Colonization patterns of Nematoda on decomposing algae in the estuarine environment: Community assembly and genetic structure of the dominant species Pellioditis marina

Abstract

We performed a field experiment in the Westerschelde Estuary (The Netherlands) to characterize the colonization dynamics of nematodes in relation to the proximity of a source population and to local environmental conditions. The effects of colonization on the population genetic structure of the dominant species, Pellioditis marina, were simultaneously investigated. Two contrasting sites, each containing four patches with defaunated algae, were sampled seven times during 1 month. Site A was situated amidst Fucus stands, which permanently harbor P. marina, while site B was approximately 100 m from any source population and experienced more stressful environmental conditions. We hypothesized that (1) colonization in site A would proceed faster than in site B and that (2) founder events and genetic bottlenecks would affect population genetic structure and differentiation at site B more than at site A. We screened 992 individuals for variation in 426 base pairs of the cytochrome oxidase c subunit 1 gene with the single-strand conformation polymorphism method. The algal deposits at site A were indeed more rapidly colonized and reached fivefold higher densities of nematodes than those in site B. Haplotype composition in site A was very similar to that of the source population, while rare haplotypes were abundant and genetic diversity was lower in site B. We conclude that founder effects and genetic bottlenecks structured the populations in site B. The genetic differences between patches in each site further indicate that effective migration in P. marina is low and that priority effects influence the genetic structure of P. marina populations.

Differences in Time until Dispersal between Cryptic Species of a Marine Nematode Species Complex

“…The species-specific differences in dispersal strategy can have important consequences for metapopulation and metacommunity dynamics, genetic diversity and species composition in newly establishing populations and assemblages, for instance if priority effects, where the first arriving species will have an advantage over the following species, occur [79], [80]. Clear priority effects within a single cryptic species of L. marina (Pm I) have been demonstrated in a field experiment, impacting the genetic structure and diversity of local populations [79]. However, we are unaware of any studies demonstrating priority effects between different nematode species.…”

Dispersal and gene flow in free-living marine nematodes

“…L. marina produces dauer larvae, and due to its high reproductive capacity and short generation time it is an efficient colonizer that can establish populations from one or a few gravid females. To investigate the effect of colonization dynamics of L. marina on neutral genetic variation within and among patches in close proximity (≤ 1 km) to each other, Derycke et al [48] performed a field experiment in which the genetic diversity of L. marina on newly colonized algae was surveyed during one month at two contrasting sites in an intertidal salt marsh: in one site, defaunated algae were incubated amongst permanent algal stands that can act as a source population, while no algal stands were present in the second site [48]. Algal deposits near the permanent algal stands were more rapidly colonized, reached a fivefold higher density of nematodes and had a higher genetic diversity than algal deposits ca 1 km away from the source population (Figure 1).…”

“…A-W represent different haplotypes. Note the late colonization and the low number of haplotypes of patches B2-B4, and the dominance of different haplotypes among B1-B4 (Figure from [48]).…”

Revisiting the meiofauna paradox: dispersal and colonization of nematodes and other meiofaunal organisms in low- and high-energy environments

“…Once in the water column, meiofaunal organisms may be carried long distances by oceanic currents, which are believed to be of crucial importance to longrange dispersal of benthic meiofauna including juvenile polychaetes (Gerlach, 1977;Hagerman & Rieger, 1981;Palmer & Gust, 1985;Butman, 1987;Derycke et al, 2007). Epibenthic harpacticoids and nematodes are more easily dispersed by currents given their typical position on the surface of sediments (Fleeger et al, 1984), while species residing deeper in the sediment are less likely to become suspended and transported passively.…”