Monique Simier

Simultaneous analysis of a sequence of paired ecological tables

In this paper, we present a statistical method called STATICO that can be used to analyze series of pairs of ecological tables. The objective of this method is to find the stable part in the dynamics of the relationships between the species and their environment. The treated data are a sequence of pairs of ecological tables. Each pair is made of a species abundance table (species in columns) and an environmental variables table (variables in columns). The sampling sites (in rows) must be the same for the two tables of one pair, but they may be different among the pairs. The environmental variables must be the same in all the environmental tables, and the list of species must be the same in all the species tables too, although some species may be absent from some tables (the corresponding columns will contain all zeros). From a statistical point of view, STATICO is a multitable analysis (partial triadic analysis) performed on the series of cross-tables resulting from the co-inertia analysis of each pair of...

Fluctuating asymmetry in fish otoliths and heterozygosity in stressful estuarine environments (West Africa)

Fluctuating asymmetry (FA) is assumed to reflect the developmental instability caused by environmental or genetic stress. Fish otoliths represent a very good tool for investigating the consequence of different effects on FA. Otolith FA analysis, coupled with genetic analysis, has been undertaken on two common West African estuarine species, Ethmalosa fimbriata (EFI) and Sarotherodon melanotheron (SME), in two neighbouring estuaries, in order to highlight the impact of salinity on developmental stability. The Gambia estuary has a normal functioning and the Saloum estuary is inverse (saltier waters in the upper river), reaching extremely high salinities (>100 psu) and constituting severe environmental stress. Five sub-populations of EFI and six of SME were studied along a salinity gradient. The differences between right and left otoliths were estimated with image processing by measuring five dimensions (area, perimeter, diameter, rostrum and posterior radii). Analyses of genetic differentiation at three EPIC and one anonymous nuclear gene loci for EFI and six polymorphic enzymatic loci for SME were carried out to measure the level of heterozygosity. Absolute FA in all otolith traits examined was unaffected by gender but increased significantly with fish size. Size-corrected absolute FA did not show any significant difference among sites differing largely in salinity, although a higher asymmetry in otolith area was recorded in the saltiest site. These findings suggest that otolith asymmetry is a poor indicator of osmotic stress. The individual heterozygosity level did not seem to have an effect on otolith FA for either species, even though a slight correlation appeared with otolith area or perimeter. Otolith FA cannot be considered to be a useful indicator for estimating changes linked with environmental or genetic stress in these estuaries.