Egg trading in the simultaneously hermaphroditic polychaete worm Ophryotrocha gracilis (Huth)

Ophryotrocha gracilis (Huth 1934) is a simultaneously hermaphroditicpolychaete worm with external fertilization and a brief protandrousphase. The mating system of this species seems to meet conditionsleading to the establishment of egg-trading behavior. Experimentsshowed that mating occurs in pairs composed of two simultaneoushermaphrodites; sex roles are sequentially alternated and self-fertilizationis avoided. Egg reciprocation is kept evolutionarily stableby laying eggs in multiple, small-sized egg clutches and reducingthe reproductive success of pairs in which one of the two partnersdoes not reciprocate egg exchange. The frequency of ovigeroushermaphrodites in mass cultures of O. gracilis is about 50".Such a high mate availability preadapts hermaphrodites of O.gracilis to change partners very frequently and to reduce investmentin parental care, contrary to what is observed in another egg-trading,simultaneously hermaphroditic species, O. diadema. Laboratorypopulations of O. diadema have a frequency of only 17% ovigeroushermaphrodites     

Nest desertion by a cowbird host: an antiparasite behavior or a response to egg loss?

Natural selection can favor songbirds that desert nests containingeggs of the parasitic brown-headed cowbird (Molothrus ater).However, the high variability in desertion of parasitized nestswithin species is perplexing in light of the typically highcosts of parasitism. Because nest desertion can also be a responseto partial clutch predation, we first asked if Bell's vireos(Vireo bellii) deserted nests in response to the presence ofcowbird eggs (antiparasite response hypothesis) or to egg removalby predators and female cowbirds (egg predation hypothesis).Second, we asked whether variation in nest desertion was dueto intrinsic differences among individuals or to variation innest contents. We monitored a large number of nests (n = 494)and performed a clutch manipulation experiment to test thesehypotheses. The number of vireo eggs that remained in a nestwas a strong predictor of desertion both within and among pairs.Neither the presence of a single cowbird egg, which leads tonest failure for this host, nor the number of cowbird eggs receivedin a vireo nest influenced nest desertion. Furthermore, vireosdid not desert experimental nests when we immediately exchangedcowbird eggs for vireo eggs but deserted if we removed vireoeggs and replaced them with cowbird eggs the following morning.Desertion of parasitized nests by Bell's vireos can be almostentirely explained as a response to partial or complete clutchloss and does not appear to have been altered by selection frombrood parasitism.     

UTILIZATION AND DEGREE OF DEPLETION OF EXOGENOUS SPERM IN THREE HERMAPHRODITIC SEA HARES OF THE GENUS APLYSIA (GASTROPODA: OPISTHOBRANCHIA)

Two series of experiments were conducted to examine the utilizationof exogenous sperm and their degree of depletion in three hermaphroditicsea hares, Aplysia kurodai Baba, 1937, A. Juliana Quoy &Gaunard, 1832, and A. parvula Guilding in MOrch, 1863. The firstseries of experiments was designed to determine whether onemating is enough for female partners to receive sufficient spermto fertilize at least one egg mass. For this purpose, isolatedindividuals were mated as females once with conspecific individualsand the viability of their subsequent eggs was examined. Whensuccessfully inseminated, individuals of all the three speciesreceived enough sperm to fertilize at least one egg mass, andthey continued to lay 3.6–8.5 viable egg masses. However,10–36% of the matings by these sea hares did not resultin any viable egg production by the female partner, indicatingthat these matings did not involve sperm transfer Such matingswithout sperm transfer tended to be shorter than matings withsuccessful sperm transfer The second experimental series wasconducted to examine whether sperm depletion actually occursor not in field-caught adults. For this purpose, adult individualscaught in the field were allowed to lay eggs under isolatedconditions without mating All the individuals of A. kurodaiand A. juliana stored enough sperm to fertilize at least oneegg mass. However, in A. parvula, 23–33% of individualslaid egg masses containing non-viable eggs at their first spawningafter isolation, indicating that these individuals were depletedin exogenous sperm (Received 17 July 1995; accepted 18 August 1995)     

EVOLUTION OF BIPARENTAL CARE IN THE HERMAPHRODITIC POLYCHAETE WORM OPHRYOTROCHA DIADEMA

Ophryotrocha diadema is a simultaneously hermaphroditic polychaete worm with a brief adolescent protandrous phase. In the mating system of this worm, pairs are formed preferentially between simultaneous hermaphrodites. Both partners of a pair regularly alternate sex roles, reciprocate egg exchange, and care for developing embryos. It was experimentally shown that neglected eggs have a 31% probability of dying, but eggs cared for by both parents, by a single parent, or even by an unrelated individual have a 95% probability of developing. In pairs experimentally prevented from caring for eggs, intruders succeeded in substituting one of the partners significantly more frequently than in pairs allowed to care for eggs. Thus, the main adaptive value of biparental care would be to guarantee a partner for egg reciprocation. Protandrous males are inefficient brooders, and biparental care becomes fully established only when individuals are able to reciprocate egg exchange, i.e., they have reached the simultaneously hermaphroditic stage.     

Brood parasitism selects for no defence in a cuckoo host

In coevolutionary arms races, like between cuckoos and their hosts, it is easy to understand why the host is under selection favouring anti-parasitism behaviour, such as egg rejection, which can lead to parasites evolving remarkable adaptations to ‘trick’ their host, such as mimetic eggs. But what about cases where the cuckoo egg is not mimetic and where the host does not act against it? Classically, such apparently non-adaptive behaviour is put down to evolutionary lag: given enough time, egg mimicry and parasite avoidance strategies will evolve. An alternative is that absence of egg mimicry and of anti-parasite behaviour is stable. Such stability is at first sight highly paradoxical. I show, using both field and experimental data to parametrize a simulation model, that the absence of defence behaviour by Cape bulbuls (Pycnonotus capensis) against parasitic eggs of the Jacobin cuckoo (Clamator jacobinus) is optimal behaviour. The cuckoo has evolved massive eggs (double the size of bulbul eggs) with thick shells, making it very hard or impossible for the host to eject the cuckoo egg. The host could still avoid brood parasitism by nest desertion. However, higher predation and parasitism risks later in the season makes desertion more costly than accepting the cuckoo egg, a strategy aided by the fact that many cuckoo eggs are incorrectly timed, so do not hatch in time and hence do not reduce host fitness to zero. Selection will therefore prevent the continuation of any coevolutionary arms race. Non-mimetic eggs and absence of defence strategies against cuckoo eggs will be the stable, if at first sight paradoxical, result.     

Nest desertion cannot be considered an egg‐rejection mechanism in a medium‐sized host: an experimental study with the common blackbird Turdus merula

Two main mechanisms of egg rejection, the main defence of hosts against brood parasites, have been described: ejection and desertion. Desertion of the parasitized nest is much more costly and is usually exhibited by small‐sized host species unable to remove the parasitic egg. However, nest desertion is frequently assumed to be an anti‐parasite strategy even in medium or large‐sized host species. This assumption should be considered with caution because: 1) large‐sized hosts able to eject the parasitic egg should eject it rather than desert the nest, and 2) breeding birds may desert their nests in response to different disturbances other than brood parasitism. This problem is especially important in the common blackbird Turdus merula because this is a medium‐sized species, potential host of the common cuckoo Cuculus canorus, in which desertion has been frequently reported as a response to cuckoo egg models. Here, we seek to determine whether nest desertion can be considered a response unequivocally directed to the parasitic egg in medium‐sized hosts using the blackbird as the study species. In an experimental study in which we have manipulated levels of mimicry and size of experimental eggs, we have found that both colour (mimetic and non‐mimetic; at least for human vision) and size (small, medium, and large) significantly affected ejection rates but not nest desertion rates. In fact, although large eggs disproportionally provoked nest desertion more frequently than did small or medium‐sized eggs, cuckoo‐sized parasitic eggs were not deserted allowing us to conclude that desertion is unlikely to be an adaptive response to brood parasitism at least for this species.     

Egg discrimination in the Australian reed warbler (Acrocephalus australis): rejection response toward model and conspecific eggs depending on timing and mode of artificial parasitism

In a coevolutionary arms race between an interspecific broodparasite and its host species, both are expected to evolveadaptations and counteradaptations. We studied egg discriminationin the Australian warbler (Acrocephalus australis). This speciesis currently not significantly parasitized by the seven speciesof cuckoo for which it is a suitable host. However, experimentalbrood parasitism in the warbler revealed a fine tuned egg discriminationresponse towards non-mimetic and conspecific eggs, the firstsuch evidence in an Australian passerine: (1) non-mimetic eggswere significantly more often rejected than conspecific eggs;(2) only non-mimetic dummy eggs were rejected selectively,whereas rejection of conspecific eggs entailed a rejectioncost; (3) replacement of a host's egg with a conspecific eggduring egg laying resulted in a significantly higher rejectionrate than after the day of clutch completion; (4) by contrast,rejection rate after addition of a conspecific egg was independentof nest stage; (5) conspecific eggs introduced into a clutchduring the egg laying period led to a significantly highernest desertion rate and a lower egg ejection rate than afterthe day of clutch completion; and (6) addition of a conspecificegg led to egg ejection while egg replacement with a conspecificegg led to nest desertion. The fact that this species respondsdifferentially toward different modes of artificial parasitismsuggests that its egg discrimination has evolved to minimizethe costs of rejection and parasitism. The ability to rejecthighly mimetic conspecific eggs may explain the current paucityof brood parasitism in this species. The significance of thisfor brood parasite-host coevolution is discussed.     

Size and material of model parasitic eggs affect the rejection response of Western Bonelli's Warbler Phylloscopus bonelli

Given the high costs of brood parasitism, avian hosts have adopted different defences to counteract parasites by ejecting the foreign egg or by deserting the parasitized nest. These responses depend mainly on the relative size of the host compared with the parasitic egg. Small hosts must deal with an egg considerably larger than their own, so nest desertion becomes the only possible method of egg rejection in these cases. The use of artificial model eggs made of hard material in egg‐recognition experiments has been criticized because hard eggs underestimate the frequency of egg ejection. However, no available studies have investigated the effect of softer material. Here, we test the potential effect of size of dummy parasitic eggs in relation to egg‐rejection behaviour (egg ejection and nest desertion rates) in Western Bonelli's Warbler Phylloscopus bonelli, a small host, using plasticine non‐mimetic eggs of three different sizes. In addition, we tested the potential effect of material, comparing ejection and desertion responses between real and plasticine eggs. As predicted, small eggs were always ejected, whereas nest desertion occurred more frequently with large eggs, thus suggesting that nest desertion occurs because of the constraints imposed by the large eggs. We found that plasticine may misrepresent the responses to experimental parasitism, at least in small host species, because this material facilitates egg ejection, provoking a decrease in nest desertion rate. Thus, particular caution is needed in the interpretation of the results in egg‐rejection experiments performed using dummy eggs made of soft materials.     

Rejection of cuckoo (Cuculus canorus) eggs by meadow pipits (Anthus pratensis)

Meadow pipits (Anthus pratensis) normally accept mimetic cuckoo(Cuculus canorus) eggs laid in their nests. In field experimentsin which a mimetic or a nonmimetic model cuckoo egg was placedin meadow pipit nests, those hosts that were simultaneouslypresented with a cuckoo dummy mounted beside the nest showeda significantly higher ability to recognize and reject (normallyby desertion) the parasite's egg than those that were not presentedwith the dummy. In the present study we sought to answer thequestion of why meadow pipits do not always (i.e., even whenno cuckoo was visible) reject cuckoo eggs. The results fromthe field experiments provide support for a theory that two"brood parasite" stimuli (a cuckoo egg in the nest and a cuckoonear the nest) are necessary to induce the meadow pipits toreject cuckoo eggs. When the threshold for rejection had beenreached, the hosts reacted in a relatively short time afterthey were faced with the parasite stimuli. The results of theseexperiments also showed that a significantly higher rate ofrejection occurred earlier rather than later in the incubationperiod. A possible explanation for the higher rate of acceptanceof model cuckoo eggs among meadow pipits in Norway comparedto those in Britain is discussed.     

Reciprocal egg trading and brood care in a hermaphroditic polychaete worm

Ophryotrocha diadema is a simultaneous hermaphrodite polychaete worm with a brief protandrous phase. Its mating behaviour was investigated in order to elucidate the relationships between mating system and reproductive biology. A genetically determined yellow or white coloration of the eggs and body walls made it possible to distinguish the egg releaser from the fertilizer. The following main features of the mating system were established. (1) Pairs are formed preferentially between simultaneous hermaphrodites, one partner releasing eggs and the other fertilizing them. There is no selfing. (2) The partners attain spawning synchronization by means of close mutual contact during a fairly time-consuming courtship. (3) Partners regularly alternate sex roles, usually with the same partner more than once in succession. (4) Both partners care for their eggs and protect cocoons of neglected eggs spawned by other pairs.     

Do male golden egg bugs carry eggs they have fertilized? A microsatellite analysis

In the golden egg bug, Phyllomorpha laciniata (Heteroptera,Coreidae), both males and females carry eggs on their back.Although females cannot carry their own eggs, males may carryeggs that they have fertilized. If males carry eggs they havefertilized, their behavior may be interpreted as paternal care.In this article, we provide genetic data for paternity assignmentof eggs carried by 40 males collected from the field. The malesand the eggs were typed by using four highly polymorphic microsatelliteDNA markers. Out of the 247 eggs typed, 87% were excluded fromthe father-offspring relationship based on single-locus (leastconservative exclusion) mismatches. Under the more conservative(exclusion by at least two single locus mismatches) method,78% of the eggs were nonpaternal. Relatedness estimates furthersupported our paternity analyses. The average relatedness ofthe eggs to the carrying males was low (b_em = -0.052 ±0.024 SE). Within the population, males were unrelated to eachother (b_mm = -0.004 ± 0.0002 SE), as were the eggs carriedby individual males (b_eggs = -0.004 ± 0.0001 SE). Thisfirst genetic study on the breeding system of the golden eggbugs did not find any support for the claim that egg carryingfunctioned as paternal care, nor did it support kin selectionas explanation for conspecific egg carrying.     

The evolution of egg size in the brood parasitic cuckoos

We compared genera of nonparasitic cuckoos and two groups ofparasitic cuckoos: those raised together with host young ("nonejectors")and those in which the newly hatched cuckoo either ejects thehost eggs or chicks, or kills the host young ("ejectors"). Nonejectorsare similar to their hosts in body size and parasitize largerhosts than do ejectors, which parasitize hosts much smallerthan themselves. In both types of parasite, the cuckoo's eggtends to match the host eggs in size. To achieve this, nonejectorshave evolved a smaller egg for their body size than have nonparasiticcuckoos, and ejectors have evolved an even smaller egg. Amongejector cuckoo genera, larger cuckoos have larger eggs relativeto the eggs of their hosts, and the relationship between cuckooegg volume (mass of the newly-hatched cuckoo) and host egg volume(mass to be ejected) did not differ from that predicted by weight-liftingallometry. However, comparing among Cuculus cuckoo species,the allometric slope differed from the predicted, so it is notclear that egg size is related to the need to give the cuckoochick sufficient strength for ejection. Comparing the two mostspeciose ejector genera, Chrysococcyx cuckoos (smaller and parasitizedome-nesting hosts) lay eggs more similar in size to their host'seggs than do Cuculus cuckoos (larger and parasitize open cup–nestinghosts). Closer size-matching of host eggs in Chrysococcyx mayreflect the following: (1) selection to reduce adult body massto facilitate entry through small domed nest holes to lay, and(2) less need for a large egg, because longer incubation periodsin dome-nesting hosts allow the young cuckoo more time to growbefore it need eject host eggs.     

Egg burial in penduline tits, Remiz pendulinus: its role in mate desertion and female polyandry

One important component in the mating strategy of an already-matedindividual is the decision to remain with the partner and carefor the offspring or to desert. Almost all research on nestdesertion has focused on the costs and benefits of continuedparental care versus desertion of both parents. However, ifit pays both parents to desert, the timing of desertion is mostimportant. In birds, where all eggs are fertilized well beforethe last egg is laid, males should be the first to desert. Evenif females try to hide their fertile period, it is likely thatthe appearance of eggs acts as a cue that males can use to calculatethe timing of their desertion. Here we examine egg burial behaviorin penduline tits and its possible effects on parental behaviorand desertion. Penduline tits perform uniparental care fromthe earliest point of breeding, and both sexes try to becomepolygamous. We found that 36% of investigated males were polygynousand deserted as soon as the first egg appeared in their nest,and 12.5% of females became polyandrous. About 27% of the nestswere deserted by both sexes, which means high costs for femalesin terms of wasted energy in eggs and for males in terms ofwasted energy and time in building elaborate nests. Femalescover the eggs, and several facts indicate that egg coveringis a deceptive behavior of females: (1) females cover the eggsin the morning before leaving the nest for the first time, (2)females are more aggressive toward their mates during the layingperiod than before laying, (3) females try to prevent malesfrom entering the nest when eggs have been experimentally uncovered,and (4) females uncover the eggs as soon as males are experimentallyremoved. Finally, we found that a female can only desert thenest before the male deserts when she covers the eggs. We concludethat the higher the proportion of eggs a female can hide, thegreater her chance of becoming polyandrous     

Reproductive behavior and mate fidelity in the monogamous goby,Valenciennea longipinnis

Reproductive behavior and mate fidelity of the gobiid fish,Valenciennea longipinnis, were studied on the coral reef at Sesoko Island, Okinawa, Japan. These fish usually live in pairs, not only foraging together for benthic animals in sandy areas, but also constructing several burrows within their home range. Before spawning, both fish, although mainly the male, constructed a mound, piling up dead-coral fragments, pebbles, shells, sand and algae onto one of the burrows. After spawning an egg mass on the ceiling of the burrow, the female stayed outside and continued the construction and maintenance of the mound for 3–5 days until hatching, while the male tended the eggs inside. Mate guarding of females seemed to prevent males from monopolizing several females. Although some pairs showed mate fidelity through several spawnings, more than half of the pairs broke up after only one spawning. The pair bond was broken by mate desertion and the disappearance of each sex. Both sexes preferred larger spawning partners; larger females spawned more eggs and larger males provided better egg care. Mate desertion occurred when larger potential mates, relative to the current partner, became available. The frequency of solitary individuals was higher in males than in females, resulting in females deserting their mates more often than males. Two factors seem to have facilitated mate desertion: (1) occurrence of size mis-matched pairing and (2) overlapping home ranges.     

Brood parasitic European starlings do not lay high-quality eggs

Chicks of obligate brood parasites employ a variety of morphologicaland behavioral strategies to outcompete nest mates. Elevatedcompetitiveness is favored by natural selection because parasiticchicks are not related to their host parents or nest mates.When chicks of conspecific brood parasites (CBPs) are unrelatedto their hosts, they and their parents would also benefit fromtraits that enhance competitiveness. However, these traits mustbe inducible tactics in CBPs, since conspecific brood parasitism(CBP) is facultative. Such tactics could be induced by resourcespassed to offspring through the egg. Thus, females engagingin CBP should allocate to their eggs resources that will enhanceoffspring competitiveness. We tested this prediction in a populationof European starlings (Sturnus vulgaris) breeding in southernSweden. Previous research showed that almost all CBPs in thispopulation are floater females that have yet to breed in thecurrent season. We identified putative brood parasitic eggsthrough monitoring egg laying and verified parasitism usingprotein fingerprinting. We then determined whether parasiticeggs were larger, larger-yolked, or had higher concentrationsof yolk testosterone or androstenedione than control eggs. The14 brood parasitic eggs laid in active nests (those with clutchesof at least two eggs that were eventually incubated) did notdiffer from controls in any of these characteristics. Ten dumpedeggs, laid in nonactive nest-boxes or on the ground, were smallerand smaller-yolked than control eggs but did not differ in yolkandrogen concentrations. The failure of our prediction couldbe the result of high costs of investing in eggs, lack of competition-basedbenefits for chicks, or physiological constraints on egg manipulation.     

Female egg dumping and the effect of sex ratio on male egg carrying in a coreid bug

Phyllomorpha laciniata Vill (Heteroptera, Coreidae) is uniqueamong terrestrial insects in that females glue eggs on the backsof other conspecifics. Egg carrying byP. laciniatamales haspreviously been considered as paternal care. We explored femaleoviposition with respect to previous mating experience of femalesand tested whether sex ratio affects male egg-carrying. Thehypothesis that male egg-carrying is a form of paternal carepredicts that a male should always accept eggs after matingwith a female. However, if male egg-carrying is a form of postcopulatorymate guarding rather than paternal care, egg carrying shouldincrease in the presence of other males. When two couples wereplaced together, females laid eggs on the backs of all individualsenclosed, including the backs of other females. However, whena female was accompanied by 2 males, 22 out of 26 females ovipositedon their mating partner. Thus, sexual competition rather thanpaternity alone, affects a male's eagerness to carry eggs. However,even if males sometimes carry their own eggs, females lay eggson the backs of all conspecifics they can easily acquire. Thus,egg carrying in P. laciniata is partially voluntary and partiallythe result of female egg dumping     

玉米螟赤眼蜂对亚洲玉米螟益它素的嗅觉反应

在实验室条件下利用四臂嗅觉仪测定了玉米螟赤眼蜂Trichogramma ostriniae Pang et Chen对来源于寄主亚洲玉米螟Ostrinia furnacalis (Guenée)成虫、卵、附腺以及性信息素的益它素的嗅觉反应。结果表明: 已交配尚未产卵亚洲玉米螟雌蛾及其附腺对玉米螟赤眼蜂有明显的吸引作用,而处女蛾、产卵前期雌蛾、产卵后期雌蛾及其附腺却没有作用;当玉米螟卵块数量为2块及卵表正己烷提取物当量为0.25块卵时,对玉米螟赤眼蜂也有明显的吸引作用,尤其以产在玻璃管内卵块吸引最为显著,达到极显著水平(P<0.01);性信息素组分之一,反-12-十四碳烯乙酸酯(E12.14: Ac)在剂量为1 μg时亦显著刺激了赤眼蜂的活动,表现为进入处理区的次数明显增加,且滞留时间明显延长。     

Cuckoos versus reed warblers: Adaptations and counteradaptations

At study sites in Cambridgeshire, England, the percentage of reed warbler, Acrocephalus scirpaceus, nests parasitized by cuckoos, Cuculus canorus, in 2 years was 22·5% and 9·1%. The warblers rejected cuckoo eggs at 19% of parasitized nests. Parasitized clutches suffered less predation than unparasitized clutches, suggesting that the cuckoo itself was the major predator, plundering nests too advanced for parasitism so that the hosts would re-lay. The cuckoos laid a mimetic egg, parasitized nests in the afternoons during the host laying period, usually removed one host egg, laid a remarkably small egg and laid very quickly. Nests were experimentally parasitized with model eggs to study the significance of this procedure. Experiments showed that host discrimination selects for: (1) egg mimicry by cuckoos (poorer matching model eggs were more likely to be rejected); (2) parasitism during the laying period (mimetic eggs put in nests before host laying began were rejected); (3) afternoon laying (mimetic eggs were less likely to be accepted in the early morning than in the afternoon, when hosts were more often absent from the nest); (4) a small egg (large eggs, typical of non-parasitic cuckoos, were more likely to be rejected); (5) rapid laying (a stuffed cuckoo on the nest stimulated increased rejection of model eggs), and (6) sets a limit to host egg removal by cuckoos (if more than one or two are removed desertion may occur). Mimicry may also be selected for because it reduced the chance that second cuckoos can discriminate the first cuckoo's egg from the host's clutch. Predation did not select for mimicry; nests with a non-mimetic egg did not suffer greater predation than those with a mimetic egg. Host rejection of model eggs did not depend on: (1) stage of parasitism once host egg laying had begun (nevertheless cuckoos were more likely to lay early in the host laying period probably to increase the chance the cuckoo chick hatched); (2) removal of a host egg (however, this reduced the incidence of unhatched eggs so cuckoos may remove a host egg so as not to exceed the host incubation limit). There were two costs of rejection, an ‘ejection’ cost (own eggs ejected as well as the cuckoo egg) and, with mimetic eggs, a ‘recognition’ cost (own eggs ejected instead of the cuckoo egg). Reed warblers did not discriminate against unlike chicks (another species) and did not favour either a cuckoo chick or their own chicks when these were placed in two nests side by side. Possible reasons why the hosts discriminate against unlike eggs but not unlike chicks are discussed.     

Multiple Lines of Egg Defense in a Neotropical Arachnid with Temporary Brood Desertion

Egg predation is the one of the main costs of brood desertion in many ectothermic animals. When stressful environmental conditions constrain parental activities to only some periods of the day, the combination of physical or chemical defenses may attenuate the costs related to egg loss during periods of temporary parental absence. Females of the harvestman Neosadocus maximus periodically abandon their clutches to shelter or forage. They also cover their eggs with a hygroscopic mucus coat and seem to lose fewer eggs to predation than other syntopic harvestmen whose eggs lack the mucus coat. Using two species of N. maximus egg predators, we demonstrate that eggs whose mucus coat was experimentally removed suffered higher predation rate than eggs whose mucus coat was left intact. We argue that this mucus provides physical protection against egg predators, especially small arthropods. A similar mucus coat has independently evolved in other two clades of Neotropical harvestman in which males care for the eggs and typically leave their clutches unattended for several hours a day. We propose that the presence of multiple lines of egg defense may have evolved as a way of lowering the costs imposed by intra‐ and interspecific egg predation during periods of temporary brood desertion.     

Egg size and reproductive allocation in eusocial thrips

Reproductive allocation, in terms of fecundity and egg size,has been given little consideration in eusocial societies. Tobegin to address this, absolute and body size–adjustedegg volumes were compared, along with fecundity, between thefoundress and her subfertile soldier offspring in the eusocial,gall-inducing thrips, Kladothrips hamiltoni, Kladothrips waterhousei,and Kladothrips habrus, and a congeneric, Kladothrips morrisi,with fully fecund soldiers. Soldiers produced significantlylarger eggs than the foundress in all species except K. morrisi,where egg volumes did not differ. After accounting for bodysize, soldiers produced significantly smaller eggs than thefoundress in K. morrisi and marginally so in K. waterhousei,but egg sizes did not differ in K. hamiltoni and K. habrus.When egg size and fecundity data are combined, K. morrisi soldiersinvest less in reproduction than the foundress, and in conjunctionwith other life-history features the species can be consideredeusocial. Maximum likelihood analyses reveal relatively lowreproductive allocation skew in the ancestral lineages and highskew in the derived lineages, but the trend is not significantwhen fecundity and egg size are considered separately. Gallsize covaried negatively with soldier-to-foundress relativebody size–adjusted egg size and reproductive allocationand marginally so with fecundity, suggesting that gall sizeis a determinant of egg size and fecundity trade-offs in eusocialthrips and providing the strongest support to date that gallsize has featured in the social evolution of this clade. Thisstudy highlights that data on fecundity alone may be insufficientfor assessing reproductive division of labor.