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The evolution of territoriality in butterflies
Stockholm University, Faculty of Science, Department of Zoology.
2011 (English)Doctoral 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.

Place, publisher, year, edition, pages
Stockholm: Department of Zoology, Stockholm University , 2011. , 27 p.
Keyword [en]
territoriality, Lepidoptera, sexual selection, mating success, mate locating behaviour, resource-holding potential, motivation, courtship solicitation
National Category
Natural Sciences
Research subject
Animal Ecology
Identifiers
URN: urn:nbn:se:su:diva-54668ISBN: 978-91-7447-182-3 (print)OAI: oai:DiVA.org:su-54668DiVA: diva2:396653
Public defence
2011-03-18, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2011-02-25 Created: 2011-02-10 Last updated: 2011-02-17Bibliographically approved
List of papers
1. Mating success of resident versus non-resident males in a territorial butterfly
Open this publication in new window or tab >>Mating success of resident versus non-resident males in a territorial butterfly
Show others...
2007 (English)In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 274, no 1618, 1659-1665 p.Article in journal (Refereed) Published
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.

Keyword
Lepidoptera; contest success; mate locating behaviour; female choice; mate choice; butterfly vision
National Category
Ecology Ecology
Identifiers
urn:nbn:se:su:diva-20780 (URN)doi:10.1098/rspb.2007.0311 (DOI)000247315400014 ()
Available from: 2007-11-30 Created: 2007-11-30 Last updated: 2014-10-28Bibliographically approved
2. Differences in mate location behaviours between residents and nonresidents in a territorial butterfly
Open this publication in new window or tab >>Differences in mate location behaviours between residents and nonresidents in a territorial butterfly
2009 (English)In: Animal Behaviour, ISSN 0003-3472, E-ISSN 1095-8282, ISSN 0003-3472, Vol. 78, no 5, 1161-1167 p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
London, England: ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD, 2009
Keyword
alternative strategy; Lepidoptera; Pararge aegeria; patrolling; perching; satellite strategy; sexual selection; speckled wood butterfly
National Category
Ecology
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-33228 (URN)10.1016/j.anbehav.2009.08.003 (DOI)000271099200019 ()
Available from: 2009-12-21 Created: 2009-12-21 Last updated: 2014-10-13Bibliographically approved
3. Visual mate detection and mate flight pursuit in relation to sunspot size in a woodland territorial butterfly
Open this publication in new window or tab >>Visual mate detection and mate flight pursuit in relation to sunspot size in a woodland territorial butterfly
2009 (English)In: Animal Behaviour, ISSN 0003-3472, E-ISSN 1095-8282, ISSN 0003-3472, Vol. 78, no 1, 17-23 p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
London, England: ACADEMIC PRESS LTD- ELSEVIER SCIENCE LT, 2009
Keyword
butterfly vision; Lepidoptera; light gap; mate searching; Pararge aegeria; sexual selection; speckled wood butterfly; territoriality
National Category
Ecology
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-33234 (URN)10.1016/j.anbehav.2009.02.005 (DOI)000267154000005 ()
Available from: 2009-12-21 Created: 2009-12-21 Last updated: 2014-10-13Bibliographically approved
4. Contest outcome in a territorial butterfly: the role of motivation
Open this publication in new window or tab >>Contest outcome in a territorial butterfly: the role of motivation
2010 (English)In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 277, no 1696, 3027-3033 p.Article in journal (Refereed) Published
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.

Keyword
sexual selection, Lepidoptera, mate locating behaviour, loser effect, resource-holding potential
National Category
Zoology
Identifiers
urn:nbn:se:su:diva-49448 (URN)10.1098/rspb.2010.0646 (DOI)000281312400018 ()
Note
authorCount :3Available from: 2010-12-17 Created: 2010-12-14 Last updated: 2014-10-28Bibliographically approved
5. Mate acquisition by females in a butterfly: the effects of mating status and age on female mate-locating behaviour
Open this publication in new window or tab >>Mate acquisition by females in a butterfly: the effects of mating status and age on female mate-locating behaviour
2011 (English)In: Animal Behaviour, ISSN 0003-3472, E-ISSN 1095-8282, Vol. 81, no 1, 225-229 p.Article in journal (Refereed) Published
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.

Keyword
courtship solicitation, Lepidoptera, life history, Pararge aegeria, sexual selection, speckled wood butterfly, territoriality
National Category
Natural Sciences
Research subject
Zoology
Identifiers
urn:nbn:se:su:diva-54265 (URN)10.1016/j.anbehav.2010.10.009 (DOI)000285412900029 ()
Available from: 2011-01-27 Created: 2011-01-27 Last updated: 2014-10-28Bibliographically approved

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