Nest architecture and distribution of the primitive stingless bee,Mourella caerulea(hymenoptera, apidae, meliponinae): Evidence for the origin ofplebeia(s. lat.) on the gondwana continent∗

Abstract

The stingless bee Mourella caerulea is distributed in the subtropical parts of Brazil, Argentina and Paraguai. In the Serra do Sudeste of Rio Grande do Sul, on the southern part of the Brazilian shield, this species is one of the most abundant meliponine bees. Nests of M. caerulea are built in the soil and exhibit architectural characters typical to all other genera of obligatory ground nesting species, like Schwarziana, and the African genera Meliple‐beia, Plebeiella and Plebeina. The possibility that the similar solutions for the construction of subterranean nests in these genera did not evolve by convergence or parallelism is discussed. The occurence of Mourella together with other more primitive representatives of the Plebeia group on the southern parts of the Brazilian Shield cannot be explained by biogeographic models proposed by some authors. Adopting an alternative model we suggest that, during the lower Cretaceous, ancestor populations of the Pleibeia‐ line inhabiting the meridional shields of Western Gondwanaland (now southern Brazil and southern Africa), were separated by the south‐northward opening of the South Atlantic. During the Cretaceous until the lower Tertiary the remnant populations on the southern parts of the Brazilian shield were isolated by the immense basalt flows and subsequent volcanic Tertiary activity bordering this area. During their dispersal in the Tertiary species of Plebeia (s. str.; post Gondwanic derived forms) may have radiated via the Patagonian shields and their terrestrial connections to Antarctica and from there to Australia, while other Plebeia (s. str.) species dispersed into the northern parts of South America. The monotypic genera Mourella and Schwarziana and most of the more primitive species of Plebeia (s. str.), however, remained restricted to their presumable subtropical centers of origin.