No. 3567 LABIDOCERA JOLLAE GROUP—FLEMINGER 43 
arrangement of morphology and morphometry seen in the jollae 
eroup seems remote indeed. 
A more likely alternative is suggested by comparing differences 
among the geographically contiguous pairs of species with those of 
the one totally allopatric pair. In contiguous species conspicuous 
differences appear in both morphology and morphometry. The 
allopatric pair, jollae and kolpos, are spatially separated by a broad, 
biogeographically inimical, zone. Morphological distinctions are 
weak and the two species share the same morphometry. 
Turning to the eastern American cognates, Fleminger and Engchow 
(1966) show that morphological and morphometrical differences among 
the geographically contiguous species, L. mirabilis and L. wilsoni, 
closely parallel differences between contiguous pairs of the jollae 
croup (table 11). In wilsoni the two sexes are similar in TL and 
PUR, in mirabilis they differ conspicuously in both features and to 
about the same degree as in kolpos and jollae. Some of the more 
notable morphological differences among the eastern species are the 
position of the female genital pore, the length of the male’s left leg 5, 
and the position and extent of development of specialized exopodal 
spines on male swimming legs. 
Table 11 also reveals another surprising feature. Males of the 
mirabilis group have a median PUR in excess of 5:1, while males of 
the jollae group have a median PUR of less than 3.5:1. Could this 
difference reflect the evolutionary imprint of earlier interactions 
when sea passages connected the eastern and western American 
coasts—or did they, too, arise by chance in isolation? 
Repetition of the pattern in contiguous species on both coasts 
and the deviation in the one totally allopatric pair within a group 
are compelling reasons for exploring further into the argument for 
interaction. We may assume with Mayr (1963) that incipient 
reproductive barriers arise in isolated daughter populations as a 
byproduct of provincial adaptation. In the case of incipient species, 
the provincialism would impose a selective disadvantage on hybrid 
mating after geographical isolation breaks down. This in turn would 
increase selection for strengthening copulation barriers among newly 
overlapping daughter populations (see reviews of Brown and Wilson, 
1956; Blair, 1958; Sibley, 1961; and discussion of Brown, 1957, 1958). 
Selection for reproductive barriers to reduce hybridization in response 
to this interaction is usually termed reinforcement. It is akin to 
character displacement, both being a product of sympatry of closely 
related species. Reinforcement leads to reproductive incompata- 
bility while character displacement permits ecological compatability. 
