Demonstration of a heritable component of the variation in segment number in the centipede Strigamia maritima

Abstract

Here we address the question of how arthropod segment number may evolve by reporting the results of further work on the model system Strigamia maritima. Recently, we showed that there was a plastic component of the variation in segment number within this species; now we demonstrate that there is also a heritable component. This is important because it enables a connection to be made between the known latitudinal trend among species of geophilomorph centipedes (more segments at lower latitudes) and the parallel trend within them. This latter trend is best documented in S. maritima but is also known in several other species. However, while a general connection between the inter- and intraspecific trends can now be made, deciding upon a specific hypothesis of the nature of the selection involved is still problematic. We provide two alternative hypotheses, one based on the temperature-related plasticity in segment number being adaptive, the other based on it being nonadaptive.

Juvenile hormone as a physiological regulator mediating phenotypic plasticity in pancrustaceans

“…Interestingly, this species shows a latitudinal cline; centipedes in southern populations possess more segments (Kettle, Johnstone, Jowett, Arthur, & Arthur, ). The variation of segment number among populations is also explained by some heritable components, suggesting the link between phenotypic plasticity and genetic variations (Vedel, Brena, & Arthur, ). Juvenoids do not only function during postembryonic development, but affect embryogenesis as shown in the case of caste differentiation in ants (Nijhout & Wheeler, ).…”

Myriapoda

“…Geophilomorphs are in fact a good model for evolutionary studies on segmentation, having a trait, the number of segments, variable, hence potentially subject to natural selection. Indeed, this trait would appear to have a hereditary component (Vedel et al 2009 ) but also a clear environmental component, where temperature during developmental time is directly proportional to the fi nal number of segments produced (Vedel et al 2008 ); this explains the inverse relationship towards latitudes on natural population (Kettle and Arthur 2000 ). Interesting enough, temperature affects the fi nal number of segments before the morphological segmentation starts or very early in the process, implying that the number of segments is infl uenced by the initial conditions of the embryo (e.g., its number of cells) more than by the segmentation process itself (Vedel et al 2010 ).…”

Early embryonic determination of the sexual dimorphism in segment number in geophilomorph centipedes

“…There is geographic variation between populations [3], probably due at least in part to the influence of temperature during embryogenesis [4,5]. There is also an influence of genetics within populations [6], and possibly also between populations. Most significantly for this work, there is also an influence of sex.…”