Evolution of the sterile caste

Biased sex ratios are expected to affect the conditions of the evolution of worker behaviour in malehaploid populations. In a subsocial, malehaploid species an association to female-biased brood sex ratios favours the evolution of worker behaviour. There are various reasons to expect such an association. The critical worker efficiency threshold required for worker behaviour to evolve is lower when looked at from the viewpoint of the mother than from that of the daughter. In this mother-daughter conflict, the mother can expect some help from her other offspring to resolve the conflict in her favour. In semisocial species the sex ratio biases have a less significant role and the worker behaviour can evolve more easily in malehaploid than in diploid populations. Furthermore, limited dispersal (due to the risks attached to it) is expected to favour worker behaviour in malehaploid but inbreeding in diploid populations. In addition to the genetic mechanisms that determine the critical worker efficiency threshold, it is essential to pay attention to those ecological factors that affect the actual worker efficiency in nature. Several such factors exist but it is not easy to associate them with the common occurrence of eusocial species in the Hymenoptera.     

STATISTICAL TESTS OF PHENOGRAMS BASED ON GENETIC DISTANCES

Methods used for estimating the confidence levels of UPGMA-type phenograms based on molecular-genetic data are examined. The methods based on internodal variances or on bootstrapping over characters are compared by simulating a three-species phylogeny with a trifurcation. The bootstrap method seems slightly better in this comparison. Weighting of OTU's when constructing the phenogram is also examined. A method that weights each OTU according to the estimated independent evolutionary information, a modified WPGMA, appears slightly better than UPGMA in estimating the branching points and branch lengths. The methods are applied to the data on restriction sites in eight Hawaiian Drosophila species. The significance of the clusters among them differ from those reported earlier.