Intergradation of the Two Rhineura (Reptilia) Populations in Central Florida and Comments on Its Scale Reduction

The area of intergradation between the two populations of R. floridana is con- firmed. The patterns of variation of small demes on adjacent sand ridges indicate that these demes are not reproductively isolated. The reduction of midbody segments can be explained by a form of scale fusion. The explanation that a reduced number of body annuli results from an increase in annulus width in relation to body length appears unacceptable. * * * The Florida worm lizard, Rhineura floridana, consists of a north-central Florida population and a Lake Wales Ridge population (Zug, 1968). Intergradation between these two populations apparently occurs in central Polk County. My initial investigation was frustrated by a paucity of specimens from the area of intergradation. Recently I received additional specimens from this region and am now able to confirm the area of intergradation. This study analyzes six characters: number of body annuli, number of rows of granular caudal segments, number of segments around midbody, total number of lateral head scales, total number of supralabials, and total number of infralabials. These six were used to define the two populations and were recorded in the previously described manner (Zug, 1968). The data from the new specimens were combined with the former samples, and the new values are presented in Fig. 1. The sample localities are comparable with those of Table 3 in my earlier article except that the Sebring specimen has been removed from the Avon Park sample. The Fort Meade and Haines City samples are new. The relative degree of similarity among the eight samples is illustrated by Table 1 and Fig. 2. Both show two distinct clusters. The Lake Wales Ridge cluster includes the Winter Haven sample in addition to the three Ridge samples. The Ridge cluster is more compact, i.e., the members differ less from one another than the central Florida cluster (Table 1). This com- pact clustering suggests that the Winter Haven specimens are members of the Lake Wales Ridge population. The greater variation of the central Florida cluster indicates that the specimens of this area are intergrades. However, on the basis of my earlier findings (Zug, 1968), I believe the Leesburg sample should be excluded from area of intergradation, since it is more similar to the samples north of it than to those to the south, i.e., Lakeland and Auburndale. The pattern of variation in the central Polk County samples clearly indicates that these demes are not isolated from one another. Although the terrain of this area would be expected to impose a moisture barrier between the demes, such a situation does not appear to exist. The similarity between the Haines City and Winter Haven samples is particularly important in illus- trating that Rhineura demes on different and separate sand ridges are not reproductively isolated. These factors indicate that the Lake Wales Ridge population is not as genetically pure as I for- merly thought. The entire Ridge population is probably influenced by the north-central popula- tion. This latter assumption presupposes an earlier isolation of the Ridge population. Although