The effect of male maturity on intra- and interspecific aggression by the , simplicicollis. Payton Beck and Wade B. Worthen Biology Department, Furman University, Greenville, SC.

ABSTRACT RESULTS AND DISCUSSION

Many male defend a territory to attract mates, and they attack other males that enter. Fitness theory 1. Maturity affected approach rates between conspecifics, but not Table 1. Repeat-measure ANOVA assessing the direct and interactive effects of predicts that territorial males should preferentially attack mature males of their own species (‘conspecifics’) that attack rates. Immature pondhawk decoys were approached significantly decoy development (mature vs. immature) and focal development (mature vs. represent a real threat to their reproductive success. Morphological differences between species, between sexes more than mature pondhawk decoys (ANOVA, ‘Approaches’, Decoy immature) on the mean number of approaches and attacks made in 30 minutes. of the same species, and between mature and immature males of the same species may be adaptations to Development effect, p = 0.01, Table 1). On average, immature decoys were Approaches Attacks reduce the costs of misplaced aggression. However, young reproductive males may benefit by maintaining a approached nearly twice as often as mature decoys (Fig. 3). In addition, Effect F p F p juvenile female-like morphology (‘female mimicry’) to enter a mature male’s territory and mate surreptitiously immature focal males approached decoys significantly more than mature with females. We tested the effects of differences in inter- and intraspecific morphology on aggression by male focal males (ANOVA, ‘Approaches’, Focal Development effect, p = 0.05, Decoy Development 7.19 0.01 0.60 ns Eastern pondhawks (Erythemis simplicicollis), which change from a female-like green to powder blue as they Table 1). On average, immature males approached decoys twice as much Focal Development 4.12 0.05 0.02 ns mature. We placed pairs of dead male decoys (mature vs. immature and conspecific vs. heterospecific) in the as mature males. There were no significant effects on attacks rates, Interaction (DD x FD) 0.51 ns 1.05 ns territory of focal E. simplicicollis males and counted the number of approaches and attacks on each decoy. Focal however (ANOVA, ‘Attacks’, all p > 0.05, ns, Table 1). males attacked conspecific decoys more than heterospecific decoys, as predicted by fitness theory. Immature E. simplicicollis decoys were approached more than mature decoys (suggesting intraspecific discrimination), but A) Approaches B) Attacks they were attacked to the same degree. Developmental changes in E. simplicicollis morphology may simply be a spurious consequence of other developmental changes (hormonal?), and have no adaptive value, itself.

INTRODUCTION • In most dragonfly species, males establish territories to acquire mates; they attack intruding males and attempt to drive them from the area (Otte & Joern, 1975). • Selection should favor males that only spend energy attacking mature males of their own species; attacking immatures and heterospecifics that do not compete for mates wastes energy (Thornhill & Alcock, 1983). • Selection should favor morphological divergence between species, between sexes of a species, and between mature and immature males to facilitate these energetically efficient choices (Corbet 1999). • In some , immature males “cheat” this adaptive system. Males become sexually mature while maintaining an immature morphology that mimics females. They enter the territories of dominant males ‘in (N = 27)(N = 15) (N =(N 15) = 27) (N = 15) (N = 27) disguise’, and surreptitiously mate with females (Hakkarainen et al. 1993, Shine et al. 2001). • Eastern pondhawks (Erythemis simplicicollis) dragonflies are sexually dimorphic; females are green and adult Fig. 3. The mean (± 1 se) number of a) approaches and b) attacks made by immature and mature focal Erythemis simplicicollis males to mature and immature E. simplicicollis decoys. males are powder blue (Fig. 1). Immature males are green, and they change to blue over the course of 2-3 weeks. However, they are sexually mature while expressing a green female-like morphology (McVey 1985). 2. Conspecifics were attacked at a higher rate than heterospecifics, Table 2. Repeat-measure ANOVA assessing the direct and interactive effects of • We wanted to know whether aggression by and towards Eastern pondhawk males varied as a function of male decoy species (P. longipennis vs. E. simplicicollis) and focal development (mature morphology, and whether they discriminated between species and between mature and immature males. We but focal maturity had no effect on interspecific discrimination. vs. immature) on the mean number of approaches and attacks made in 30 minutes. conducted choice experiments, placing paired, mounted, dead decoys into the territories of mature and Conspecific and heterospecific decoys were approached at the same rate by both mature and immature focal males (ANOVA, ‘Approaches’, p > 0.05, immature males, and compared the number of approaches and attacks made on these decoys. Approaches Attacks ns, Table 2, Fig. 4a). However, both immature and mature focal males • We hypothesized that conspecifics should be attacked more frequently than heterospecifics, and that mature Effect F p F p conspecific male decoys should be attacked more frequently than immature conspecifics. attacked conspecific mature pondhawk (E. simplicicollis) decoys significantly more than heterospecific blue dasher (P. longipennis) decoys Decoy Species 18.38 ns 18.38 0.001 (ANOVA, ‘Attacks’, decoy species effect, p = 0.05, Table 2). On average, Focal Development 1.11 ns 2.61 ns conspecifics were attacked at three times the rate of heterospecifics (Fig. Interaction (DS x FD) 0.89 ns 0.01 ns MATERIALS and METHODS 4b).

• This study was conducted at two sites in Greenville Co., SC: Swan Lake A) Approaches B) Attacks on the campus of Furman University, Greenville, SC, and Pleasant Ridge County Park in Cleveland, SC. P. longipennis E. simplicicollis P. longipennis E. simplicicollis • Immature and mature male Eastern pondhawks (Erythemis simplicicollis) Decoy Decoy Decoy Decoy and mature male blue dashers (Pachydiplax longipennis) were collected, killed, painted, and glued to dowels as decoys (Worthen 2010). • A pair of decoys (immature/mature or mature/dasher) were presented to a focal territorial male using a two-arm apparatus that centered the focal male between the decoys (Fig. 2). We recorded the number of approaches and attacks made on each decoy by the focal in 15 minutes, and then reversed their position and recorded encounters for another 15 minutes to control for environmental differences between positions. Fig. 2. Two-arm apparatus in position, with the • Repeat measure ANOVA were used to compare the direct and interactive decoys (top: P. longipennis, bottom: mature E. effects of focal development and decoy type on the mean number of simplicicollis male) on either side of a mature (N = 23) (N = 32) (N = 23) (N = 32) approaches and attacks in the total 30 minute interval. E. simplicicollis focal male (yellow circle). Fig. 3. The mean (± 1 se) number of a) approaches and b) attacks made by immature and mature focal Erythemis simplicicollis males to P. longipennis and mature E.simplicicollis decoys. a. b. c. d. CONCLUSIONS LITERATURE CITED Corbet PH (1999) Dragonflies: behavior and ecology of .Cornell Univ. Press, Ithaca, NY. p. 464. • As predicted by fitness theory, conspecific decoys were attacked more Hakkarainen H., Korpimäki E., Huhta E. and Palokangas P. (1993) Delayed maturation in plumage colour: evidence for the female- a. b. mimicry hypothesis in the Kestrel. Behavioral Ecology and Sociobiology, 33:247-251. than heterospecific decoys. McVey ME. (1985) Rates of color maturation in relation to age, diet, and temperature in male Erythemis simplicicollis (Say) (Anisoptera: ). Odonatologica 14(2):101-114. • Immature decoys were investigated more often than mature decoys, Shine R, Phillips B, Wayne H, LeMaster M, & Mason RT. (2001) Benefits of female mimicry in snakes. Nature. 414:267. Thornhill,R.,& Alcock, J. (1983).The evolution of mating systems. HarvardUniversity Press, Cambridge, MA. suggesting intraspecific discrimination based on morphology. Worthen WB (2010) Flying dragons: A colorful field experiment in resource partitioning. American Biology Teacher 72:432-436. • However, contrary to the ‘female-mimicry hypothesis’ there was no significant difference in the rate of attacks on mature and immature decoys. ACKNOWLEDGEMENTS • Change in male morphology of E. simplicicollis may simply be a This research was supported by a Fig. 1. a) Erythemis simplicicollis mature male with powder-blue thorax and abdomen, b) E. simplicicollis immature male with green thorax and anterior spurious consequence of other developmental changes (hormonal?), Furman Advantage research grant abdomen, c) E. simplicicollis female, with green thorax and green and black striped abdomen, and d) Pachydiplax longipennis mature male. and have no adaptive value, itself. to PB, from Furman University.