The effects of phenology, time constraints and latitude of origin on damselfy life historiesSubmitted by editor on 23 July 2021.Get the paper!
The hatching date and length of the growth season can impact ecological interactions. We expected that organisms that hatch early in the season will perform better compared to organisms that hatch later in the season. This is because early hatchers have size advantage, and so competitive advantage over late hatchers. In addition, the differences in performance between these two groups should be more pronounced in populations from high latitudes where the time window of the growth season is strongly limited. This is because organisms usually react to increased time constraints with increased competition towards conspecifics. Better performance in early hatched individuals will be reflected in fitness related traits, like survival and premature growth rate, and physiological traits, like immune function. We collected adult common spreadwing females from high latitude Swedish populations and low latitude Polish populations. In captured conditions, these females laid eggs which then hatched and gave rise to larval stage. By manipulating hatching dates, we created the following groups — early and late hatched larvae with a two-weeks interval between hatching dates. We reared larvae in groups of individuals that hatched on the same date, and on different dates. These groups were reared in two different temperatures and photoperiods - native to the latitude of origin or foreign. These alternative rearing conditions posed more (Swedish) or less (Polish) seasonally time constrained rearing conditions. We showed that the early hatched individuals in mixed hatching groups had the highest survival, confirming better performance in survival of early individuals over late hatched ones. However, neither Swedish nor Polish early hatched larvae changed their survival rate when grown in high latitude conditions, suggesting that time constraints do not impact antagonistic interactions with a benefit for early hatchers. Interestingly, none of the other life history and physiological traits measured were the highest in early hatched individuals. Instead, these traits were shaped by the rearing conditions in a way that strongly time constrained individuals, i.e. larvae grown in Swedish temperature and photoperiod, shortened their development time and increased growth rate, at the same time decreasing their investment in immune functions. Our study shows that, across different populations and geographic regions, early hatched organisms show advantage over later hatched ones, but the advantage is reflected only in some traits that are linked to fitness.
Photo description: Experimental setup. In each container we reared 16 Swedish or Polish larvae, either of the two hatching dates, i.e. non-mixed hatching groups, or 8 from early and 8 from late hatching date groups, i.e. mixed hatching groups. During the following spring conditions, newly hatched early and late individuals from both study regions were divided into additional experimental groups which experienced native and foreign temperatures and photoperiods. At emergence, we measured life history and physiology traits. The time scale on the x-axis is arbitrary and does not represent the time length of each experimental stage.
Photos showing larvae of Lestes sponsa - the experimental damselfly. All were taken by Ulf Norling