Selection in Natural Populations

By Jeffry B. Mitton | Go to book overview

Table 3.4 Percentage of polymorphic loci (P) and average heterozygosity (H) in groups of plants and animals differing in levels of environmental heterogeneity
NH SE P SE
Plants
Geographic Range
Endemic 81 0.096 0.010 40.0 3.2
Narrow 101 0.137 0.011 45.1 2.8
Regional 193 0.150 0.008 52.9 2.1
Widespread 105 0.202 0.015 58.9 3.1
Succession
Early 226 0.149 0.008 49.0 2.0
Mid 152 0.141 0.010 47.6 2.3
Late 95 0.161 0.011 58.9 3.0
Animals
Ecological range
Invertebrate habitat specialists 33 0.064 0.010
Invertebrate habitat generalists 54 0.149 0.020
Vertebrate habitat specialists 82 0.037 0.002
Vertebrate habitat generalists 56 0.071 0.001
Geographic range
Endemic and relict 96 0.045
Narrow 97 0.074
Regional 267 0.074
Widespread 211 0.076
Note: Data for plants from Hamrick and Godt 1990: data for animals from Nevo, Beiles, and Ben-Shlomo 1984. Envi-
ronmental heterogeneity is not measured directly, but is inferred from the extent of the geographic range, successional sta-
tus, or the degree of specialization. N is the number of species in a group: H is the average heterozygosity based on Hardy
Weinberg expectations; and SE is the standard error of the mean heterozygosity of that group.

mately 800 mm per year, but it drops to less than 100 mm in the deserts. As the annual rainfall decreases, the year-to-year variability in rainfall increases dramatically. Thus this transect through Israel describes a gradient of rising stress and environmental uncertainty. Nevo and Beiles ( 1988) summarized allozyme surveys in two plants, two mollusks, two insects, three amphibians, one lizard, and three mammals, testing for correlations with both rainfall and the variation in rainfall across Israel. In the full data set, both heterozygosity and gene diversity increased with the variation in rainfall. Genetic diversity increased toward the deserts in all species studied except the aquatic frog, Rana ridibunda. When the data were analyzed by enzyme locus, rather than by species, variation at 10 of the 13 polymorphic loci increased with the variability of rainfall.


Summary

Several population genetic models predict a positive relationship between environmental variability and genetic variability. In laboratory studies with population cages, higher levels of allozyme and additive genetic variation are generally maintained in cages with

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Selection in Natural Populations
Table of contents

Table of contents

  • Title Page iii
  • Preface vii
  • Contents ix
  • 1 - Natural Selection, Fitness Determination, and Molecular Variation 3
  • Summary 12
  • 2 - Classes of Abundant Genetic Variation 14
  • 3 - Environmental Variability and Enzyme Polymorphism 29
  • Summary 37
  • 4 - The Impact of a Single Gene 39
  • Summary 57
  • 5 - Patterns of Variation Among Loci 58
  • Summary 71
  • 6 - The Axis of Individual Heterozygosity: Theory 73
  • Summary 86
  • 7 - The Axis of Individual Heterozygosity: Empirical Data 87
  • Summary 126
  • 8 - Female Choice and Male Fitness 127
  • Summary 142
  • 9 - Patterns Among Species 144
  • Summary 156
  • 10 - The Sisyphean Cycle 157
  • Summary 166
  • 11 - Comments on Natural Selection 167
  • Appendices 175
  • Bibliography 199
  • Index 233
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