The genetic variance but not the genetic covariance of life‐history traits changes towards the north in a time‐constrained insect

Abstract

Seasonal time constraints are usually stronger at higher than lower latitudes and can exert strong selection on life-history traits and the correlations among these traits. To predict the response of life-history traits to environmental change along a latitudinal gradient, information must be obtained about genetic variance in traits and also genetic correlation between traits, that is the genetic variance-covariance matrix, G. Here, we estimated G for key life-history traits in an obligate univoltine damselfly that faces seasonal time constraints. We exposed populations to simulated native temperatures and photoperiods and common garden environmental conditions in a laboratory set-up. Despite differences in genetic variance in these traits between populations (lower variance at northern latitudes), there was no evidence for latitude-specific covariance of the life-history traits. At simulated native conditions, all populations showed strong genetic and phenotypic correlations between traits that shaped growth and development. The variance-covariance matrix changed considerably when populations were exposed to common garden conditions compared with the simulated natural conditions, showing the importance of environmentally induced changes in multivariate genetic structure. Our results highlight the importance of estimating variance-covariance matrixes in environments that mimic selection pressures and not only trait variances or mean trait values in common garden conditions for understanding the trait evolution across populations and environments.

Two experimental designs generate contrasting patterns of behavioral differentiation along a latitudinal gradient in Lestes sponsa—Common‐garden not so common after all?

“…This is not surprising since L. sponsa larvae regulate its life cycle by means of environmental signals such as photoperiod (Norling, 2018; Sniegula & Johansson, 2010). Within a geographic gradient, increasingly longer days cue individuals to develop, grow, and emerge faster in order to complete the life cycle prior to the end of the season (Sniegula et al., 2018; Sniegula & Johansson, 2010). At high latitudes summer, photoperiods are very long and may even consist of continues light (24 hr).…”

“…Abiotic factors, such as thermal conditions, changing along geographic gradients have been shown to influence life‐history traits and can also affect behavioral correlations (Roff, 1992; Sniegula, Golab, Drobniak, & Johansson, 2018). This is especially so in ectothermic organisms whose metabolism is temperature dependent (Clarke & Fraser, 2004; Wieser, 1973).…”

“…For example, variation in thermal conditions influence foraging and activity rate in insects (Matthews & Matthews, 2010). Assuming that different environmental conditions may, and often do, result in different selective pressures (“adaptive hypothesis,” Bell, 2005; Dingemanse et al., 2007; Wilson, 1998), it is expected that behavioral correlations covary with life‐history traits across environmental gradients to overcome constraints linked to seasonal time limitations (Dmitriew, 2011; Foster, 1999; Sniegula et al., 2018).…”

Size‐mediated priority and temperature effects on intra‐cohort competition and cannibalism in a damselfly

“…Larvae hatch the following spring, and larval development takes a couple of months; adults emerge during the summer (Jödicke, ). L. sponsa shows ample phenotypic and genetic variation in hatching dates as well as in larval growth rates and emergence dates (Sniegula, Drobniak, Golab, & Johansson, ; Sniegula, Golab, & Johansson, ; Sniegula, Golab, Drobniak et al, 2016; Sniegula et al., ), suggesting that intraspecific size‐related priority effects might occur in nature. In addition, data from the field in Northern Europe show a large variation in larval size distribution, ranging from a length of 11–24 mm at beginning of June (Corbet, ).…”

“…Since time is limited in seasonal environments, the optimal timing of maturation and reproduction is highly important for individual fitness (Stearns, ). However, in nature, there is often variation in hatching, development and growth, which can constrain the optimal timing of life‐history events (Dmitriew, ; Rowe & Ludwig, ; Sniegula, Golab, Drobniak, & Johansson, 2016, ). Individuals that hatch or emerge earlier within a season often have advantages over those that hatch or emerge later within a season; these advantages are presented in terms of competition, predation and cannibalism (Murillo‐Rincon, Kolter, Laurila, & Orizaola, ; Takatsu & Kishida, ; Yang & Rudolf, ).…”