Abstract
Reproductive traits differ between intralacustrine Arctic charr morphs. Here, we examine three sympatric lacustrine Arctic charr morphs with respect to fecundity, egg size and spawning time/site to assess reproductive investments and trade‐offs, and possible fitness consequences. The littoral omnivore morph (LO‐morph) utilizes the upper water for feeding and reproduction and spawn early in October. The large profundal piscivore morph (PP‐morph) and the small profundal benthivore morph (PB‐morph) utilize the profundal habitat for feeding and reproduction and spawn in December and November, respectively. Females from all morphs were sampled for fecundity and egg‐size analysis. There were large differences between the morphs. The PB‐morph had the lowest fecundity (mean = 45, SD = 13) and smallest egg size (mean = 3.2 mm, SD = 0.32 mm). In contrast, the PP‐morph had the highest fecundity (mean = 859.5, SD = 462) and the largest egg size (mean = 4.5 mm, SD = 0.46 mm), whereas the LO‐morph had intermediate fecundity (mean = 580, SD = 225) and egg size (mean = 4.3, SD = 0.24 mm). Fecundity increased with increasing body size within each morph. This was not the case for egg size, which was independent of body sizes within morph. Different adaptations to feeding and habitat utilization have apparently led to a difference in the trade‐off between fecundity and egg size among the three different morphs.
Highlights
In studies of life history evolution, consideration of traits related to reproduction is important because of their role in determining individual fitness (Stearns, 1992)
Fish reproductive effort can be measured as the egg mass per female, which is the product of fecundity and egg size (Duarte & Alcaraz, 1989)
Energy availability and/or female size are factors that constrain both egg number and egg size, as larger eggs only can be produced at the cost of
Summary
In studies of life history evolution, consideration of traits related to reproduction is important because of their role in determining individual fitness (Stearns, 1992). In several fish species, such as the Atlantic salmon (Salmo salar), dace (Leuscicus leuscicus) and coho salmon (Oncorhynchus kisutch), both fecundity and egg size increase with female body size (van den Berghe & Gross, 1984; Mann & Mills, 1985; Thorpe, Miles, & Keay, 1984). This means that for salmonids, larger individuals, which may have higher absolute fecundity compared with smaller individuals, invest more energy into each offspring reducing relative fecundity (number of eggs per unit body weight) compared with smaller individuals. In Fjellfrøsvatn northern Norway, the profundal morph spawn in February in the profundal zone, while the littoral morph spawn in September in the littoral zone (Klemetsen, Amundsen, & Hermansen, 1997)
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