Male sand crickets trade-off flight capability for reproductive potential

In this paper, we test the hypothesis that male sand crickets, Gryllus firmus, experience a trade-off between flight capability and reproductive potential expressed as reduced testis weight in flight-capable morphs. We used a half-sib design with 130 sires, three dams per sire and an average of 5.66 males per dam family, for a total of 2206 F1 offspring. Traits measured were head width, somatic dry weight, testis weight, wing morph (micropterous/macropterous), weight of the dorso-longitudinal flight muscles (DLM) and the functional status of these muscles. Heritabilities of all traits were significant and ranged from 0.14 to 0.43. All traits were positively correlated with body size, but removal of this covariance revealed a highly significant trade-off, both phenotypically and genetically, between testes size and flight capability as measured by wing morph, DLM size or DLM status. The possible implications of this for morph-specific reproductive tactics are discussed.     

A Life History Trade-Off Between Flight Ability and Reproductive Behavior in Male Field Crickets (<Emphasis Type="Italic">Gryllus texensis</Emphasis>)

Male field crickets (Gryllus texensis) that differ in flight ability incur a life history trade-off between flight ability and reproduction, where flight ability comes with a male fitness cost. In courtship trials, flight-capable males produced courtship song, a necessary signal for mating success, with a significantly lower probability than flight-incapable males. The trade-off was evident in young males, and a similar trend occurred in older males. Males that lost the ability to fly through histolysis of flight muscles produced courtship song with a similar probability as males incapable of flight for their entire lives. Time of day did not affect the expression of the trade-off. Neither male morph nor time of day influenced female mating behavior.     

长颚斗蟋长翅和短翅型雄成虫营养物质的积累与分配差异

[目的]翅多型雄虫在繁殖方面的能量投入与雌虫相异,这种差异可能会导致雄虫飞行与繁殖权衡的生理机制发生改变.因此,本研究旨在探究翅二型长颚斗蟋Velarifictorus aspersus雄成虫在营养物质积累与分配方面是否存在飞行与繁殖的权衡关系.[方法]选取长颚斗蟋V.aspersus头幅相近的长翅和短翅型雄成虫,对羽...     

Does Reproduction Shorten Telomeres? Towards Integrating Individual Quality with Life‐History Strategies in Telomere Biology

Reproduction, a basic property of biological life, entails costs for an organism, ultimately detectable as reduction in survival prospects. Telomeres are an excellent candidate biomarker for explaining these reproductive costs, because their shortening correlates with increased mortality risk. For similar reasons, telomeres are perceived as biomarkers of individual “quality.” The relationship between reproduction and telomere dynamics is reviewed, emphasizing that cost and quality perspectives, commonly presented in isolation, should be integrated. While a majority of correlative studies have confirmed the relationship between telomere dynamics and various reproductive outputs, only limited experimental support exists showing that reproduction causes telomeres to shorten. A shift of focus to experimental manipulations of reproductive effort/telomere dynamics is crucial. However, the observation of survival reduction in response to these manipulations is essential for establishing telomeres as genuine biomarkers, allowing to unravel trade‐offs related to reproduction.     

Seasonal differences in body mass and circulating metabolites in a wing‐dimorphic pygmy grasshopper: implications for life history?

1. Functional wing polymorphism in insects is an intriguing topic, especially with respect to the adaptive advantage of each wing morph. The common pygmy grasshopper in Germany, Tetrix subulata, displays wing polymorphism skewed towards macropterous (LW) individuals capable of flight. Furthermore, T. subulata is known to undergo adult diapause in winter and reproduce in spring. 2. Morphometric and biochemical parameters were examined in field‐collected grasshoppers during autumn and spring to obtain a ‘snapshot’ from the same/one cohort of grasshoppers in the wild. 3. Flight muscles are largely reduced in brachypterous (SW) specimens, whereas they are well developed in LW individuals. Body mass measurements indicated gain in female T. subulata in spring, especially in LW morphs, which could be attributed to increased reproductive activity (egg production). 4. Metabolic fuel in haemolymph is differentially distributed in autumn: the concentration of lipids is highest in males, while carbohydrates are most abundant in LW specimens. The metabolic data imply that dispersal in T. subulata is predominantly in autumn, by flight in the case of LW specimens and by hopping/walking in males. 5. The season seems to be an important factor for the reproductive versus dispersal trade‐off in this species. Moreover, this study shows that morphological differences in T. subulata individuals are reflected in physiological differences that may ultimately affect behaviour and ecology.     

The effects of reproduction on courtship, fertility and longevity within and between alternative male mating tactics of the horned beetle, Onthophagus binodis

Life history theory provides a powerful tool to study an organism's biology within an evolutionary framework. The notion that males face a longevity cost of competing for and displaying to females lies at the core of sexual selection theory. Likewise, recent game theory models of the evolution of ejaculation strategies assume that males face a trade-off between expenditure on the ejaculate and expenditure on gaining additional matings. Males of the dung beetle Onthophagus binodis adopt alternative reproductive tactics in which major males fight for and help provision females, and minor males sneak copulations with females that are guarded by major males. Minor males are always subject to sperm competition, and consistent with theoretical expectation, minor males have a greater expenditure on their ejaculate than major males. We used this model system to seek evidence that mating comes at a cost for future fertility and/or male expenditure on courtship and attractiveness, and to establish whether these traits vary between alternative mating tactics. We monitored the lifespan of males exposed to females and nonmating populations, and sampled males throughout their lives to assess their fertility and courtship behaviour. We found a significant longevity cost of reproduction, but no fertility cost. On average, males from mating populations had a lower courtship rate than those from nonmating populations. This small effect, although statistically nonsignificant, was associated with significant increases in the time males required to achieve mating. Minor males had lower courtship rates than major males, and took longer to achieve mating. Although we did not measure ejaculate expenditure in this study, the correlation between lower courtship rate and longer mating speed of minor males documented here with their greater expenditure on the ejaculate found in previous studies, is consistent with game theory models of ejaculate expenditure which assume that males trade expenditure on gaining matings for expenditure on gaining fertilizations.     

Analysis of the importance of genotypic variation, metabolic rate, morphology, sex and development time on immune function in the cricket, Gryllus firmus

Immune defence is hypothesized to be a trait that bears significant fitness costs as well as benefits in that mounting a defence depreciates the value of other life‐history traits. Thus the cost of mounting an immune response could affect the evolution of both the immune system and correlated life history traits. In this study we examined, by means of a diallel cross of four inbred lines, the genetic basis of two measures of immune function, metabolic rate and several traits in the sand cricket, Gryllus firmus. We specifically addressed the following questions: (1) is immune function determined primarily by genetic constitution or correlations with phenotypic traits that could reduce the effectiveness of the immune response; (2) do the two measures of immune function covary; (3) What are the contributions of additive, nonadditive and maternal effects to the immune function? As estimates of immune function, we used lytic activity and encapsulation rate. We found that inbred crickets were smaller than individuals from the crossed lines and took longer to develop. However, inbred lines did not differ from the crossed lines in immune function nor metabolic rates, suggesting that increased homozygosity has little or no effect on these traits in G. firmus. We found that both immune parameters showed significant genetic variation but no consistent relationships with the other phenotypic traits (metabolic rate, head width, body mass, development time and activity). There was significant additive genetic variation only in encapsulation rate, but, with the exception of the activity measure, significant nonadditive and reciprocal variances were found in all traits. Metabolic rate of crickets was heritable, but there was neither phenotypic nor genetic association between metabolic rate and the two parameters of immune function. Further, there was no correlation between these two measures. Females showed a higher encapsulation response than males, but there was no sex differences in lytic activity. Our study indicates that genetic variation in immune parameters can be a very significant contributor to phenotypic variation in immune function.     

Reverse evolution: selection against costly resistance in disease-free microcosm populations of Paramecium caudatum

Evolutionary costs of parasite resistance arise if genes conferring resistance reduce fitness in the absence of parasites. Thus, parasite-mediated selection may lead to increased resistance and a correlated decrease in fitness, whereas relaxed parasite-mediated selection may lead to reverse evolution of increased fitness and a correlated decrease in resistance. We tested this idea in experimental populations of the protozoan Paramecium caudatum and the parasitic bacterium Holospora undulata. After eight years, resistance to infection and asexual reproduction were compared among paramecia from (1) "infected" populations, (2) uninfected "naive" populations, and (3) previously infected, parasite-free "recovered" populations. Paramecia from "infected" populations were more resistant (+12%), but had lower reproduction (-15%) than "naive" paramecia, indicating an evolutionary trade-off between resistance and fitness. Recovered populations showed similar reproduction to naive populations; however, resistance of recently (<3 years) recovered populations was similar to paramecia from infected populations, whereas longer (>3 years) recovered populations were as susceptible as naive populations. This suggests a weak, convex trade-off between resistance and fitness, allowing recovery of fitness, without complete loss of resistance, favoring the maintenance of a generalist strategy of intermediate fitness and resistance. Our results indicate that (co)evolution with parasites can leave a genetic signature in disease-free populations.     

Horn growth rate and longevity: implications for natural and artificial selection in thinhorn sheep (Ovis dalli)

We used horn measurements from natural and hunted mortalities of male thinhorn sheep Ovis dalli from Yukon Territory, Canada, to examine the relationship between rapid growth early in life and longevity. We found that rapid growth was associated with reduced longevity for sheep aged 5 years and older for both the hunted and natural mortality data sets. The negative relationship between growth rate and longevity in hunted sheep can at least partially be explained by morphologically biased hunting regulations. The same trend was evident from natural mortalities from populations that were not hunted or underwent very limited hunting, suggesting a naturally imposed mortality cost directly or indirectly associated with rapid growth. Age and growth rate were both positively associated with horn size at death for both data sets, however of the two growth rate appeared to be a better predictor. Large horn size can be achieved both by individuals that grow horns rapidly and by those that have greater longevity, and the trade-off between growth rate and longevity could limit horn size evolution in this species. The similarity in the relationship between growth rate and longevity for hunted and natural mortalities suggests that horn growth rate should not respond to artificial selection. Our study highlights the need for the existence and study of protected populations to properly assess the impacts of selective harvesting.