Filogenia molecular e biogeografia histórica de Caenonomada Ashmead, 1899 (Hymenoptera: APidae, Tapinotaspidini)

Abstract

Resumo: Caenonomada (Apidae: Tapitaspidini) e um genero de abelhas Neotropicais distribuido pela diagonal de biomas aridos da America do Sul. Tres especies sao atualmente reconhecidas: C. bruneri endemica do Chaco e Pampa; C. labrata endemica do Cerrado; e C. unicalcarata endemica da Caatinga, mas com populacoes disjuntas fora dos limites deste dominio, provavelmente constituindo uma especie distinta, a qual esta sendo tratada como C. aff. unicalcarata ate receber validacao taxonomica formal. Este padrao de endemismo oferece uma oportunidade para investigar a evolucao e as relacoes biogeograficas das areas secas da America do Sul. Assim, os objetivos deste estudo foram (1) resolver as relacoes filogeneticas entre as especies de Caenonomada com base em caracteres moleculares; (2) estimar o tempo de divergencia entre as linhagens de Caenonomada; e (3) avaliar as relacoes entre a historia biogeografica do genero com a historia da diagonal de areas abertas da America do Sul. Foram utilizados dois locos nucleares (wingless e EF-1ƒ¿) e dois locos mitocondriais (COI e 16S rRNA) para investigar as relacoes filogeneticas das especies de Caenonomada (incluindo C. aff. unicalcarata). Quatro generos de Tapinotaspidini (Chalepogenus, Lanthanomelissa, Monoeca e Tapinotaspoides) foram selecionados como grupo externo. Estes dados foram analisados pelos metodos de parcimonia, maxima verossimilhanca e inferencia Bayesiana. A datacao molecular foi realizada com base no loco COI. Todos os resultados sugeriram a monofilia de Caenonomada e as seguintes relacoes entre suas especies: ((C. labrata, C. bruneri), (C. unicalcarata, C. aff. unicalcarata)). Os dados tambem suportaram fortemente a distincao de C. aff. unicalcarata. A sobreposicao do cladograma das especies com suas respectivas areas de ocorrencia sugeriu que a Caatinga e o Cerrado apresentam uma relacao proxima com o Chaco, indicando que este ultimo seja uma area biogeografica hibrida. A datacao molecular indicou que a primeira separacao no clado Caenonomada ocorreu ha cerca de 11 Ma, durante o Mioceno Superior. As outras cladogeneses, que deram origem a C. bruneri + C. labrata e a C. unicalcarata + C. aff. unicalcarata ocorreram, respectivamente, ha cerca de 5 e 4 Ma, durante a transicao entre o Mioceno e o Plioceno. Mudancas geologicas durante o Mioceno, como o surgimento dos mares epicontinentais na America do Sul, sao discutidas como os possiveis fatores causais de vicariancia entre as especies de Caenonomada.

Abstract: Caenonomada (Apidae: Tapinotaspidini) is a Neotropical bee genus distributed on the diagonal of arid biomes of South America. Three species are currently recognized: C. bruneri, endemic to the Chaco and the Pampa; C. labrata, endemic to the Cerrado; and C. unicalcarata endemic to the Caatinga. However, C. unicalcarata has disjunct populations outside the boundaries of the Caatinga, which are likely to represent a distinct species, and thus have been treated as Caenonomada aff. unicalcarata while awaiting for a formal taxonomic validation. This pattern of endemism offers an opportunity to explore the evolution and the biogeographic relationships among the South American dry areas. Therefore, this study focused on (1) depicting the phylogenetic relationships among the species of Caenonomada based on molecular characters; (2) estimating the times that the lineages of Caenonomada have diverged from one another; and (3) assessing the relationship between the biogeographic history of the genus and the history of the South American arid diagonal. Two nuclear (wingless and EF-1á) and two mitochondrial (COI and 16S rRNA) gene loci were sampled to investigate the phylogenetic relationships among the species of Caenonomada (including C. aff. unicalcarata). Four other Tapinotaspidini genera (Chalepogenus, Lanthanomelissa, Monoeca and Tapinotaspoides) were selected as outgroups. This data set was analyzed by means of parsimony, maximum likelihood and Bayesian inference. Molecular dating was conducted based on the COI data. All results supported the monophyly of Caenonomada, and following relation among its species: ((C. labrata, C. bruneri), (C. unicalcarata, C. aff. unicalcarata)). Likewise, the distinctiveness of C. aff. unicalcarata was widely supported. Superimposing the species cladogram on their respective geographic areas of occurrence suggested that both the Caatinga and the Cerrado exhibit a close relationship with the Chaco, indicating the latter as a hybrid biogeographic area. Molecular dating suggested that the first split in the Caenonomada clade occurred 11 Mya, during the late Miocene. The other two splits giving origin to C.bruneri + C. labrata and to C.unicalcarata + C. aff. unicalcarata would have occurred at about four to five Mya, respectively, during the transition between Miocene and Pliocene. Geological changes during the Miocene, such as the rising of epicontinental seas in South America, are discussed as potential causal factors in the vicariance of the Caenonomada species.