RESUMO
Leafcutter ants propagate co-evolving fungi for food. The nearly 50 species of leafcutter ants (Atta, Acromyrmex) range from Argentina to the United States, with the greatest species diversity in southern South America. We elucidate the biogeography of fungi cultivated by leafcutter ants using DNA sequence and microsatellite-marker analyses of 474 cultivars collected across the leafcutter range. Fungal cultivars belong to two clades (Clade-A and Clade-B). The dominant and widespread Clade-A cultivars form three genotype clusters, with their relative prevalence corresponding to southern South America, northern South America, Central and North America. Admixture between Clade-A populations supports genetic exchange within a single species, Leucocoprinus gongylophorus. Some leafcutter species that cut grass as fungicultural substrate are specialized to cultivate Clade-B fungi, whereas leafcutters preferring dicot plants appear specialized on Clade-A fungi. Cultivar sharing between sympatric leafcutter species occurs frequently such that cultivars of Atta are not distinct from those of Acromyrmex. Leafcutters specialized on Clade-B fungi occur only in South America. Diversity of Clade-A fungi is greatest in South America, but minimal in Central and North America. Maximum cultivar diversity in South America is predicted by the Kusnezov-Fowler hypothesis that leafcutter ants originated in subtropical South America and only dicot-specialized leafcutter ants migrated out of South America, but the cultivar diversity becomes also compatible with a recently proposed hypothesis of a Central American origin by postulating that leafcutter ants acquired novel cultivars many times from other nonleafcutter fungus-growing ants during their migrations from Central America across South America. We evaluate these biogeographic hypotheses in the light of estimated dates for the origins of leafcutter ants and their cultivars.
Assuntos
Agaricales/genética , Formigas/microbiologia , Coevolução Biológica , Animais , Formigas/classificação , América Central , Marcadores Genéticos , Genética Populacional , Genótipo , Repetições de Microssatélites , América do Norte , Filogenia , Filogeografia , América do Sul , SimbioseRESUMO
Megalomyrmex Forel (Myrmicinae: Solenopsidini) consists of 44 species with diverse life history strategies. Most species are predatory and may also tend honeydew-producing insects. A morphologically derived group of species are social parasites that consume the brood and fungus garden within fungus-growing ant nests. The reproductive strategies of Megalomyrmex queens are somewhat aligned with these life-style patterns. Predatory species in the leoninus species group are large in body size and have ergatoid (i.e., permanently wingless) queens whereas the social parasitic species are smaller and typically have winged queens. We examined two ergatoid phenotypes of Megalomyrmex foreli Emery and Megalomyrmex wallacei Mann and compared them to winged species, one a social lestobiotic or "thief ant" parasite (Megalomyrmex mondabora Brandão) and the other a predator (Megalomyrmex modestus Emery). Megalomyrmex foreli colonies have a single queen with an enlarged gaster that is morphologically distinct from workers. Megalomyrmex wallacei colonies have several queens that are similar in body size to workers. Queens in both species showed a simplification of the thorax, but there was a dramatic difference in the number of ovarioles. Megalomyrmex foreli had 60-80 ovarioles compared to eight in M. wallacei and M. mondabora and M. modestus had 22-28. Along with flight loss in queens, there is an obligate shift to dependent colony founding (also called budding or fission) consequently influencing dispersal patterns. These constraints in life history traits may help explain the variation in nesting biology among Megalomyrmex species.
Assuntos
Formigas/fisiologia , Evolução Biológica , Voo Animal , Animais , Formigas/classificação , Costa Rica , Feminino , Reprodução/fisiologiaRESUMO
Megalomyrmex Forel is a distinctive lineage of Neotropical ants, some of which are specialized parasites or predators of the fungus-growing ants Attini. Here we review and key the Central American fauna. Six new species are described from both female castes: M. brandaoi sp. n., M. fungiraptor sp. n., M. longinoi sp. n., M. milenae sp. n., M. megadrifti sp. n. and M. osadrifti sp. n. A worker-based key to all Central American species is presented, and all species are illustrated. Megalomyrmex drifti Kempf is redescribed and the first descriptions of queens for M. miri Brandão and M. foreli Emery are provided. New biological information, several new geographic records, and a discussion of the species-group schema of Brandão (1990) are presented. The male sex of Megalomyrmex is diagnosed at the genus-level and keyed to species for the Central American fauna, where known. The male of each species treated in the key is diagnosed, described, or redescribed. Males are known for fourteen out of twenty total Central American Megalomyrmex species. A distinct but unassociated male is described and keyed (M. male 01). The males of M. miri Brandão and M. wettereri Brandão are described for the first time, and the distinctness of these two species is confirmed. One potential synapomorphy of Megalomyrmex present in males and workers is the presence of a carina which posteriorly delimits the basalmost region of the petiolar dorsum.
Assuntos
Formigas/anatomia & histologia , Formigas/classificação , Animais , América Central , Feminino , Masculino , Especificidade da EspécieRESUMO
Workers of the ant Carebarella bicolor collected in Panama were found to have two major poison-frog alkaloids, cis- and trans-fused decahydroquinolines (DHQs) of the 269AB type, four minor 269AB isomers, two minor 269B isomers, and three isomers of DHQ 271D. For the first time in an ant, however, the DHQs were accompanied by six histrionicotoxins (HTXs), viz., 283A, 285A, 285B, 285C, 287A, and 287D. This co-occurrence of the HTX and DHQ alkaloids is the usual pattern seen in dendrobatid frogs. This finding contrasts with our earlier study, where workers of a Brazilian ant, Solenopsis (Diplorhoptrum) sp., were found to have a very similar DHQ complex but failed to show HTXs. Several new DHQ alkaloids of MW 271 (named in the frog as 271G) are reported from the above ants that have both m/z 202 and 204 as major fragment ions, unlike the spectrum seen for the poison-frog alkaloid 271D, which has only an m/z 204 base peak. Found also for the first time in skin extracts from the comparison frog Oophaga granulifera of Costa Rica is a trace DHQ of MW 273. It is coded as 273F in the frog; a different isomer is found in the ant.