 4, e82 doi:10.1371/journal.pbio.1000082
I'm finally getting back on this after my computer crash. Where is everybody?
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