Multiple scale patterns of shell and anatomy variability in land snails: the case of the Sicilian Marmorana (Gastropoda: Pulmonata, Helicidae)

Certain major aspects of phenotypic diversity are still largely unexplained. When phenotypic patterns do not relate to habitat variables, fine analysis of morphological patterns and their distribution sheds light on the origin of diversity. Among invertebrates, snails are an ideal model for studying the roles of the neutral processes and selection involved in creating diversity. To understand patterns and processes of variability on different scales (regional: areas; local: sites), morphological variability of two sets of characters (shell and genitalia) was quantified in a group of rock-dwelling land snails of the genus Marmorana (Pulmonata, Helicidae). To analyse shell variability, partitioning of the overall variation into size and shape components was analysed by a principal component-based approach. Shell shape and size variability is not significantly influenced by any environmental pressure. Variability at site scale is mainly attributed to shell size, which is a trait demonstrated to have a high degree of phenotypic plasticity. No sharp changes were observed for genitalia. Moreover, allometries between shell size and genitalia measurements involve a few populations. The observed multiple scale patterns are in line with the hypothesis that genital variance may be selectively controlled to maintain function.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 359–370.     

The cytological origin of the polyads and their significance in the reproductive biology of Mimosa bimucronata

The mechanism of polyad formation in Mimosa bimucronata (DC.) Kuntze is described and its significance in the reproductive biology is discussed. In this species c . 500 complexes of two coupled pollen mother cells (PMCs) per pollen sac are formed after the last mitotic division of the sporogenous tissue. All the pollen grains of each complex remain attached and form a bitetrad. This mechanism leads to the formation of many polyads per pollen sac. On this basis, we propose that in Mimosa the number of pollen grains per polyad (eight or 16) is determined by the number of cells that remain attached after the last mitotic divisions of the sporogenous tissue. Concerning the biological significance of the polyads in M. bimucronata , we find that the number of pollen grains per polyad is correlated with the number of ovules per ovary, and that the internal dimensions of the pit-shaped stigma are sufficient just for one polyad to be localized in it. Based on the number of polyads per flower this species has a high pollen/ovule ratio characteristic of xenogamous plants, in opposition to that expected for plants with composite pollen dispersal units. In contrast, it has low pollination efficiency, low fruit set, a 1/1 relationship between the pollen grains of a polyad and the number of ovules per ovary, and high seed set per fruit. These facts support the hypothesis that the occurrence of polyads in M. bimucronata would be an adaptation helping to ensure high seed set following a single cross pollination event.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 144 , 343–349.     

Cyanogenesis variation in the Turnera sidoides L. polyploid complex (Turneraceae)

This study constitutes the first investigation of cyanogenesis variation within the Turnera sidoides autopolyploid complex. The qualitative and quantitative analysis carried out in 38 populations showed that the five subspecies of the complex are cyanogenic, although the levels of cyanide released varied both between and within subspecies. Between the subspecies, carnea , holosericea and integrifolia showed higher values of HCN released than subspecies pinnatifida and sidoides . Within subspecies, there is a tendency toward an increment of mean cyanide values with ploidy levels and different hypotheses are considered in order to explain this variation. The study of cyanogenesis in populations from different geographical areas cultivated under uniform greenhouse conditions showed that, in the widespread subspecies pinnatifida , HCN variation may also reflect the action of different selection pressures, since populations having dissimilar cyanide levels grow in different phytogeographical provinces with different climatic regimes. On the other hand, the fact that the variation of HCN released was greater between populations from different geographical areas than that observed between diploid and tetraploid populations of the same area provides additional evidence for the multiple origins of polyploids of the T. sidoides complex.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 141 , 85–94.