. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. E F G H Figure 25. Assumed evolutionary relationships in Triodopsis. Solid dots mark the 20 closely related taxon pairs, utilized in making up Table XVI. Stippling indicates hybridization; horizontal lines, primary intergradation; dashed line, uncertain relationship. range was plotted against population size (Fig. 27), or the natural samples were con- \'erted into samples of standard size, and the range of variation of these standardized samples was caleulated and compared (Fig. 4; method adapted from Simpson, 1941).
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. E F G H Figure 25. Assumed evolutionary relationships in Triodopsis. Solid dots mark the 20 closely related taxon pairs, utilized in making up Table XVI. Stippling indicates hybridization; horizontal lines, primary intergradation; dashed line, uncertain relationship. range was plotted against population size (Fig. 27), or the natural samples were con- \'erted into samples of standard size, and the range of variation of these standardized samples was caleulated and compared (Fig. 4; method adapted from Simpson, 1941). The advantage of the first method was that it avoided the use of the standard devia- tion, \\'hich is high in samples with a skewed distribution curve, and which, as may be recalled, is the situation in many hybrid populations of Triodopsis. The ad- vantage of the second method is its clarity. Both methods were used for species in which samples with skewed distribution cunes occurred. The second method was used alone in species with nonnal distri- bution curves. The samples which showed considerably greater \'ariability than the average were considered hybrids. These samples were always intermediate between two "paren- tal" taxa, and they always occurred in the zone of contact between the two, or in a ring along the periphery of one of them (the latter also can be considered a con- tact zone, if we assume that one taxon is presently in the process of surrounding the other one). The morphological intermedi- acy and the described distribution pattern are consistent with the interpretation that the populations in question are of hybrid origin. The range of variation in the hybrid pop- ulations is wider than nomial, but it never spans the entire range of variation of the species, as is the case in some other hy- brids. This may be because most of the characters utilized in the analysis of varia- tion are polygenic; such characters often do. Please note that these images a
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