Biology subjects

Hanel, R.

Publications and source records attributed to Hanel, R..

3 recordsLinked to original sources

bioRxiv2023

To hear or not to hear: How Selective Tidal Stream Transport Interferes with the Detectability of Migrating Silver Eels in a Tidal River

Acoustic telemetry provides valuable insights into behavioural patterns of aquatic animals such as downstream migrating European eels (Anguilla anguilla). The behaviour of silver eels during the migration is known to be influenced by environmental factors, yet so is the performance of acoustic telemetry networks. This study focusses on quantifying the impact of these environmental factors on both, migration behaviour and receiver performance, in order to determine possible limiting conditions for detecting tagged eels in tidal riverine areas and estuaries. A dominance analysis of the selected models describing migration speed, activity and receiver performance was conducted following 234 silver eels that were tagged with acoustic transmitters and observed by a receiver network in the Ems River during two subsequent migration seasons. The results suggest a passive locomotion of silver eels during their downstream migration by taking advantage of selective tidal stream transport (STST) It is further shown that water temperature, salinity, turbidity, precipitation, and especially current velocity were major parameters influencing migration activity and speed. At the same time, analyses of the detection probability of tagged eels under varying environmental conditions indicated a decreased receiver performance during high current velocities, resulting in a coincidence of high migration activity and reduced detection probability. Correspondingly, there is a risk that particularly during phases of increased activity, due to limited telemetry performance, not all fish will be detected, resulting in an underestimation of migration activity. To avoid misleading interpretations and underestimates of migration numbers of eels and other migratory fish using STST, this study highlights the need to conduct range tests and adjust the receiver placement in areas and conditions of high current velocities.

animal behavior and cognition↗

bioRxiv2020

Opsin gene expression in larval and adult deep-sea fishes supports a conserved cone-to-rod pathway in teleost visual development

Vertebrates use cone cells in the retina for colour vision and rod cells to see in dim light. Many deep-sea fishes have adapted to their environment to have only rod cells in the retina, while both rod and cone genes are still preserved in their genomes. As deep-sea fish larvae start their lives in the shallow, and only later submerge to the depth, they have to cope with diverse environmental conditions during ontogeny. Using a comparative transcriptomic approach in 20 deep-sea fish species from eight teleost orders, we report on a developmental cone-to-rod switch. While adults mostly rely on rod opsin (RH1) for vision in dim light, larvae almost exclusively express middle-wavelength-sensitive ("green") cone opsins (RH2) in their retinas. The phototransduction cascade genes follow a similar ontogenetic pattern of cone-followed by rod-specific gene expression in most species, except for the pearleye and sabretooth (Aulopiformes), in which the cone cascade remains dominant throughout development. By inspecting the whole genomes of five deep-sea species (four of them sequenced within this study: Idiacanthus fasciola, Chauliodus sloani; Stomiiformes; Coccorella atlantica, and Scopelarchus michaelsarsi; Aulopiformes), we found that deep-sea fish possess one or two copies of the rod RH1 opsin gene, and up to seven copies of the cone RH2 opsin genes in their genomes, while other cone opsin classes have been mostly lost. Our findings hence provide molecular evidence for a limited opsin gene repertoire and a conserved vertebrate pattern whereby cone photoreceptors develop first and rod photoreceptors are added only at later developmental stages.

evolutionary biology↗

bioRxiv2018

Vision using multiple distinct rod opsins in deep-sea fishes

Vertebrate vision is accomplished through a set of light-sensitive photopigments, which are located in the photoreceptors of the retina and consist of a visual opsin protein bound to a chromophore. In dim-light, vertebrates generally rely upon a single rod opsin (RH1) for obtaining visual information. By inspecting 101 fish genomes, we found that three deep-sea teleost lineages have independently expanded their RH1 gene repertoires. Amongst these, the silver spinyfin (Diretmus argenteus Johnson 1863) stands out as having the highest number of visual opsins known for animals to date (2 cone and 38 rod opsins). Spinyfins simultaneously express up to 14 RH1s encoding for photopigments with different peak spectral sensitivities ({lambda}max=448-513 nm) that cover the range of the residual daylight, as well as the bioluminescence spectrum present in the deep-sea. Our findings present novel molecular and functional evidence for the recurrent evolution of multiple rod opsin-based vision in vertebrates.\n\nSHORT ABSTRACTContrary to the single rod opsin used by most vertebrates, some fishes use multiple rod opsins for vision in the dimly lit deep-sea.

evolutionary biology↗