Extra-pair paternity in the strongly monogamous Wandering Albatross Diomedea exulans has no apparent benefits for females

Although 92% of avian species are socially monogamous, extra-pair copulation (EPC), resulting in extra-pair paternity (EPP), is a common reproductive strategy in birds. Among seabirds, in which the rate of social monogamy reaches 100%, Procellariiformes (albatrosses and petrels) show low EPP rates, with the noticeable exception of the only albatross investigated in this regard, the Waved Albatross Phoebastria irrorata . This species, in which forced copulations are known to occur, showed a surprisingly high rate of EPP (25% of chicks). We investigate here EPP rates in another albatross species, the Wandering Albatross Diomedea exulans , subject to a demographic survey conducted for 38 years. We combined data on pair bonds with analysis of ten microsatellite loci and found that 10.7% of 75 chicks had an extra-pair sire. Although there was some evidence for inbreeding avoidance, within-pair and extra-pair chicks showed similar levels of heterozygosity, and the incidence of EPP was independent of age, experience or past reproductive success. Hence, we found no evidence that females benefit from EPCs. Owing to the male-biased sex ratio in adults, widowed and divorced males required more time to find a new mate (+28 and +72%, respectively) than did females. Combined with high sexual size dimorphism, this phenomenon might promote the forced copulations observed in this species. Our data therefore suggest that EPC is beneficial to unpaired males but occurs at random in females, consistent with the hypothesis that EPP results solely from forced EPCs. However, the importance of the latter for EPP and the part played by solitary males require further investigation.     

MATING SYSTEM ANALYSIS USING PROTEIN ELECTROPHORESIS IN THE SELF-FERTILE HERMAPHRODITE SPECIES BULINUS TRUNCATUS (GASTROPODA: PLANORBIDAE)

Uniparental reproduction in the tetraploid hermaphrodite speciesBulinus truncatus has been suggested to occur via self-fertilization,on the basis of cytological and genetic studies. However, recentanalyses of population genetic structure by protein electrophoresisindicated the occurrence of multi-banded phenotypes referredto as ‘fixed hetero-zygosity’. Although intrapopulationand geographical variation of multibanded phenotypes occur,many populations bear only one type of such patterns. This ledto the suggestion that parthenogenesis may well be the matingsyste in B. truncatus. However, such fixed heterozygosity patternsare expected in some tetraploid species in which double disomicinheritance of alleles occurs. It is therefore not possibleto determine from population genetic structure analysis alonewhether segregation occurs or not. Here, we investigate thestability of such patterns over one generation of uniparentalreproduction among four populations. We also present resultsof crossing experiments between individuals from two populations,using two diagnostic loci to analyse their offspring. Our resultsclearly indicate Mendelian segregation of alleles, and confirmsexual reproduction by self-fertilization and cross-fertilization.We interpret the multibanded patterns observed in populationsas the product of both diploid loci of the tetraploid genomewhen they are monomorphic for different alleles. Our study alsoallows us to suggest that partial selfing may be the regularmating system in B. truncatus. (Received 12 February 1992; accepted 7 September 1992)     

Density and variability of dinucleotide microsatellites in the parthenogenetic polyploid snail Melanoides tuberculata

Characterization of microsatellites in the parthenogenetic polyploid snail Melanoides tuberculata revealed an unusual high density of dinucleotide repeats. Multiple banding patterns were obtained at these loci, and interpreted as a consequence of polyploidy. Microsatellite variability was low within, but high between, shell morphotypes. Genotypes were wholly transmitted from mothers to offspring. These results suggest that reproduction is strictly apomictic, and that shell morphotypes are genetic clones.     

Ten polymorphic microsatellite markers in the wandering albatross Diomedea exulans

We describe 10 new variable dinucleotide microsatellites in the wandering albatross Diomedea exulans, as well as conditions for multiplexing and simultaneous genotyping sets of loci. Their variability was assessed in two and one populations from the Crozet and Kerguelen archipelagos (southern Indian Ocean), respectively. Two to 13 alleles were detected per population, and the mean gene diversity was around 0.4. The low genetic differentiation suggests that these populations constitute a single panmictic unit. Cross‐species amplification provided some variability at three and five loci in two other marine birds (Bulweria bulwerii and Pagodroma nivea), but none in Calonectris diomedea.     

Selfing and outcrossing in hermaphrodite freshwater gastropods (Basommatophora): where, when and why

Hermaphrodite freshwater snails offer the opportunity to study the evolution of selling and outcrossing. Laboratory studies using genetic markers have shown that selling is possible in all species investigated, although outcrossing seems to be favoured in most. Predominance of outcrossing is promoted by sperm storing for up to several months. Studies using electrophoretic markers also suggest that outcrossing is the main breeding system in natural populations. However, heterozygote deficiencies found in some populations could indicate (partial) selfing. The evolution of self-fertilization and cross-fertilization is driven by numerous forces. Inbreeding depression is thought to select for outcrossing, and has been experimentally investigated in hermaphrodite freshwater snails. Other traits have evolved that prevent selfing. On the other hand, selfing could be selected under low density, or to preserve local adaptation, or when aphallic individuals occur within populations.     

COMPARATIVE FITNESS AND REPRODUCTIVE ISOLATION BETWEEN TWO BULINUS GLOBOSUS(GASTROPODA: PLANORBIDAE) POPULATIONS

Bulinus globosus, an intermediate host of schisto-somes, isa self-fertile hermaphrodite species whose regular mating systemis cross-fertilization. Fitness of selfing individuals originatingfrom two geographically remote populations (Elevi, Ivory Coast;Daikaina, Niger) was scored. Individuals were then paired eitherwith individuals from their own population, or with individualsfrom the other population. Electrophoretic analysis showed thatpairing ‘female’ Elevi and ‘male’ Daikainaindividuals results in only a low level of outcrossing, whereasthe reverse pairings produced almost only outcrossed offspring.This could reflect unilateral partial isolation between thetwo populations. However, analysis of fitness values withinand among groups of self-fertilizing and cross-fertilizing individuals,as well as electrophoretic data, suggest that selfing (or partialselfing) is the regular mating system in Elevi. Such experimentsare relevant to the biological control of schistosiomasis byintroducing resistant snails from allopatric populations, becausethey allow an assessment of the fate of introduced resistantgenes. (Received 30 December 1991; accepted 13 March 1992)     

Nine polymorphic microsatellite markers in Crepis sancta (Asteraceae)

We describe nine new variable di‐ and trinucleotide microsatellites in the plant Crepis sancta, as well as conditions for multiplexing and simultaneous genotyping sets of loci. Their variability was assessed in four populations. Four to 33 alleles were detected per locus; two to 23 alleles per population. Significant deviations from Hardy–Weinberg equilibrium could be attributed either to a mating system involving partial selfing or to null alleles. Genetic differentiation over all loci was significant among the four populations studied. These markers will constitute an efficient tool for investigating dispersal patterns in fragmented landscapes. Cross‐species amplification provided few loci variability in three other Crepis species (C. pulcra, C. foetida and C. rubra).     

POPULATION GENETICS OF LYMNAEA PEREGRA (MULLER) (GASTROPODA: PULMONATA) IN LAKE GENEVA

Using gel electrophoresis, a study was made of genetic exchangeamongst populations of Lymnaea peregra in Lake Geneva. Geneticvariability is high. A within-population heterozygote deficiencyis shown and the role of null alleles as an explanation of thisdeficiency is discussed. High values of gene flow show thatthe inter-population structure is weak. Exchange between populationspropably occurs by both active and passive means. (Received 9 January 1989; accepted 15 August 1989)