Abstract
Atlantic herring (Clupea harengus) is a euryhaline species, occupying fully marine habitats (35 psu) in the North Atlantic, as well as brackish waters (<20 psu) such as in the adjacent Baltic Sea. We co-reared Atlantic purebreds and Atlantic/Baltic F1 hybrids in two salinity regimes (16 and 35 psu) in a common garden experiment for 3 years until their first maturity. This setup enabled for the first time a direct comparison between adults and their larval siblings at respective salinity regimes in terms of larval growth indicated by otolith microstructure. We validated that otolith microstructure analysis of adult otoliths is reflecting the experienced otolith growth during the larval stage. No major selection in terms of otolith growth had taken place during the juvenile stage, except for one experimental group. Surviving adult Atlantic purebreds reared at 16 psu had higher otolith growth compared to their larval stages. The validation that otolith microstructure analyses of adult herring can reliably be extracted and used to examine larval growth even after several years adds strong support for further use of such analyses. Among the parental generation, Baltic herring had a faster initial otolith growth than Atlantic herring. The growth of their laboratory-reared F1 progeny was intermediate compared to their parents. In general, larval growth of both Atlantic purebreds and Atlantic/Baltic hybrids reared in 16 psu was significantly larger than for those herring reared at 35 psu. There was no significant difference in larval growth between Atlantic purebreds and Atlantic/Baltic hybrids reared at 35 psu, but hybrid larval growth was significantly higher compared to larval growth of Atlantic purebreds at 16 psu. This was not reflected at the adult stage where purebreds were ultimately larger than hybrids (Berg et al., 2018). This indicates the influence and importance of environmental and genetic factors throughout the life of Atlantic herring, along with genetic contributions to phenotypic variability.
Highlights
Phenotypic characteristics of marine fish are the result of the interaction between their genotype and the prevailing environmental conditions (Swain and Foote, 1999; MitchellOlds et al, 2007; Barrett and Hoekstra, 2011)
Where Width is the width between the increment j and the increment, Dis the log-transformed distance from the core to the increment j, Pop the parental population (Atlantic vs. Baltic), Sal the rearing salinity (16 vs. 35 psu), and Gen the genetics of the F1 progeny (Atlantic purebreds vs. Atlantic/Baltic hybrids)
The somatic growth of F1 adults has been previously described in Berg et al (2018). This is, to our knowledge, the first study contrasting the otolith microstructure of Atlantic herring (Clupea harengus) larvae and full sibling adults originating from identical larval environments
Summary
Phenotypic characteristics of marine fish are the result of the interaction between their genotype and the prevailing environmental conditions (Swain and Foote, 1999; MitchellOlds et al, 2007; Barrett and Hoekstra, 2011). The formation of daily increments was validated for several life stages from larvae to adults (Panfili and Tomas, 2001; Cermeño et al, 2003). Otolith chemistry studies validated that the information stored during the larval stage can be still detected in adult otoliths (Gillanders, 2002; Reis-Santos et al, 2013; Rogers et al, 2019). It is, justifiable to assume that the observed microstructure of adult otoliths still reflects the larval daily growth even after several years of living. All studies using adult otoliths to investigate the early life history of fish assume that the otolith microstructure reflects the growth pattern experienced at the larval stage
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