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  • 1.
    Bergman, Martin
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Fjärilar, revirslagsmål och parningsframgång2009In: Schedula Ranae, no 1, p. 12-13Article in journal (Other (popular science, discussion, etc.))
  • 2.
    Bergman, Martin
    Stockholm University, Faculty of Science, Department of Zoology.
    The evolution of territoriality in butterflies2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Competition over mating opportunities is a conspicuous characteristic of animal behaviour. In many butterfly species the males establish territories in places advantageous for encountering females. This thesis addresses questions about how territoriality has evolved and is maintained in butterflies. The studies have been conducted using the speckled wood butterfly, Pararge aegeria, as a model species. Males of P. aegeria are found in sunspots on the forest floor (paper I-V), on the lookout for females visiting the sunspots. However, males are only found in sunspots above a certain size (paper III). This behavior is maintained by a mating success advantage, where using large sunspots instead of small sunspots as perching areas generates a higher reproductive output (paper I). The mating success asymmetry is not explained by female choice or by a female preference for large sunspots per se (paper I, V), but rather the large sunspot facilitates visual performance of perching males and improves flight pursuit and interception of females (paper III). Winners of territorial contests gain sole ownership of large sunspot territories, while losers search for a new suitable sunspot territory (paper I, II & IV) or use smaller, suboptimal sunspots as perching sites (paper II). Territorial contests between P. aegeria males are not settled due to an obvious morphological/physiological asymmetry (paper I). Rather, variation in resource value and motivational asymmetries are important for settling contests (paper IV). A majority of male-female interactions (paper V) and matings (paper I) are initiated by a perching male detecting and intercepting a flying female. Furthermore, females can affect their chances of being detected by a perching male by behaving more conspicuously (paper V). This thesis highlights the role of female behaviour, variation in resource value and motivation asymmetries to understand the evolution of territoriality in butterflies.

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  • 3.
    Bergman, Martin
    Stockholm University, Faculty of Science, Department of Zoology. Zoologisk ekologi.
    Visual mate detection and mating success by resident and nonresident males in a territorial woodland butterfly, Pararge aegeria.2008Licentiate thesis, monograph (Other academic)
  • 4.
    Bergman, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Gotthard, Karl
    Stockholm University, Faculty of Science, Department of Zoology.
    Berger, David
    Stockholm University, Faculty of Science, Department of Zoology.
    Olofsson, Martin
    Stockholm University, Faculty of Science, Department of Zoology.
    Kemp, Darrell J.
    James Cook University, Australia.
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology.
    Mating success of resident versus non-resident males in a territorial butterfly2007In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 274, no 1618, p. 1659-1665Article in journal (Refereed)
    Abstract [en]

    Male–male competition over territorial ownership suggests that winning is associated with considerable benefits. In the speckled wood butterfly, Pararge aegeria, males fight over sunspot territories on the forest floor; winners gain sole residency of a sunspot, whereas losers patrol the forest in search of females. It is currently not known whether residents experience greater mating success than nonresidents, or whether mating success is contingent on environmental conditions. Here we performed an experiment in which virgin females of P. aegeria were allowed to choose between a resident and a nonresident male in a large enclosure containing one territorial sunspot. Resident males achieved approximately twice as many matings as non-residents, primarily because matings were most often preceded by a female being discovered when flying through a sunspot. There was no evidence that territorial residents were more attractive per se, with females seen to reject them as often as nonresidents. Furthermore, in the cases where females were discovered outside of the sunspot, they were just as likely to mate with non-residents as residents. We hypothesize that the proximate advantage of territory ownership is that light conditions in a large sunspot greatly increase the male’s ability to detect and intercept passing receptive females.

  • 5.
    Bergman, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Gotthard, Karl
    Stockholm University, Faculty of Science, Department of Zoology.
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology.
    Mate acquisition by females in a butterfly: the effects of mating status and age on female mate-locating behaviour2011In: Animal Behaviour, ISSN 0003-3472, E-ISSN 1095-8282, Vol. 81, no 1, p. 225-229Article in journal (Refereed)
    Abstract [en]

    In most species, female reproductive success is determined by realized fecundity, which depends on the amount of female reproductive reserves and the availability of time for oviposition. Consequently, selection is likely to favour behaviour in virgin females that increases the likelihood of encountering males and thereby minimizing time without sperm. We used the speckled wood butterfly, Pararge aegeria, to test the hypothesis that virgin females increase the probability of encountering males by behaving more conspicuously. We also tested for an effect of age on behaviour, with the prediction that females behave more conspicuously if they remain unmated for a longer period. To do this we conducted controlled behavioural studies in large outdoor cages, comparing the behaviour of young and old, virgin and mated, females. We also assessed the time it took for a male to discover virgin versus mated females. Our results show an effect of age and mating status: old virgin females behaved more conspicuously than young virgin females and mated females, and spent more time in flight and performed more individual flights. Males also discovered virgin females faster than mated females. Furthermore, virgin females did not specifically locate the large sunspot, where perching males are found. Hence, females of P. aegeria adjust their behaviour in accordance with mating status and age, making them more likely to encounter a male and thereby maximize their reproductive success. This study underlines the importance of taking the distribution and behaviour of receptive females into account when studying mate-locating behaviour.

  • 6.
    Bergman, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Olofsson, Martin
    Stockholm University, Faculty of Science, Department of Zoology.
    Wiklund, Christer
    Contest outcome in a territorial butterfly: the role of motivation2010In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 277, no 1696, p. 3027-3033Article in journal (Refereed)
    Abstract [en]

    In many butterfly species, males compete over areas advantageous for encountering females. Rules for contest settlement are, however, largely unknown and neither morphological nor physiological traits can reliably predict the contest outcome. Here, we test the hypothesis that contests are settled in accordance with a motivation asymmetry. We staged contests between males of Pararge aegeria and after removing the resident, the non-resident was allowed (i) either to interact with a non-receptive female for 30 min (n = 30) or (ii) to spend 30 min alone in the cage (n = 30), after which the initial resident was reintroduced. The results show that males that had interacted with a female had a higher probability of becoming dominant and reversing contest outcome. Moreover, males that were faster to take over a vacant territory when the resident was removed were more likely to become dominant. Here, we show for the first time, to our knowledge, that frequent encounters with a mated female can increase male motivation to persist in a territorial contest in a butterfly. Further, we suggest that variation in intrinsic motivation reflects male eagerness to take over vacant territory. This study indicates that variation in resource value and motivational asymmetries are important for settling contests in butterflies.

  • 7.
    Bergman, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology.
    Differences in mate location behaviours between residents and nonresidents in a territorial butterfly2009In: Animal Behaviour, ISSN 0003-3472, E-ISSN 1095-8282, ISSN 0003-3472, Vol. 78, no 5, p. 1161-1167Article in journal (Refereed)
    Abstract [en]

    Mate location strategies vary between species. Among butterflies two strategies are recognized: 'patrolling' males spend their life on the wing searching for females and 'perching' males stay at a specific site waiting to intercept passing females. In the speckled wood butterfly, Pararge aegeria, two alternative male strategies have been described: dominant males adopt a perching strategy monopolizing large sunspots on the forest floor, and subdominant males adopt a patrolling strategy. However, comparative analyses have shown that body design differs between perching and patrolling species, hence constraining opportunity for within-species variation in mate location strategy. We tested whether males differ in their propensity to adopt perching or patrolling behaviour by recording time spent flying during 30 min when alone in a large cage with only one large sunspot and many smaller ones, and whether subdominant males adopt a patrolling strategy by allowing dyads of males to interact in the cage for 60 min and recording the same behaviours again. All males adopted perching behaviour when alone, and subdominant males in dyads spent only a short time in extended flights after losing contests over territory ownership, soon returning to a perching strategy and making the best of a bad job from the vantage point of a small sunspot. We argue that previous descriptions of subdominant male P. aegeria adopting a patrolling strategy are based on too short observation periods, and have mistaken males in temporary transit for males adopting patrolling behaviour.

  • 8.
    Bergman, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Erratum to: Differences in mate location behaviours between residents and nonresidents in a territorial butterfly2010In: Animal Behaviour, ISSN 0003-3472, E-ISSN 1095-8282, Vol. 80, p. 593-Article in journal (Other (popular science, discussion, etc.))
  • 9.
    Bergman, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Territorialitet hos dagfjärilar2011In: Fauna & Flora, Vol. 106, no 1, p. 20-25Article in journal (Other (popular science, discussion, etc.))
  • 10.
    Bergman, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology.
    Visual mate detection and mate flight pursuit in relation to sunspot size in a woodland territorial butterfly2009In: Animal Behaviour, ISSN 0003-3472, E-ISSN 1095-8282, ISSN 0003-3472, Vol. 78, no 1, p. 17-23Article in journal (Refereed)
    Abstract [en]

    Territory residency is associated with considerable benefits. In the speckled wood butterfly, Pararge aegeria, males fight over ownership of large sunspots in open forest habitats; winners become sunspot residents, and losers become nonterritorial and sit and wait for females in small sunspots. A previous study has shown that residents have higher mating success than nonterritorial males, although females are not more attracted to territorial males or sunspot territories per se. Here we tested the hypotheses (1) that the higher success of resident males is caused by visual mate detection being more efficient in a large than in a small sunspot, and (2) that only sunspots above a certain size are defended as territories. Field assessment of territorial sunspot size showed that defended sunspots were significantly larger than 'average sunspots' on the forest floor. Experimental tests of male ability to detect visually a model butterfly passing through a sunspot showed that males were more successful in pursuing and intercepting a passing model when. own a longer distance in the sunspot. Hence, we conclude that light conditions and associated visual mate detection and ability to complete mate flight pursuit can explain why P. aegeria males defend territories in large sunspots in forest habitats.

  • 11.
    Friberg, Magne
    et al.
    Stockholm University, Faculty of Science, Department of Zoology. Zoologisk ekologi.
    Bergman, Martin
    Stockholm University, Faculty of Science, Department of Zoology. Zoologisk ekologi.
    Wahlberg, Niklas
    Kullberg, Jakkoo
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology. Zoologisk ekologi.
    Niche separation in space and time between two sympatric sister species—a case of ecological pleiotropy2008In: Evolutionary Ecology, ISSN 0269-7653Article in journal (Refereed)
    Abstract [en]

    Abstract We investigate the niche separation in space and time between the Palearctic sister species Leptidea sinapis and L. reali (Lepidoptera, Pieridae) in central Sweden. Using field sampling, we show that L. reali is a habitat specialist confined to meadows, whereas L. sinapis is a habitat generalist also inhabiting forests. This difference in habitat utilization was corroborated by experimental release of laboratory-reared L. sinapis and L. reali in two adjacent forest and meadow habitats during their natural flight period; virtually all recaptured L. reali that were released in the forest were later caught in the meadow, whereas L. sinapis shifted equally often from meadow to forest as in the opposite direction. In the field, both species fly in May–June, but L. reali appears on average a week earlier in spring and has a substantial second generation in July, whereas L. sinapis is practically univoltine. When overwintered pupae were incubated under identical conditions in the laboratory, females did, however, not differ in phenology, and L. sinapis males actually emerged earlier than L. reali males. When larvae were reared at 23°C on the host plant Lotus corniculatus at a range of daylengths, both species produced a substantial proportion of directly developing individuals at an 18.5 h daylength or longer. When reared at 23°C and a 22 h daylength, L. reali showed an overall higher propensity to develop directly than L. sinapis on plant species originating from both the meadow and the forest habitat. Both Leptidea species showed a lower propensity to enter direct development on forest associated plants than on meadow associated plants. Hence, we suggest that the difference in phenology and voltinism between L. sinapis and L. reali is largely the result of environmentally implemented ecological pleiotropic effects caused by the between-species difference in habitat preference.

  • 12.
    Gotthard, Karl
    et al.
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Berger, David
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Bergman, Martin
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Merilata, Sami
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    The evolution of alternative morphs: density-dependent determination of larval colour dimorphism in a butterfly2009In: Biological Journal of the Linnean Society, ISSN 0024-4066, E-ISSN 1095-8312, Vol. 98, no 2, p. 256-266Article in journal (Refereed)
    Abstract [en]

    Understanding the ultimate causes for the presence of polymorphisms within populations requires knowledge of how the expression of discrete morphs is regulated. In the present study, we explored the determination mechanism of a colour dimorphism in larvae of the butterfly Pararge xiphia (Satyrinae: Nymphalidae) with the ultimate aim of understanding its potential adaptive value. Last-instar larvae of P. xiphia develop into either a green or a brown morph, although all individuals are invariably green during the preceding three instars. A series of laboratory experiments reveal that morph development is strongly environmentally dependent and not the result of alternative alleles at one locus. Photoperiod, temperature, and in particular larval density, all influenced morph determination. The strong effect of a high larval density in inducing the brown morph parallels other known cases of density-dependent melanization in Lepidopteran larvae. Because melanization is often correlated with increased immune function, this type of determination mechanism is expected to be adaptive. However, the ecology and behaviour of P. xiphia larvae suggests that increased camouflage under high-density conditions may be an additional adaptive explanation. We conclude that the colour dimorphism of P. xiphia larvae is determined by a developmental threshold that is influenced both by heredity and by environmental conditions, and that selection for increased immune function and camouflage under high-density conditions may be responsible for maintaining the dimorphism. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 256–266.

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