Some Contributions of Snails to the Development of Ecological Genetics. In: Brussard PF, editor. Ecological Genetics: The Interface. New York: Springer; 1978. pp. 159-70. [DOI: 10.1007/978-1-4612-6330-2_9]

Evolution and extinction of Partulidae, endemic Pacific island land snails

The broad outline of the systematics of the endemic Pacific island land snail family Partulidae has been understood for some time. The family is divided into three genera: Eua has four species, confined to Tonga and Samoa; Samoana has about 23 species, widely but sporadically distributed in Polynesia and the Mariana Islands; Partula has about 100 species, distributed from Belau to the Society Islands. This review integrates this systematic and biogeographic knowledge with work on ecology, population genetics and speciation that has concentrated especially on the recently speciated Partula spp. of Moorea in the Society Islands. Explanations of Moorean diversity (much of which seems unrelated to ecological factors) based on parapatric speciation and the evolution of morph ratio dines in the absence of isolation have predominated, although without incontrovertible support. Unitary explanations are probably not appropriate. Rather little is known of the basic biology of partulids. They are generally arboreal; feed on a wide range of partially decayed and living plant material; and are relatively long-lived, slow reproducing, ovoviviparous, cross- or self-fertilizing hermaphrodites. The phylogenetic and geographical origins of the three genera are unknown. Partula may have evolved, somewhere unknown, from Samoana, which evolved from Eua in the Tonga-Sam oa region, this being the region of origin of Eua; but the opposite sequence has also been postulated. The question is unresolved. Origins of the Moorean species are better understood as their inter-relationships are relatively clear. Rather few dispersal events probably took place and the Society Island fauna as a whole may be derived from but two colonization events - first by a Samoana sp. and later by a Partula sp., both of which then speciated in situ - with a few intra-archipelago colonization events taking place subsequently, predominantly in a southwesterly direction from the older to the younger islands. Many of the questions posed by the group may never be answered. Some species, notably those of Moorea, are already extinct in the wild; others are severely threatened. Artificial introductions of both plants and animals, combined with urban and agricultural development, have had significant impacts, but ill-conceived biological control programmes, targeted at the Giant African Snail, Achatina fulica , constitute currently the most serious threat. However, significant areas are still open to research. Analysis of DNA variation, combined with modern ideas of Pacific biogeography, should allow the whole range from the broad origins of the fauna to the detailed evolution within groups of species to be addressed. Some species may yet be relatively secure in the wild and allow field studies, but extraction of DNA from museum specimens provides an exciting opportunity to continue unravelling the evolutionary history of these endangered snails and to contribute further to our understanding of evolutionary processes and the biogeography of the Pacific.

Population biology of two land snails (Mesomphix spp.): variation among six southern appalachian sites with differing disturbance histories

Ecological and genetic properties of two North American terrestrial gastropods (Mesomphix spp.) were characterized in paired control and previously logged watersheds in two North Carolina forests (Coweeta and the Great Smoky Mountains National Park) of the Southern Appalachian Biosphere Reserve Cluster. Shell growth was greater in the control sites, but density and mortality were largely independent of prior logging history and forest reserve. Based on starch gel electrophoresis data, both species showed their highest levels of genetic diversity in the Coweeta forest, the component of the reserve cluster which had the most extensive and variable history of logging disturbance. M. subplanus also exhibited higher levels of heterozygosity in logged than in control watersheds, and M. andrewsae showed over twice as many rare alleles in disturbed sites as in control sites. F-statistic analysis depicted both excess levels of homozygosity and moderate genetic differentiation among the populations, reflecting the effects of small population size and perhaps drift and inbreeding. Estimated gene flow was relatively low. These results correspond to the recent finding by Bryant et al. (1987) and others on the effects of bottlenecks, and to the contrasting history of habitat instability of the two major study forests.

Microgeographic variation in body size and development time in the waterstrider, Limnoporus notabilis

Body size and development time were compared among four population of Limnoporus notabilis (Heteroptera: Gerridae), in the southwestern corner of mainland British Columbia, Canada. Comparisons based on both field-caught and lab-reared animals indicated significant, heritable variability in body size among these four populations. Although body size and development time tended to be positively correlated, the variability in development time among populations was significant only for females. Comparisons of food availability at two of the study sites indicated that the observed patterns of variability in body size and development time could not be the result of genetic or phenotypic adaptations to food supply. These patterns also do not appear to reflect direct adaptation to season length. Both body size and development time were, however, positively associated with environmental heterogeneity, as indicated by habitat stability and continuity. In seasonal habitats, this positive association is complicated by selection for rapid development, leading to populations of large L. notabilis with relatively short development times. The hypothesis is thus advanced that microgeographic variability in body size and development time in L. notabilis reflects the interplay between selective adaptation to environmental heterogeneity, as proposed by Roff (1977, 1978) and dingle et al. (1980), and selection for rapid development in seasonal habitats.