LATITUDINAL GRADIENTS IN DIVERSITY OF THE FRESHWATER COPEPOD FAMILY CYCLOPIDAE (COPEPODA, CYCLOPOIDA)

Abstract

Contrary to the most common latitudinal pattern of taxonomic richness, certain freshwater crustacean and molluscan groups show antitropical peaks of diversity. A previous analysis of the cyclopid and canthocamptid copepods in the Americas did not support the well-known negative relationship of taxonomic diversity and latitude, either.A recent catalogue of the continental Cyclopoida by Dussart & Defaye (2006) allowed world-scale comparisons of the species richness and rate of endemism of Cyclopidae in: the northern cold, northern temperate, tropical, southern temperate, and southern cold regions. Separate analyses of the three inland-water subfamilies revealed different latitudinal trends in these groups: while the halicyclopine and eucyclopine species richness significantly increases towards the tropics, the cyclopine diversity is very similar in the northern temperate and tropical regions despite the smaller area size of the northern temperate zone. Separate analysis of the American fauna also supported a tropical diversity peak in Eucyclopinae but showed a relatively diverse cyclopine fauna in the northern temperate zone.The aforementioned distribution patterns and tropical dominance in Euryteinae, a small marine subfamily of Cyclopidae, indicate that the family Cyclopidae originated in the tropics. This paper also discusses the latitudinal distribution of the large cyclopine genera, and attempts to infer the main features of their evolution in the temperate region: (1) cyclopine copepods invaded the temperate region at an early phase of the evolution of the subfamily; (2) a major evolution of the extant temperate taxa occurred in the northern hemisphere; (3) a substantial part of the temperate cyclopine fauna occurs in groundwater, which might indicate that in addition to a longer evolutionary time in the tropics, the greater extinction rate of the surface-water forms in the temperate region is an important factor in shaping the latitudinal diversity patterns in Cyclopidae.