Terrestrial Isopod Biology

A.M. Alikhan

• Publisher: CRC Press
• Year: 2018
• eBook ISBN: 9781351411554
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Marine Biology
• Index: Biological Sciences

This text contains the papers of a meeting on American isopods, the only crustacean group with representatives in all terrestrial ecosystems ranging from the sea shore to the desert. Due to such adaptibility, this group can be seen as a model for the successful transition on land. The text deals with two main subjects: the effects of stressful conditions on the individual animal as reflected by its survival or by the disruption of its normal reproductive pattern; and the distribution of the isopods and their selection of microhabitat.

Population genetics of Armadillidium vulgare in Europe and North America

R. L. Garthwaite

Institute of Marine Sciences, University of California, Santa Cruz, Calif., USA; and Osher Foundation Laboratory for Molecular Systematics, California Academy of Sciences, San Francisco, Calif., USA

R. Lawson

Osher Foundation Laboratory for Molecular Systematics, California Academy of Sciences, San Francisco, Calif., USA; and Leeds City Museum, Natural History Dept., Calverly St., Leeds, UK

C. Sassaman

Department of Biology, University of California, Riverside, Calif., USA

Abstract

A survey of genetic variation at up to nine enzyme loci in the synanthropic oniscid isopod Armadillidium vulgare (Latreille, 1804) was conducted from 1980 to 1992 using 157 population samples comprising over 10,000 individuals from throughout Europe and North America. Based on analysis of F-statistics, most observed genetic variation in this species in both Europe and North America was found within populations. In Europe, allele frequencies were generally found to be highly variable among populations with large differences occurring over relatively short distances. Northern Europe was found to be substantially different from southern Europe. In contrast, in North America, allele frequencies were found to be more broadly similar with smaller differences among regions. Similarities of allele frequencies among regions of North America and Europe, as measured by F-statistics and allele distributions, were found to correlate with expected similarities based on the history of human colonization of North America by Europeans. However, due to the similarity in climatic and environmental factors between likely European source areas and areas of potential colonization in North America, the observed similarities in allele frequencies would also support a selective interpretation of the data. The patterning of genetic variation in A. vulgare in Europe and North America is discussed in light of selective and historic theories.

1 Introduction

It is a primary goal of population geneticists and evolutionary biologists to delineate the factors which effect genes in populations and to determine how these factors contribute to evolutionary change. Unfortunately, evolutionarily important factors often, though not always, have important effects over time periods far longer than scientific careers. For this reason, observations of single populations over time rarely contribute substantially to our understanding of evolution. An alternate approach is the study of spatial variation. Spatially separated populations are a reasonable substitute for temporally separated generations since spatially separated populations are separated in time from a common ancestor (Singh & Long 1992). The nature of genetic variation among populations can tell us about the mechanism of evolutionary change. The importance of spatial variation in evolutionary studies is obvious and has been a major area of investigation since the early days of the evolutionary synthesis (Singh & Long 1992; see Darwin 1859).

Oniscid isopods possess a number of biological characteristics which make them particularly interesting subjects for evolutionary studies. These characters include multiple mating and the production of broods with multiple paternity (Howard 1943; Sassaman 1978b), sperm retention and the production of multiple broods from a single mating (Vandel 1941; Howard 1943; Hatchett 1947; Lueken 1962), high fecundity with up to over 200 offspring per brood possible (Collinge 1915), and tolerances for wide ranges of geographic, altitudinal, and environmental variation.

Due in part to these characteristics and its synanthropic nature, the oniscid isopod Armadillidium vulgare (Latreille 1804) is a very successful colonizer. From its origins in southern Europe (Vandel 1962), A. vulgare has spread into terrestrial habitats over much of the temperate and subtropical areas of the earth. Europe and the Mediterranean (Sars 1899, Vandel 1962, this paper), the Arabian Peninsula (Taiti & Ferrara 1991), much of North and South America (Van Name 1936, 1942; Mulaik 1960; this paper), southern Africa (Ferrara & Taiti 1979), and Australia (Green 1961) have been colonized as well as New Zealand (Chilton 1901; Jackson 1941), Japan and China (Silvestri 1927; Saito 1986), and many smaller Pacific and Atlantic islands (Van Name 1942; Vandel 1962; Ferrara & Taiti 1979, this paper). In the contiguous United States A. vulgare is ubiquitous with populations ranging from high elevations, e.g. Denver, Colorado and Santa Fe, New Mexico, to the subtropics south of Miami, Florida.

Because Armadillidium vulgare has been introduced by man into a wide range of environments from its ancestral home in southern Europe, it represents an excellent model system to test theories concerning the adaptive importance of genetic variation. By sampling genetic variation in this species over a wide range of non-native localities, we can observe its genetic response to new and vastly different environmental conditions. These observations should give insights into the role of genetic variation in adaptation to the environment. For example, correlations of genetic variation in new, non-native localities with the source of colonization regardless of climatic or environmental factors would indicate that historical rather than selective factors dictate the patterning of genetic variation in this species, whereas correlations of genetic variation with new climatic or environmental factors regardless of source of introduction would argue for genetic adaptation to these new environments.

In this initial paper on genetic variation in Armadillidium vulgare, we document patterns of allele frequencies at nine polymorphic enzyme-coding loci in natural populations from collection sites throughout Europe and North America. This data is used to determine whether the pattern of genetic variation in North American populations of A. vulgare correlates with known patterns of settlement of North America by European peoples, or whether there is evidence that this genetic variation is the result of adaptation to a variety of terrestrial habitats.

2 Materials and Methods

Horizontal starch gel electrophoresis was used to determine allele frequencies at up to nine loci coding for soluble proteins in 157 population samples of Armadillidium vulgare collected from 1980 to 1992 and comprising a total of over 10,000 individuals from throughout Europe and North America. Samples were usually collected from areas not exceeding 2m² and for the purposes of this study we consider each of these to represent a deme. These samples were transported either alive or frozen to our laboratories in California where they were maintained as live cultures or kept frozen at –80°C until required for electrophoresis. Collection localities for these samples are listed in Appendix 1. Collection sites are shown in Fig. 1.

Tissue extracts were prepared for electrophoresis by homogenizing whole isopods or one or more isopod legs in 0.05M Tris-HCl pH 7.5, or in 0.25M sucrose, lOmM dithiothreitol, lOmM EDTA, lOmM MgCl₂, and 0.01M Tris adjusted to pH 7.5 with HC1. Approximately two volumes of homogenizing buffer were used for each volume of isopod tissue. The enzyme loci surveyed and electrophoretic procedures are summarized in Table 1.

Allelomorphs were detected using methods from Murphy et al. (1990) and Aebersold et al. (1987) with minor modifications. Most population samples (143) were assayed for variation at the AAT-1, IDH-1, MDH-1, MDH-2, GPI, and PGM loci, but for MPI, IDH-2, and PEPGL a smaller number of populations was assayed.

For some data analyses, the populations were grouped into six regions. Europe was divided into two regions (north Europe and south Europe) at 46° north latitude (Fig. 1). North America was divided into four regions (northeast, southeast, northwest, and southwest) at 36°30’ north latitude and 98° longitude (Fig. 1).

For two loci (GPI and PGM), the relationship between the frequency of the most common allele and latitude were measured using the Pearson product-moment correlation coefficient (Sokal & Rohlf 1981). Resulting coefficients were tested for significance using a table of critical values for correlation coefficients (Rohlf & Sokal 1981).

Average number of alleles per locus, mean observed heterozygosity by direct count, and expected heterozygosity (unbiased estim...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Contents
• Preface
• Introduction
• Comparative study of metal bioaccumulation, and oxygen and nitrogen metabolism in three terrestrial isopod species from contaminated and uncontaminated sites in Northeastern Ontaria
• Comparative anatomy and functional aspects of the digestive system in amphibious and terrestrial isopods (Isopoda: Oniscidea)
• Water vapour absorption and ammonia volatilization: Adaptations for terrestriality in isopods
• Ligia: A prototypal terrestrial isopod
• Mechanism and function of turn alternation in Armadillidium vulgare (Latreille)
• Reproduction in woodlice: Flexibility to maximise individual fitness
• Isopod distribution at different scaling levels
• Diversity and spatial community structure of terrestrial isopods (Isopoda, Oniscidea) in a mosaic of plant assemblages
• Effects of temperature and photoperiod on the breeding patterns of two isopod species
• The effect of leaf litter, microorganisms and Collembola on the food allocation of Oniscus asellus (Isopoda)
• Microhabitat selection by Armadillidium vulgare in a riparian forest: Lack of apparent influence by leaf litter food quality
• Population genetics of Armadillidium vulgare in Europe and North America
• Contributors
• Index