Early dispersal of ayu during marine stages as inferred from geographic variation in the number of vertebrae

Abstract

Marine environments often allow interbreeding of individuals over the species range, and analyses using neutral molecular markers may lose extant genetic boundaries laid between geographic majorities. Ayu Plecoglossus altivelis has a typical amphidromous life history, migrating between rivers and the sea. In order to clarify reproductive elements of the species, migrants from 64 rivers and streams sampled over a wide latitudinal range were examined for their vertebral number (VN) and dorsal pterygiophore number (DPN) as morphological markers to estimate the temperature history. The irregular variability in VN without a geographic cline suggests that the ascending schools of fish are composed of conspecifics sharing incubation temperature or hatching site. The intersample difference in DPN indicates that larvae and juveniles of ayu spend their marine life inside a water body with a distinct temperature. Site tenacity during the marine stage may be helpful to enhance the opportunity to return to the river where they hatched. Each assemblage of fish ascending to rivers and streams is deemed to mostly represent a reproductive element, and therefore, each acts as an evolutionarily significant unit within a metapopulational structure.KEY WORDS: amphidromy, dorsal pterygiophore number, metapopulation, Plecoglossus altivelis, vertebral number, water temperature.

Occurrence of skeletal deformities and osteological development in red porgy Pagrus pagrus larvae cultured under different rearing techniques

“…Generally, in teleosts, variations in the number of vertebrae can be attributed to modified physical and chemical variables during early development and pre‐fertilization period (Lindsey, 1988), such as temperature, which has been shown to be the most important inductor of this anomaly. For instance, in ayu Plecoglossus altivelis (Temminck & Schlegel), an increase in the number of vertebrae has been found in relation to low incubation temperature, according to Jordan's rule which is the tendency for fishes from higher latitudes and cold waters to have more vertebrae than related fishes from lower latitudes and warmer waters (Iguchi et al , 2006). In contrast, Georgakopoulou et al (2007) did not find any vertebral number variation when European sea bass Dicentrarchus labrax (L.) larvae were reared under a range of 15–20° C. Besides, genetically distinct populations as well as siblings may have divergent responses in the number of vertebrae to the same environmental factor (Beacham & Murray, 1986).…”

Using dense locality sampling resolves the subtle genetic population structure of the dispersive fish species Plecoglossus altivelis

“…The ayu inhabits mainly the coastal areas of East Asia and is an annual fish with an amphidromous life history, migrating between the sea and streams (Iguchi et al . ). This species spawns in the lower reaches of rivers in autumn, and the drifting larvae flow with the rivers downstream to coastal waters just after hatching.…”

“…Here, we evaluate the usefulness of an analysis based on dense locality sampling in resolving genetic population structure in a dispersive fish species, the ayu (Plecoglossus altivelis). The ayu inhabits mainly the coastal areas of East Asia and is an annual fish with an amphidromous life history, migrating between the sea and streams (Iguchi et al 2006). This species spawns in the lower reaches of rivers in autumn, and the drifting larvae flow with the rivers downstream to coastal waters just after hatching.…”

Egg size plasticity corresponding to maternal food conditions in an annual fish, Ayu Plecoglossus altivelis

“…In pelagic spawners, females cannot anticipate the environment of their offspring (Einum and Fleming 2002). However, the site fidelity during the pelagic stages of Ayu enhances an opportunity to return to the natal streams and rivers (Iguchi et al 2006), which makes offspring environmental conditions predictable. Phenotypic traits that reflect maternal experiences might be useful to construct the egg size-offspring fitness function.…”