Quantitative genetics of signal evolution: A comparison of the pheromonal signal in two populations of the cabbage looper, Trichoplusia ni

Pheromones are important in reproductive isolation among populations of mot hs, but the genetics associated with diversification of pheromonal signals is poorly understood. To gain insight into processes that may lead to diver sification we examined the genetic architecture underlying the production o f the sex pheromone of the cabbage looper moth, Trichoplusia ni. We compare d genetic parameters of two populations; one with a wild-type pheromone phe notype (N) and one where a single-gene mutation affecting the pheromone ble nd produced by females had been established (M). Using a half-sib breeding design we estimated heritabilities, coefficients of additive genetic variat ion, and phenotypic, genetic, and environmental correlations of the pheromo ne components. In both populations, narrow sense heritabilities were genera lly moderate and genetic correlations were mostly positive. Comparisons bet ween the two populations showed that, while the pattern of phenotypic corre lations showed significant agreement between populations, the patterns of g enetic (co)variation (i.e. the shapes of the within population matrix) were dissimilar between the two populations. The presence of additive genetic v ariation in both populations indicates that there is the potential for furt her evolution of individual pheromone components. However, because of the d ifferences between the populations in the pattern of genetic variation and covariation, the populations will evolve along different evolutionary traje ctories even under identical selection pressures. These results suggest tha t single gene mutations, once established, can be associated with further a lterations in the genetic architecture and this has implications for the ev olution of pheromone communication.