Key themes in the study of seasonal adaptations in insects II. Life-cycle patterns

Abstract

Recent work on selected topics of particular interest for understanding insect life-cycles is reviewed, including habitat patterns, kinds of variation, the spreading of risk and prolonged diapause, trade-offs and developmental plasticity, circannual rhythms, the concept of life cycles as developmental choices, and development or delay as the default response. Seasonal adaptations have a wider range of components than has often been appreciated. Variation in lifecycle traits, including the duration of development and the timing of emergence, can be wide, narrow, or discontinuous. Trade-offs encompass multiple simultaneous traits and are not always structured as might be expected. Diapause, cold hardiness, reproductive pattern, and other traits have evolved many times independently. Such complex interactions can be understood only by examining the detailed features of a species' habitat, because how developmental decisions are made and whether continuous development or delays are programmed reflect the predictability of habitats and the environmental signals they supply. Ecological context is important, not just mechanisms of adaptation. Therefore, although most previous studies have paid more attention to insect response than to habitat, interpreting the seasonal relevance of life-cycle patterns requires measurement and analysis for individual species of habitat characteristics and their variation, on a range of temporal and spatial scales, in much more detail than has been customary.

Latitudinal patterns of phenology and age‐specific thermal performance across six Coenagrion damselfly species

“…Thirdly, Lowe et al (2009) found, in the most exhaustive study to date, that egg laying was strongly right-skewed in C. puella. This right-skewness is likely a general pattern in summer-active species, as it has been observed previously in diverse taxa, including plants, insects, and birds (Rabinowitz et al 1981, Danks 2006, Laaksonen et al 2006.…”

Daily Temperature Cycle Induces Daily Hatching Rhythm in Eastern Lubber Grasshoppers,Romalea microptera

“…In some cases the rhythmic activity is stimulated or elicited exogenously by an acute rhythmic environmental factor, such as when a threshold level of light, temperature, moisture, or mechanical disturbance is reached (Lockwood & Story 1985;Tomioka et al 1991;Danks 2005;Bradshaw & Holzapfel 2010). In other cases, the timing of the activity is determined endogenously by an internal biological clock, which itself was previously set by a zeitgeber (an external oscillating environmental factor that entrains a biological rhythm) (Bünning 1967;Danks 2006;Koštál 2011;Saunders & Bertossa 2011). Often, both exogenous and endogenous processes work together to determine the specific pattern; i.e., acute, current environmental stimuli alter the expression of existing circadian rhythms (Lockwood & Story 1985;Tomioka et al 1991).…”

The occurrence of summer diapause in the large white butterfly Pieris brassicae (Lepidoptera: Pieridae): A geographical perspective

“…Insects have evolved numerous life history strategies, which have enabled them to adapt their ontogeny and reproduction to seasonal changes in their environment (Masaki, 1996;Tauber et al, 1986;Musolin & Saulich, 1999;Danks, 2002Danks, , 2006a. In terms of population development, the diversity in life history traits divides insect species into two categories (Danks, 2001): First, those with only one generation (univoltinism) and second those with several generations per year (multivoltinism).…”