Biology subjects

Heim, S.

Publications and source records attributed to Heim, S..

4 recordsLinked to original sources

bioRxiv2024

Specialization into Host Sea Anemones Impacted Clownfish Demographic Responses to Pleistocene Sea Level Changes

Fluctuating sea levels during the Pleistocene led to habitat loss and fragmentation, impacting the evolutionary trajectories of reef fishes. Species with specialized ecological requirements or habitat preferences, like clownfishes (Amphiprioninae), may have been particularly vulnerable due to their intricate dependence on sea anemones. The diverse host specializations within this group likely contributed distinct responses to sea-level fluctuations, differentially shaping their recent evolutionary histories. Leveraging a comprehensive genomic dataset, we reveal demographic patterns and connectivity dynamics across multiple populations of ten clownfish species under different host specializations. Host-generalist species demonstrated strong resilience to habitat perturbations, while those specialized on single hosts suffered dramatic bottlenecks linked to sea-level fluctuations. Spatial analyses revealed the significant role of oceanic currents in shaping clownfish genetic diversity landscapes. Dispersal barriers were driven by environmental variables, with the Coral Triangle emerging as a hub of genetic diversity. Our results reveal how clownfish associative behavior influences their population dynamics, holding major implications for their conservation such as the need to consider their mutualism with sea anemones, particularly on host-specialists, to ensure their survival in the face of climate threats. These findings extend broader principles of conservation, improving our understanding of species responses to ecological constraints and environmental changes over evolutionary timescales.

genomics↗

bioRxiv2024

Eluding anemone nematocysts: are clownfish deprived of N-acetylated sugars in their skin mucus?

The clownfish - sea anemone system is a great example of symbiotic mutualism where host << toxicity >> does not impact its symbiont partner, although the underlying protection mechanism remains unclear. The regulation of nematocyst discharge in cnidarians involves N-acetylated sugars like sialic acid, that bind chemoreceptors on the tentacles of sea anemones, leading to the release of stings. It has been suggested that clownfish could be deprived of sialic acid on their skin surface, sparing them from being stung and facilitating mutualism with sea anemones. In this study, we sampled the skin mucus of two anemone symbionts, the clownfish Amphiprion akindynos and the juvenile damselfish Dascyllus trimaculatus, as well as two non-symbiotic adult damselfish Pomacentrus moluccensis and P. pavo. The free and total sialic acid content, including its conjugated form, and three other intermediates of this pathway were quantified using a stable isotope dilution mass spectrometry approach. We found significantly higher levels of sialic acid and its precursor in the non-symbiotic damselfishes. Concentrations of total sialic acid in anemone symbionts ranged between 13 {micro}M and 16 {micro}M, whereas the non-symbiotic damselfishes ranged between 21 {micro}M and 30 {micro}M. The presence of this metabolite and its precursors, as triggers of nematocyst discharge, in anemone symbionts, suggests that this is not the direct mechanism of protection or that the trigger is concentration dependent. This experiment demonstrates that anemone symbionts are not spared by nematocysts because of a lack of N-acetylated sugars, as previously thought.

molecular biology↗

bioRxiv2023

Recurrent gene flow events shaped the diversification of the clownfish skunk complex

Clownfish (subfamily Amphiprioninae) are an iconic group of coral reef fish that evolved a mutualistic interaction with sea anemones, which was shown to have triggered the adaptive radiation of the group. Within clownfishes, the skunk complex is particularly interesting as, besides ecological speciation, gene flow between species and hybrid speciation are suggested to have shaped the diversification of the group. We investigated, for the first time, the mechanisms underlying the diversification of this complex. By taking advantage of their disjunct geographical distribution, we obtained whole-genome data of sympatric and allopatric populations of the three main species of the complex (Amphiprion akallopisos, A. perideraion and A. sandaracinos). We examined the population structure, genomic divergence patterns and introgression signals, and performed demographic modeling to identify the most realistic diversification scenario. We excluded scenarios of strict isolation, of hybrid origin of A. sandaracinos, and ruled out the presence of extensive gene flow in sympatry. We discovered moderate gene flow from A. perideraion to the ancestor of A. akallopisos + A. sandaracinos and weak gene flow between the species in the Indo-Australian Archipelago throughout the diversification process of the group. We identified introgressed regions in A. sandaracinos and detected two large regions of high divergence in A. perideraion, likely maintained by the disruption of recombination. Altogether, our results show that ancestral hybridization events shaped the groups diversification. However, more recent gene flow is less pervasive than initially thought and suggests a role of host repartition or behavioral barriers in maintaining the genetic identity of the species in sympatry.

evolutionary biology↗

bioRxiv2023

Gene flow throughout the evolutionary history of a polymorphic and generalist clownfish

Even seemingly homogeneous on the surface, the oceans display high environmental heterogeneity across space and time. Indeed, different soft barriers structure the marine environment, which offers an appealing opportunity to study various evolutionary processes such as population differentiation and speciation. Here, we focus on Amphiprion clarkii (Actinopterygii; Perciformes), the most widespread of clownfishes that exhibits the highest colour polymorphism. Clownfishes can only disperse during a short pelagic larval phase before their sessile adult lifestyle, which might limit connectivity among populations, thus facilitating speciation events. Consequently, the taxonomic status of A. clarkii has been under debate. We used whole-genome resequencing data of 67 A. clarkii specimens spread across the Indian and Pacific Oceans to characterise the species population structure, demographic history, and colour polymorphism. We found that A. clarkii spread from the Indo-Pacific Ocean to the Pacific and Indian Oceans following a stepping-stone dispersal and that gene flow was pervasive throughout its demographic history. Moreover, edge populations exhibited more similar colouration patterns compared to central populations. However, we demonstrate that colour polymorphism is not associated with population structure, thus, colour phenotype is unreliable in assessing the taxonomic status of A. clarkii. Our study further highlights the power of whole-genome comparative studies to determine the taxonomy of geographically wide-ranging and phenotypically diverse species, supporting the status of A. clarkii as a single species.

evolutionary biology↗