Individual variation in the duration of territory occupation by males of the dragonfly Perithemis tenera (Odonata: Libellulidae)

In the dragonfly Perithemis tenera Say, males defend territories around oviposition sites and defense of a site is critical for reproductive success. This study first demonstrated that individual males varied consistently in how long they defended a particular territory within a day (their “tenure”) and in the quality of the sites they defended. I then investigated a number of factors that may have affected territory tenure and may have led to the observed variation among males. Territory occupations that ended “voluntarily” were significantly longer than those that ended because the male was evicted from his territory. For voluntary desertions, tenure duration was unrelated to age, wing length, the amount of time the male fought that day, or site quality. However, tenure durations were longer for males that arrived earlier in the day than for those that arrived later, and consistent differences existed among males in arrival time. Furthermore, tenure durations were longer when males had successfully mated than when they did not mate; available evidence suggests that this pattern may be because mating success causes them to stay longer. Thus, the results suggest that the problem of explaining tenure duration in P. tenera can be largely broken down into identifying factors that affect a male’s likelihood of being evicted and his relative arrival time. Overall, males that defended better sites and males that had longer wings were territorial for fewer total days. Of these two factors, site quality seems to have a larger effect than wing length on the number of days, suggesting that males may incur an increased cost by defending sites that are more attractive to other males

Individual variation in the duration of territory occupation by males of the dragonfly Perithemis tenera (Odonata: Libellulidae)

In the dragonfly Perithemis tenera Say, males defend territories around oviposition sites and defense of a site is critical for reproductive success. This study first demonstrated that individual males varied consistently in how long they defended a particular territory within a day (their “tenure”) and in the quality of the sites they defended. I then investigated a number of factors that may have affected territory tenure and may have led to the observed variation among males. Territory occupations that ended “voluntarily” were significantly longer than those that ended because the male was evicted from his territory. For voluntary desertions, tenure duration was unrelated to age, wing length, the amount of time the male fought that day, or site quality. However, tenure durations were longer for males that arrived earlier in the day than for those that arrived later, and consistent differences existed among males in arrival time. Furthermore, tenure durations were longer when males had successfully mated than when they did not mate; available evidence suggests that this pattern may be because mating success causes them to stay longer. Thus, the results suggest that the problem of explaining tenure duration in P. tenera can be largely broken down into identifying factors that affect a male’s likelihood of being evicted and his relative arrival time. Overall, males that defended better sites and males that had longer wings were territorial for fewer total days. Of these two factors, site quality seems to have a larger effect than wing length on the number of days, suggesting that males may incur an increased cost by defending sites that are more attractive to other males

Factors affecting the spatial distribution of oviposition sites for tandem black saddlebags dragonflies (Odonata: Libellulidae)

Oviposition site location may be affected by (1) factors influencing the costs and benefits to the offspring (e.g., resource availability, competition, predation risk) and (2) factors influencing the costs and benefits to the female (e.g., predation risk or mate ha- rassment). In cases in which both the male and female are involved in locating a site, costs and benefits may differ for each parent and the resulting oviposition site location may represent the outcome of selection pressures on one or both of them. We studied oviposi- tion behavior in the black saddlebags dragonfly (Tramea lacerata Hagen), a species in which the male and female typically remain to- gether (i.e., in tandem) while traveling among potential oviposition locations. Oviposition sites tended to be away from pond shoreline at the outer edge of the vegetation on the water’s surface. We found that tandems distributed their oviposition locations widely around the pond, and interactions with other dragonflies (typically other T. lacerata, either territorial males or tandems) led to a larger distance between consecutive oviposition locations. Interestingly, for 10% of the tandems, the female became separated from the male and oviposited solitarily multiple times. These solitary females spent significantly less time and traveled significantly smaller distances between successive oviposition sites than when in tandem. Our results indicate that while some aspects of oviposition behavior and site selection may be consistent between the male and female (e.g., the characteristics that make a site suitable), other aspects, such as the distribution of sites, may be a result of a differing benefits and costs for the two sexes, perhaps as a consequence of potential sperm competition

Proximate constraints on intruder detection in the dragonfly Perithemis tenera (Odonata: Libellulidae): effects of angle of approach and background

The implications of insects’ vision for territorial defense have been relatively little studied in the field. In the dragonfly Perithemis tenera Say we investigated whether either the angle at which an intruder was viewed by a territorial resident or the background against which it was viewed affected the detection of that intruder. Residents detected intruders at a greater distance if the intruders were directly in front of them; they also detected more intruders in front of them than from other angles. Intruders viewed against distant vegetation were detected more readily than were intruders against near vegetation. Residents detected more intruders viewed against distant vegetation than viewed against near vegetation; however, more intruders than expected were detected against near vegetation. The probability of detecting intruders depends on the angle at which they are viewed and the background behind them. Hence, there may be selection on territorial residents to adjust their orientation and space use to enhance their view of their territory and intruders

Proximate constraints on intruder detection in the dragonfly Perithemis tenera (Odonata: Libellulidae): effects of angle of approach and background

The implications of insects’ vision for territorial defense have been relatively little studied in the field. In the dragonfly Perithemis tenera Say we investigated whether either the angle at which an intruder was viewed by a territorial resident or the background against which it was viewed affected the detection of that intruder. Residents detected intruders at a greater distance if the intruders were directly in front of them; they also detected more intruders in front of them than from other angles. Intruders viewed against distant vegetation were detected more readily than were intruders against near vegetation. Residents detected more intruders viewed against distant vegetation than viewed against near vegetation; however, more intruders than expected were detected against near vegetation. The probability of detecting intruders depends on the angle at which they are viewed and the background behind them. Hence, there may be selection on territorial residents to adjust their orientation and space use to enhance their view of their territory and intruders