Blar i forfatter "Folstad, Ivar"

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    • Cannibalism and protective behavior of eggs in Arctic charr (Salvelinus alpinus) 

      Frye, Marilena; Egeland, Torvald Blikra; Nordeide, Jarle Tryti; Folstad, Ivar (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-09-28)
      From video recordings of spawning events, we quantified protective and cannibalistic behavior of Arctic charr occurring immediately after spawning. The number of fish cannibalizing on stray eggs was examined regarding (a) whether more than one male shed milt during the spawning event, that is, whether sperm competition occurred, (b) whether the sperm competition included few or many males, that is, ...

    • Do mothers also "manipulate" grandparental care? 

      Busch, Mari Veierud; Olaisen, Sandra; Bruksås, Ina Jeanette; Folstad, Ivar (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-11-15)
      Paternity uncertainty has proven to be a robust ultimate hypothesis for predicting the higher investment in grandchildren observed among maternal grandparents compared to that of the paternal grandparents. Yet the proximate mechanisms for generating such preferred biases in grandparental investment remain unclear. Here we address two different questions for better understanding the proximate mechanisms ...

    • Do the fastest sperm within an ejaculate swim faster in subordinate than in dominant males of Arctic char? 

      Vaz Serrano, Jonathan; Folstad, Ivar; Rudolfsen, Geir; Figenschou, Lars (Journal article; Tidsskriftartikkel; Peer reviewed, 2006)
      Theoretical models predict that subordinate males should have higher sperm velocity to compensate for their disadvantaged mating role and because they experience sperm competition more frequently than dominant males. Differences in mean velocity between sperm of dominants and subordinates in the predicted direction are also documented for a few species, including the Arctic char, Salvelinus alpinus ...

    • No support for cryptic choice by ovarian fluid in an external fertilizer 

      Kleppe, April Snøfrid; Nordeide, Jarle Tryti; Rudolfsen, Geir; Figenschou, Lars; Larsen, Berner; Reiss, Katrin; Folstad, Ivar (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-12-22)
      Whether the ovarian fluid (OF) represents a selective environment influencing cryp‐tic female choice was tested using an external fertilizer experiencing intense sperm competition and large effects of OF on sperm swimming behavior—the Arctic charr (<i>Salvelinus alpinus</i>). We physically separated the OF from the eggs of reproductively active females and reintroduced either their ...

    • On the relative effect of spawning asynchrony, sperm quantity, and sperm quality on paternity under sperm competition in an external fertilizer 

      Egeland, Torvald Blikra; Rudolfsen, Geir; Nordeide, Jarle Tryti; Folstad, Ivar (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-07-14)
      How much of a fitness benefit is obtained by dominant males of external fertilizers from releasing ejaculates in synchrony with female egg-release when engaging in sperm competition, and what is the most important sperm trait for paternity in these situations? The Arctic charr (Salvelinus alpinus) is an external fertilizer experiencing intense male-male competition over reproductive opportunities ...

    • Own,but not foreign seminal fluid inhibits sperm activation in a vertebrate with external fertilization 

      Rudolfsen, Geir; Vaz, Jonathan Serrano; Folstad, Ivar (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-08-03)
      Seminal fluids are known to have a variety of effects on rival sperm, but in externally fertilizing species it is still unclear what effects seminal fluid can induce under sperm competition. We recorded sperm activity from natural ejaculates (including own seminal fluid) of an external fertilizer, the Arctic charr (Salvelinus alpinus), after activation either in water (the natural medium for ...

    • The relative effect of parasites and social status on sperm traits in Arctic charr 

      Figenschou, Lars; Folstad, Ivar; Rudolfsen, Geir; Hanssen, Sveinn Are; Kortet, Raine; Skau, Philip; Killie, Jan Eirik; Oskam, Irma Caroline; Strand, Harald (Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
      Sperm production and sperm swimming speed, which most likely affect fertilization under sperm competition, are modified by proximate mechanisms. In a comprehensive observational study of free-living and reproductively active Arctic charr (Salvelinus alpinus), we examined the possible modulating effects of male social status (including ornamental development), parasite intensities, and immunity ...

    • Resemblance Reporting on Children: Sisters Are More Proactive than Brothers 

      Fisktjønmo, Guro Hole; Bårdsen, Bård-Jørgen; Folstad, Ivar (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-05-02)
      The asymmetric grandparental investment in humans may ultimately be explained by the paternity uncertainty hypothesis. The proximate mechanisms leading to grandparental bias in investment in grandchildren are, however, unclear. In a study of 233 males and females with an opposite sexed sibling, we examined whether comments on resemblance regarding one’s own child, or one’s sibling’s child, ...

    • Spawning behavior of Arctic charr (Salvelinus alpinus): Spawning synchrony, vibrational communication, and mate guarding 

      Brattli, Magnus B.; Egeland, Torvald B.; Nordeide, Jarle Tryti; Folstad, Ivar (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-07-20)
      A mismatch in synchrony between male and female gamete release in external ferti - lizers can result in reduced or failed fertilization, sperm competition, and reduced paternity. In Arctic charr ( Salvelinus alpinus ), males can adopt either a guard or sneak tactic resulting in both pre- and postcopulatory ...

    • Spawning behaviour of Arctic charr (Salvelinus alpinus) : risk of sperm competition and timing of milt release for sneaker and dominant males 

      Sørum, Vidar; Figenschou, Lars; Rudolfsen, Geir; Folstad, Ivar (Journal article; Tidsskriftartikkel; Peer reviewed, 2011)
      A mismatch in timing between the release of male and female gametes in external fertilizers may lead to failed fertilization or, under sperm competition, reduced paternity. To quantify the actual synchrony of gamete release and the level of sperm competition we placed video cameras on two spawning grounds of a naturally spawning population of Arctic charr ( Salvelinus alpinus). Females release eggs ...

    • The spectacular human nose: An amplifier of individual quality? 

      Mikalsen, Åse Kristine Rognmo; Folstad, Ivar; Yoccoz, Nigel Gilles; Laeng, Bruno (Journal article; Tidsskriftartikkel; Peer reviewed, 2014)

    • Status specific tailoring of sperm behavior in an external fertilizer 

      Egeland, Torvald Blikra; Rudolfsen, Geir; Nordeide, Jarle Tryti; Folstad, Ivar (Journal article; Tidsskriftartikkel; Peer reviewed, 2016-11-24)
      Why dominant males experiencing intense sperm competition sometimes show low investments in sperm production is not always obvious. One well-documented example is that of the external fertilizing teleost, the Arctic charr (Salvelinus alpinus), where individuals becoming dominant reduce sperm production and sperm swimming speed in water compared to subordinates. Here, we report how ovarian ...