Biology subjects

Heimbrand, Y.

Publications and source records attributed to Heimbrand, Y..

4 recordsLinked to original sources

bioRxiv2026

Intra-specific evidence to support the drift-barrier hypothesis of mutation rate evolution

Rates of de novo mutations ({micro}) are highly variable among different taxa but less is known about their variability at the intraspecific level. Using a large data set (n=364 trios) from eight nine-spined stickleback (Pungitius pungitius) populations differing in their effective population sizes (Ne), we tested the prediction of the drift-barrier hypothesis (DBH) that {micro} scales negatively with increasing Ne. Indeed, {micro} was a negative function of Ne, also after correcting for phylogenetic non-independence of populations. While the range of variation in mutation rates across populations spanned more than a 4-fold range ({micro} = 1.60 - 6.99 x 10-9), we discovered one highly mutable family with a five-times higher mutation rate than the population average. Evidence was also found (i) for reduced efficiency of selection in small freshwater populations subject to strong genetic drift, (ii) that maternal age associates positively with {micro}, and shorter generation time elevates per-year mutation rates, (iii) that both replication errors and DNA repair efficiency contributed to {micro}, and that (iv) mutation rate variation has a polygenic basis. In general, the results provide support for the DBH identifying elevated mutation rates in populations subject to strong genetic drift.

genomics↗

bioRxiv2026

Navigating the salinity gradient: Individual variation in habitat use and migration of European eel revealed by otolith microchemistry

Knowledge regarding variation in habitat use among individuals is crucial for understanding population dynamics and for management and conservation measures. This is especially important for diadromous fishes that shift between habitats, being affected by external pressures and environmental change in different habitats over ontogeny. Herer, we assessed individual variation in habitat use of European eel along a salinity gradient, ranging from fully marine to freshwater in northern Europe, using otolith microchemistry data from >3600 eel together with established time-series segmentation and clustering methods. We show that eel display high degree of individual variation in habitat use. Assigned life-histories included coastal resident, freshwater resident, and coastal and freshwater habitat shifting individuals. Coastal resident eels were observed in a large range of salinities. Given the widespread occurrence of migration barriers in freshwater, it is unknown whether the coastal resident eel preferred that habitat, or if it was the only available habitat for them. Our findings nonetheless highlight the need to include coastal habitats when assessing population development and silver eel production of the critically endangered European eel.

ecology↗

bioRxiv2026

Assessing local adaptation and divergence at early life stages within Eastern Baltic cod

Many commercially exploited fish stocks have declined over the last few decades. It is therefore essential to identify natural populations and understand local adaptation for sustainable management. Salinity is a key environmental factor shaping local adaptation, and adaptive trait divergence often occurs at the egg and larval stages. The strong salinity gradient in the brackish Baltic Sea has driven rapid adaptation in multiple taxa. The Eastern Baltic cod (Gadus morhua) has adapted to low salinity with buoyant and tolerant eggs and larvae, but the stock has declined both in abundance and geographical range during the last decades. The main reproduction area of this stock is in the Bornholm Basin (ICES subdivision (SD) 25) in the southern Baltic Proper. Cod in this area, however, exhibit stunted growth and small body sizes. In contrast, large and healthy cod in reproductive condition have been observed in the [A]land Sea in the northern Baltic Proper (SD 29), raising the question of whether these fish represent a locally adapted population capable of successful reproduction in the lower salinities (5-10 psu in the northern Baltic Proper (SD 27, 29 and 32). Here, we experimentally assessed egg and yolk-sac larvae survival across salinities, egg size, egg and larval neutral buoyancy and egg survival on sediment, to test whether northern ([A]land) cod show adaptation to low salinity at early life stages as compared to southern cod. Mortality of larvae increased with decreasing salinity in cod from both areas, with the lowest survival at 7 psu. At 9 psu, more than 50% of northern cod larvae survived, suggesting that development could occur in SD29. Egg size and buoyancy were similar between northern and southern cod, and eggs and larvae were negatively buoyant, sinking under local salinity conditions. Nevertheless, the eggs survived and hatched well on sediment, indicating potential for demersal spawning. Our findings show no strong evidence of adaptive divergence to lower salinity in northern cod; however, their ability to tolerate sediment contact at early life stages suggests that Eastern Baltic cod may reproduce outside their historical spawning grounds.

ecology↗

bioRxiv2024

Evolution of fast-growing piscivorous herring in the young Baltic Sea

The circumstances under which species diversify to genetically distinct lineages is a fundamental question in biology1. Atlantic herring is an extremely abundant zooplanktivorous species that is subdivided into multiple ecotypes that differ regarding spawning time and genetic adaption to local environmental conditions such as temperature, salinity, and light conditions2,3. Here we show using whole genome analysis that multiple populations of piscivorous (fish-eating) herring have evolved sympatrically after the colonization of the brackish Baltic Sea within the last 8,000 years postglaciation. The piscivorous ecotype grows faster, and is much larger and less abundant than the zooplanktivorous Baltic herring. Lesions of the gill rakers in the piscivorous ecotype indicated incomplete adaptation to a fish diet. This niche expansion of herring in the young Baltic Sea with its paucity of piscivorous species suggests that empty niche space is more important than geographic isolation for the evolution of biodiversity.

evolutionary biology↗