Molecular phylogenetics of the allodapine bee genus Braunsapis: A-T bias and heterogeneous substitution parameters.

Extreme AT bias in Hymenopteran mitochondrial genes have created difficulties for molecular phylogenetic analyses, especially for older divergences where multiple substitutions can erode signal. Heterogeneity in the evolutionary rates of different codon positions and different genes also appears to have been a major problem in resolving ancient divergences in allodapine bees. Here we examine the phylogeny of relatively recent divergences in the allodapine bee genus Braunsapis. We examined heterogeneity in nucleotide substitution parameters for one nuclear gene and codon positions in two mitochondrial genes, exploring various phylogenetic analyses for recovering relationships among species from Africa, Madagascar, southern Asia, and Australia. We explored maximum parsimony, maximum likelihood, Log determinant and Bayesian analyses. Broad topological features of best fit trees tended to be similar for equivalent data sets (e.g., total, or with 3rd mt positions excluded), regardless of the analytic method used (e.g., maximum likelihood or Bayesian). Analyses that used the total data set without modelling partitions separately gave unlikely results, indicating that the Malagasy species was most closely related to Australian species. However, analyses that excluded 3rd mitochondrial positions, or modelled partitions separately, suggested that the Malagasy species falls within the African clade. The unlikely topologies apparently result from long branch attraction, and this problem is ameliorated where modelling allows more realistic estimates of base composition and evolutionary rates for 3rd mitochondrial positions. However, we found that even when codon positions are modelled separately, estimated evolutionary rates for 3rd mitochondrial positions are likely to underestimate true rates. Long branch attraction and multiple substitutions are likely to be much more difficult to circumvent in analyses that explore older, generic-level, divergences in allodapine bees where overwriting is expected to be much more extreme. Our results indicate an African origin for Braunsapis, followed by a single, very early, dispersal event into Asia and then by a later dispersal event into Australia. The Malagasy species is derived from within the African clade.

Phylogenetic divergence of the Australian allodapine bees (Hymenoptera: Apidae).

Allodapine bees are most diverse in Africa but are distributed throughout the Old World tropical and Austral regions. They are considered useful for studies into the evolution of social behaviour since they exhibit the full range of social organisation from solitary to highly eusocial (sensu; ). Five genera are found in Australia, namely Braunsapis, Exoneurella, Exoneura, Brevineura, and Inquilina. Sociality and life histories are well documented for the exoneurine genera (review in ) and Inquilina is an obligate social parasite of species of Exoneura (). In this paper, maximum parsimony and maximum likelihood methods using molecular sequence data from two mitochondrial gene regions (cyt b and COI) and a single nuclear gene region (EF-1alpha) are used to reconstruct phylogenetic relationships of the Australian allodapine genera. Results suggest that the exoneurine group (Brevineura, Exoneurella, and Exoneura+Inquilina) diverged very rapidly and are monophyletic to the exclusion of other (primarily African) allodapine genera. A clade containing Australian species of Braunsapis is also monophyletic to the exclusion of African congeners. Braunsapis is not phylogenetically close to, and is a more derived group than the exoneurine group and probably came to occupy the Australian plate via a later dispersal through the southern Asian region. It is unclear at this point how the exoneurine group came to occupy the Australian plate and possible scenarios are discussed.

Molecular phylogenetics of allodapine bees, with implications for the evolution of sociality and progressive rearing.

Allodapine bees have long been regarded as providing useful material for examining the origins of social behavior. Previous researchers have assumed that sociality arose within the Allodapini and have linked the evolution of sociality to a transition from mass provisioning to progressive provisioning of brood. Early phylogenetic studies of allodapines were based on morphological and life-history data, but critical aspects of these studies relied on small character sets, where the polarity and coding of characters is problematic. We used nucleotide sequence data from one nuclear and two mitochondrial gene fragments to examine phylogenetic structure among nine allodapine genera. Our data set comprised 1506 nucleotide positions, of which 402 were parsimony informative. Maximum parsimony, log determinant, and maximum likelihood analyses produced highly similar phylogenetic topologies, and all analyses indicated that the tropical African genus Macrogalea was the sister group to all other allodapines. This finding conflicts with that of previous studies, in which Compsomelissa + Halterapis formed the most basal group. Changing the basal node of the Allodapini has major consequences for understanding evolution in this tribe. Our results cast doubt on the previous hypotheses that progressive provisioning and castelike social behavior evolved among lineages leading to the extant allodapine taxa. Instead, our results suggest that mass provisioning in Halterapis is a derived feature and that social behavior is an ancestral trait for all allodapine lineages. The forms of social behavior present in extant allodapines are likely to have resulted from a long evolutionary history, which may help explain the complexity of social traits found in many allodapine bees.