Genotype x environment interactions. IV. The effect of the background genotype

Host-specific phenotypic plasticity of the turtle barnacle Chelonibia testudinaria: a widespread generalist rather than a specialist

Turtle barnacles are common epibionts on marine organisms. Chelonibia testudinaria is specific on marine turtles whereas C. patula is a host generalist, but rarely found on turtles. It has been questioned why C. patula, being abundant on a variety of live substrata, is almost absent from turtles. We evaluated the genetic (mitochondrial COI, 16S and 12S rRNA, and amplified fragment length polymorphism (AFLP)) and morphological differentiation of C. testudinaia and C. patula from different hosts, to determine the mode of adaptation exhibited by Chelonibia species on different hosts. The two taxa demonstrate clear differences in shell morphology and length of 4-6(th) cirri, but very similar in arthropodal characters. Moreover, we detected no genetic differentiation in mitochondrial DNA and AFLP analyses. Outlier detection infers insignificant selection across loci investigated. Based on combined morphological and molecular evidence, we proposed that C. testudinaria and C. patula are conspecific, and the two morphs with contrasting shell morphologies and cirral length found on different host are predominantly shaped by developmental plasticity in response to environmental setting on different hosts. Chelonibia testudinaria is, thus, a successful general epibiotic fouler and the phenotypic responses postulated can increase the fitness of the animals when they attach on hosts with contrasting life-styles.

The resolution of genotype x environment interaction in segregation analysis of nuclear families

A model is presented for the effects of one or two loci, a measured index of the environment and genotype x environment (G x E) interaction of risk for a discontinuous trait. Initial properties of the model are explored for the single locus case, with and without the effects of environment and G x E interaction. Seven data sets were simulated, each comprising 500 nuclear families on whom an environmental index has been measured. Maximum-likelihood estimation procedures were used to obtain parameter estimates under seven models for each data set. Likelihood ratio tests were constructed, and in all cases it was possible to identify the "correct" model for the simulated data. The matrices of information realized showed that the parameters could be estimated with acceptable precision and that the effects of genes, environment, and G x E interaction could be resolved in the simulated populations. The effects on conventional segregation analysis of ignoring the environment and G x E are considered.