Larval competition within seeds: From the behaviour process to the ecological outcome in the seed beetle Callosobruchus maculatus

Abstract Environmental conditions experienced by organisms during development can have profound impacts on adult fitness and behaviour. Internally feeding larvae unable to leave the seed selected by their mother face limitations of resource suitability and competition. The host seed may guide the larval behaviour within the seed leading to differential intensity of competition and determining its process and outcome, which varies in strains of the legume seed beetle Callosobruchus maculatus (Coleoptera: Bruchidae). However, the intensity, process and outcome of larval competition in different hosts have yet to be simultaneously considered, the objective of the present study. Here we assessed the intensity, process and outcome of intrastrain larval competition as related to host type, and how they are interrelated. Larval competition was faced with two distinct strategies – scramble and contest competition depending on the insect strain and host seed species. The intensity of competition did not show any straight link with the process and outcome of competition. Only a single strain showed a contest competition process with likely interference between larvae, while the four other strains studied showed the process of scramble competition. The process of scramble competition, however, led to variable outcomes in mung beans based on larval competition curves. Such differences were not apparent on cowpea seeds and either the plateau or the peak expected on the larval fitness curves were not reached preventing the distinction of the competition outcome, a likely consequence of the egg laying behaviour of these strains limiting the maximum number of eggs laid per seed. Seed host species rather than seed size are the likely cause of the differences observed from the initial expectation. The strain showing the process of contest competition increased larval fitness with density of larvae emerged per seed regardless of the host species, an unexpected outcome based on theoretical models. In this case the egg laying behaviour of the adult female is probably the main fitness determinant of its progeny.     

The effects of copulation duration in the bruchid beetle Callosobruchus maculatus

Control over copulation duration is a potentially importantgenerator of sexual conflict that has received little empiricalattention. The copulatory behavior of the bruchid beetle Callosobruchusmaculatus may reflect a sexual conflict over copulation duration.Males have spines on their intromittent organs that puncturethe female reproductive tract, and females kick their matesduring copulation. If females are prevented from kicking, copulationslast longer and the injuries females sustain are more severe.Males supposedly use the spines as anchors to prolong copulationduration, and females kick to terminate copulations. We manipulatedcopulation duration experimentally and quantified its effectson male and female fitness components to test whether or notthere is a conflict over copulation duration in C. maculatus.Females did not suffer from long copulations but instead experiencedincreased lifetime fecundity. Ejaculate size increased withcopulation duration, and females apparently derive materialbenefits from the ejaculates. Males that mated first and hadlong copulations were relatively unsuccessful when competingwith sperm from other males. However, there was a trend forfemale remating propensity to decrease with long copulationdurations, and first males may therefore also benefit from longcopulations. The copulation duration of the second male to matedid not have a significant effect on sperm precedence. We concludethat even though it seems likely that the male spines have evolvedto act as an anchor during copulation, there seems to be littleconflict over copulation duration per se in C. maculatus.     

Relationships between larval density, adult size and egg production in the cowpea seed beetle, Callosobruchus maculatus

ABSTRACT.

• 1 The eggs of the cowpea seed bettle Callosobruchus maculatus (Fab.) are attached to cowpeas. On hatching, the larvae penetrate the testa and remain in the seed until development is complete and adult eclosion has occurred. The adults do not need to feed and were not allowed to do so.
• 2 Strains from Brazil and Nigeria can produce more than twelve adults from a seed bearing numerous eggs, whereas a strain from the Yemen Republic rarely produced more than three.
• 3 In all three strains the mean weight of the adults produced from a single cowpea declined with increasing initial larval density in the seed.
• 4 Egg production by females is positively correlated with their weight at the time of mating, shortly after emergence.
• 5 Lifetime egg production by females of the Brazilian and Nigerian strains was lower if they came from cowpeas with higher initial larval densities. No such relationship could be demonstrated in the Yemen strain.
• 6 The fecundity of one generation of these beetles, at least in some geographical strains, is significantly affected by the number of larvae entering the hosts in which the adults of that generation have developed.

     

加快棕种子萌发和幼苗生长的研究

棕种子萌发和幼苗生长十分缓慢 ,为了探索加快种子萌发和幼苗生长的方法 ,对棕种子进行不同处理、不同时间催芽和催芽后不同处理等试验 ,结果表明 :(1)生长调节剂 3号 ABT生根粉、吲哚丁酸和 2 ,4 - D可提高种子萌发率 ,促进幼苗生长。 (2 )播种前催芽可促使种子提前萌发 ,延长幼苗生长期 ,使当年生苗更粗壮 ;贮藏 3个月后催芽可提高 10 %～ 15%的发芽率。 (3)催芽后用 50 mg/ L和 10 0 mg/ L的 3号 ABT生根粉、或者 10 0 mg/ L的萘乙酸浸泡都可以提高幼苗出土率 ,但对幼苗生长没有明显影响。     

The function of multiple mating in oviposition and egg maturation in the seed beetle Callosobruchus maculatus

Abstract.  To comprehend the significance of multiple mating in female Callosobruchus maculatus , the material-benefits hypothesis is tested, as well as the potential function and mechanism of additional mating for females. The results show that longevity and lifetime fecundity are significantly higher in doubly-mated females, whereas females subject to an interrupted second copulation (which transfers no ejaculate) show resemblance with singly-mated females in lifetime fecundity and daily fecundity, supporting the material-benefits hypothesis. Female lifetime fecundity increases with ejaculate size in doubly-, but not singly-mated females. Doubly-mated females exhibit an immediate increase in fecundity on the day of remating. Moreover, dissection of ovaries after remating shows that the number of unlaid eggs is lower in doubly-mated females in comparison with singly-mated females, whereas the total number of unlaid and laid eggs shows no significant difference. This suggests that the second mating increases the oviposition rate, but not the egg maturation rate in female C. maculatus . Thus, ejaculate serves as a stimulus for oviposition, at least on the remating day. However, because doubly-mated females lay more eggs in total than singly-mated females, doubly-mated females appear to mature more eggs than the singly-mated counterparts. This is attributed to the 'indirect-driven' hypothesis, which states that the reduction in the number of mature eggs in the oviducts brought about by oviposition stimulates the maturation of oocytes in ovarioles to replenish the number of mature eggs.     

Host suitability, respiration rate and the outcome of larval competition in strains of the cowpea weevil, Callosobruchus maculatus

Abstract.  Variation between strains of Callosobruchus maculatus in several life-history traits is well known. Differences in functional anatomy of egg pores and larval respiration rates have also been reported in strains from Brazil and Yemen. The response of five strains of C. maculatus to seeds of two host species, cowpea ( Vigna unguiculata ) and mung bean ( Vigna radiata ), was measured along with the larval respiration rates of the same strains on both hosts. There was significant variability of response to the two hosts. Strains with higher larval respiration rate (µL O₂/insect/day) showed higher seed consumption, which significantly affected adult emergence per seed on both hosts. This finding provides support for the hypothesis that differential feeding rate is an important mechanistic component of the larval competition outcome observed in strains of C. maculatus .     

Dynamics of genomic change during evolutionary rescue in the seed beetle Callosobruchus maculatus

Rapid adaptation can prevent extinction when populations are exposed to extremely marginal or stressful environments. Factors that affect the likelihood of evolutionary rescue from extinction have been identified, but much less is known about the evolutionary dynamics (e.g., rates and patterns of allele frequency change) and genomic basis of successful rescue, particularly in multicellular organisms. We conducted an evolve‐and‐resequence experiment to investigate the dynamics of evolutionary rescue at the genetic level in the cowpea seed beetle, Callosobruchus maculatus, when it is experimentally shifted to a stressful host plant, lentil. Low survival (~1%) at the onset of the experiment caused population decline. But adaptive evolution quickly rescued the population, with survival rates climbing to 69% by the F5 generation and 90% by the F10 generation. Population genomic data showed that rescue likely was caused by rapid evolutionary change at multiple loci, with many alleles fixing or nearly fixing within five generations of selection on lentil. Selection on these loci was only moderately consistent in time, but parallel evolutionary changes were evident in sublines formed after the lentil line had passed through a bottleneck. By comparing estimates of selection and genomic change on lentil across five independent C. maculatus lines (the new lentil‐adapted line, three long‐established lines and one case of failed evolutionary rescue), we found that adaptation on lentil occurred via somewhat idiosyncratic evolutionary changes. Overall, our results suggest that evolutionary rescue in this system can be caused by very strong selection on multiple loci driving rapid and pronounced genomic change.     

Competition strategies and correlated selection on responses to polyandry in the seed beetle Callosobruchus maculatus

Abstract Polyandry reflected in multiple mating with different mates is regarded as favoured by natural selection in males but not necessarily in females, where conflicting effects on fitness components can occur. The present study aims to provide empirical evidence to predict which fitness components may be affected in this sexual conflict using a species that demonstrates potential between‐population variation in their resolution: the cowpea weevil Callosobruchus maculatus. Two strains showing contrasting competition outcomes (scramble × contest) and contrasting life‐history strategies based on trade‐offs between longevity and fecundity are crossed for subsequent selection based on larval‐competition strategy, expecting the production of a correlated response to multiple (polyandrous) mating. Such a response is expected because the scramble strain shows high fecundity (and lower longevity) and would benefit from multiple mating, in contrast with the contest strain, which shows high juvenile mortality. The scramble‐selected lines would evolve a response of increased fecundity and reduced longevity under multiple and potentially polyandrous mating but the contest‐selected lines would not respond to multiple (polyandrous) mating. Instead, both scramble‐ and contest‐selected lines show increased fecundity and reduced longevity with multiple (polyandrous) matings, which did not affect egg weight. Indirect benefits of multiple (polyandrous) mating appear to be relevant for lines showing contest competition among juveniles.     

Effect of seed moisture content and d‐limonene on oviposition decisions of the seed beetle Callosobruchus maculatus

Callosobruchus maculatus (Fabricius) (Coleoptera: Bruchidae) is a cosmopolitan pest of stored pulses and legumes. Under legume storage conditions neither adults nor larvae drink, with larvae obtaining their hydration from metabolic water. However, lack of water limits female fecundity and longevity, thus females might be expected to preferentially oviposit on seeds with high moisture content so as to minimize water stress on their offspring. This was tested by offering females a choice of seeds that differed in relation to their level of water content. After controlling for differences in seed size, females were found to preferentially oviposit on the driest seeds. Offspring size and larval survival were equivalent on seeds that differed in moisture content, which in combination with the preference to lay on the driest seeds would indicate that the egg laying decisions of C. maculatus females do not function to minimize larval water stress. Analysis of the chemical volatiles released by seeds that differed in their moisture content revealed a greater level of d ‐limonene in the environment surrounding high moisture seeds. d ‐limonene has known anti‐herbivory properties, thus we suggest the observed female preference for dry seeds may be related to the observed difference in the level of d ‐limonene in the immediate vicinity of beans that differ with respect to their moisture content.     

黑果枸杞种子萌发及幼苗生长对盐胁迫的响应

研究不同浓度(0、1、2、3、6、9、14、18g.L-1)的盐溶液(NaCl、MgSO4、盐渍土壤)对河西走廊中部荒漠边缘的黑果枸杞种子吸胀、萌发和幼苗生长的影响,并观察胁迫解除后种子的反应。结果表明:黑果枸杞种子吸胀速率随NaCl、MgSO4和土壤溶液浓度的增大呈先升后降的趋势,吸水速度随胁迫时间的延长而减慢;种子萌发率随3种盐浓度的增大而降低,盐胁迫解除后种子仍具有较高的萌发率;发芽指数、活力指数、根长、下胚轴随3种盐浓度的增大而降低或先升后降,根轴比随盐胁迫的增强先升后降;随3种盐浓度的增大,种苗损害率增大,3种盐的胁迫效应依次NaCl>MgSO4>盐渍土壤溶液。黑果枸杞种子萌发和幼苗生长对NaCl胁迫较为敏感,其耐受的临界阈值是6g.L-1;种子萌发能耐受较高浓度的MgSO4的胁迫,幼苗生长对MgSO4胁迫较敏感,其耐受的临界阈值是9g.L-1;种子萌发和幼苗生长对生境盐渍土壤具有较强的耐受能力和适应性。     

巴茅草水浸提液对3种作物种子萌发及幼苗生长的化感作用

本文以发芽率、发芽速度指数、发芽指数、根长、茎长和生物量为种子萌发和幼苗生长参数,研究不同生长时期巴茅草叶片和茎秆水浸提液对白菜、生菜、水稻的化感作用。结果表明: 巴茅草叶水浸提液化感作用强于茎秆水浸提液,叶水浸提液处理后受体植物的发芽指数和生物量均显著低于茎水浸提液。枯萎期巴茅草的化感作用强于生长旺盛期。不同浓度巴茅草叶水浸提液对3种作物的化感作用存在明显的量效关系,浸提液浓度越高,巴茅草的化感抑制作用越强。巴茅草叶水浸提液对白菜和生菜各萌发指标100%抑制的浓度分别为0.075和0.10 g·mL^-1;而0.10 g·mL^-1巴茅草叶水浸提液对水稻发芽率、发芽速度指数、发芽指数的抑制率分别为13.8%、27.2%、19.3%。巴茅草叶水浸提液对白菜和生菜各生长指标100%抑制的浓度分别为0.05和0.10 g·mL^-1;而0.10 g·mL^-1巴茅草叶水浸提液对水稻根长、茎长、生物量的抑制率分别为64.6%、92.9%、21.8%。结合种子萌发和幼苗生长的综合化感指数,3种供试作物对巴茅草化感作用的敏感程度为白菜>生菜>水稻。     

光照对辽东栎种子萌发和幼苗生长的影响

研究了不同光照梯度[55.4%自然全光照(natural sunlight,NS)、18.9%NS、5.5%NS、2.2%NS、0.5%NS和0.3%NS]对辽东栎种子萌发和幼苗生长的影响.结果表明:辽东栎种子的萌发率和萌发指数在55.4%NS处理达到最大,分别为72.5%和0.22,然后随着光照减弱而逐渐减小,在0.3%NS处理下最小,分别为42.5%和0.11;强光照对种子萌发进程有一定的延迟作用,萌发活力指数随着光照的减弱而增大(0.5%NS处理最大);强光下种子萌发的延迟可能是其对多种命运的权衡性选择.强光照有利于辽东栎幼苗基径和根系生长,以及幼苗干物质的积累,但株高最小(6.06 cm);不同光强处理的辽东栎幼苗具有较大的形态学可塑性,其幼苗阶段对光环境的适应性较强,0.5%NS处理的幼苗比叶面积、比枝长、比根长、叶片叶绿素b含量及叶绿素总量均最大,分别为142.57 cm2.g-1、156.86 cm.g-1、271.87 cm.g-1、0.07 g.cm-2和0.24 g.cm-2,55.4%NS处理下最小,分别为44.89 cm2.g-1、52.84 cm.g-1、101.98 cm.g-1、...     

紫茎泽兰叶片化感作用对10种草本植物种子萌发和幼苗生长的影响

化感作用在生物入侵过程中具有重要的意义,紫茎泽兰具有化感物质,它能抑制豌豆等一些对化感物质敏感的植物种子萌发,但它对入侵早期直接与之竞争的植物的影响以及化感作用与其入侵性的关系还知之甚少。以紫茎泽兰入侵早期直接与之竞争的草本植物和为替代控制紫茎泽兰引进的牧草为材料,利用培养皿滤纸法研究紫茎泽兰叶片提取液对种子萌发和幼苗生长的影响,探讨化感作用与其入侵性的关系,并为其替代控制提供依据。紫茎泽兰叶片提取液对10种受体植物种子萌发和幼苗生长均有化感作用,不同浓度的提取液对植物的化感作用强度不同,低浓度时较弱,高浓度时较强。高浓度的提取液能降低种子发芽率、发芽速率、胚轴和胚根长度,增加幼苗丙二醛含量,其中发芽速率更敏感,可能是衡量化感作用的最敏感指标。不同植物对紫茎泽兰化感作用的敏感程度不同,无芒虎尾草、白三叶、细叶苦荬和莎草砖子苗对紫茎泽兰化感作用较敏感,紫花苜蓿最不敏感。     

油菜对3种作物种子萌发和幼苗生长的化感作用

油菜是我国重要的绿肥作物,除增加土壤肥力外,对后茬作物也有一定的化感作用。本文研究了不同浓度油菜浸提液(0.025、0.05和0.1 g·mL^-1)对3种作物(燕麦、玉米和向日葵)种子萌发、幼苗生长及生理生化的影响。结果表明: 油菜浸提液对3种作物种子发芽率的影响不显著,但对燕麦有“低促高抑”的趋势,对向日葵有抑制的趋势。油菜浸提液高浓度处理对燕麦幼苗根和茎长、玉米幼苗茎长以及向日葵幼苗根长起抑制作用,低浓度处理对玉米幼苗根茎长起促进作用。燕麦和向日葵幼苗在浸提液浓度为0.05 g·mL^-1时蛋白质含量最大,玉米在0.025 g·mL^-1时蛋白质含量最大,显著高于对照。3个浓度下,向日葵脯氨酸含量均显著降低,玉米脯氨酸含量在浓度为0.05 g·mL^-1时显著高于对照。玉米过氧化物酶(POD)活性在浸提液浓度为0.05 g·mL^-1时最大,向日葵POD活性在浓度为0.025 g·mL^-1时最大,与对照有显著差异,其余浓度处理与对照无显著差异。油菜浸提液浓度为0.025 g·mL^-1时显著降低了燕麦超氧化物歧化酶(SOD)活性,3种作物幼苗过氧化氢酶(CAT)活性与对照均无显著差异。加入油菜浸提液后,向日葵幼苗丙二醛(MDA)含量在浓度为0.1 g·mL^-1时显著增加,玉米幼苗MDA含量在不同浓度处理下均显著低于对照。综合分析,油菜浸提液对向日葵的化感抑制作用最强,其次为玉米、燕麦。     

The fecundity and oviposition behavior of a South Indian strain of Callosobruchus maculatus

The fecundity of the South India strain of Callosobruchus maculatus (Fab.) (Bruchidae: Coleoptera) is 73 eggs for females developing in 31 days and increases to 94 eggs for females emerging after 41 days. Fed females lay 45–55 more eggs which is the egg-equivalent of the reserves unfed females had to sacrifice for activity. Competition as a larva did not reduce a female's fecundity. Oviposition is inhibited when females are given 25 or fewer beans for oviposition and it is reversed if females find fresh beans. Oviposition is generally released by beans carrying a below average number of eggs, thus, the eggs are almost uniformly distributed over the beans. Eggs are preferentially placed on the largest egg-free beans as expected if oviposition is released when a beetle goes from a smaller to a larger bean. The cues resulating host preferences, cowpea > mung pigeonpea chickpea, are secondary to the cues producing hyperdispersion and the selection of larger beans. We present a model for the oviposition behavior that accounts for the observed responses to species, size, and egg load of oviposition sites.

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Résumé La fécondité de femelles isolées avec un mâle, sans aliment ni eau, et laissées sans perturbation avec 50 graines au moins sert de fécondité standard. Elle augmente avec le temps de développement de l'uf à l'adulte de 73 ufs (32 j) à 94 ufs (44 j). La fécondité potentielle, obtenue avec des femelles alimentées sur sucre est de 125 ufs. Des femelles maintenues avec moins de 25 graines réduisent leur fécondité.Plus de la moitié des femelles distribuent leurs ufs uniformément jusqu'à une densité de 1,5 uf. L'uniformité peut provenir de l'induction de réactions de ponte par les graines portant moins d'ufs que l'effectif moyen. L'hyperdistribution au dessus des densités de 3 ufs/graine révèle l'aptitude à distinguer les graines avec 3 ufs des graines avec 4 ufs. Il y a moins d'écarts par rapport à l'uniformité (erreurs) avec des graines à surface rugueuse. Des femelles avec 10 graines font moins d'erreurs que des femelles avec 50 ou 100 graines.Les ufs sont ajoutés aux plus grosses graines sans ufs; ainsi, plus il y a de graines qui portent des ufs, plus le poids des graines avec ufs diminue. Un tel schéma est prévisible si la ponte est induite par des graines plus grosses que les graines rencontrées précédemment. Les femelles présentent un ordre de préférence clair quand elles sont en rapport avec leurs hôtes classiques: Vigna unguiculata > V. radiata > Cajanus cajan > Cicer arietinum Les caractères spécifiques de l'hôte, plutôt que la taille ou la texture de la surface servent à la distinction entre les graines d'un même hôte.Ces résultats expérimentaux peuvent être utilisés pour la modélisation du comportement de ponte d'une femelle.

     

Effects of search experience in a resource-heterogeneous environment on the oviposition decisions of the seed beetle, Callosobruchus maculatus (F.)

Abstract.  1. This study investigates how female seed beetles, Callosobruchus maculatus , distribute their eggs on various-sized seeds when the size of seed was varied during the egg-laying period.
2. Beetles were allowed to lay eggs on one of three arrays of 64 adzuki beans ( Vigna angularis ). Each array contained four size classes of seed, ranging from small (5.0–5.5 mm diameter) to large (6.5–7.0 mm), but differed in how they were distributed within the environment. In the most heterogeneous condition (the 64-patch design), the four sizes were interspersed, while in the least heterogeneous condition (the four-patch design) they were grouped into four separate blocks. Thus, a beetle exploring the 64-patch design would frequently encounter all four seed sizes, whereas a beetle exploring the four-patch design would only rarely encounter a change in bean size.
3. Beetles experiencing greater seed size heterogeneity were more likely to lay eggs on larger seeds, whereas those in the blocked condition were more likely to oviposit on small seeds. Beetle responses to seed size heterogeneity suggest that the degree of preference for large seeds depends on a female's recent experience.
4. Female beetles exhibited size discrimination throughout their egg-laying process; however, there was a trade-off between seed size and egg discrimination (i.e. avoiding those seeds already containing developing eggs) in response to the change in fitness gained from either laying on larger seeds or lower egg-load seeds during the egg-laying process.
5. Our model provides the first evidence that evolving seed size discrimination ability is adaptive for the seed beetle with egg-discrimination ability.     

Consequences of inbreeding for the cowpea seed beetle, Callosobruchus maculatus (F.)(Coleoptera: Bruchidae)

Inbreeding is said to reduce vigour and fitness. It may also determine how a population responds to selection. Local populations of Callosobruchus maculatus , the cowpea seed beetle, are established annually from small numbers of founders and the species has been distributed to many parts of the world where isolated populations may have been founded by very small numbers of individuals. After more than 20 generations of inbreeding, inbred lines have been shown to diverge from a common ancestral stock in similar directions with respect of some variables such as developmental speed, but haphazardly in respect of other parameters such as male weight. The respective roles of drift and of selection as effective evolutionary forces in inbred lines are discussed in the light of these results. It is argued that some intraspecific differences in C. maculatus may be explained as a product of periodic inbreeding, but that the process does not impair the ability to adapt to local conditions so contributing to the status of the species as a pest of international importance.     

紫穗槐叶片浸提液对长柄扁桃种子萌发和幼苗生长的影响

紫穗槐和长柄扁桃是中国西北干旱和半干旱地区的常见绿化植物.为探索紫穗槐搭配长柄扁桃进行绿化建设和生态修复的可行性,采用培养皿滤纸法和土培法测定了5种质量浓度的紫穗槐叶片浸提液(0.025、0.05、0.10、0.15和0.20 g ? mL-1)对长柄扁桃8个品种(YY1、YY3、YY4、YY5、YY6、SM6、SM7...