Solution:
Instead of using a list to send the arguments to the function, I did it explicitly:
# 3 --- Example with n arguments -----------------------------------
k <- seq(1:3)
a <- rep(2,3)
transa <- c(function(x,a) x*a, function(x,a) 1/x*a, function(x,a) x^2*a)
ktransa <- mapply(function(f, x, a) f(x,a), transa,x = k , a = a)