Alternative reproductive tactics in atlantic salmon: factors affecting mature parr success

Abstract

SUMMARYIn Atlantic salmon, as in most salmonids, males can mature early in the life cycle, as small freshwater fish, termed parr, and\or undergo a sea migration before maturing as full-size adults. The alternative life histories are contingent on environmental and social circumstances, such as growth rate, territory quality or any other factor that affects the individual's state. In order to model the choice of life history in this group of commercially valuable species, it is necessary to understand not only the relative contribution of the different male types to subsequent generations, but also to know the factors that affect reproductive success in each type.In this paper we present the results of a study designed to investigate the factors that affect the reproductive success of mature parr. We used highly polymorphic minisatellite DNA markers to analyse paternity in a series of mating experiments where the number and body size of parr were manipulated. The fraction of eggs fertilized by mature parr ranged from 26 to 40 %, with individual parr fertilizing up to 26 % of the eggs. A strong positive correlation was found between parr size and reproductive success. The relative success of parr decreased with increasing parr number. Data from this and other studies on variation in the timing and degree of parr reproductive success are discussed in relation to the evolution of male mating strategies and life history in salmonids.

Age Structure, Changing Demography and Effective Population Size in Atlantic Salmon (Salmo salar)

“…Second, the genetic effects of annual variance in individual reproductive success will be buffered under iteroparity, since individuals that failed to breed in one year may succeed in the future (Nunney 1993). Indeed, individual parr often obtain very little reproductive success in (experimental) spawning events (e.g., Thomaz et al 1997;Hutchings 2001, 2002;Weir et al 2005) as mature parr also establish dominance hierarchies during spawning (Hutchings and Myers 1988;Fleming 1996). Instead, N e may be mainly affected by the reproductive variance of anadromous males (Mjølnerod et al 1998;Jones and Hutchings 2002).…”

“…We attempted to account for the influence of male parr maturation on age-specific reproductive contribution of males as follows. In the absence of data for the rivers, we used empirical values from observations under natural ( Jordan and Youngson 1992;Martinez et al 2000;Garant et al 2001;Taggart et al 2001) and experimental conditions (Hutchings and Myers 1988;Moran et al 1996;Thomaz et al 1997;Garcia-Vazquez et al 2001;Hutchings 2001, 2002). These studies suggest that mature male parr account for $30% of the fertilizations in direct competition with anadromous fish, over a wide range of operational sex ratios.…”

“…Reproduction among anadromous (male) age classes was allocated on the basis of age composition (weighted by body size). For the (two) mature parr age classes, we assumed a slight reproductive advantage for older parr (60%), since male parr size can affect reproductive success (Thomaz et al 1997; but see Jones and Hutchings 2002). Using these criteria, we estimated the projected reproductive contribution of each age class as p x ¼ l x b x , after adjusting b x values to generate a constant population size (Sl x b x ¼ 1).…”

Individual adjustment of sperm expenditure accords with sperm competition theory

“…Sneakers, however, were always competing with the territorial male; therefore, the situation tested here is partly different from that (a fair lottery) envisaged in the theoretical models, unless the fraction of eggs cuckolded by sneakers in a spawning does not increase with the number of sneakers, as observed in the Atlantic salmon (Salmo salar; ref. 36). If this pattern of paternity sharing also applies to the fishes studied here, the sperm allocation strategy adopted by goby sneakers at a given spawning should be influenced only by the presence of other sneaker competitors and therefore be qualitatively equivalent to that predicted for ''true'' groupspawning fish.…”

Genetic variation in threshold reaction norms for alternative reproductive tactics in male Atlantic salmon,Salmo salar

“…As a group, parr fertilization success per egg nest can vary between 15 and 60% (e.g. Hutchings & Myers 1988;Jordan & Youngson 1992;Thomaz et al 1997); at the individual level, parr fertilization success tends to be low and highly variable ( Jones & Hutchings 2001.…”