FOOD-INDUCED BODY PIGMENTATION QUESTIONS THE TAXONOMIC VALUE OF COLOUR IN THE SELF-FERTILIZING SLUG CARINARION SPP

Body pigmentation is a popular taxonomic marker in slugs to discriminateclosely related species. However, the genetic background ofbody pigmentation is known only for a few species, while inmany others body pigmentation is influenced by age, food and/orclimate. In this study, we investigated the effects of differentfood items on body pigmentation expression in two selfing pulmonategastropods, Arion (Carinarion) silvaticus and Arion (Carinarion) fasciatus.Both species mainly differ in the distribution of yellow-orangegranules on the body, which in A. fasciatus are concentratedin lateral bands, and in A. silvaticus are evenly scattered.Animals were raised individually under the same conditions, whilethey laid eggs as a consequence of selfing. This F₁ generation wasafterwards divided into two groups, which were fed with different fooditems. A diet of carrot, lettuce or paper had no effect on the distributionof the yellow-orange granules in A. silvaticus, but provokeda loss of the yellow-orange lateral bands in A. fasciatusso that externally these F₁ specimens became similar to A. silvaticus.In both species, a diet of nettle resulted in a strong yellow-orangepigmentation, which often formed yellow-orange lateral bands.These results indicate that food can probably influence the'species-specific' body pigmentation in Carinarion, and thusquestion the reliability of colour traits to distinguish A.silvaticus and A. fasciatus. (Received 5 May 2000; accepted 29 September 2000)     

VARIABILITY OF THE GENITAL SYSTEM OF HELIX POMATIA L., 1758 AND H. LUCORUM L., 1758 (GASTROPODA: STYLOMMATOPHORA)

This paper examines the variability of the genital characters ofHelix pomatia and H. lucorum. Some of these characters are commonlyused to distinguish the two closely related species. Variationswithin and between populations are also investigated. The highvariability of these characters can frequently lead to identificationerrors, especially in eastern Europe. Correct identificationof these edible snails is also of commercial importance, differentspecies having a different price. The reciprocal nature of themale parts of the genitalia and the bursa stalk and diverticulumcomplex is pointed out. A possible function of the diverticulumis suggested on the basis of size relations between genitalsystem features. (Received 12 August 1999; accepted 11 April 2000)     

Assortative mating among rock-dwelling cichlid fishes supports high estimates of species richness from Lake Malawi

It has been estimated that Lake Malawi, Africa, contains 500–650 endemic species of cichlid fishes, the largest number of vertebrate species endemic to any comparable sized area on the planet. As many of these putative species cannot be distinguished anatomically, these estimates of species richness depend to a great extent on the assumption that sympatrically occurring male colour morphs represent biological species. We have tested this assumption using a combination of behavioural observations of courtship and microsatellite DNA analysis for six putative species of the Pseudotropheus ( Tropheops ) complex and three of the Pseudotropheus ( Maylandia ) complex occurring sympatrically at Nkhata Bay. We were unable to demonstrate assortative courtship for the species pairs Pseudotropheus ( Maylandia ) zebra / P . 'gold zebra' or P. ( Tropheops ) 'band'/ P. ( T .) 'rust' because we were unable to distinguish between the females of these taxa. All other taxa showed clear assortative courtship, except for P. ( T .) 'deep', a deep-water species which was rarely observed. Fixation indices (θ_ST for the infinite allele model, and R _ST for the stepwise mutation model) calculated from six microsatellite DNA loci demonstrated significant deviations from panmixia in all pairwise comparisons of putative species, indicating little or no gene flow between populations. All taxa showed high levels of allelic diversity providing evidence that genetic bottlenecking may have been of limited importance in the speciation process. Assortative mating among taxa differing only in male colouration is supportive of theories that speciation in these fishes has been driven by sexual selection by female choice.