THE FIRST FOSSIL MOLINARANEA (ARANEAE), WITH A FOCUS ON THE PALEOBIOGEOGRAPHY OF THE GENUS AND IMPLICATIONS FOR THE COLONIZATION OF HISPANIOLA

The origin of the West Indian fauna has long been debated, and discussion has focused on whether dispersal or vicariance constitutes the primary mode of colonization. If dispersal was the chief means of colonization, questions arise as to what dispersal mechanism dominated (i.e., passive over-water dispersal or via a land bridge) and from where most immigrants were arriving (i.e., South, Central or North America). The first fossil (Molinaranea mitnickii) of the spider genus Molinaranea was described from Dominican Republic amber (middle Miocene in age); this extends the known range of the genus back 16 million years. A parsimony-based phylogenetic analysis was performed using PAUP v. 4.0 to determine where the fossil species fits within the extant genus. The analysis shows that the fossil, M. mitnickii, is not basal and nests with M. clymene and M. magellanica. The genus Molinaranea has not been found in the fauna of the modern Dominican Republic or the surrounding areas. While this could reflect deficient knowledge of the spider diversity in the region, it is unlikely since members of Molinaranea are fairly large, conspicuous spiders and weavers of orb webs. The presence of Molinaranea in Dominican amber therefore presents an interesting palaeobiogeographical question, since extant members of the genus are currently found only in the southwestern portion of South America. The phylogeny was used in a modified Brooks Parsimony Analysis to elucidate biogeographic patterns and to examine the origins of the genus in the West Indies. The analysis suggests M. mitnickii arrived in Hispaniola from South America as a result of a chance dispersal event. A chance dispersal event from South America could have occurred by 1) ballooning (whereby spiders release silk and are carried by air currents), 2) over-water dispersal on flotsam, or 3) dispersal via a land bridge, among other options.