Optimal number of matings in two aphidophagous ladybirds

Abstract.  1. The present study was designed to identify the optimal number of matings required for maximum fecundity and egg viability in two aphidophagous ladybirds, Cheilomenes sexmaculata and Propylea dissecta .
2. For this purpose, ladybirds were subjected to different numbers of matings and the reproductive responses were recorded thereafter.
3. The Gompertz model was used to draw asymptotic graphs for fecundity and per cent egg viability in both ladybird species. Ninety-five per cent and 50% of maximum theoretical fecundity and per cent egg viability were predicted from the model.
4. Ninety-five per cent maximum theoretical fecundity was obtained after 13.25 and 12.95 matings in C. sexmaculata and P. dissecta , respectively; and 8.95 and 11.25 matings were required for 95% maximum theoretical per cent egg viability in C. sexmaculata and P. dissecta , respectively.
5. The results of these experiments clearly support the existence of an optimal number of matings in these two ladybird species leading to maximum adult fitness.     

Effect of age on reproductive attributes of an aphidophagous ladybird, Cheilomenes sexmaculata

The effect of both male and female age was investigated on certain reproductive attributes, viz. mating incidence, mating duration, fecundity, percent egg viability, ratio of reproductive and non‐reproductive periods and reproductive rate, of an aphidophagous ladybird, Cheilomenes sexmaculata (Fabricius). Females started mating at the age of 8 hours post‐emergence (PE) and males at the age of 2 days PE. Mating in the laboratory was a male‐dominated phenomenon. The mating duration and reproductive rate of 10‐day‐old females when mated with males of varying ages increased up to the male age of 60 days, and thereafter decreased, whereas, fecundity, egg viability and ratio of reproductive and non‐reproductive periods increased up to the male age of 50 days, and thereafter declined. However, when females of varying ages were mated with 10‐day‐old males, fecundity and reproductive rate increased up to 40 days of female age, respectively, then decreased. The ratio of reproductive and non‐reproductive periods increased with increasing age of females. Mating age for optimal reproductive output was 10J50‐day‐old males and NE to 40‐day‐old females. Reproductive cessation in males was recorded after 50 days PE, whereas in females at the age of 40 days PE. Higher mating durations lead to elevated reproductive rates. Delay in the reproductive phase was positively correlated with longevity. The results of this study may aid mass multiplication of this ladybird by identifying and promoting usage of adults of optimal age. Our results also enhance our understanding of the effect of age on reproductive attributes in ladybirds.     

Mating in aphidophagous ladybirds: costs and benefits

Abstract:  Mating costs and benefits were studied in three aphidophagous ladybirds, viz. Cheilomenes sexmaculata , Coccinella septempunctata and Propylea dissecta by subjecting them to different numbers of matings. Longevity, fecundity and percent egg viability were regressed with number of matings to determine the costs and trade-offs, if any. Longevity decreased with increasing number of matings in both C. sexmaculata and P. dissecta indicating a cost of mating. The lack of such a cost in C. septempunctata has been ascribed to spermatophore consumption by females of this ladybird. Both fecundity and percent egg viability increased with increasing number of matings and are probably indicative of the benefits. Short-lived females distributed their reproduction uniformly in their lifetime while long-lived females showed a high burst of reproductive activity followed by a gradual decline. Percent egg viability decreased after the completion of the requisite number of matings.     

Costs and benefits of reproduction in predaceous ladybird: Effect of multiple matings on reproduction and offspring development

A few matings are sufficient for females to maximize their reproductive success, while male fitness usually increases with an increase in the number of matings. However, females of a majority of insects mate multiple times. This presents an evolutionary puzzle and brings an understanding that some benefits are associated with it. Therefore, to understand the costs and benefits of multiple matings, we performed an experimental study in a ladybird beetle, Anegleis cardoni and observed reproductive performance and longevity of adults as direct benefits and offspring development and survival as indirect benefits. This is the first time that the effect of multiple matings is being evaluated on offspring development and survival in a ladybird beetle. Results clearly reveal that females directly benefit from multiple matings in terms of increased lifetime fecundity and egg viability, but their longevity decreases with increased number of matings. Best-fit curves on lifetime fecundity and percent egg viability revealed that maximum fecundity and egg viability were both attained after 17 matings. Developmental duration of offspring decreased and their survival increased with an increase in number of matings. Developmental duration was shortest after 20 matings and longest after a single mating.     

Conspecific interference by adults in an aphidophagous ladybird Propylea dissecta (Coleoptera: Coccinellidae): effect on reproduction

The effects of conspecific adult interference on the reproductive output of an aphidophagous ladybird, Propylea dissecta (Mulsant) were investigated. Ovipositing females were subjected to physical interference with conspecific adults (0 to 4 males or females) in Petri dishes and the effects on egg cannibalism, oviposition and egg viability were recorded. The absence of interference was related to the lowest egg cannibalism (0.00%) and higher fecundity (336.30+/-32.16 eggs) and egg viability (95.83+/-1.60%). Fecundity decreased with increasing physical interference from either sex. Egg viability declined with increasing male density, but was not influenced by conspecific females. In a second experiment, evaluating the role of conspecific adult chemical tracks on fecundity and egg viability, it was observed that adult chemical track density (fresh and ten-day-old) was negatively correlated. Egg viability was not affected by the presence of adult chemical tracks. The decrease in fecundity was not affected by the sex of the adults making the tracks, thus revealing that the chemical constitution of these deterrent compounds was not sex-specific. Conspecific interference in a Petri dish reduces reproductive output, as a result of physical interference and response to what seem to be oviposition-deterring pheromones present in adult tracks.     

Polyandry restores female fertility and paternal effects diminished by inbreeding in Hippodamia convergens

1. The fertility restoration hypothesis posits that polyandry can evolve when female fertility is reduced by matings with related males, but restored by matings with unrelated ones. 2. Using a promiscuous ladybird, this hypothesis was tested by mating mature, virgin females twice with sib and non‐sib males in all four permutations and observing female fertility. The development of progeny from the first and 10th clutches was also followed to test for differences in paternal effects. 3. Mating treatment did not affect fecundity, but egg viability was reduced by sib matings, and restored by non‐sib matings, regardless of mating sequence. In addition, negative paternal effects of sib matings on progeny (lower survival) were compensated by non‐sib matings. 4. The survival of offspring in first clutches was sensitive to the paternal mating sequence and was higher if a sibling male was preceded by a non‐sib male, compared with the reverse, consistent with a time lag in response to male epigenetic signals. Offspring survival did not differ between these two treatments in the 10th clutch, suggesting a blending of paternal effects over time. 5. The results are indicative of interactions between the paternal effects contributed by different males, and between paternal and maternal effects, the latter causing faster development in later clutches. 6. Thus, the reproductive benefits of polyandry for H. convergens females are potentially both genetic and epigenetic, as both egg fertility and beneficial paternal effects were diminished by sib matings, but restored by matings with unrelated males.     

The short-term and long-term effects of parental age in the bean weevil (Acanthoscelides obtectus)

We examined the influence of parental age on life history traits of their offspring in the lines of bean weevil that have evolved different rates of senescence. Measurements included preadult traits (egg size, embryonic developmental time, total preadult developmental time, preadult viability) and adult traits (body weight, total realized fecundity of females, first day of egg laying, early fecundity, late fecundity and longevity). The negative parental age effects were observed for all traits except for the early and total realized fecundity. We did not detect statistically significant line×parental age interactions for either preadult- or adult-survival, so offspring survival did not change with parental age after selection for early vs. late reproduction. It seems that selection acting on the quality of offspring produced by parents of different ages has not been responsible for the evolution of senescence in bean weevil. This revised version was published online in August 2006 with corrections to the Cover Date.     

Maternal effects and their consequences for offspring fitness in the Yellow Dung Fly

1. Maternal adult diet and body size influence the fecundity of a female and possibly the quality and the performance of her offspring via egg size or egg quality. In laboratory experiments, negative effects in the offspring generation have often been obscured by optimal rearing conditions.
2. To estimate these effects in the Yellow Dung Fly, Scathophaga stercoraria , how maternal body size and adult nutritional status affected her fecundity, longevity and egg size were first investigated.
3. Second, it was investigated how female age and adult nutritional experience, mediated through the effects of egg size or egg quality, influenced the performance of offspring at different larval densities.
4. Maternal size was less important than maternal adult feeding in increasing reproductive output. Without food restriction, large females had larger clutch sizes and higher oviposition rates, whereas under food restriction this advantage was reversed in favour of small females.
5. Offspring from mothers reared under nutritional stress experienced reduced fitness in terms of egg mortality and survival to adult emergence. If the offspring from low-quality eggs survived, the transmitted maternal food deficiency only affected adult male body size under stressful larval environments.
6. Smaller egg sizes due to maternal age only slightly affected the performance of the offspring under all larval conditions.     

Adult dietary protein has age‐ and context‐dependent effects on male post‐copulatory performance

The highly conserved effect of dietary protein restriction on lifespan and ageing is observed in both sexes and across a vast range of taxa. This extension of lifespan is frequently accompanied by a reduction in female fecundity, and it has been hypothesized that individuals may reallocate resources away from reproduction and into somatic maintenance. However, effects of dietary protein restriction on male reproduction are less consistent, suggesting that these effects may depend on other environmental parameters. Using the neriid fly, Telostylinus angusticollis, we examined age‐specific effects of adult dietary protein restriction on male post‐copulatory reproductive performance (fecundity and offspring viability). To explore the context dependence of these effects, we simultaneously manipulated male larval diet and adult mating history. We found that protein‐restricted males sired less viable offspring at young ages, but offspring viability increased with paternal age and eventually exceeded that of fully fed males. The number of eggs laid by females was not affected by male dietary protein, whereas egg hatching success was subject to a complex interaction of male adult diet, age, larval diet and mating history. These findings suggest that effects of protein restriction on male reproduction are highly context dependent and cannot be explained by a simple reallocation of resources from reproduction to somatic maintenance. Rather, these effects appear to involve changes in the scheduling of male reproductive investment with age.     

A comparison of maternal effects and current environment on vital rates of Aphis nerii, the milkweed–oleander aphid

Abstract.  1. Non-Mendelian maternal effects, the effects of maternal phenotype or environment on offspring phenotype, have been documented in numerous taxa. By affecting offspring vital rates (birth, death, and movement), maternal effects have the potential to influence population dynamics. However, relatively few studies have directly linked maternal phenotype or environment to offspring vital rates. Additionally, even fewer studies have compared the magnitude of across-generation effects (i.e. maternal effects) to within-generation effects.
2. Because of their telescoping generations, aphids can be strongly influenced by maternal effects. The effects of maternal density and maternal host-plant species on offspring survival, fecundity, and alate formation were investigated experimentally in Aphis nerii , the milkweed–oleander aphid.
3. Additionally, the relative strength of maternal effects were compared with those operating within a generation. Therefore, in another set of experiments, the effects of current density and host-plant species (within-generation effects) on aphid vital rates were examined.
4. While maternal effects were present, within-generation effects were much stronger and more strongly influenced aphid vital rates. Within a generation, aphids exhibited density-dependent survival, fecundity, and alate formation and these effects varied among host-plant species.
5. These results indicate that while maternal effects have the potential to affect population dynamics, this potential is not always met. Additionally, the current environment, not the environment of previous generations, more strongly impacts population dynamics.     

Links between parental life histories of wild salmon and the telomere lengths of their offspring

The importance of parental contributions to offspring development and subsequent performance is self‐evident at a genomic level; however, parents can also affect offspring fitness by indirect genetic and environmental routes. The life history strategy that an individual adopts will be influenced by both genes and environment; and this may have important consequences for offspring. Recent research has linked telomere dynamics (i.e., telomere length and loss) in early life to future viability and longevity. Moreover, a number of studies have reported a heritable component to telomere length across a range of vertebrates, although the effects of other parental contribution pathways have been far less studied. Using wild Atlantic salmon with different parental life histories in an experimental split‐brood in vitro fertilization mating design and rearing the resulting families under standardized conditions, we show that there can be significant links between parental life history and offspring telomere length (studied at the embryo and fry stage). Maternal life history traits, in particular egg size, were most strongly related to offspring telomere length at the embryonic stage, but then became weaker through development. In contrast, paternal life history traits, such as the father's growth rate in early life, had a greater association in the later stages of offspring development. However, offspring telomere length was not significantly related to either maternal or paternal age at reproduction, nor to paternal sperm telomere length. This study demonstrates both the complexity and the importance of parental factors that can influence telomere length in early life.     

Impairment of reproduction in the red flour beetle, Tribolium castaneum (Herbst) (Col., Tenebrionidae) due to larval feeding on triflumuron-treated diet

The larvae of Tribolium castaneum (Herbst) of different ages were exposed to various concentrations viz., 0.0001, 0.001 and 0.01 ppm of triflumuron up to pupation. The adults were allowed to feed on untreated diet. The preoviposition period, fecundity, egg viability and incubation period of the eggs laid were studied. Triflumuron significantly lengthened the preoviposition and incubation periods (P < 0.001). Fecundity and egg viability were also reduced (P < 0.001) due to the treatment. Both the strains were affected by the treatment.     

Age-specific mating and reproductive senescence in the seven-spotted ladybird, Coccinella septempunctata

Abstract:  Adults of the seven-spotted ladybird, Coccinella septempunctata Linnaeus (Col., Coccinellidae) were paired for mating from very young to old age (1–50 days) to record the willingness to mate, attainment of sexual maturity and onset of reproductive senescence in both the sexes. Mating commenced after 4 and 2 days of emergence of male and female, respectively, and 100% mating was achieved at the young age in both cases (10 days). Willingness to mate decreased with increase in the age from 40 to 50 days of both the sexes. Ladybird exhibited protandry. Mating duration, fecundity and per cent viability of eggs of middle-aged males (20–30 days old) and females (20 days old) were the highest. Mating duration and per cent viability of eggs were male age dependent, whereas pre-oviposition and oviposition periods were mating stimulus dependent. Oviposition period and fecundity were female age-dependent responses. Fecundity was highest when 20-day-old female and 30-day-old male were paired. Onset of reproductive senescence started at the age of 30 days in males and 20 days in females. The present study confirms the effect of ageing on male and female C. septempunctata and supports the Hansen and Price [J. Evol. Biol. (1995) vol. 8, pp. 759–778] model that females mating with young and middle-aged males yield optimal quality progeny.     

Cryptic maternal effects in Hippodamia convergens vary with maternal age and body size

Maternal effects can mold progeny phenotypes in various ways and may constitute ecological adaptations. By examining the effect of oviposition sequence on progeny produced by different size classes of female ladybird beetles (produced by controlling larval access to food), we show that maternal signals can change through adult life and alter the developmental programs of progeny, ostensibly to synchronize their life histories with predictable resource dynamics, thus maximizing maternal fitness. We also show that female body size, as determined by larval food supply, interacts with female age to influence progeny fitness. When fed ad libitum as adults, small females reared with limited food access laid fewer, smaller eggs than large females reared with ad libitum food access. Maternal body size interacted with oviposition sequence to influence progeny development, but the latter had greater impact. Eggs laid later by medium and large females hatched faster than those laid earlier, larvae fed longer in the fourth instar, their pupation period was shorter, total developmental time was reduced, and adults emerged with greater mass, most notably daughters. Oviposition sequence effects on progeny from small mothers were non‐significant for total developmental time and progeny mass. Only large mothers increased egg size over time and egg mass was not consistently correlated with developmental parameters, indicating that progeny phenotype was impacted by other, more cryptic, maternal signals. Such signals appear costly, as food limitation during development constrained not only fecundity and egg size but also maternal ability to manipulate progeny phenotype. The production of faster‐developing offspring that mature to larger sizes late in the oviposition cycle may be adaptive for exploitation of ephemeral aphid outbreaks with predictable dynamics of prey abundance and competition.     

MATERNAL EFFECTS ON OFFSPRING SIZE: VARIATION THROUGH EARLY DEVELOPMENT OF CHINOOK SALMON

We performed two breeding experiments with chinook salmon (Oncorhynchus tshawytscha) to explore maternal effects on offspring size. We estimated the magnitude of maternal effects as the differences between sire-offspring and dam-offspring regression slopes. Early in life, offspring size is largely influenced by maternal size, but this influence decreases through early development, with the maternal effect becoming negative at intermediate offspring ages (corresponding to a period of reduced growth of progeny hatching from large eggs) and converging on zero as offspring age. Also, egg size was positively correlated with early survival, but negatively correlated with maternal fecundity.     

Maternal allocation of androgens and antagonistic effects of yolk androgens on sons and daughters

Mothers can influence the phenotype of their offspring by adjustingthe quality of their eggs in relation to sex and reproductivevalue of the progeny. Maternal androgens in the eggs of vertebratesmay mediate such adaptive early maternal effects. However, theevolution of early maternal effects mediated by egg androgensmay be constrained by the inability of mothers to differentiallyallocate androgens to eggs with a male or a female if androgenshave different effects on sons and daughters. In this study,we increased the concentration of androgens in the eggs of barnswallows (Hirundo rustica) within the physiological range ofvariation and analyzed the effect on nestling growth and beggingbehavior. Egg androgens increased body size and mass of sonsbut reduced these characters in daughters when compared to twocontrol groups in a repeated-measures analysis of variance ofdata collected at different ages. However, the differentialeffect of androgen on the two sexes was no longer significantwhen the analysis was restricted to the age of 12 days, whenfinal body size is attained. In a second experiment, we testedwhether mothers differentially allocated androgens to eggs withsons rather than daughters while manipulating a paternal secondarysexual character. Androgen concentration did not vary in relationto paternal ornamentation or embryo sex. Hence, antagonisticeffects of egg androgens on sons and daughters may exist inthe very early posthatching life and may constrain the evolutionof adaptive maternal effects because mothers do not differentiallyallocate androgens in relation to embryo sex.     

DECLINE IN OFFSPRING VIABILITY AS A MANIFESTATION OF AGING IN DROSOPHILA MELANOGASTER

Abstract The evolutionary explanation of senescence proposes that selection against alleles with deleterious effects manifested only late in life is weak because most individuals die earlier for extrinsic reasons. This argument also applies to alleles whose deleterious effects are nongenetically transmitted from mother to progeny, that is, that affect the performance of progeny produced at late ages rather than of the aging individuals themselves. We studied the effect of maternal age on offspring viability (egg hatching success and larva-to-adult survival) in two sets of Drosophila melanogaster lines (HAM/LAM and YOUNG/OLD), originating from two long-term selection experiments. In each set, some lines (HAM and YOUNG, respectively) have been selected for early reproduction, whereas later reproduction was favored in their counterparts (LAM and OLD). In the HAM and LAM lines, both egg hatching success and larval viability declined with mother's age and did so with accelerating rates. The hatching success declined significantly faster with maternal age in HAM than in LAM lines, according to one of two statistical approaches used. Egg hatching success also declined with maternal age in YOUNG and OLD lines, with no difference between the selection regimes. However, the relationship between mother's age and offspring larva-to-adult viability differed significantly between these two selection regimes: a decline of larval viability with maternal age occurred in YOUNG lines but not in OLD lines. This suggests that the rate with which offspring viability declines with mother's age responded to selection for early versus late reproduction. We suggest broadening the evolutionary concept of senescence to include intrinsically caused declines in offspring quality with maternal age.     

Environmental and senescent related variations in Weddell seal body mass: implications for age-specific reproductive performance

Recent studies have found age-specific variations in reproductive performance amongst Weddell seals, Leptonychotes weddellii , and we hypothesized age-related variations in maternal body mass as a mechanism linking maternal age and the observed patterns of reproductive performance. We evaluated the effects of maternal traits such as age and reproductive experience and the effects of environmental variations on maternal body mass at parturition. Maternal body mass at parturition showed substantial age- and environmental-related variations. Maternal body mass increased with age through the young and middle ages, and evidence of senescent declines in body mass was found amongst the oldest ages. Additionally, body mass at parturition was strongly influenced by environmental variations during the pregnancy period, specifically sea-ice extent and the state of the El-Niño Southern Oscillation. Patterns of age-specific variations in body mass were consistent with age-specific patterns of offspring survival probability, which supported our hypothesis that changes in body mass link maternal age and reproductive performance in the Weddell seal. Further, environmental conditions during pregnancy may be an important component of Weddell seal reproductive performance.     

Association of paternal age with prevalence of selected birth defects

BACKGROUND: Unlike maternal age, the effect of paternal age on birth defect prevalence has not been well examined. We used cases from the Texas birth defect registry, born during 1996-2002, to evaluate the association of paternal age with the prevalence of selected structural birth defects. METHODS: Poisson regression was used to calculate prevalence ratios (PRs) and 95% confidence intervals (CIs) associated with paternal age for each birth defect, adjusting for maternal age, race/ethnicity, and parity. RESULTS: Relative to fathers ages 25-29 years, fathers 20-24 years of age were more likely to have offspring with gastroschisis (PR 1.47, 95% CI: 1.12-1.94), and fathers 40+ years old were less likely to have offspring with trisomy 13 (PR 0.40, 95% CI: 0.16-0.96). No association was seen between paternal age and prevalence of anencephaly and encephalocele. A selection bias was observed for the other birth defects in which cases of younger fathers were more often excluded from study. CONCLUSIONS: In studies of birth defect risk and paternal age, the source of information may affect the validity of findings.     

Inverse relationship between age at onset of Huntington disease and paternal age suggests involvement of genetic imprinting.

It is well recognized that age at onset of Huntington disease (HD) is strongly influenced by the sex of the affected parent, and this has lead to suggestions that genetic imprinting or maternal specific factors may play a role in the expression of the disease. This study evaluated maternal and paternal ages, birth order, parental age at onset, and sex of the affected parent and grandparent in 1,764 patients in the National HD Roster by using linear-regression techniques which incorporated a weighted least-squares approach to accommodate the correlation among siblings. It was found that paternal age is negatively associated with age at onset of HD, particularly among subjects who inherit the mutant gene from grandfathers. Apparent associations between age at onset and birth order and between age at onset and maternal age were not significant after adjustment for paternal age. The paternal age effect is strongest among juvenile-onset cases and individuals with anticipation of greater than or equal to 10 years, although it is detectable across the entire age-at-onset distribution. The tendency for older fathers, including those not transmitting the HD gene, to have affected offspring with early-onset disease may be consistent with a gene imprinting mechanism involving DNA methylation. Because paternal age in unaffected fathers is also a significant determinant of age at onset, methylation in this context might involve HD modifier genes or the normal HD allele.