Intra‐population variation in anadromy and reproductive life span in rainbow trout introduced in the Santa Cruz River, Argentina

Abstract

Scale patterns, maturational status and otolith microchemistry (strontium to calcium ratios) were analysed in sympatric anadromous and non-anadromous rainbow trout Oncorhynchus mykiss in the Santa Cruz River (Patagonia, Argentina) to investigate the life-history differences of anadromous and non-anadromous lifestyles and the association between maternal origin and progeny life history. The analyses revealed that both forms can give rise to one another, indicating a single population with alternative phenotypes. Anadromous fish smolted at ages 2 and 3 years, matured after 1 to 2 years in the ocean, and survived up to 11 years, spawning up to eight times. Non-anadromous fish survived up to 6 years, spawning up to three times. The extended reproductive life span associated with anadromy in this river suggests that increased energetic and physiological demands associated with ocean migration may not necessarily result in reduced postspawning survival, as has been suggested for salmonids in general. Alternatively, reduction in parity may be regarded as the evolutionary outcome of reproductive traits resulting from the adoption of anadromy (i.e. augmented reproductive investment) coupled with longrange migrations to and from the ocean. The life-history patterns of Santa Cruz River rainbow trout provide a natural experiment for investigating the evolutionary transition and maintenance of anadromy and non-anadromy within salmonid populations.

Anadromy and residency in steelhead and rainbow trout (Oncorhynchus mykiss): a review of the processes and patterns

“…Similar observations of residents producing anadromous offspring have been documented in other populations (Zimmerman et al 2009;Zimmerman and Reeves 2000), in addition to female steelhead producing resident offspring . Interchange between forms was also observed in the Santa Cruz River, Argentina, where steelhead apparently evolved from resident trout (Pascual et al 2001;Riva-Rossi et al 2007). Perhaps not surprisingly, molecular analysis has seldom revealed genetic divergence between anadromous and resident individuals where fish displaying these life histories patterns are sympatric (Docker and Heath 2003;McPhee et al 2007;Olsen et al 2006), consistent with evidence for considerable interbreeding between life histories from parentage analysis (Christie et al 2011;Seamons et al 2004) and direct observation (McMillan et al 2007).…”

Seasonal age distributions and maturity stage in a naturalized rainbow trout (Oncorhynchus mykissWalbaum) population in southern Chile reveal an ad-fluvial life history

“…Additionally, the presence of older and mature trout (aged from 5 + to 8 + ) in the inlet streams during the reproductive period may be an indicator of repeat spawners, as reported in their native range (Lindsay et al, 1959) and in naturalized populations such as southern Argentina (Sakai and Espinos, 1994;Riva-Rossi et al, 2007), suggesting the presence of an iteroparous population in Lago Llanquihue. On the other hand, the proportion of trout (2 + to 4 + ) observed in the streams during summer may indicate protracted rearing periods for some trout or that some individuals spend their entire lives in these streams as seen in British Columbia (Mellina et al, 2005).…”

“…Rainbow trout (Oncorhynchus mykiss Walbaum) is one of the most popular game species that has been introduced all over the world (Crawford and Muir, 2008). Similar patterns of habitat use have been reported in both native and introduced populations, with adults using inlet streams to spawn and juveniles occupying streams as nursery areas before they emigrate to the lake (Youngs and Oglesby, 1972;Hayes, 1988;Rosenau, 1991;Seelbach, 1993;Sakai and Espinos, 1994;Graynoth, 1996;Dedual et al, 2000;Riva-Rossi et al, 2007). However, naturalized populations currently exist across a diverse array of habitats (Crawford and Muir, 2008).…”

“…This technique has been used in rainbow trout populations of New Zealand (e.g., Graynoth, 1996) and the Argentinean Patagonia (e.g., Pascual et al, 2001;Riva-Rossi et al, 2007). Scales were removed from an area below the posterior margin of the dorsal fin and approximately five scale rows above the lateral line (Pascual et al, 2001;Riva-Rossi et al, 2007).…”

The Genetic Basis of Smoltification-Related Traits in Oncorhynchus mykiss

“…However, more recent molecular Salmonidae and Salmonine phylogenies suggest multiple origins of anadromy when mapped to these trees (Stearley 1992;Stearley and Smith 1993;Oakley and Phillips 1999). On a finer level, observations within species suggest plasticity in the trait and multiple parallel accounts of both the gain and the loss of anadromy in both natural and introduced populations (Quinn et al , 2001Unwin et al 2000;Pascual et al 2001;Stockwell et al 2003;Riva-Rossi et al 2007). While many of the above studies support the theory that timing of and propensity for anadromy is a derived character, having evolved from a freshwater ancestor, alternative views suggest that anadromy is ancestral and that extant salmonids evolved from a marine ancestor (McDowall 1997).…”