AN ELECTRON PARAMAGNETIC RESONANCE (E.P.R.) STUDY OF ENDOGENOUS TRANSITION METALS IN THE TERRESTRIAL SLUG DEROCERAS RETICULATUM

E.P.R. spectroscopy was used to detect and characterise transitionmetal ions, notably Fe and Mn, and organic free radicals withinthe tissues of the slug Deroceras reticulatum. Tissue Cu wasE.P.R. silent. The calcium complexes found within the varioussoft tissues and the shell were shown to be of the calcite configuration.It was suggested that the presence of the organic free radicalswithin the digestive gland and reproductive organ may be dueto the peroxidation of subcellular membrane lipids. (Received 15 October 1987; accepted 2 January 1988)     

CONCENTRATIONS OF METALS (Cu, Pb, Cd, Zn, Ca) IN SIX SPECIES OF BRITISH TERRESTRIAL GASTROPODS NEAR A DISUSED LEAD AND ZINC MINE

Heavy metal concentrations in 6 terrestrial slug species inhabitinga disused Pb/Zn mine site were measured by atomic absorptionspectrophotometry. Differences in metal accumulation patternswere such that the species could be ranked in order of overallmetal accumulation capability: Arion hortensis < Deocerasreticulatum < Milax budapestensis < Arion ater < Derocerascaruanac < Arion subfuscus. Species belonging to the samegenus were widely separated by this simple ranking scheme. Theresults are discussed in the context of inter-species competitionand resource partitioning, and cautionary comments are madeconcerning the utility of slugs as biomonitors of terrestrialheavy metal pollution. (Received 25 November 1987; accepted 2 January 1988)     

FACTORS AFFECTING THE GROWTH AND FECUNDITY OF BULINUS TROPICUS (KRAUSS) (GASTROPODA)

Growth, monitored as changes in wet weight or shell length,varies inversely with population density in closed cultures,irrespective of whether the volume of water is kept constant,or increased in proportion to the number of snails. Feedingand locomotor activity are also lower in high density populationsand the size differences recorded are reflected in the proteinand nucleic acid content of the snails. Similar attenuation of growth and inhibition occurs in snailscultured in continuously dialysed medium and the differencesare not attributable solely to changes in the inorganic ioncontent. Instead the results are consistent with the hypothesisthat some unidentified inhibitory compound accumulates in thewater. (Received 23 June 1986;     

Microsatellite markers for the earthworm Lumbricus rubellus

We describe eight microsatellite markers for the earthworm Lumbricus rubellus, a commonly used ‘biological sentinel’ species in ecotoxicology studies. Thirty‐four individuals from a single population were tested for polymorphism. Markers possessed between two and 15 alleles per locus, and expected heterozygosity ranged between 0.06 and 0.92 (observed heterozygosity 0.03–0.92). Unfortunately, no consistent cross‐species amplification was observed in the related congeners Lumbricus castaneus and Lumbricus terrestris.     

Molecular systematics and paleobiogeography of the South American sigmodontine rodents [published erratum appears in Mol Biol Evol 1998 Feb;15(2):224]

The murid rodent subfamily Sigmodontinae contains 79 genera which are distributed throughout the New World. The time of arrival of the first sigmodontines in South America and the estimated divergence time(s) of the different lineages of South American sigmodontines have been controversial due to the lack of a good fossil record and the immense number of extant species. The "early-arrival hypothesis" states that the sigmodontines must have arrived in South America no later than the early Miocene, at least 20 MYA, in order to account for their vast present-day diversity, whereas the "late-arrival hypothesis" includes the sigmodontines as part of the Plio-Pleistocene Great American Interchange, which occurred approximately 3.5 MYA. The phylogenetic relationships among 33 of these genera were reconstructed using mitochondrial DNA (mtDNA) sequence data from the ND3, ND4L, arginine tRNA, and ND4 genes, which we show to be evolving at the same rate. A molecular clock was calibrated for these genes using published fossil dates, and the genetic distances were estimated from the DNA sequences in this study. The molecular clock was used to estimate the dates of the South American sigmodontine origin and the main sigmodontine radiation in order to evaluate the "early-" and "late-arrival" scenarios. We estimate the time of the sigmodontine invasion of South America as between approximately 5 and 9 MYA, supporting neither of the scenarios but suggesting two possible models in which the invading lineage was either (1) ancestral to the oryzomyines, akodonts, and phyllotines or (2) ancestral to the akodonts and phyllotines and accompanied by the oryzomyines. The sigmodontine invasion of South America provides an example of the advantage afforded to a lineage by the fortuitous invasion of a previously unexploited habitat, in this case an entire continent.