Ecological Traits and Genetic Variation in Amazonian Populations of the Neotropical Millipede Poratia obliterata

The periodic flood pulse of the Amazon River has been the main controlling factor in the local ecosystems for at least two million years. Numerous adaptations, in some cases along with speciation, have evolved in local terrestrial invertebrates. The small millipede Poratia obliterata (Kraus, 1960), which probably originates from the Andes, is currently known from a remarkably broad range of Central Amazonian biotopes, i.e. various seasonal inundation forests, upland forest and plantations. Like most native millipedes, P. obliterata appears to escape flooding by tree ascents. Such developed survival strategies adaptive to annual inundation can either reflect ecological plasticity or implicate ecological speciation, .i.e. ‘biotope-specific races’ or ecotypes. To assess the causal mode of adaptation, ecological studies with genetic analyses are combined in this work. Comparing the distribution, biotope range, population subdivision and genetic diversity of different millipedes, the species P. obliterata appears to feature a generalist strategy. The book shows low divergence between Amazonian populations of this diverse and widespread species, which seems to cope well with various biotopes and thus successfully invaded seasonal inundation forests. The book is addressed to specialists in evolution, ecological genetics, ecology and conservation of wetlands, millipede research and conservation.

Contents

 Introduction  13
1.1 Study Area  13
1.1.1 Geology of the Amazon Basin  13
1.1.2 Climate  15
1.1.3 Water Level Regime  16
1.1.4 Seasonal Inundation Forests  16
1.2 The Millipede Poratia obliterata  17
1.2.1 Classification and Biology  17
1.2.1.1 Systematics  17
1.2.1.2 Basic Anatomy  18
1.2.1.3 Characterisation  19
1.2.1.4 Development  20
1.2.1.5 Ecology  21
1.2.1.6 Dispersal Ability  23
1.2.2 Origin and Range of P. obliterata Populations  23
1.2.3 Biotope-Related Adaptation and Speciation?  24
1.3 Survival Strategies in Central Amazonian Floodplains  26
1.4 Molecular Markers in Population Genetics  29
1.4.1 Definition of Molecular Markers  29
1.4.2 Subject of Population Genetics  29
1.4.3 Application of Molecular Markers  29
1.4.3.1 Classification and Speciation  29
1.4.3.2 Adaptive Divergence among Populations  31
1.4.4 Technique  31
1.4.5 Appraisal: Choice of an Appropriate Marker  32
2 Thesis Outline  33
2.1 Part I: Ecological Traits  33
2.2 Part II: Genetic Variation  33
3 Ecological Traits  35
3.1 Material and Methods  35
3.1.1 Study Sites  35
3.1.1.1 Varzea  35
3.1.1.2 Igaps  38
3.1.1.3 Varzea & Igaps  41
3.1.1.4 Terra firme  44
3.1.1.4.1 Banana Plantation at CPPA/Embrapa  44
3.1.1.4.2 Upland Forest Reserve Reserva A. Ducke  45
3.1.2 Monitoring and Sampling of P. obliterata in the Field  46
3.1.2.1 Inundation Forests  46
3.1.2.2 Banana Plantation  47
3.1.3 Estimation of Flood Periods for Individual Sample Trees  47
3.1.4 Determination of Humidity in Microhabitats  47
3.1.5 Identification of Collected Millipedes  48
3.1.6 Laboratory Experiments  49
3.1.6.1 Flooding Experiment  49
3.1.6.2 Reproduction Experiment  49
3.1.7 Data Analysis and Statistics  52
3.2 Results  54
3.2.1 Abiotic Factors  54
3.2.1.1 Precipitation  54
3.2.1.2 Water Level  55
3.2.1.3 Minimum Flood Period at Study Sites  56
3.2.1.4 Humidity in the Microhabitat  58
3.2.2 Morphology  59
3.2.2.1 Poratia obliterata  59
3.2.2.2 Other Millipede Species  59
3.2.3 Ethology  60
3.2.3.1 Inundation Forests  60
3.2.3.1.1 Seasonal Vertical Migration  60
3.2.3.1.2 Preferred Microhabitats and Gregarious Behaviour  61
3.2.3.2 Banana Plantation  79
3.2.4 Phenology  79
3.2.4.1 Life Cycle (Progress of Stages, Sex Ratio)  79
3.2.4.1.1 Inundation Forests  79
3.2.4.1.2 Banana Plantation  84
3.2.4.2 Reproduction (Mating, Eggs)  84
3.2.4.2.1 Inundation Forests  84
3.2.4.2.2 Banana Plantation  86
3.2.5 Laboratory Experiments  87
3.2.5.1 Flooding Experiment  87
3.2.5.2 Reproduction Experiment  89
3.3 Discussion  97
3.3.1 Abundance in Different Biotopes  97
3.3.2 Life History Traits  100
3.3.2.1 Seasonal Vertical Migration  100
3.3.2.2 Microhabitat Selection and Social Behaviour  104
3.3.2.2.1 Choice of Adequate Microhabitats  104
3.3.2.2.2 Gregarious Behaviour  107
3.3.2.2.3 Species Interactions  110
3.3.2.3 Life Cycle and Postembryonic Development  113
3.3.2.3.1 Life Cycle in the Field  113
3.3.2.3.2 Evolution of the Univoltine Life Cycle  117
3.3.2.3.3 Regulation by Maternal Effects  118
3.3.2.3.4 External Cues for Reproduction and Development  121
3.3.3 Synopsis  125
4 Genetic Variation  127
4.1 Material and Methods  127
4.1.1 Sample Collection  127
4.1.2 Agarose Gel Isoelectric Focussing (AGIF)  128
4.1.2.1 Sample Preparation  128
4.1.2.2 Preparation of the Agarose Gel  131
4.1.2.3 Isoelectric Focussing  132
4.1.2.4 Staining Procedure  132
4.1.2.5 Interpretation of Zymograms  133
4.1.3 Data Analysis and Statistics  133
4.2 Results  134
4.2.1 Zymograms  134
4.2.2 Allelic Variation within and among Biotope Types  135
4.2.3 Heterozygosis and Hardy-Weinberg Distribution  138
4.2.4 Effective Number of Alleles per Locus  138
4.2.5 Genotypic Linkage Equilibrium between Loci  139
4.2.6 Genetic Differentiation among Populations  139
4.2.6.1 Within-Subpopulation Variance of Genetic Diversity  139
4.2.6.2 Genetic Variability between Subpopulations  143
4.2.6.3 Genotypic Distinction of Biotope Types  150
4.2.7 Population Genetic Structure  151
4.2.8 Isolation by Distance and Effective Number of Migrants  153
4.2.9 Cluster Analysis of Genetic Similarity  155
4.3 Discussion  158
4.3.1 Population Dynamics and Adaptation in P. obliterata  158
4.3.1.1 Concept of Dispersal  158
4.3.1.2 Adaptation Hypothesis  159
4.3.1.3 Population Genetic Implications from Allozyme Data  159
4.3.1.3.1 Random Mating and Outcrossing  159
4.3.1.3.2 Gene Flow and Population Subdivision  161
4.3.1.3.3 Unidirectional Dispersal and Biotope-Related Differentiation  163
4.3.1.4 Local Adaptation versus Phenotypic Plasticity  165
4.3.2 Allozyme Variability within Populations of P. obliterata  168
4.3.3 Synopsis  169
5 Conclusions  171
6 Acknowledgements  173
7 References  175

Author: Natalie Bergholz
Publisher: Pensoft
Extra Details: 165x240, Richly illustrated by color and b/w photos, graphs and maps, in English, 198 pp., paperback