44 PROCEEDINGS OF THE NATIONAL MUSEUM VOL. 120 
Natural selection against interactions that waste gametes can be 
expected to act upon the ethology of mating as well as on the cop- 
ulatory mechanism. Evidence of ritualization and species-specificity 
in copepod copulation has already been discussed above. Lacking 
direct observations, mating ethology, morphology, and morphometry 
in the jollae and mirabilis groups can be related only by inference. 
Another necessary assumption is that sympatry of the contiguous 
species has been more extensive in the past than is indicated by the 
known distributions. In support of more extensive sympatry is 
substantial evidence that the California-Mexico coastline has con- 
tinuously experienced both large and small-scale climatic and 
hydrographic flux. 
The development of the jollae group as a distinct evolutionary 
unit probably begins with complete emergence of the Panamanian 
Isthmus and we can safely assume that the group is the outcome 
of a Quaternary history. Alternating periods of extensive sympatry 
and allopatry could have followed the familiar pattern of successive 
warming and cooling trends during North American Pleistocene. 
Zeuner (1959) points out that biotope replacement occurred about 
10 times or more on the continent. Paleontological-geological 
evidence of the extensive changes that occurred along the Pacific 
coast has been reviewed by Durham and Allison (1960), Hubbs 
(1960), and Allison (1964). 
Opportunities for variation in range relationships within the jollae 
group are not necessarily tied to the more or less 10,000-year intervals 
of glacial and interglacial stages. Within geological epochs we have 
evidence of more provincial warming and cooling trends that can 
shift hydrographic and faunal properties hundreds of miles off Cali- 
fornia and Baja California (Hubbs, 1948; Brinton, 1960; Berner, 1960; 
Reid, 1960; Berner and Reid, 1961); moreover, on an annual basis 
seasonal countercurrents flowing from the south alternate with periods 
of upwelling and concomitant strengthening of California Current 
flow from the north (Reid, Roden, and Wyllie, 1958; Reid, 1960; 
Schwartzlose, 1963) provide the pathways for range extensions and 
intermingling of diandra and jollae. In the Gulf of California mon- 
soonal wind conditions (Roden, 1964) provide diandra and kolpos with 
similar opportunities. The polymorphism observed in diandra can be 
regarded as evidence that the species is regularly subjected to exten- 
sive environmental changes (Ford, 1964). 
Considering their morphological affinities jollae and kolpos were 
separated recently, perhaps in connection with Wisconsin and post- 
Wisconsin events. The cooler phase would have extended the range 
of the ancestral population south beyond Cabo San Lucas. A north- 
ward shift in the range could be expected to follow diminution of the 
