Abstract
The winter survival of three closely related univoltine heteropterans that overwinter as adults, Nabis rugosus, N. erice- torum and N. pseudoferus was investigated. After 150 days of low temperature treatment (3-5°C, 16L : 8D, r.h. 70-80%) more males than females died. The mortality rate ranged from 88.8 to 93.8% in males and from 54.2 to 60.7% in females. However, these sexual differences in mortality did not differ significantly across the three species and populations of different geographic origin. It remains a general question whether this considerable evolutionary stability in the sex-specific investment into reproduction and sur- vival phylogenetically conserved or frequently evolves anew to similar levels in separated populations and species. In Nabis rugosus, the relative loss of body mass during overwintering was up to 37.8%. This reflects dramatic somatic costs of adult overwin- tering and indirectly supports the hypothesis that food supply during overwintering is important for some heteropteran predators. However, body mass before overwintering did not significantly explain the survival pattern in N. rugosus in either sex. The similar sex-specific survival rate of overwintering adult nabids regardless of species and geographic origin can be useful for studies on population dynamics of nabids in agroecosystems and biocontrol.
Highlights
Dormancy, a typical feature in the life cycle of many animals in temperate zones (Danks, 1987) allows organisms to synchronize their reproductive or developmental cycle with predictably changing environmental conditions by suppression of growth, development and reproduction, the depression of metabolism and the enhancement of stress resistance to promote survivorship (Danks, 1987)
Some Drosophila studies show that sexual differences in senescence, stress resistance or thermal adaptations vary between populations (Sørensen et al, 2005; Norry et al, 2006) but in others the sexual dimorphism of life-history traits was consistent across populations or related species (Robinson et al, 2000; Hoffmann et al, 2001; Sharmila Bharathi et al, 2003)
There is evidence that sex-specific trade-offs lead to sexual dimorphism of life-history traits, such as differences in cold resistance of males and females (Hoffmann et al, 2005)
Summary
A typical feature in the life cycle of many animals in temperate zones (Danks, 1987) allows organisms to synchronize their reproductive or developmental cycle with predictably changing environmental conditions by suppression of growth, development and reproduction, the depression of metabolism and the enhancement of stress resistance to promote survivorship (Danks, 1987). There is an extensive literature on insect seasonality, the diversity and complexity of dormancy in insects (reviewed in Tauber et al, 1986; Danks, 1987, 2007) from which two important issues emerge: sexual dimorphisms and geographic variation. In this paper we examine the winter survival of both sexes in three species of damselbugs from different geographic origins. Pener (1992) suggested that enhanced survival during unfavourable conditions should benefit males and females and one should not expect sex differences in dormancy. Given that the way males and females maximise fitness is fundamentally different, gender differences in resource allocation to current and future reproductive investment, and winter survival may well be expected. In some insect species only females survive to the following spring, storing viable sperm for reproduction (Danks, 1987; Pener, 1992). There are sexual differences in the intensity of dormancy (Selander & Weedle, 1972; Sims & Shapiro, 1983), photoperiodic, temperature and food requirements (Meinke & Slosser, 1985; Tachibana & Watanabe, 2007) development during reproductive dormancy (Tatar et al, 2001) and duration of dormancy (e.g. protandry)
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