Reproductive allocation and reproductive ecology of seven species of Diptera

1. Variation in resource allocation to egg size and number was investigated in seven sympatric species of Piophilidae that oviposit on carcasses or discarded cervid antlers: Liopiophila varipes (Meigen), Prochyliza xanthostoma Walker, Protopiophila latipes (Meigen), Protopiophila litigata Bonduriansky, Stearibia nigriceps (Meigen), and two unidentified species of Parapiophila McAlpine. 2. Following optimal reproductive allocation theory, relatively larger, fewer eggs were expected in (1) species that oviposit on antlers, where larvae probably experience lower risk of predation and greater competition than larvae in carcasses, and (2) species with aggressive males and male-biased sex ratios on the oviposition substrate, where risk of injury during oviposition may have favoured females laying fewer eggs. 3. Variation in reproductive allocation strategies could not be explained by known differences in larval or adult environment, but congeneric species clustered by reproductive allocation patterns. The Parapiophila species produced larger, fewer eggs than the other species, and egg number increased slowly with body size. The Protopiophila species did not deviate from expected egg sizes and numbers, and egg number increased steeply with body size. 4. An interspecific egg size–egg number trade-off resulted in a tight linear scaling of ovary volume to body size, suggesting common physiological constraints on relative ovary mass. 5. Within each species, egg size was nearly constant whereas egg number increased with female body size, suggesting species-specific stabilising selection on egg size.     

Geographic variation and the evolution of reproductive allocation in the pitcher-plant mosquito, Wyeomyia smithii

We measured the egg size of six geographic populations of the pitcher-plant mosquito, Wyeomyia smithii, from Florida (30 degrees N) to Ontario (49 degrees N). Populations from northern latitudes produced larger eggs than populations from southern latitudes. Egg size increased with increasing latitude more rapidly when larvae were reared under low rather than high density. One southern (30 degrees N) and one northern (49 degrees N) population of W. smithii that persisted through 10 generations of selection for increased persistence under conditions of chronic thermal- and nutrient-limiting stress (conditions similar to southern rather than northern habitats) produced smaller eggs more rapidly than unselected control lines. However, there were no differences in lifetime fecundity or fertility between control and selected lines. Thus, laboratory evolution in an environment representative of extreme southern latitudes caused evolutionary changes consistent with geographic patterns of egg size. These results implicate temperature as a selective factor influencing the geographic variation of egg size in W. smithii, and demonstrate a novel trade-off in reproductive allocation between egg size and egg maturation time.     

Subsociality and female reproductive success in a mycophagous thrips: An observational and experimental analysis

Oviparous females of the haplodiploid, facultatively viviparous thrips Elaphrothrips tuberculatus(Thysanoptera: Phlaeothripidae) guard their eggs against female conspecifics and other egg predators. The intensity of maternal defense increases with clutch size. Field and laboratory observations indicate that cannibalism by females is an important selective pressure favoring maternal care. Experimental removals of guarding females showed that egg guarding substantially increases egg survivorship and that the survivorship of undefended eggs is higher in the absence of nonguarding female conspecifics than in their presence. The fecundity of viviparous females increases with the number of eggs cannibalized. The reproductive success of oviparous females increases with body size and local food density and decreases with local density of breeding females. Social behavior may not have advanced beyond maternal care in Elaphrothrips tuberculatusbecause, relative to Hymenoptera, capabilities for helping relatives are few or nonexistent, and the causes of variation in female reproductive success are not influenced easily by cooperation among females.     

Colony genetic structure in a facultatively eusocial hover wasp

The degree of genetic heterogeneity among the individuals inan animal society depends on the society's genetic structure.Genetic heterogeneity, in turn, means that group members willdiffer in their reproductive objectives and conflicts over reproductionmay arise. The resolution of these conflicts may be reflectedin the way that reproduction is partitioned between potentialreproductives. We used 5 microsatellite loci to investigategenetic structure and reproductive skew in 17 nests of the Malaysianhover wasp, Parischnogaster alternata. Parischnogaster alternatacolonies are small (1–10 females), and all adult colonymembers are capable of mating and producing offspring. We foundthat colonies tended to consist of closely related individualsand that at any one time the production of both female and maleoffspring was nearly always monopolized by a single dominantfemale, despite considerable variation between nests in parameterspredicted to affect skew. Subordinate females that remainedin their natal colonies obtained indirect fitness benefits byhelping to raise offspring to which they were related. Subordinatefemales also appeared to be positioned within an age-based queuefor inheritance of the dominant egg-laying position. We suggestthat the high skew in P. alternata may result from strong ecologicalconstraints on solitary nesting, high relatedness, and a relativelyhigh probability that subordinates will eventually inherit theposition of dominance.     

Influence of adult nutrition on the relationship between body size and reproductive parameters in a parasitoid wasp

Abstract.  1. An important constraint upon life-history evolution in parasitoids is the limit imposed by body size on allocation of limited metabolic resources to different fitness-related physiological functions such as reproduction and survival.
2. The influence of adult nutrition on reproductive and maintenance variables was studied in the synovigenic ectoparasitoid Mastrus ridibundus , and it was determined whether resource allocation to these different functions depends on body size.
3. Over the course of adult life there was a positive relationship between body size and the number of mature eggs in adult females both in the presence and absence of food. However, only in the presence of food did egg maturation rates increase significantly with body size. Starved wasps produced significantly smaller eggs than fed ones, which has not been documented before. Moreover, starved wasps produced fewer offspring than fed wasps, and attacked fewer hosts.
4. The availability of food had a major effect on longevity, with fed females living about 10 times longer than starved ones. There was also a positive relationship between body size and longevity. In starved wasps, this relationship was the same both in the presence and absence of hosts, but in fed wasps there was a positive relationship between body size and longevity in the absence of hosts only. Allocation to initial eggs relative to lifetime progeny production did not decline with body size.
5. The data reveal that in M. ridibundus the trade-off between maintenance and reproduction varies with life expectancy.     

蒙古沙冬青花序内性分配的变化、传粉者运动与繁殖成功

性分配理论主要研究繁殖资源在雌雄功能间的最优分配,从雌雄功能的角度考虑其个体适合度.对花序内不同部位花的雌性与雄性资源分配变化的研究,对于我们理解植物采取哪种繁殖对策保障繁殖成功具有重要意义.本文对生长在中国科学院吐鲁番沙漠植物园内的蒙古沙冬青(Ammopiptanthus mongolicus)连续开花花序内不同部位...     

羊草种群生物量生殖分配的初步研究

对羊草种群生物量生殖分配的研究表明,在生殖生长过程中,种群用于根茎和营养生长的生物量生殖分配占有绝对优势比例,而用于有性生殖的生物量生殖分配比例较小,在10%以下。在羊草种群构件生物量生殖分配中,根茎和营养枝的叶占有较大比例(20%～40%),而用于有性繁殖体种子生产的比例很小,在1.5%以下。对有性繁殖的小比例投资是导致羊草种群有性繁殖体种子产量低的重要原因.     

Life history of Kladothrips ellobus and Oncothrips rodwayi: insight into the origin and loss of soldiers in gall-inducing thrips

1. The evolution of eusociality in Australian gall‐inducing thrips cannot be understood without comparisons among closely related solitary species. The life history of two solitary, gall‐inducing thrips, Kladothrips ellobus and Oncothrips rodwayi, was investigated, and data for solitary and eusocial species from previous studies were re‐analysed. Kladothrips ellobus is in a clade that is closely related to the eusocial species. Oncothrips rodwayi is in the same clade as the eusocial species and appears to have undergone an evolutionary loss of eusociality. It is the only galling thrips on Acacia in temperate environments. 2. The brood size of K. ellobus is eight to 23 times larger than broods of foundresses in eusocial species whereas the brood size of O. rodwayi is not significantly different from those of foundresses in eusocial species. 3. In K. ellobus, the mean sex ratio was not significantly different from parity but in O. rodwayi the mean sex ratio was 0.13 male. In O. rodwayi, 77% of females were inseminated by their brothers before dispersal, which is consistent with high levels of inbreeding in eusocial species of the same clade. Sex ratios suggest random mating in K. ellobus whereas female‐biased sex ratios in O. rodwayi are consistent with inbreeding and local mate competition. 4. Comparisons among solitary and eusocial species suggest that large brood size is an ancestral trait for eusociality in thrips, and this trait persists in solitary species as an r‐selection strategy. Soldiers may have evolved in arid environments to minimise the risks of dispersal and the costs of latency to reproduction, and to maximise gall defence. 5. Temperate conditions could have facilitated the evolutionary loss of soldiers in O. rodwayi, as there should be a shorter, safer, more predictable window period between dispersal and gall induction, reducing the period of latency to reproduction following dispersal and lowering risks of dispersal. 6. The loss of soldiers in O. rodwayi is not associated with a reversion to the large brood sizes of solitary species in ancestral lineages.     

Geographic variation in reproductive traits and trade-offs between size and number of eggs of the Chinese cobra (Naja atra)

We collected gravid Chinese cobras (Naja atra) from one island (Dinghai) and three mainland (Yiwu, Lishui and Quanzhou) populations in south‐eastern China to study geographical variation in female reproductive traits and the trade‐off between the size and number of eggs. We then conducted an common experiment on cobras from two of the four populations to further identify factors contributing to the observed trade‐offs. The mean size (snout–vent length) of the smallest five reproductive females increased with increasing latitude. Oviposition occurred between late June and early August, with females from the warmer localities laying eggs earlier than those from the colder localities. Maternal size was a major determinant of the reproductive investment in all populations, with larger females producing not only more but also larger eggs. Clutch size was more variable than egg size within and among populations. The observed geographical variation in clutch size, egg size, clutch mass and post‐oviposition body condition was not a simple consequence of variation in maternal size among populations, because interpopulation differences in these traits were still evident when the influence of maternal size was removed. The upper limit to reproductive investment was more likely to be set by the space availability in the island population, but by the resource availability in the three mainland populations. Trade‐offs between size and number of eggs were detected in all populations, with females that had larger clutches for their size having smaller eggs. Egg size at any given level of relative fecundity differed among populations, primarily because of interpopulation differences in the resource availability rather than the space availability. Except for the timing date of oviposition and the mean size of the smallest five reproductive females, all other examined traits did not vary in a geographically continuous trend. The common garden experiment, which standardized environmental factors, synchronized the timing date of oviposition, but it did not modify the conclusion drawn from the gravid females collected from the field. The observed geographical variation in the female reproductive traits could be attributed to the consequence of the effects of either proximate or ultimate factors. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 85 , 27–40.     

Measuring temporal variation in reproductive output reveals optimal resource allocation to reproduction in the northern grass lizard, Takydromus septentrionalis

We measured the reproductive output of Takydromus septentrionalis collected over 5 years between 1997 and 2005 to test the hypothesis that reproductive females should allocate an optimal fraction of accessible resources in a particular clutch and to individual eggs. Females laid 1–7 clutches per breeding season, with large females producing more, as well as larger clutches, than did small females. Clutch size, clutch mass, annual fecundity, and annual reproductive output were all positively related to female size (snout–vent length). Females switched from producing more, but smaller eggs in the first clutch to fewer, but larger eggs in the subsequent clutches. The mass-specific clutch mass was greater in the first clutch than in the subsequent clutches, but it did not differ among the subsequent clutches. Post-oviposition body mass, clutch size, and egg size showed differing degrees of annual variation, but clutch mass of either the first or the second clutch remained unchanged across the sampling years. The regression line describing the size–number trade-off was higher in the subsequent clutch than in the first clutch, but neither the line for first clutch, nor the line for the second clutch varied among years. Reproduction retarded growth more markedly in small females than in large ones. Our data show that: (1) trade-offs between size and number of eggs and between reproduction and growth (and thus, future reproduction) are evident in T. septentrionalis ; (2) females allocate an optimal fraction of accessible resources in current reproduction and to individual eggs; and (3) seasonal shifts in reproductive output and egg size are determined ultimately by natural selection.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 315–324.     

Macrogeographic clines in fecundity, reproductive allocation, and offspring size of the forest tent caterpillar Malacosoma disstria

1. The fecundity of the forest tent caterpillar varies considerably across its geographic range. Field data indicate that populations in the southern United States (Gulf States) produce nearly twice as many eggs as females from Canada or the Lake States, with little or no difference in the size of adult females. 2. In controlled rearing experiments, female forest tent caterpillar from the southern United States (Louisiana) had much larger clutch sizes than same sized females from northern populations in Michigan or Manitoba, Canada. Increased fecundity in Louisiana females was achieved through a significant reduction in egg size and a concomitant increase in the allocation of resources to egg production. 3. Comparison of 10 forest tent caterpillar populations spanning a 27° latitudinal gradient, validated the results of detailed comparisons among the three populations above by confirming the strong negative correlation between latitude and clutch size. 4. Neonate forest tent caterpillars from Manitoba were significantly larger than larvae from either Michigan or Louisiana. Michigan larvae were intermediate in size. It is postulated that large neonates are advantageous in thermally limiting environments. More than three times as many degree‐days are available to Louisiana neonates during the first 2 weeks after hatching. A consistently favourable climate during the vulnerable post‐hatching period may have allowed the evolution of larger clutches at the expense of neonate size in southern populations.     

Migratory costs and contemporary evolution of reproductive allocation in male chinook salmon

Energetically demanding migrations may impact the resources available for reproductive trait development and activity, and hence favour evolution of new investment strategies for remaining resources. We conducted a large-scale experiment to evaluate the proximate cost of migration on male reproductive investment in chinook salmon (Oncorhynchus tshawytscha) and contemporary evolution of reproductive allocation. Experimentally induced differences in migratory costs (17 km inland and 17 m elevation vs. 100 km and 430 m) influenced dorsal hump size and upper jaw length, two traits influencing male mating success that are developed during migration. Longer migration also reduced tissue energy reserves available for competition and length of breeding life. Corresponding shifts in the balance between natural and sexual selection appear to have been responsible for heritable population divergence in secondary sexual trait investment, in approximately 26 generations, following colonization of spawning sites with different migratory demands.     

Senescence in growth and reproductive allocation in a bunchgrass

• Senescence is a puzzling phenomenon. Few convincing studies of senescence in perennial herbaceous plants exist. While ramets are known to senesce, whether senescence of bunchgrasses actually occurs is not clear.
• In this study, we grew a set of plants of Elymus excelsus, a bunchgrass, to examine plant size, sexual reproduction and bud formation in individual plants in relation to their gradual ageing, in order to determine whether E. excelsus experiences senescence. We collected data in two consecutive years (2009 and 2010) from field samples of plants from 1 to 5 years old. Using regression models, we performed age‐related analyses of growth and reproduction parameters.
• Our results showed that individual plant size (diameter, individual biomass), total biomass of ramets, number and biomass of reproductive ramets, percentage of ramets that were reproductive, reproductive allocation, over‐wintering buds and juvenile ramets all declined with age. However, vegetative growth (number and biomass of vegetative ramets) did not decrease with age.
• Those plants that survived, dwindled in size as they aged. However, no plants shifted their resource allocation between growth and reproduction as they aged, so the shift in allocation did not account for the fall in size.

     

Egg composition and reproductive investment in aphidophagous ladybird beetles (Coccinellidae: Coccinellini): egg development and interspecific variation

Abstract Most studies of insect reproductive allocation concentrate on propagule size and number and very few consider egg composition, which is likely to be equally important. In the present study, data are provided on changes in egg lipid, glycogen, free carbohydrate and protein during embryonic development of the aphidophagous ladybird Adalia bipunctata (L.) and the compositions of A. bipunctata, Adalia decempunctata and Anisosticta novemdecimpunctata eggs are compared. In A. bipunctata, egg mass, lipid and glycogen decline strongly during development and egg protein declines more weakly. Free carbohydrate declines early in egg development and increases at egg hatching. Lipid is energetically the most important developmental fuel, although approximately half of the initial egg lipid remains in the neonate larva. Across the three species, energy per unit egg mass is lowest in the least specialized species, A. bipunctata, which also has the largest eggs, and is highest in the most specialized, An. novemdecimpunctata, which has the smallest eggs. Two possible explanations for the observed pattern are discussed: (i) species laying smaller eggs may incur higher developmental costs per unit mass than species laying larger eggs and (ii) more specialized species, which reproduce at lower aphid densities, may provision neonate larvae better to facilitate location and capture of aphids.     

Differences in productive robustness in rabbits selected for reproductive longevity or litter size

The aim of this work was to evaluate the ability of a line selected for reproductive longevity (LP) to confront productive challenges compared to a line selected during 31 generations for litter size at weaning (V). A total of 133 reproductive rabbit does were used (72 and 61 from LP and V lines, respectively). Within each line, three groups with different levels of productive effort were planned: PP9, inseminated at day 4 after the first partum and with nine kits during the second partum, and inseminated after first weaning (30 days) and with nine (PW9) or five kits (PW5) during the second partum. The reproductive performance, body condition (perirrenal fat thickness (PFT)) and lipolytic response were controlled. LP does showed greater mean live weight (LW; +128 g; P < 0.05), PFT (+0.47 mm; P < 0.05) and estimated body energy (EBE; +0.29 MJ/kg; P < 0.01) than V does at second partum. However, LP does that mated at first post partum did not significantly differ in EBE relative to V does at second partum. During the first week of lactation, dry matter (DM) intake was similar for both lines (94 and 95 g DM/kg LW0.75 day for V and LP does, respectively). There was a significant difference in milk yield between both lines during the first week when litter size was nine (60 v. 54 g of milk/kg LW0.75 day for LP and V does, respectively; P < 0.01), but no difference when litter size was five. Consequently, when litter size was nine, LP does showed a lower recovery of PFT (0.6 mm less; P < 0.05) than V does during the first 10 days of lactation. However, when litter size was five, LP does showed a higher LW (+210 g; P < 0.05) than V does at 10 days of lactation and a similar recovery of PFT. During the last 3 weeks of the lactation, LP does showed a higher feed intake (+6 g DM/kg LW0.75 day; P < 0.05) and milk yield (+27 g/day; P < 0.001) than V does when litter size was nine, resulting in no significant differences in LW at 30 days of lactation. However, when litter size was five, both lines showed similar feed intake and milk yield, maintaining their differences in LW at 30 days of lactation (+206 g for LP does; P < 0.05). These results show that the rabbit line selected for reproductive longevity is more robust with respect to coping with productive challenges, than a line selected for reproductive intensity.     

Egg size,embryonic development time and ovoviviparity in Drosophila species

Lengths, widths and volumes of eggs from 11 species of Drosophila whose genomes have been fully sequenced exhibit significant variation that is not explained by their phylogenetic relationships. Furthermore, egg size differences are unrelated to embryonic development time in these species. In addition, two of the species, Drosophila sechellia and, to a lesser degree, D. yakuba, both ecological specialists, exhibit ovoviviparity, suggesting that female control over oviposition in these species differs from what is observed in D. melanogaster. The interspecific differences in these reproductive characters, coupled with the availability of whole genome sequences for each, provide an unprecedented opportunity to examine their evolution.     

产卵次序对山麻雀卵色、卵大小和重量的影响

产卵次序可对鸟类卵黄中的营养成分、卵壳色素以及卵壳厚度等产生影响。一些鸟类可通过产卵次序对不同卵的资源进行分配,从而实现繁殖成效的最大化。本研究对不同产卵次序下山麻雀(Passer cinnamomeus)的卵色、卵大小和卵重量进行分析,结果表明,山麻雀的卵重和卵大小随着产卵次序并无显著变化,卵色与卵的大小和重量均无显著相关性,但卵背景的色度随产卵次序有明显下降趋势,而卵斑点密度则呈相反的变化。卵背景的色度随产卵次序下降可能是山麻雀有限的色素在卵中不均匀分配的结果,而卵斑点密度的增加则可能是对后期卵壳厚度变薄的一种补偿。     

Tree size and its relationship with flowering phenology and reproductive output in Wild Nutmeg trees

Reproductive strategies, sexual selection, and their relationship with the phenotype of individuals are topics widely studied in animals, but this information is less abundant for plants. Variability in flowering phenology among individuals has direct impact on their fitness, but how reproductive phenology is affected by the size of the individuals needs further study. We quantified the flowering intensity, length, and reproductive synchronization of two sympatric dioecious Wild Nutmeg tree species (Virola, Myristicaceae) in the Brazilian Atlantic forest, and analyzed its relationships with tree size. Two distinct strategies in flowering timing and intensity were found between species (annual versus biennial flowering), and among individuals in the annual flowering species (extended versus peak flowering). Only for the annual flowering species the reproductive output is related to tree size and large trees present proportionally higher flower coverage, and lower synchronization than smaller ones. Flowering is massive and highly synchronized in the biennial species. Sex ratios are not different from 1:1 in the two species, and in the two segregated reproductive subgroups in the biennial flowering species. The biennial flowering at individual level is a novelty among reproductive patterns in plants, separating the population in two reproductive subgroups. A proportional increase in the reproductive output with size exists only for the annual flowering species. A biennial flowering can allow resource storage favouring massive flowering for all the individuals diluting their relationship with size.     

Body size, reproductive allocation, and maximum reproductive rate of two species of aphidophagous Coccinellidae exploiting the same resource

To test the predictions of allometric analyses of laboratory data on aphidophagous ladybirds, a study was carried out on a small [Propylea quatuordecimpunctata (L.); dry female body mass 3.7 mg] and large species (Coccinella septempunctata L.; 15.4 mg) (both Coleoptera: Coccinellidae) of predatory ladybird, which regularly exploit cereal aphids. In 2003–2006, females of C. septempunctata and in 2006 P. quatuordecimpunctata were collected at 2‐ to 5‐day intervals during the 30‐day period around the peak in cereal aphid abundance, and the number of eggs they laid in the following 24 h in the laboratory was recorded. In addition to the number of eggs laid, clutch mass, live weight, and scutum width of ovipositing females and the sizes of the clutches laid in the field were recorded. As predicted, the reproductive allocation in both species was similar. The weight of the eggs of C. septempunctata (0.20 mg) and P. quatuordecimpunctata (0.18 mg) differed little, and the proportion of body mass allocated to daily reproduction (ca. 12%) was identical in both species. In addition, the maximum number of eggs laid per day in the field by the large species was, as predicted, greater than by the small species. Interestingly, the size of the egg clutches laid by C. septempunctata in the field was similar to the daily oviposition of field‐collected adults recorded in the laboratory, whereas for P. quatuordecimpunctata it was significantly smaller. The role of morphology and physiology of ladybirds in structuring aphidophagous ladybird guilds is discussed.