Spatial patterns of disparity and diversity of the Recent cuttlefishes (Cephalopoda) across the Old World
Diversity and disparity metrics of all Recent cuttlefishes are studied at the macroevolutionary scale (1) to establish the geographical biodiversity patterns of these cephalopods at the species level and (2) to explore the relationships between these two metrics. Location
Sampling uses what is known about these tropical, subtropical and warm temperate cephalopods of the Old World based on a literature review and on measurements of museum specimens. Some 111 species spread across seventeen biogeographical areas serve as basic units for exploring diversity and disparity metrics in space. Methods
Landmarks describe the shape of the cuttlebone (the inner shell of the sepiids) and differences between shapes are quantified using relative warp analyses. Relative warps are thus used as the morphological axis for constructing morphospaces whose characteristics are described by disparity indices: total variance, range, and minimum and maximum of relative warps. These are analysed and then compared with the diversity (species richness) metric. Results
Results show no significant latitudinal or longitudinal gradients either for diversity or for disparity. Around the coast of southern Africa, disparity is high regardless of whether diversity (species richness) is high or low. In the ‘East Indies’ area disparity is low despite the high diversity. Main conclusions
The relationship between diversity and disparity is clearly not linear and no simple adjustment models seem to fit. The number of species in a given area does not predict its disparity level. The particular pattern of southern Africa may be the result of paleogeographical changes since the Eocene, whereas that of the ‘East Indies’ may indicate that this area could act as a centre of origin. However, the lack of any clear phylogenetical hypothesis precludes the study from providing any explanation of the observed patterns.