榕小蜂的产卵模式及其对子代性比的影响

于2007年4月—2007年7月在中国科学院西双版纳热带植物园,通过干预控制榕小蜂产卵的方法研究了聚果榕的传粉榕小蜂Ceratosolen fusciceps和非传粉小蜂Platyneura mayri及垂叶榕的非传粉小蜂Acophila sp.1和Wakerella benjamini等的产卵顺序。对传粉榕小蜂,在完成放蜂后不同间隔时间向榕果内注入乙醚杀死小蜂;对非传粉榕小蜂,在放蜂后不同间隔时间将其从纱网袋内全部放出,从而控制了各种榕小蜂的产卵时间。到榕果成熟后,收集了榕果内的小蜂,并分析比较各种榕小蜂在不同产卵时间下的子代性比。结果表明：Ceratosolen fusciceps、P. mayri和Acophila sp.1在产卵的最初时间内倾向于产下更多的雄性后代,而随后的时间内则产下更多的雌性伴随少量的雄性后代,这样的产卵顺序导致子代性比随着母代产卵时间的延长而下降,榕小蜂后代雌性比例显著高于雄性。同时,子代榕小蜂数量随母代产卵时间的延长而增加,这在一定程度上解释了单头繁殖雌蜂的子代性比随子代数量的增加而减少的现象。而Wakerella benjamini在产卵顺序上是随机的,在其开始产卵后的不同时间段内子代性比都接近于50%。这一结果表明榕小蜂的产卵顺序与母代产卵时间的长短对子代性比有极为重要的影响。     

Opportunistic predation and offspring sex ratios of cicada-killer wasps (Sphecius speciosus Drury)

Abstract.  1. The way in which hunting of prey affects the sex ratio of the predator's offspring is not well understood. Female cicada-killer wasps are convenient for study because they specialise in capturing cicadas to provision their offspring. Cicada prey are nearly twice as heavy as the wasps that carry them, hence some degree of prey selectivity by the wasps is to be expected. It has been suggested that wasps bias their offspring towards females by foraging selectively for female prey, whereas there is some evidence that sex ratios are actually male-biased. This study was designed to establish the connection between foraging and offspring sex ratio.
2. Three, non-exclusive, hypotheses of selective predation were tested. The frequency of predation on different classes of prey in conjunction with their availability was estimated by intercepting the wasps on their way to their nests and by sampling cicadas in the environment. The hypothesis of selective predation was not supported; predation appears to be opportunistic and non-selective. Cicada prey weight was not a simple linear function of wasp weight, although the smallest wasps were constrained to carry small prey.
3. Wasp offspring (larvae) were excavated from subterranean nests and found to be male-biased (3 : 1 or 4 : 1) in 2 years. The observed ratios are close to expectation from Fisher's equal-investment model, taking account of sexual size dimorphism, and are evidently unrelated to the sex of the prey. A simple binomial probability rule of sex allocation provides a behavioural mechanism for producing the observed sex ratio of offspring.     

Finding hidden females in a crowd: Mate recognition in fig wasps

Multi-species mating aggregations are crowded environments within which mate recognition must occur. Mating aggregations of fig wasps can consist of thousands of individuals of many species that attain sexual maturity simultaneously and mate in the same microenvironment, i.e, in syntopy, within the close confines of an enclosed globular inflorescence called a syconium – a system that has many signalling constraints such as darkness and crowding. All wasps develop within individual galled flowers. Since mating mostly occurs when females are still confined within their galls, male wasps have the additional burden of detecting conspecific females that are “hidden” behind barriers consisting of gall walls. In Ficus racemosa, we investigated signals used by pollinating fig wasp males to differentiate conspecific females from females of other syntopic fig wasp species. Male Ceratosolen fusciceps could detect conspecific females using cues from galls containing females, empty galls, as well as cues from gall volatiles and gall surface hydrocarbons.In many figs, syconia are pollinated by single foundress wasps, leading to high levels of wasp inbreeding due to sibmating. In F. racemosa, as most syconia contain many foundresses, we expected male pollinators to prefer non-sib females to female siblings to reduce inbreeding. We used galls containing females from non-natal figs as a proxy for non-sibs and those from natal figs as a proxy for sibling females. We found that males preferred galls of female pollinators from natal figs. However, males were undecided when given a choice between galls containing non-pollinator females from natal syconia and pollinator females from non-natal syconia, suggesting olfactory imprinting by the natal syconial environment.     

Putting your sons in the right place: the spatial distribution of fig wasp offspring inside figs

Abstract. 1. Pollinating fig wasps (Hymenoptera, Agaonidae) display sex ratio adjustment, producing less female‐biased combined sex ratios as the number of ovipositing females (foundresses) inside a fig increases. Because males have low mobility, the oviposition sites (galled ovules) chosen by each foundress are likely to have consequences for the mating structure of wasp populations within the figs. 2. In this study, the spatial location of male and female progeny of the pollinating fig wasp Liporrhopalum tentacularis developing within figs of its host plant Ficus montana was examined to investigate two questions: (i) are male and/or female wasp offspring clustered together or interspersed? and (ii) is their distribution affected by whether one or two foundresses are present? Microsatellite markers were used to identify the progeny of different foundresses in dual‐foundress figs. 3. More offspring developed in the central part of the figs, compared with the ostiolar and basal parts, irrespective of foundress number. Neither male nor female wasp offspring were clustered within a fig. 4. The sons of the second foundress to enter a fig were positioned at similar minimum distances to both sibling and non‐sibling females, whereas the sons of the first foundress were closer to their sibling females than to non‐sibling females. If male wasps mate predominantly with females in adjacent galls, then the positioning of sons by the second foundresses is beneficial for them both in terms of reduced sibling mating and because they are provided with ready access to the female progeny of the first foundress.     

Maternal predator‐exposure affects offspring size at birth but not telomere length in a live‐bearing fish

The perception of predation risk could affect prey phenotype both within and between generations (via parental effects). The response to predation risk could involve modifications in physiology, morphology, and behavior and can ultimately affect long‐term fitness. Among the possible modifications mediated by the exposure to predation risk, telomere length could be a proxy for investigating the response to predation risk both within and between generations, as telomeres can be significantly affected by environmental stress. Maternal exposure to the perception of predation risk can affect a variety of offspring traits but the effect on offspring telomere length has never been experimentally tested. Using a live‐bearing fish, the guppy (Poecilia reticulata), we tested if the perceived risk of predation could affect the telomere length of adult females directly and that of their offspring with a balanced experimental setup that allowed us to control for both maternal and paternal contribution. We exposed female guppies to the perception of predation risk during gestation using a combination of both visual and chemical cues and we then measured female telomere length after the exposure period. Maternal effects mediated by the exposure to predation risk were measured on offspring telomere length and body size at birth. Contrary to our predictions, we did not find a significant effect of predation‐exposure neither on female nor on offspring telomere length, but females exposed to predation risk produced smaller offspring at birth. We discuss the possible explanations for our findings and advocate for further research on telomere dynamics in ectotherms.     

Determination of the optimal parasitoid‐to‐host ratio for efficient mass‐rearing of the parasitoid,Sclerodermus pupariae (Hymenoptera: Bethylidae)

Sclerodermus pupariae Yang et Yao (Hymenoptera: Bethylidae) is used as a potential biocontrol agent for several buprestid and cerambycid larvae. This study aimed to enhance the efficiency of mass‐rearing of this parasitoid by investigating the fitness gain of this bethylid wasp, including the proportion of successful parasitism and development, brood size, sex ratio, proportion of winged female offspring, body size and longevity of female offspring, under eight different maternal parasitoid density treatments using Thyestilla gebleri Faldermann as host in the laboratory. The results indicated that the foundress densities did not affect the parasitism or emergence rate of this parasitoid. Brood size of the parasitoids increased significantly when the number of maternal wasps ranged from one to four. However, further increases in foundress number did not affect the parasitoid brood size. The sex ratios of S. pupariae were always female‐biased. The proportions of male in the progeny colonies were <10% throughout all experimental treatments. The percentage of winged female progeny was not significantly influenced by the density of adult maternal parasitoids. Body sizes of parasitoids significantly declined with increasing maternal parasitoid densities. Although the parasitoid body size reduced when maternal wasp number was higher, it could be compromised by the relatively higher number of female offspring produced. Further, more than 70% of the parasitoids remained alive when they were stored at 12°C for four months throughout the experiments. These findings suggest that exposure of four female wasps to a single host larva would result in the highest fitness of S. pupariae. Our findings might provide a new approach to enhance the efficiency of mass‐rearing of this bethylid wasp.     

Increased performance of offspring sired by parasitic males in bluegill sunfish

Males of many species are characterized by alternative matingtactics. In bluegill sunfish (Lepomis macrochirus), some malesdelay maturation and become "parentals" while other males matureprecociously and become "cuckolders." Parentals use an overt,territorial mating tactic, defending a nest and courting females.Cuckolders instead use a sneaking tactic to parasitize parentals.It has previously been shown that parentals that are heavilycuckolded provide less care to their young, yet females do notappear to discriminate against cuckolders, and they may actuallyrelease more eggs when a cuckolder is present than when spawningonly with a parental. Here I examined growth rate of fry ofknown paternity through the yolk-sac stage of development usingcomplementary laboratory and field studies to assess a potentialindirect benefit for females that mate with cuckolders. Comparisonof maternal half-siblings sired in vitro shows that cuckolderoffspring grow faster and to a larger size than parental offspringwhile feeding endogenously on their yolk sac. Because both foodresource and maternal genes are equivalent across treatments,these data indicate a genetic difference in growth between thetwo male life histories. In the field, fry from nests that haveproportionately more cuckolder offspring are larger when theyemerge from the nest. This increased size can lead to threefoldhigher survivorship for cuckolder offspring than parental offspringfrom Hydra canadensis predation, a major predator of bluegillfry. These results are discussed in the context of mate choicefor direct and indirect benefits and in the context of the evolutionof alternative mating tactics.     

Phenotypic selection and function of reproductive behavior in the subsocial bug Elasmucha putoni (Heteroptera: Acanthosomatidae)

To investigate the function of maternal care and determinantsof reproductive success in the subsocial bug Elasmucha putoni (Heteroptera: Acanthosomatidae), I used two different approaches,the measurement of phenotypic selection and female-removalexperiments under conditions differing in biotic-environmentalpressure. For two field populations, unattended eggs and youngernymphs consistently suffered severe predation pressure andattendance by parent females greatly enhanced their survival.In contrast, under enemy-excluded conditions, offspring performance was not reduced in broods without parent females, indicatingthat maternal care functions as a physical defense againstpredators. However, the determinant of female reproductivesuccess in E. putoni in the field was not the care behavioralone. Selection gradient analysis showed that early seasonoviposition and larger clutch size, as well as a longer durationof care by a female, was favored during the breeding episode.This study is the first to evaluate phenotypic selection onparental care and other reproductive traits in arthropods.     

Strike Fast,Strike Hard: The Red-Throated Caracara Exploits Absconding Behavior of Social Wasps during Nest Predation

Red-throated Caracaras Ibycter americanus (Falconidae) are specialist predators of social wasps in the Neotropics. It had been proposed that these caracaras possess chemical repellents that allow them to take the brood of wasp nests without being attacked by worker wasps. To determine how caracaras exploit nests of social wasps and whether chemical repellents facilitate predation, we: (1) video recorded the birds attacking wasp nests; (2) analyzed surface extracts of the birds'' faces, feet, and feathers for potential chemical repellents; and (3) inflicted mechanical damage on wasp nests to determine the defensive behavior of wasps in response to varying levels of disturbance. During caracara predation events, two species of large-bodied wasps mounted stinging attacks on caracaras, whereas three smaller-bodied wasp species did not. The “hit-and-run” predation tactic of caracaras when they attacked nests of large and aggressive wasps reduced the risk of getting stung. Our data reveal that the predation strategy of caracaras is based on mechanical disturbance of, and damage to, target wasp nests. Caracara attacks and severe experimental disturbance of nests invariably caused wasps to abscond (abandon their nests). Two compounds in caracara foot extracts [sulcatone and iridodial] elicited electrophysiological responses from wasp antennae, and were also present in defensive secretions of sympatric arboreal-nesting Azteca ants. These compounds appear not to be wasp repellents but to be acquired coincidentally by caracaras when they perch on trees inhabited with Azteca ants. We conclude that caracara predation success does not depend on wasp repellents but relies on the absconding response that is typical of swarm-founding polistine wasps. Our study highlights the potential importance of vertebrate predators in the ecology and evolution of social wasps.     

Spatial Nest‐Settlement Decisions in Digger Wasps: Conspecifics Matter more than Heterospecifics and Previous Experience

Research into the driving forces behind spatial arrangement of wasp nests has considered abiotic environmental factors, but seldom investigated attraction or repulsion towards conspecifics or heterospecifics. Solitary female digger wasps (Hymenoptera) often nest in dense aggregations, making these insects good models to study this topic. Here, we analysed the nesting patterns in an area shared by three species of the genus Bembix, in a novel study to discover whether female wasps are attracted to or repulsed by conspecific nests, heterospecific nests or their own previously established nests when choosing nest‐digging locations. Early in the season, each species showed a clumping pattern of nests, but later in the season, a random distribution of nests was more common, suggesting an early conspecific attraction. Such behaviour was confirmed by the fact that females started building their nests more frequently where other females of their species were simultaneously digging. The distances between subsequent nests dug by individual females were shorter than those obtained by random simulations. However, this pattern seemed to depend on the tendency to dig close to conspecifics rather than remain in the vicinity of previous nests, suggesting that females' experience matters to future decisions only on a large scale. Nesting patches within nest aggregations largely overlapped between species, but the nests of each species were generally not closer to heterospecific nests than expected by chance, suggesting that females are neither repulsed by, nor attracted to, congenerics within nest aggregations. A role of the spatial distribution of natural enemies on the observed nesting patterns seemed unlikely. Bembix digger wasp nest aggregations seem thus to be primarily the result of female–female attraction during nest‐settlement decisions, in accordance with the ‘copying’ mechanisms suggested for nesting vertebrates.     

美丽青背姬小蜂生物学特性研究

美丽青背姬小蜂Chrysonotomyiaformosa（Westwood）是美洲斑潜蝇的优势天敌,在美洲 斑潜蝇的自然控制中发挥着非常重要的作用。本文对其生物学进行了研究,结果表明：在实验 温度范围内,随着温度的升高,寄生蜂羽化趋早,羽化时间更集中,羽化高峰也更明显;随着 温度的升高,成蜂的寿命逐渐缩短。在提供清水时,寄主可以显著地延长雌蜂的寿命;在有寄 主时,提供10%蜂蜜水,雌蜂的寿命显著延长。美丽青背姬小蜂对3龄寄主幼虫有偏好,对3龄寄 主幼虫的致死率和寄生率都高于对1～2龄寄主幼虫的,且产下后代的雌雄性比为5.11∶1。在 实验温度范围内,发育历期随温度的升高而缩短。     

Sex ratio manipulation by the parasitoid waspSpalangia cameroni in response to host age: A test of the host-size model

Summary A sex ratio response to host resources as measured by external host dimensions has been demonstrated in many parasitoid wasps, includingSpalangia cameroni. The responses generally are in the direction predicted by sex ratio theory, specifically the host-size models. Here I show that femaleS. cameroni also respond to differences in resource availability not associated with changes in external host dimensions, and this response is in the direction predicted by host-size models. When given old and young hosts simultaneously, femaleS. cameroni oviposit a greater proportion of sons in old than in young host pupae, at least for 0-day old versus 3-day old hosts. Old hosts weigh less than young hosts but are not significantly different in external width. Thus it appears that the offspring sex ratio response may result from mothers detecting physical or chemical changes within the host which are associated with host age. No evidence is found that the manipulation in response to host age has been selected for via an effect of host age on wasp size; there was no significant effect of host age on either male of female wasp size. A second prediction of the host-size models is also supported by this study: when each female is presented with only a single host age, rather than two host ages simultaneously, host age has no effect on offspring sex ratio.     

Host influences on sex ratio, longevity, and egg load of two Metaphycus species parasitic on soft scales: implications for insectary rearing

Metaphycus flavus (Howard) and M. stanleyi Compere (Hymenoptera: Encyrtidae) are currently being screened for use as augmentative biological control agents of citrus-infesting soft scales (Homoptera: Coccidae). Two factors were investigated, host quality-dependent sex allocation and local mate competition, which likely influence these parasitoid's sex allocation strategies and are therefore of interest for their mass-rearing. The results of these studies suggested that, under the mass-rearing protocol that is envisioned for these parasitoids, offspring sex ratios in both M. flavus and M. stanleyi are dominated by host quality (= size) influences, but not by interactions with other females. These results indicated that host size strongly influences offspring sex ratios and brood sizes; larger hosts led to more female offspring and larger broods. In contrast, increasing the number of parental females did not lead to fewer female offspring as expected under local mate competition. Additionally, within-brood sex ratios did not vary with brood size; this result is inconsistent with expected sex ratios due to local mate competition. Other results also indicated that host quality was a dominant influence on M. flavus' and M. stanleyi's sex ratios. Larger hosts led to a larger size in the emerging wasps, and larger wasps had greater egg loads and lived longer than smaller wasps. However, wasp longevity, and the influence of wasp size on longevity were mediated by a wasp's diet. Metaphycus flavus females lived the longest when they had access to hosts, honey, and water, followed by honey and water, and shortest when they had access to water alone; M. stanleyi females lived longest with honey and water, followed by hosts, honey, and water, and shortest with water alone. Greater wasp size led to greater longevity in females only when they had access to food (honey, or hosts and honey). Finally, other results suggested that both M. flavus and M. stanleyi are facultatively gregarious. Wasp size did not decrease with brood size as expected under superparasitism. Overall, the results of these studies suggested that holding newly emerged females of both M. flavus and M. stanleyi for several days in the presence of an appropriate food source before field release could enhance a female's performance as an augmentative biological control agent. It increases their initial life expectancy following release, and maximizes the females' egg load (both Metaphycus species) and resources for replacing oviposited eggs (M. flavus only).     

Social wasps desert the colony and aggregate outside if parasitized: parasite manipulation?

Infection of the paper wasp, Polistes dominulus (Christ), bythe strepsipteran parasite Xenos vesparum Rossi results in adramatic behavioral change, which culminates in colony desertionand the formation of extranidal aggregations, in which up to98% of occupants are parasitized females. Aggregations formedon prominent vegetation, traditional lek-sites of Polistes males,and on buildings, which were later adopted as hibernating sitesby future queens. First discovered by W.D. Hamilton, these aberrantaggregations are an overlooked phenomenon of the behavioralecology of this intensively studied wasp. For 3 months in thesummer of 2000, during the peak of colony development, we sampled91 extranidal aggregations from seven areas, numbering 1322wasps. These wasps were parasitized by both sexes of X. vesparum,but males were more frequent from July until mid-August, duringthe mating season of the parasite. Aggregations were presentfor days at the same sites (in one case a leaf was occupiedfor 36 consecutive days) and were characterized by extreme inactivity.After artificial infection, parasitized "workers" deserted thenest 1 week after emergence from their cell and before the extrusionof the parasite through the host cuticle. Infected individualsdid not work, were more inactive, and did not receive more aggressionthan did controls. We suggest that early nest desertion andsubsequent aggregations by parasitized nominal workers and "futurequeens" is adaptive manipulation of host behavior by the parasiteto promote the completion of its life cycle.     

Why make daughters larger? Maternal sex-allocation and sex-dependent selection for body size in a mass-provisioning wasp, Trypoxylon politum

Mass-provisioning wasps package maternal investment into broodcells, sealed structures that contain all the provisions necessaryfor an offspring's growth and development. Optimal sex-allocationtheory predicts that if maternal provisions determine the sizeof each offspring, and the amount of provisions available toeach offspring varies, females should allocate well-stockedbrood cells to the sex that benefits most from being large.I tested this hypothesis using observations of organ-pipe wasps,Trypoxylon politum, and dissections of their nests. A Mississippipopulation of T. politum was intensively studied from 1993 to1995. This population fit the assumptions of optimal sex-allocationmodels by Green and Brockmann and Grafen. Female weight at emergencewas 1.29 times that of males, and wing length was 1.15 timesthat of males. This discrepancy in size occurred because thevolume of parental provisions strongly influenced adult bodysize, and better-stocked brood cells were preferentially allocatedto daughters. Brood-cell volume correlated with both wing lengthand weight at emergence in both sexes, and the chance that agiven brood cell contained a female offspring increased withincreasing brood-cell volume. Fitness was positively relatedto body size for females, but I found no evidence of an advantageto large males. Although there was evidence of stabilizing selectionfor male wing length in one year, there was no evidence of anincreasing relationship between body size and fitness (directionalselection) for males in either 1993 or 1994. Female fecunditywas positively related to body size in both years, indicatingthat larger females have increased reproductive success. Therate at which females provisioned brood cells was also correlatedwith body size. Observed patterns of investment in brood cellsare quantitatively consistent with the predictions of optimalsex-allocation theory, but certain aspects of female provisioningbehavior suggest females are not following a single "optimal"strategy. Patterns of provisioning were variable among differentfemales at the study site during the same year. Large femalestended to produce larger offspring. Although Brockmann and Grafen'smodel predicts a single, population wide "switchpoint" fromthe production of male to female offspring, there was no evidencefor such a switchpoint     

Biased oviposition and biased survival together help resolve a fig–wasp conflict

We report evidence that helps resolve two competing explanations for stability in the mutualism between Ficus racemosa fig trees and the Ceratosolen fusciceps wasps that pollinate them. The wasps lay eggs in the tree's ovules, with each wasp larva developing at the expense of a fig seed. Upon maturity, the female wasps collect pollen and disperse to a new tree, continuing the cycle. Fig fitness is increased by producing both seeds and female wasps, whereas short‐term wasp fitness increases only with more wasps, thereby resulting in a conflict of interests. We show experimentally that wasps exploit the inner layers of ovules first (the biased oviposition explanation), which is consistent with optimal‐foraging theory. As oviposition increases, seeds in the middle layer are replaced on a one‐to‐one basis by pollinator offspring, which is also consistent with biased oviposition. Finally, in the outer layer of ovules, seeds disappear but are only partially replaced by pollinator offspring, which suggests high wasp mortality (the biased survival or ‘unbeatable seeds’ explanation). Our results therefore suggest that both biased oviposition and biased survival ensure seed production, thereby stabilizing the mutualism. We further argue that biased oviposition can maintain biased survival by selecting against wasp traits to overcome fig defenses. Finally, we report evidence suggesting that F. racemosa balances seed and wasp production at the level of the tree. Because figs are probably selected to allocate equally to male and female function, a 1:1 seed:wasp ratio suggests that fig trees are in control of the mutualism.     

Measuring the discrepancy between fecundity and lifetime reproductive success in a pollinating fig wasp

Lifetime reproductive success in female insects is often egg‐ or time‐limited. For instance in pro‐ovigenic species, when oviposition sites are abundant, females may quickly become devoid of eggs. Conversely, in the absence of suitable oviposition sites, females may die before laying all of their eggs. In pollinating fig wasps (Hymenoptera: Agaonidae), each species has an obligate mutualism with its host fig tree species [Ficus spp. (Moraceae)]. These pro‐ovigenic wasps oviposit in individual ovaries within the inflorescences of monoecious Ficus (syconia, or ‘figs’), which contain many flowers. Each female flower can thus become a seed or be converted into a wasp gall. The mystery is that the wasps never oviposit in all fig ovaries, even when a fig contains enough wasp females with enough eggs to do so. The failure of all wasps to translate all of their eggs into offspring clearly contributes to mutualism persistence, but the underlying causal mechanisms are unclear. We found in an undescribed Brazilian Pegoscapus wasp population that the lifetime reproductive success of lone foundresses was relatively unaffected by constraints on oviposition. The number of offspring produced by lone foundresses experimentally introduced into receptive figs was generally lower than the numbers of eggs carried, despite the fact that the wasps were able to lay all or most of their eggs. Because we excluded any effects of intraspecific competitors and parasitic non‐pollinating wasps, our data suggest that some pollinators produce few offspring because some of their eggs or larvae are unviable or are victims of plant defences.     

Costs and benefits of colony aggregation in the social wasp, Polistes annularis

Females of the social wasp, Polistes annularis, nest in largeaggregations onriverside cliffs in central Texas. Aggregationsoccur where there is an overhang under which wasps build theirnests. Colony aggregations appear to occur partly because individualfemales do notdisperse far from the natal site where most coloniesare successful. In most taxa greater reproductive success nearthe natal nest site is related to unique physical features orto advantages ofbeing in a group. In P. annularis, the physicalfactors and not the social factors appear to be most important.Advantages to remaining near the natal nest site include protectionprovided by the cliff overhang from rain and afternoon sun.Central colonies are as likely to suffer predation as are peripheralcolonies, which indicates an absence of selfish herd advantagesto being in the center of the group. A cost of being in a denseaggregation is often increased reproductive competition, andthis is the case for P. annularis. Colonies in the center ofthe aggregation suffer high usurpation rates by unrelated femalesand in 1 of 3 years produced fewer reproductives than edge colonies.     

Influence of Inter-Lake Variation in Natural Nest Predation Pressure on the Parental Care Behaviour of Smallmouth Bass (Micropterus dolomieu)

Predation risk has the ability to greatly influence the behaviour of reproducing individuals. In large long-lived species with low risk of predation for parents, reproductive behaviours often involve caring for offspring (i.e. defending broods from predators) and these behaviours are essential for offspring survival. Our objectives were to test for the presence of natural variation in nest predation pressure in an aquatic environment for a species that provides sole-paternal care, smallmouth bass ( Micropterus dolomieu ), and to determine if natural variation in predation pressure influences parental care behaviour. We used snorkeler observations and a series of metrics to assess predation pressure and parental care behaviour in six lakes within a narrow geographical range. Lakes differed in all predation pressure metrics: number of predators in proximity to nest when males were present, time to predator arrival and number of predators that consumed eggs when males were absent and total number of nests that was preyed upon. Similarly, parental behaviour varied between lakes. Parental smallmouth bass spent more time engaged in anti-predator defences in lakes with high predation pressure, while males from low predator pressure lakes remained close to their nest. Conversely, males from lakes with low and high predation pressure showed a similar willingness to defend their nests during simulated nest predation events. Our results show that natural variation in aquatic nest predation pressure across multiple lakes can be significant and has the ability to influence baseline parental care behaviour. Such variation provides opportunities to study the costs and consequences of parental care and to evaluate how this could influence demography and community interactions in aquatic systems.     

Mothers modify eggs into shields to protect offspring from parasitism

Eggs are an immobile, vulnerable stage of development and their success often depends on the oviposition decisions of the mother. Studies show that female animals, and sometimes males, may invest parental resources in order to increase the survival of their offspring. Here, we describe a unique form of parental investment in offspring survival. The seed beetle Mimosestes amicus may lay eggs singly, or may cover eggs with additional egg(s). This egg stacking serves to significantly reduce the mortality of the protected egg from parasitism by the parasitic wasp, Uscana semifumipennis. The smaller top eggs serve only as protective shields; they are inviable, and wasps that develop in them suffer negative fitness consequences. Further, we found egg stacking to be inducible; M. amicus increase the number of stacks they lay when parasitoids are present. However, stacking invokes a cost. When wasps are absent, beetles lay more single eggs, and produce more offspring, highlighting the adaptive value of this extraordinary example of behavioural plasticity in parental investment.