Disentangling the determinants of symbiotic species richness in native and invasive gammarids (Crustacea, Amphipoda) of the Baltic region

Symbiotic species diversity can explain invasion success and host–parasite system stability: The case of gammarid hosts

“…Differences between freshwater and brackish environments were significant for both levels and facets of diversity. The dissimilarity between habitats is linked to the significantly higher species richness in freshwater habitats compared to brackish ones, 53 versus 28 symbiotic species (Sarabeev, Balbuena, et al, 2023). Geographical distance proved to be less significant than local habitat characteristics in determining the diversity of symbiotic communities of gammarids at the regional scale of Pomerania of the Baltic Sea.…”

“…Our study is based on a database of eukaryotic symbiotic species from gammarid hosts previously collected in the cold season of 2020-2021 and identified morphologically or molecularly as described in Sarabeev, Balbuena, et al (2023) and . This dataset represents 20 host-locality samples, consisting of over 15,067,600 symbiotic organisms from 612 host individuals belonging to seven gammarid species sampled at 16 localities in the Baltic region of Poland (Figure 1).…”

“…Ponto-Caspian and Balkan gammarids, which were self-dispersed or were transported short distances along migration corridors, harbor several co-introduced symbiotic organisms typical of their native regions in the new distribution range of the Baltic region (Bacela-Spychalska et al, 2012;B alcescu-Codreanu, 1974;Codreanu-B alcescu, 1995;Ovcharenko et al, 2010;Quiles et al, 2020). The American invader, G. tigrinus, which was transported by ballast water over long distances (across the open sea), has lost its native symbiotic organisms and acquired a new species complex from native European gammarids (Sarabeev, Balbuena, et al, 2023). This specific pattern of symbiotic species distribution was also confirmed in Cases 1 and 2 revealing a significant differentiation according to host origin (see Figure 4b; Table 1 [Case 1]; Appendix S1: Figure S3b; Appendix S2: Table S9) and the absence of significant distinctions between sympatric hosts of the same origin (see Table 1 [Case 2]; Appendix S2: Table S3).…”

“…All free-living animals are exposed to and interact with a diverse array of symbionts including micro and macroorganisms. Even small crustacean hosts, for example, gammarids, may harbor several hundred individual symbionts, with the host population harboring a community of 18 different species including parasites and epibionts (Sarabeev, Balbuena, et al, 2023;. Understanding the factors that underlie the distribution patterns of symbiotic organisms is essential to identifying ecological principles controlling biodiversity which is critical for wildlife management and mitigating risks to ecosystems and communities (Illia et al, 2022;Nunn et al, 2003).…”

Database on eukaryotic symbionts of native and invasive gammarids (Crustacea, Amphipoda) in the Baltic region of Poland with information on water parameters for sampling sites

“…The objective was to evaluate the role of parasites in maintaining ecosystem diversity and resilience, as effective regulators of invasive species. Our first papers prepared in the framework of this project provide a taxonomic overview of the revealed symbiotic species gammarid hosts and analyse their variability across different habitats and localities to shed light on the key factors determining the richness of microorganisms in native and invasive host species [2] , [3] , [4] .…”