1969] 
Brady — Oxyopes apollo 
427 
Text Figure 1. Dendrogram illustrating the hypothetical relationships of 
North American members of the Apollo species group. 
tively recent common ancestry. Likewise the similarity between the 
palpal structure of O. lynx and O. cougar (compare figs. 66, 67 of 
Brady, 1964 with Figs. 9, 10 of this paper) indicate a recent linkage. 
In fact, the entire apollo species group appears to have originated 
in Mexico and/or Central America, perhaps after being separated via 
the Panamian bottle-neck from earlier South American ancestors. 
Expanding northward these founder populations extended into the 
southwestern United States on the one hand and along the Gulf 
Coast into Florida on the other hand. 
I suggest that the exploitation of widely dissimilar ecological realms 
in the southwestern and the southeastern United States produced 
entirely different sets of selective pressures. Gene flow between the 
western and eastern populations would tend to be limited, and it is 
doubtful whether the eastern and western populations would remain 
conspecific for long. Exceptional cases would involve ancestral Neo- 
tropical populations that remained as a strong connecting link be- 
tween east and west, or species populations that might be genetically 
flexible enough to meet the widely differing environments of the 
southern United States from east to west. 
Thus, in general, the effect of expansion into North America 
would be to produce biological divergence and subsequent speciation 
in many cases. This idea would be supported if one were to find 
examples of closely related allopatric species in the southeast and 
the southwest. Oxyopes apollo is predominately southeastern in dk- 
