Drivers of cryptic species coexistence in stream ecosystems – a case study using gammarid amphipods from Sicily
Final Report Abstract
Over the past decades, DNA-based bioassessments have uncovered that species diversity has been greatly underestimated due to the presence of cryptic species. Because cryptic species are morphologically undistinguishable, the true number of cryptic species as well as their distribution and ecological characteristics remain largely unknown. Present evidence supports that cryptic species typically do not co-occur but rather live in different regions or if co-occurring in a region, they are rarely found in syntopy. Interestingly, few studies have reported coexisting cryptic species. One prominent example could have been the occurrence of four potential cryptic species of a gammaridean amphipod taxon (Echinogammarus sicilianus), co-occurring with Echinogammarus adipatus, in a river basin in Sicily. In this project, we wanted to study this unexpected finding by first evaluating the actual species diversity within E. sicilianus. We have detected up to 12 potential cryptic species co-occurring in the studied river system based on the mitochondrial COI gene. However, combining the mitochondrial data with genome-wide ddRAD-seq data as well as detailed morphological and behavioural data, revealed that most of the observed genetic diversity could be ascribed a single, hyperdiverse species. This finding rejected the possibility of a cryptic species coexistence and raised the importance of using a highly integrative approach for studying hyperdiverse species complexes. Based on that finding, we focused on studying the unique case of species coexistence between hyperdiverse E. sicilianus and E. adipatus which co-occurred in the studied river system. We aimed to evaluate if that coexistence is stable or unstable, and how it is maintained. Different mechanisms have been proposed by community ecological theory that allow stable coexistence of species: i) resource partitioning e.g. through differential dietary habits, ii) spatial avoidance strategies e.g. by choosing different microhabitats, and iii) densitydependent biotic mechanisms such as apostatic selection that balance communities e.g. through parasite infections. To evaluate the stability of observed co-occurrence, we aimed to study the prevalence and diversity of microsporidian and acanthocephalan parasites in the individual host species. We tested whether prevalence and host specificity change over time to test the density-dependent control of the species through parasites. Subsequently, we studied the gut contents of different species per site and microhabitat using DNA metabarcoding and stable isotope analyses to evaluate whether there is a dietary specialisation between the species. In the last step, we also used the data on the spatial distribution of the species at a microhabitat level. Finally, we planned to use all data together with abiotic water parameters to test competing hypotheses on the impact of those factors on species presence and coexistence. From this, we aimed to derive whether the coexistence of the studied species is stable or unstable. The results of the project indicate resource partitioning between the species supporting also stability of observed patterns across the seasons. However, the overall results do not fully support the stable coexistence between the species rather suggesting a scenario of stable co-occurrence where both species can survive together for extended time. However, as revealed with genetic data, recent colonisation of the studied system by both species and likely competition between the species, indicate that in the longer timescale one will outcompete the other, so further research is needed to evaluate the long-term species dynamics in this peculiar river system. The results of this project provide a comprehensive insight into the diversity of a unique freshwater system in Sicily. Within the project framework, we highlighted the tremendous advantages of using a molecular toolbox for studying Mediterranean freshwater biodiversity, delivering a first such comprehensive study of species coexistence using molecular methods. With that, the project provide a valuable piece towards a better understanding of ecological and evolutionary processes shaping freshwater biodiversity.
Publications
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Fresh insights into Mediterranean biodiversity: environmental DNA reveals spatio-temporal patterns of stream invertebrate communities on Sicily. Hydrobiologia, 849(1), 155-173.
Hupało, Kamil; Schmidt, Saskia; Macher, Till-Hendrik; Weiss, Martina & Leese, Florian
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Morphology, nuclearSNPsand mate selection reveal thatCOIbarcoding overestimates species diversity in a Mediterranean freshwater amphipod by an order of magnitude. Cladistics, 39(2), 129-143.
Hupało, Kamil; Copilaș‐Ciocianu, Denis; Leese, Florian & Weiss, Martina
