Unraveling the diversification history of "Trimerotropis pallidipennis' (Oedipodinae: Acrididae) species group in South America: a delimitation analysis reveals new genetic lineages

GUZMAN N. V.; CIGLIANO M. M.; PIETROKOVSKY S.; CONFALONIERI V.A.

Congreso; 11th International Congress of Orthopterology; 2013

Unraveling the diversification history of “Trimerotropis pallidipennis” (Oedipodinae: Acrididae) species group in South America: a delimitation analysis reveals new genetic lineages. Guzmán, NV1, Cigliano, MM2, Pietrokovsky, S and Confalonieri VA1. 1Departamento de Ecología, Genética y Evolución, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina, 2División Entomología, Museo de La Plata, La Plata, Argentina. The “Trimerotropis pallidipennis species complex” represents a group of band-winged grasshoppers distributed over North and South America. Since diagnostic characters are vague and intraspecific variability is high, the taxonomic status of the South American representatives of this group has a high degree of uncertainty, hindering taxonomic decisions on the basis of morphological traits only. Originally, six species had been described: T. pallidipennis, with the subspecies T. pallidipennis pallidipennis (Burmeister, 1838) and T. pallidipennis andeana Rehn, 1939; Trimerotropis ochraceipennis (Blanchard, 1851), Trimerotropis atacamensis (Philippi, 1860), Trimerotropis chloris (Philippi, 1863), Trimerotropis flavipennis (Philippi, 1863) and Trimerotropis irrorata (Philippi, 1863). Yet, the latter four names are now considered synonyms of T. ochraceipennis (Amedegnato & Carbonell, 2001), while T. pallidipennis andeana has been raised to the status of species (Otte, 1995). More recently, species delimitation analyses based on molecular markers revealed that the complex would be composed by at least three distinct genetic linages: Trimerotropis pallidipennis from North America, Trimerotropis ochraceipennis from Chile and an undescribed Trimerotropis species from Argentina (Husemann et al., 2013). Peruvian specimens taxonomically assigned to T. andeana resolved as paraphyletic, i.e. they joined either to T pallidipennis from Argentina or T. ochraceipennis. Moreover, these genetic lineages can also be distinguished on cytological grounds: in Trimerotropis sp. from Argentina the four medium chromosomes are polymorphic for inversions, a karyotypic feature that differentiates this species from North American T. pallidipennis, in which the same chromosomes are always monomorphic. In contrast, in T. ochraceipennis two of the medium-sized chromosomes are fixed for the submetacentric state (La Fuente. Finally, the karyotype of Peruvian specimens remains unknown. Biogeographic analysis indicated a North American origin of the species complex and suggested that colonization of South America would have occurred during the Pleistocene after the closure of the Isthmus de Panama. Subsequent diversification in South America was the result of range expansion and vicariance, possibly in response to later Plesitocene glaciations. In this study, we performed phylogenetic and coalescent analyses in order to establish the specific status of Peruvian specimens (i.e. T. andeana), by sequencing two mitochondrial and one nuclear genes. To this purpose we included new specimens from Peru, Chile and Argentina. Our results indicated that Peruvian specimens are clustered in at least two different genetic lineages: one integrated by those individuals collected at the central coast of Peru, at sea level. The other one includes those individuals collected at higher altitudes along the Andes Mountains, along with those individuals from Chile, taxonomically identified as T. ochraceipennis. This latter group is closer to the Trimerotropis sp clade from Argentina. Interestingly, the new genetic lineage from Peru identified in this study has the same karyotype as T.pallidipennis form from North America. Biogeographic analyses along with molecular clock approaches indicate that after the second dispersal event leading to range expansion from Peru and Ecuador to southern latitudes, at least two vicariant events occurred. The first one led to the split between the more northern Peruvian form and the ancestor of the two remaining lineages. A second vicariant event led to the split between the Chilean plus Southern Peruvian specimens from the Argentinian clade. The time estimated for both split events corresponds to the periods when the Andes were substantially covered with ice sheets, undoubtedly constituting a physical barrier leading to allopatric diversification. It can be speculated that during this process, chromosomal rearrangements could have played an important role.