Ivar Folstad

Ivar Folstad
UiT The Arctic University of Norway

Cand Scient

About

92
Publications
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6,590
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Publications

Publications (92)
Article
Full-text available
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...
Article
Full-text available
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 spe...
Data
Video showing spawning event with sperm competition and filial cannibalism.
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Video showing a spawning event with its definitions.
Data
Video showing sound producing vibrational communication.
Article
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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 ques...
Article
Full-text available
The article (in Norwegian) is about the relationship between human mountain climbing and Zahavi's "Handicap Principle". Is climbing a sophisticated way to advertise individual quality? Yes, it is argued, and there are multiple indicators to this relationship and to why "the handicap principle" may explain the paradoxical - in Darwinian terms - clim...
Article
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Whether the ovarian fluid (OF) represents a selective environment influencing cryptic female choice was tested using an external fertilizer experiencing intense sperm competition and large effects of OF on sperm swimming behavior—the Arctic charr (Salvelinus alpinus). We physically separated the OF from the eggs of reproductively active females and...
Preprint
Full-text available
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 que...
Preprint
Full-text available
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 que...
Article
Full-text available
A mismatch in synchrony between male and female gamete release in external fertilizers 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 competition between males with alternative repr...
Article
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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...
Article
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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 activa...
Article
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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...
Article
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In species exhibiting intersexual conflict over mating, the outcome of female-male sexual encounters may depend on the phenotypic value of traits of either sex that are important for precopulatory behaviors. To explore this prediction, we investigated the relationship between female morphology and male mating success using mate choice experiments i...
Article
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In 2001, Hamilton and Brown proposed a controversial hypothesis of handicap signalling to potential insect parasites as an adaptive explanation for autumn leaf colouration. In subsequent studies there has been little attention to the costs and benefits of early autumnal colour change. Yet, in an observational study by Hagen et al. (2003) it was dem...
Article
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Amplifiers are signals that improve the perception of underlying differences in quality. They are cost free and advantageous to high quality individuals, but disadvantageous to low quality individuals, as poor quality is easier perceived because of the amplifier. For an amplifier to evolve, the average fitness benefit to the high quality individual...
Preprint
Background: Amplifiers are signals that improve the perception of underlying differences in quality. They are cost free and advantageous to high quality individuals, but disadvantageous to low quality individuals, as poor quality is easier perceived because of the amplifier. For an amplifier to evolve, the average fitness benefit to the high qualit...
Preprint
Full-text available
Background: Amplifiers are signals that improve the perception of underlying differences in quality. They are cost free and advantageous to high quality individuals, but disadvantageous to low quality individuals, as poor quality is easier perceived because of the amplifier. For an amplifier to evolve, the average fitness benefit to the high qualit...
Article
Full-text available
Fluctuating asymmetry and averageness is correlated with our perception of beauty in human faces. Yet, whether deviations of centrality in the positioning of the eyes, the nose, and the mouth have different effects on our perception of asymmetry in a holistic human face, is still uncertain. In this study we aimed to test the relative effect of dece...
Article
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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 de...
Article
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This study reports on the importance of the size of the kype (lower jaw) and the adipose fin for establishing and maintaining social dominance in pair-wise interactions among size-matched, reproductively active male Arctic charr Salvelinus alpinus. The size of these traits seems not to have a large influence on establishing dominance, but after 4 d...
Article
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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 spe...
Article
Full-text available
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 Arcti...
Article
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Within a species, different males may display different mating strategies. For example, some males may be selected to invest in attractiveness and mate guarding, whereas others are selected for increased sperm production and sneaky breeding. In systems with a hierarchical structure, dominant males are expected to adopt mate-guarding behaviour and s...
Article
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Hamilton and Zuk proposed that elaborate male secondary sexual characters have evolved through female choice because they reveal information about heritable resistance against parasites. The courtship dance of the threespine stickleback (Gasterosteus aculeatus) is a secondary sexual character that has previously been suggested to be of minor import...
Article
Full-text available
Sexually selected characters may reveal information about individual quality during mate choice. Fin display and sound emitted with the aid of specific drumming muscles are characters described as being of importance in the reproductive behaviour of cod (Gadus morhua L.). We examined whether the mass of drumming muscles or fin size was sexually dim...
Article
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p>Similar defence behaviours were exhibited by a reindeer when experimentally exposed to three different species of tethered, flying parasitic Diptera, Cephenemyia trompe (Modeer), Hypoderma tarandi (L) and Tabanid. Defencive behavioural responses appeared to be related to attack angle, and were not elicited by auditory stimuli. These observations...
Article
1. In reindeer, the variation in fur coloration is higher in semi-domesticated than in wild populations. This difference might result from impacts of natural enemies acting on conspicuously coloured individuals with higher intensity in natural than semi-domesticated populations. 2. While predator pressure is rather similar for wild and semi-domesti...
Article
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A high proportion of female diaptomid copepods mate several times and more often than needed for each clutch production. Our understanding of the adaptive significance of this behaviour and the underlying process is limited. Theory suggests that polyandry may arise when whatever benefits females accrue from multiple mating outweigh the costs or, al...
Article
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Sperm velocity has been shown to be a major determinant of fertilization success of external fertilizers. Yet, sperm velocity varies both within and between ejaculates and only a small number of fast sperm cells within an ejaculate are likely to have the potential of fertilizing the eggs. Having such fast cells should be of special importance durin...
Article
Full-text available
Sexual selection theory predicts that females should choose males that signal viability and quality. However, few studies have found fitness benefits among females mating with highly ornamented males. Here, we use Arctic charr (Salvelinus alpinus), a teleost fish with no parental care, to investigate whether females could gain fitness benefits by m...
Article
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In postcopulatory sexual selection both sperm competition and cryptic female choice are considered to be important selective agents, but their relative importance for male fertilization success has received little attention. We tested whether sperm quality, male spawning coloration, male heterozygosity, and genetic overlap with the female explained...
Article
Full-text available
Studies of ornaments as indicators of individual quality have hitherto focused on males, while studies of female ornaments have been almost absent. However, females within the same species may show large variation in both outer appearance and individual quality. We experimentally examined the effect of an immune challenge on the size of white fring...
Article
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To evaluate whether paternal effects occur on offspring traits, eggs from Arctic charr Salvelinus alpinus were fertilized with similar amount of sperm from size-matched dominant and subordinate males, in a nested design. Eggs fertilized by subordinate fathers resulted in more offspring produced than eggs fertilized by the same amount of sperm from...
Article
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2007: Zebra stripes as an amplifier of individ-ual quality? — Ann. Zool. Fennici 44: 368–376. Amplifiers belong to a class of signals that alone do not indicate an individual's qual-ity, but through design they improve the receiver's ability to assess pre-existing cues and signals. Amplifiers are cost free to produce and maintain, but may yield dis...
Article
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Recent studies have shown that the detrimental effects of anthropogenic pollutants may be worse if organisms are exposed to natural stress. In this study, we examined whether negative effects of organochlorines (OCs) could be influenced by parasites. In two breeding seasons, we administered an anti-helminthic drug to groups of breeding glaucous gul...
Article
Full-text available
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 spe...
Article
Full-text available
Sperm competition models predict that males typically mating in disfavoured roles should be selected to compensate for their disadvantage by investing more into sperm. We studied the effect of rapid changes in social status on ejaculate investments during experimental trials with an externally fertilizing teleost--the Arctic charr (Salvelinus alpin...
Article
Sexual selection predicts that males should signal their viability and health and this is often achieved with elaborate ornaments. However, females' phenotypic and genotypic quality may also be related to ornamental expression. We investigated the association between a female ornamental trait (white wing plumage) and female quality in the common ei...
Article
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Carotenoids are a large group of biochemicals, with similar properties, synthesised by bacteria, fungi, algae and plants. Vertebrates obtain these biologically active pigments through the diet, and they are a disproportionately common component of animal colour signals and play important roles in immune functions and as antioxidants. Carotenoids ar...
Article
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The relationship between parasite infection and breeding ornamentation in an Arctic charr Salvelinus alpinus population was examined. Interrelationships between the intensities of parasites with different dietary transmission routes suggested that hosts were segregated by habitat and diet preferences. That is, intensities of parasites transmitted t...
Article
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Life-history theory predicts that increased current reproductive effort should lead to a fitness cost. This cost of reproduction may be observed as reduced survival or future reproduction, and may be caused by temporal suppression of immune function in stressed or hard-working individuals. In birds, consideration of the costs of incubating eggs has...
Article
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Numbers of studies in externally fertilizing fish species provide evidence for an effect of ovarian fluid on sperm motility characteristics such as duration of forward mobility, velocity or percent motile sperm cells. Yet, because of variations among females in the quality of their ovarian fluid, such effects might differ between individuals. Addit...
Article
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The production of high-quality ejaculates may represent significant costs during male reproduction. Spermatozoa are perceived as nonself by the immune system and are exposed to immunological attacks in the male reproductive tract. Autoimmunity to spermatozoa results in the production of antisperm antibodies that reduce sperm quality and hence ferti...
Article
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Genes of the major histocompatibility complex (MHC) are remarkably polymorphic. Several selection mechanisms have been invoked to account for this diversity, including disassortative mating preferences. In addition, eggs may discriminate between sperm based on MHC. To investigate the effects of MHC-genotype on fertilization success, we obtained mat...
Article
Little evidence of benefits from female mate choice has been found when males provide no parental care or resources. Yet, good genes models of sexual selection suggest that elaborated male sexual characters are reliable signals of mate quality and that the offspring of males with elaborate sexual ornaments will perform better than those of males wi...
Article
Organochlorine contaminants (OCs) are known to affect the immune systems of wildlife, and in this study we assessed the relationship between blood concentration of different OCs and measurements relevant to immune status and function in arctic breeding glaucous gulls (Larus hyperboreus). In 1997 and 2001, we counted white blood cells (heterophils a...
Article
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Life histories are state-dependent, and an individual's reproductive decisions are determined by its available resources and the needs of its offspring. Here we test how a chick's needs for food and protection influence parental decisions in the Antarctic petrel, Thalassoica antarctica, where the parents, due to their long breeding lifespan, are ex...
Article
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For males, the reproductive advantage of joining a lek varies among leks; consequently, males should join the lek yielding the highest fitness. When males experience low reproductive opportunities at one lek, it may pay to move to another. By observing tagged male Arctic charr (Salvelinus alpinus L., 1758) at three different lek sites within one la...
Article
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Immune defences are undoubtedly of great benefit to the host, reducing the impact of infectious organisms. However, mounting immune responses also entails costs, which may be measured by inducing immune responses against artificial infections. We injected common eider (Somateria mollissima) females with three different non-pathogenic antigens, shee...
Article
Full-text available
Hamilton and Brown suggested that bright autumn coloration in trees is an energetically expensive and therefore honest (handicap) signal of defensive commitment against insects. If this is so, one should expect that the intensity of the proposed signal should depend strongly on tree health. However, to the best of our knowledge, the link between vi...
Article
Full-text available
Primary and secondary sex traits are influenced by the same sex hormones, and the expression of secondary sex traits may consequently signal males' capacity for sperm production. Sperm quality may also be influenced by immune activity, as sperm are non-self to the male. Parasite infections alter immune activity and may thus reduce ejaculate quality...
Article
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Immunocompetence may be especially important in long-lived species where infectious organisms may have detrimental effects upon future reproductive value of hosts. The resource demand for immunocompetence may reduce resource availability for reproduction and a trade-off between these traits has therefore been proposed. Capital breeders, such as the...
Article
We explored Hamilton and Brown's autumn signalling hypothesis in mountain birch (Betula pubescens). As predicted by the hypothesis, early autumn colour change (i.e. high degree of autumn colouration in September) was negatively correlated with insect damage the following season. Furthermore, as expected, indices of physiological stress (i.e. leaf f...
Article
Parasites are exploiting their host for the resources required for the parasite's reproduction and survival. The effects of antiparasitic treatment during incubation on body mass and return rate in female common eiders Somateria mollissima were examined in a two year study (1998 and 1999). There was no effect of treatment on nest success, but unsuc...
Article
Full-text available
Ejaculate quality may limit male reproductive success, and consequently, sperm quality is of importance. Spermatozoa are perceived as "non-self" by the immune system and are exposed to immunological attacks in the male reproductive tract. To reduce immunological reactions against their own sperm, males are dependent on the testis being an immunopri...
Article
Summary Non-directional asymmetries (fluctuating asymmetry, FA) from bilateral symmetry in morphological traits have been used as an indicator of environmental stress and may become an important diagnostic tool in environmental sciences, such as ecotoxicology. In this study the relationship was examined between wing feather asymmetry, measured as t...
Article
Full-text available
Secondary sexual characters are assumed to be costly to develop, and the costs of parasite infections and immune suppression are currently an active area of research within sexual selection. We investigated differences in parasitic infections and immunological activity between reproductively active and inactive Arctic charr (Salvelinus alpinus). Sp...
Article
Full-text available
Secondary sexual characters are assumed to be costly to develop, and the costs of parasite infections and immune suppression are currently an active area of research within sexual selection. We investigated differences in parasitic infections and immunological activity between reproductively active and inactive Arctic charr (Salvelinus alpinus). Sp...
Article
The evolution of alternative male mating phenotypes inevitably involves variation in risk or intensity of sperm competition. Males that typically mate in disfavoured roles (i.e. sneakers/parasitic males) are predicted to experience higher magnitudes of sperm competition than males mating in favoured roles (preferred by females/exhibiting mate monop...
Article
Full-text available
One striking aspect of certain types of animal assemblages, for example fish schools or bird flocks, is the level of synchrony and spatial regularity that group members achieve. Although the evolutionary mechanisms leading to the formation of animal aggregations appear to be understood reasonably well, the evolution of spatial regularity and the hi...
Article
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The mating system of cod (Gadus morhua) has been described as promiscuous with few options for exercising mate choice. We, on the other hand, argue that cod fulfil the prerequisites of a conventional lekking mating system. A review of papers on cod mating behaviour suggests that mature males aggregate and possibly defend small territories on the sp...
Article
Full-text available
Ejaculate quality may limit male reproductive success. Sperm cells are immunologically perceived as non-self in the male reproductive tract and may therefore be attacked by the immune system. Males may consequently have to suppress their immune system in order to produce high-quality ejaculates. This suppression may be influenced by the current lev...
Article
Full-text available
An experiment was performed on semiwild reindeer with naturally acquired parasite infections to assess whether measures of serum pepsinogen concentration and fecal egg counts can be used to predict effects of abomasal nematodes on reindeer weight gain and food intake. Food intake and weight gains were lower in infected calves compared with calves w...