Sex ratio estimation and survival analysis for Orthetrum coerulescens (Odonata, Libellulidae)

Abstract

There is controversy over whether uneven sex ratios observed in mature dragonfly populations are a mere artifact resulting from the higher observability of males. Previous studies have at best made indirect inference about sex ratios by analysis of survival or recapture rates. Here, we obtain direct estimates of sex ratio from capture–recapture data based on the Cormack–Jolly–Seber model. We studied Orthetrum coerulescens (Fabricius, 1798) at three sites in the Swiss Jura Mountains over an entire activity period. Recapture rates per 5-day interval were 3.5 times greater for males (0.67, SE 0.02) than for females (0.19, SE 0.02). At two sites, recapture rate increased over the season for males and was constant for females, and at one site it decreased with precipitation for both sexes. In addition, recapture rate was higher with higher temperature for males only. We found no evidence for higher male survival rates in any population. Survival per 5-day interval for both sexes was estimated to be 0.77 (95% CI 0.75–0.79) without significant site-or time-specific variation. There were clear effects of temperature (positive) and precipitation (negative) on survival rate at two sites. Direct estimates of sex ratios were not significantly different from 1 for any time interval. Hence, the observed male-biased sex ratio in adult O. coerulescens was an artifact resulting from the better observability of males. The method presented in this paper is applicable to sex ratio estimation in any kind of animal.

Sex ratio, survival, and recapture rate in a Cuban population of the damselfly Hypolestes trinitatis (Odonata: Megapodagrionidae)

“…Similar results were observed in Coenagrion puella and Orthetrum coerulescens where males outnumbered females 3.5 and 1.6 times, respectively, and also were almost four times more likely to be recaptured than females (Anholt et al 2001;Kéry and Juillerat 2004). Differential habitat use by the different sexes could explain the recapture rates estimated for H. trinitatis, since males spend more time in visible places than females.…”

“…Modern Cormack-Jolly-Seber mark-recapture methods (CJS) allow for the independent assessment of recapture and survival rates (Lebreton et al 1992). The application of these methods has led to the general conclusion that, at least in some species, males have higher recapture rates than females, while survival rates are similar for both sexes (Kéry and Juillerat 2004). However, this argument cannot be used as a general explanation, since a lower survival rate of females during the pre-reproductive period seems to be the cause of the male-biased sex ratio in some populations, where survival and recapture rates are similar in both sexes at the reproductive period (Anholt 1997;Stoks 2001b).…”

Ecological factors limiting the distributions and abundances of Odonata

“…Mortality rates of adults are quite high for most species, with most individuals living on average only a few days or weeks after they metamorphose into adults (Fincke 1982(Fincke , 1986(Fincke , 1994Anholt 1991Anholt , 1997Córdoba-Aguilar 1994;Bennett and Mill 1995b;Cordero 1995;Marden and Rowan 2000;Beukema 2002;Thompson and Fincke 2002). Also, because of the differences in breeding tactics of males and females, females sometimes have higher mortality rates than males (Bennett and Mill 1995b;Anholt 1997;Marden and Rowan 2000;Beukema 2002;Kery and Juillerat 2004;Córdoba-Aguilar et al 2006). Females of most species spend considerable time away from water bodies to forage and presumably to reduce harassment by males, but at the expense of greater mortality (Anholt 1997;Marden and Rowan 2000;Anholt et al 2001).…”

Adult Movement Pattern and Habitat Preferences of the Maghribian EndemicGomphus lucasii(Odonata: Gomphidae)

“…The resighting rate at the watercourse was very small (8.13%) with respect to other dragonflies like Somatochlora alpestris Selys (10.2%), Leucorrhinia hudsonica Selys (31%), and Orthetrum coerulescens Selys (40–55%) ( Knaus and Wildermuth 2002 , Kéry and Juillerat 2004 , Chin and Taylor 2009 ). Moreover, less than 1% of G. lucasii Selys tenerals (only males) were resighted as mature at the water and an even smaller proportion was recorded at their emergence site (philopatry).…”