SYSTEMATICS OF THE CRYPTIC FUNGUS-FARMING ANT GENUS Myrmicocrypta FR. SMITH, WITH THE DESCRIPTION OF A NEW GENUS AND SPECIES OF FUNGUS-FARMING ANTS (HYMENOPTERA: MYRMICINAE).

Abstract

Fungus-farming ants (Hymenoptera: Formicidae) have become model systems for exploring questions regarding the evolution of symbiosis. However, robust phylogenetic studies of both the ants and their cultivars are needed to address whether or not the attine ant symbiosis is a result of strict or diffuse coevolution.

Chapter One, deals with the relationships of the species within the ant genus Myrmicocrypta, and their fungal cultivars. Analyses conducted, recovered the genus as monophyletic and the sister group of Mycocepurus. In addition, the species M. tuberculata was recovered as the sister to the rest of Myrmicocrypta. The time-calibrated phylogeny recovered the age of stem-group Myrmicocrypta plus its sister group as 35.16 Ma, whereas the inferred age for the crown-group Myrmicocrypta was recovered at 30.05 Ma.

Chapter Two, represents the first species-level taxonomic revision of the fungus-farming ant genus Myrmicocrypta. Myrmicocrypta is distributed in the New World tropics from Mexico to northern Argentina, and, as far as it is known, absent in the Caribbean and in the fossil record. Sixty-five species are recognized, of which 37 are described as new species. The revision includes a taxonomic key to the species of Myrmicocrypta based on the worker caste. When possible, descriptions and photographs of the reproductive forms (i.e., queens and males), geographic distribution, and notes on natural history are presented.

Finally, Chapter Three, deals with the description of Cyatta abscondita, a new genus and species of fungus-farming ant from Brazil, based on morphological study of more than 20 workers, two dealate gynes, one male, and two larvae. Ecological field data are summarized, including natural history, nest architecture, and foraging behavior. Phylogenetic analyses of DNA sequence data from four nuclear genes indicate that C. abscondita is the distant sister taxon of the genus Kalathomyrmex, and that together they comprise the sister group of the remaining neoattine ants, an informal clade that includes the conspicuous and well-known leaf-cutter ants. Morphologically, C. abscondita shares very few obvious character states with Kalathomyrmex. It does, however, possess a number of striking morphological features unique within the fungus-farming tribe Attini. It also shares morphological character states with taxa that span the ancestral node of the Attini. The morphology, behavior, and other biological characters of C. abscondita are potentially informative about plesiomorphic character states within the fungus-farming ants and about the early evolution of ant agriculture.