Finding the relevant scale: clonality and genetic structure in a marine invertebrate (Crambe crambe, Porifera)

Abstract

Important changes in genetic relatedness may occur at extremely small scales in benthic invertebrates, providing key information about structuring processes in populations of these organisms. We performed a small-scale study of the population structure of the sponge Crambe crambe, in which 177 individuals from the same rocky wall (interindividual distances from 0 to 7 m) were genotyped using six microsatellite markers. 101 sponges had unique genotypes and the remaining 76 individuals formed 24 groups of sponges sharing genotypes (clones). Mean intraclone distances were found to be c. 20 cm. Spatial autocorrelation analyses showed a drastic decrease in genetic relatedness over the first 100 cm of distance. If the contribution of clonality to this pattern was eliminated, the trend was attenuated, but remained a marked one and was still significant within the first distance classes (30-40 cm). Estimated mean dispersal distances per generation were c. 35 cm, and neighbourhood sizes were estimated at c. 33 sponges. Genetic similarities with sponges of the same locality, or from other Mediterranean localities, were within the same range as those found in sponges 2-7 m apart. It is concluded that asexual reproduction plays an important role in structuring populations in this species. However, over and above the effects of clonality, a strong fine-scale genetic structure was present at distances in the range of tens of centimetres, probably as a result of short dispersal of larvae. This fine-scale genetic structure may be common in invertebrates with lecitotrophic larvae.

Decadal demographic trends of a long-lived temperate encrusting sponge

“…Therefore, the population of Crambe crambe relied more on fission than sexual recruitment. The importance of asexual inputs is corroborated by genetic studies of population structure in this species (Calderón et al 2007). However, it is important to note that < 40% and 20% of the population underwent fission and fusion, respectively, with a minor annual contribution to the studied population (mean probability of fission ~0.1 and of fusion ~0.03 annually) ( Table 1).…”

“…Summary of events affecting the population size over the entire study period. Note the differentiation between genets (considering the entire specimen) and ramets (all the fragments) Calderón et al (2007) highlighted the importance of long-term demographic data to understand processes acting in the clonality and genetic structure of this species. To our knowledge, the present study is the first to provide solid long-term demographic data for this species, with observations spanning more than a decade.…”

Small-scale spatial genetic structure in Scopalina lophyropoda, an encrusting sponge with philopatric larval dispersal and frequent fission and fusion events

“…The only sponge study focusing on SGS at short distances (from cm to m) dealt with a Mediterranean encrusting species Crambe crambe with continuous distribution and relatively high larval dispersal (Calderon et al 2007). The present study focuses on another encrusting sponge: Scopalina lophyropoda (Schmidt), which has an aggregated distribution (Blanquer 2007) and philopatric larval behaviour , Mariani et al 2006).…”

“…Vacelet 1979), and have life-history traits that might lead to a high level of spatial genetic structure (e.g. Uriz et al 1998), only 1 study to date addresses sponge genetic structure at small spatial scales (Calderon et al 2007).…”

Novel polymorphic microsatellite markers developed for a common reef sponge, Stylissa carteri

“…Until now, microsatellites have only been developed for eight species within all the Porifera (Duran et al 2002;Knowlton et al 2003;Blanquer et al 2005;Hoshino and Fujita 2006;Noyer et al 2009;Dailianis and Tsigenopoulos 2010;Gigliarelli et al 2010;Guardiola et al 2011) and have only been used for population-wide analyses in few species (Duran et al 2004a;Calderón et al 2007;Hoshino et al 2008;Blanquer et al 2009;Uriz 2010, 2011;Noyer 2010;Dailianis et al 2011;Guardiola et al 2011). The highly variable markers presented herein will be useful for determining fine scale variability between sponge populations and tools for determining species identification for cryptic taxa within this group.…”