Male aggression in the banded demoiselle damselfly Calopteryx splendens

Abstract

Abstract
The banded demoiselle damselfly Calopteryx splendens is a sexually dimorphic insect that is currently moving north, into new geographic areas of Fennoscandia. In doing so, this damselfly species is coming into contact with naïve populations of a closely related conspecific: the beautiful demoiselle damselfly, Calopteryx virgo. This study revealed that male C. splendens’ aggression appears to be influenced by both age and experience; however, there was no evidence of learned species recognition in outdoor cage experiments. Teneral (immature) and mature males responded at significantly different strengths to intruding males, indicating that the age at which they were caught affected the development of territorial responses. Whether C. splendens came from allopatric or sympatric populations did not statistically significantly influence their response to intruding males. Average male aggression levels were positively correlated with male survival rate, although the causal factor behind this correlation is unknown. Moreover, C. splendens survived longer in the cages than C. virgo revealing interspecific differences in longevity, and C. splendens individuals from an allopatric population survived significantly longer compared to C. splendens individuals from a sympatric population. This result might indicate that C. splendens suffer from shorter life span in the presence of the heterospecific competitor C. virgo. Male C. splendens responded differently to female con- and heterospecific individuals depending on the male’s origin, suggesting that field experience with the opposite sex and species was important in determining male mate preferences towards females. Finally, cage density had no significant impact on male C. splendens’ aggression towards conspecifics.

Abstract

Popular science summary

As the climate warms and species move northwards, some species encounter populations of a similar species. In this case, the banded demoiselle damselfly Calopteryx splendens is moving north, further into Fennoscandia than it has been known to go before, and is meeting populations of the beautiful demoiselle damselfly Calopteryx virgo. Males of both species set up and defend territories along the banks of freshwater streams. If these two species are to co-exist, one or both should theoretically be able to discriminate between individuals of their own and of the other species to avoid hybridising. This project aimed to understand whether learning or genetics determine how a male C. splendens responds to intruding males of his own species and of the other species, C. virgo. The response to females of both species was also tested.

The work was carried out in 27m3 mesh cages at Stensoffa field station, in southern Sweden and 2 nearby sites were used to capture the insects. At one site, only C. splendens was present, at the other both C. splendens and C. virgo were present. One male and one female of each species were tethered to a stick of roughly 1.5 m in length and were then presented to free-flying, but caged, males. A four-point scale was used to record the reaction from the free-flying male. A threat response is illustrated in the figure opposite. The effect of cage density on aggression in C. splendens was tested by keeping males and females in cages with a ratio of 2 males to 1 female. Low density cages had a maximum of six individuals; high density cages had a maximum of twelve.

In this study, mature individuals of neither species were more or less aggressive towards males of their own of the other species. This finding contrasts with previous field studies which found that C. virgo males show stronger species recognition than C. splendens males (Svensson, et al. 2007). C. splendens males caught as sexually mature individuals responded more aggressively towards intruders than did those caught as sexually immature. This is not surprising as sexually immature individuals are not yet competing for territories. Interestingly, this species appears to go against the classic trade-off hypothesis of “live fast, die young” as the longer an individual lived, the more aggressive it appeared to become. Sexually immature male C. splendens responded less aggressively towards females of either species than did sexually mature male C. splendens. Males from populations where both species are present responded more strongly to females of their own species than to females of the other species. This supports the hypothesis that age or experience is important in determining the response to intruders. Cage density did not affect the average aggression levels displayed by male C. splendens. Origin also had no significant impact on the aggression level therefore hinting at a possible genetic component in the response to intruders. Individuals showed repeatability in their response to different intruders indicating a possible genetic component, but further study would be needed to confirm this. In conclusion, it is likely that both genetics and experience play a role in determining the reaction of male C. splendens’ to intruders and that experience is necessary in fixing the genetic response.

Advisor: Erik Svensson
Master´s Degree Project 30 credits in Nature Conservation 2013/2014
Department of Biology, Lund University

• author: Hutchison, Lorna
• supervisor: Erik Svensson
• organization: Degree Projects in Biology
• course: BIOM24 20131
• year: 2014
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 4360319
• date added to LUP: 2014-03-18 13:52:03
• date last changed: 2014-03-18 13:52:03